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Title:
AN EMERGENCY POWER CONTROL DEVICE
Document Type and Number:
WIPO Patent Application WO/2019/048558
Kind Code:
A1
Abstract:
The invention relates to an emergency power control device (1) for a DC motor (3). In a non-emergency mode the DC motor (3) is supplied with armature current and shunt current by a power converter (2). The emergency power control device (2) comprises connecting means configured to connect in an emergency mode at least one of a armature winding (31), a shunt winding (32), or a serial winding (33) of the DC motor (3) to an emergency power supply. For supplying the DC motor (3) in an emergency mode with armature current and shunt current the emergency power control device (1) comprises at least one of an armature connecting means controls the current supplied to the armature winding (31) of the DC motor (3) in emergency mode such that in an initial time period the current supplied to the armature (31) of the DC motor (3) is lower than in a time period following the initial time period, and a shunt connecting means controls the current supplied to the shunt winding of the DC motor (30) in emergency mode such that in an initial time period the current supplied to the shunt winding (33) is higher than in a time period following the initial time period.

Inventors:
THEOPOLD, Tobias (Elbinger Strasse 10, Dortmund, 44263, DE)
Application Number:
EP2018/074038
Publication Date:
March 14, 2019
Filing Date:
September 06, 2018
Export Citation:
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Assignee:
MOOG UNNA GMBH (Max-Born Str. 1, Unna, 59423, DE)
International Classes:
H02P7/298
Foreign References:
US20080129234A12008-06-05
JP2004308645A2004-11-04
Attorney, Agent or Firm:
WITHERS & ROGERS LLP et al. (4 More London Riverside, London Greater London SE1 2AU, SE1 2AU, GB)
Download PDF:
Claims:
Claims

An emergency power control device (1) for a DC motor (3), the DC motor (3) being supplied in a non-emergency mode from a power converter (2), the emergency power control device (2) comprising connecting means configured to connect in an emergency mode at least one of a armature winding (31) or a shunt winding (32) of the DC motor (3) to an emergency power supply (4)

characterized in that

at least one of

— an armature connecting means controls the current supplied to the armature winding (31) of the DC motor (3) in emergency mode such that in an initial time period the current supplied to the armature (31) of the DC motor (3) is lower than in a time period following the initial time period, and

— a shunt connecting means controls the current supplied to the shunt winding of the DC motor (30) in emergency mode such that in an initial time period the current supplied to the shunt winding (33) is higher than in a time period following the initial time period.

An emergency power control device (1) according to claim 1 wherein the at least one of an armature connecting means or the shunt connecting means comprises at least one power transistor, particularly an insulated gate bipolar transistors, or an insulated gate bipolar transistor having a diode with its cathode connected to the collector of the insulated gate bipolar transistor, or that the insulated gate bipolar transistor is a reverse blocking insulated gate bipolar transistor.

An emergency power control device (1) according to claim 1 or 2 wherein the at least one of the armature connecting means or the shunt connecting means is controlled by pulse width modulated signals.

An emergency power control device (1) according to claim 3, wherein the at least one of

— the pulse width ratio of a first pulse width modulated signal (Gl) controls the ratio of the armature connecting means being switched on and being switched off, and

— the pulse width ratio of a second pulse width modulated signal (G2) controls the ratio of the shunt connecting means being switched on and being switched off. The emergency power control device (1) according to claim 4, characterized that one of the first pulse width modulated signal (Gl) or the second pulse width modulated signals is an input signal for a semiconductor switch.

The emergency power control device (1) according to claim 4 or 5, in case the armature connecting means controls the current supplied to the armature winding (31) of the DC motor (3) in emergency mode such that in an initial time period the current supplied to the armature (31) of the DC motor (3) is lower than in a time period following the initial time period the pulse width ratio of the first pulse width modulated signal (Gl) is controlled such that the current supplied to the armature winding (31) of the DC motor (3) gradually increases over time.

The emergency power control device (1) according to claim 6, characterized that the pulse width ratio of the first pulse width modulated signal (Gl) is controlled as a function of the time passed since the emergency power control device (1) was set into an emergency power mode.

An emergency power control device (1) according to claim 2, wherein the at least one transistor comprises a pair of a first transistor and a second transistor, wherein the emitter of the first transistor is connected to the collector of the second transistor and the collector of the first transistor is connected to the emitter of the second transistor, respectively the first transistor is connected with its collector to a cathode of a first diode and the collector of the second transistor is connected to a cathode of a second diode, and wherein the anode of the first diode is connected to the emitter of the second transistor and the emitter of the first transistor is connected to the anode of the second diode.

The emergency power control device (1) according to claim 8, wherein a control circuit is adapted to keep the second transistor connected for a short time period after the first transistor has been disconnected.

The emergency power control device (1) according to one of claims 1 to 9 wherein the DC motor is a DC motor with a series winding (32) with a first series winding end (Dl) and a second series winding end (D2) and wherein a flux bridge (34) is connected with a first flux bridge terminal (343) to the first series winding end (Dl), with a second flux bridge terminal (344) to the second series winding end (D2), with a third flux bridge terminal (342) connected to a second armature winding end (B2) and wherein the connecting means is adapted to connect a fourth flux bridge terminal (341) to the emergency power supply (4).

1. The emergency power control device (1) according to one of claims 1 or 2, characterized in that the armature connecting means comprises a resistor with a negative temperature coefficient which is connectable by the semiconductor to the emergency power supply (4) and the armature winding (31).

2. The emergency power control device (1) according to claim 5, wherein the pulse width ratio of the second pulse width modulated signal (G2) is controlled such that the current supplied to the shunt winding (33) of the DC motor (3) gradually decreases over time.

3. The emergency power control device (1) according to claim 4 or 5, wherein the pulse width ratio of the second pulse width modulated signal (G2) is controlled as a function of the time passed since the emergency power control device (1) was set into emergency power mode.

4. The emergency power control device (1) according to one of claims 1 to 4, characterized in that the shunt connecting means (12) comprises a voltage dependent resistor (VDR), connectable in emergency power mode to the emergency power supply (4) and the shunt winding (33).

5. The emergency power control device (1) according to one of claims 3 to 7 wherein the emergency power control device (1) measures continuously the voltage of the emergency power supply (4) and adjusts the pulse width ratio of the at least one of the first pulse width modulated signal (Gl) or the second pulse width modulated signal (G2) to compensate for a decreasing voltage of the emergency power supply (4).

6. The emergency power control device (1) according to one of the claims 1 - 15, wherein disconnecting means for disconnecting the power converter (2) from the emergency power supply device (1) are arranged in the power lines connecting the power converter (2) with the emergency power supply (1).

7. The emergency power control device (1) according to claim 16 wherein the disconnecting means is a fuse or a magnetic circuit breaker.

18. The emergency power control device (1) according to one of claims 1 - 16, characterized in that the components of the emergency power control device (1) are arranged in a housing that is separate to a housing of the power converter (2) or a housing of the DC motor (3).

19. The emergency power control device (1) according to claim 18 wherein the housing of the emergency power control device ( 1), the housing of the power converter (2) and the emergency power supply (4) are arranged in one cabinet. 20. The emergency power control device (1) according to claim 18 or 19 wherein the housing of the emergency power control device (1) provides an external first input terminal (U') for being connected to a first output terminal (U) of a power converter (1) and an external first output terminal (U") for being connected to the first end (Al) of the armature (32), wherein the external first input terminal (U') and the external first output terminal (U") are internally connected by disconnecting means

(SI).

21. The emergency power control device (1) according to one of claims 18, 19 or 20 wherein the housing of the emergency power control device (1) provides an external second input terminal (V) for being connected to a second output terminal (V) of a power converter (2) and an external second output terminal (V") for being connected to the first end (Fl) of the shunt winding (32), wherein the external third input terminal (V) and the third external output terminal (V") are internally connected by disconnecting means (SI).

22. The emergency power control device (1) according to claim one of claims 18 to 21 wherein the housing of the emergency power control device (1) provides an external third input terminal (W) for being connected to a third output terminal (W) of a power converter (2) and an external third output terminal (W") for being connected to the second end (B2) of the armature (31), wherein the external third input terminal (W) and the external second output terminal (W") are internally connected by disconnecting means (SI).

23. The emergency power control device (1) according to one of claims 18 to 22 wherein the housing of the emergency power control device (1) provides an external fourth input terminal (ZK'-) for being connected to a fourth output terminal (ZK-) of a power converter (2) and an external fourth output terminal (ZK"-) for being connected to the second end (F2) of the shunt winding (33), wherein the external fourth input terminal (ΖΚ'-) and the external fourth output terminal (ZK"-) are internally connected by disconnecting means (SI).

24. The emergency power control device (1) according to one of claims 18 to 23 wherein the housing provides an external seventh input terminal (Bat+) for being connected to the positive pole (+) of the emergency power supply (4).

25. The emergency power control device (1) according to one of claims 18 to 24 wherein the housing provides an external eighth input terminal (Bat-) for being to the negative pole (-) of the emergency power supply (4).

26. The emergency power control device (1) according to one of claims 1 - 25 characterized in that at least one of the armature connecting means or the shunt connecting means are implemented as hardware circuits without any software control.

27. The emergency power control device of claim 26 wherein the hardware circuits comprises operation amplifiers (OP1) wired as integrators and Schmitt-triggers.

28. A method

of installing an emergency power control device (1) according to one of the claims 1 - 24, the method comprising :

— cutting in two at least one of supply wires connecting

— an armature power supply (U) of the power converter (20) with the armature winding (31) of the motor (3)

— a shunt power supply (V) of the power converter (20) with the shunt winding (33) of the motor (3)

— a series power supply (W) of the power converter (20) with a series winding (32)

— a common ground (ZK-) of the power converter with the series winding (32)

resulting in at least first end of the at least one of supply wires and a at least second end of the at least one of the supply wires;

— connecting the at least first end of the cut in two at least one of supply wires that lead to the power connector (20) with an respective input terminals (U', V, W) of emergency power control device (1);

— connecting the at least second end of the cut in two at least one of supply wire that lead to at least one of a first armature winding end (Al), a first shunt winding end (Fl), a serial winding end (Bl), a second shunt winding end (F2) to the respective first output terminals (U", V", W", ZK"-)) of the emergency power device (1);

— connecting a positive pole (Bat+) of the emergency power supply (4) to a first battery input terminal (Bat'+) of the emergency power device (1)

— connecting a negative pole (Bat-) of the emergency power supply (4) to a second battery input terminal (Bat'-) of the emergency power device (1)

— connecting the first battery output terminal (ZK'+) to a supply voltage output (ZK+) of the power converter (20)

— connecting the common ground input terminal (ZK'-) of the emergency power device (1) to a common ground output terminal (ZK-) of the power converter (2).

A wind turbine (100) with an emergency power device (1) according to one of claims 1 - 27.

Description:
An Emergency Power Control Device

The invention relates to an emergency power control device being connectable to a power converter by interrupting means for interrupting the supply of electrical current from the power converter to the emergency power control device, and being connectable to a DC motor by connecting means for supplying at least one of an armature winding, a shunt winding, and a series winding of the DC motor from an emergency power supply. The invention further relates to a method for retrofitting an emergency power control device. When DC motors are used in safety critical applications, such as motors for pumps in nuclear reactors, motors for lifts transporting persons, or pitch motors in wind turbines for controlling the speed of a wind turbine, emergency power supply is a necessity in case the general power supply fails to be able to power the DC motor with electrical power from the emergency power supply until power supply from another power source is established, or the charge that is propelled by the motor has been advanced to a secure position. Such a secure position, for example, in case of an elevator is at the next floor level where the passengers can leave the lift cabin. In case of a wind turbine, such a secure position can't be established by using the emergency power supply to turn the rotor blades of the wind turbine in a so-called feathering position.

In the following the state of the machinery when the power supply works as planned will be called normal operation mode. In case power supply from the emergency power supply is invoked, this will be called emergency operation mode. Figure 1 shows a schematic diagram of a multiple axis pitch system of a wind turbine. The wind turbine in normal operation mode is supplied from an AC power grid 8 with electrical power of approximately 400V AC. This electrical power is distributed to three pitch control devices 2a, 2b, 2c. A pitch system controller 7 is in communication with the three drive units 2a, 2b, 2c. The pitch system controller 7 receives control commands from a wind turbine controller 6, which could be for example a wind turbine controller. The control command sent by the wind turbine controller for example comprises the position, i.e. the angle to which a specific rotor blade should be turned to. The pitch system controller 7 evaluates the received control commands and forwards a specific command only to a respective pitch drive unit 2a, 2b, 2c to which the command is addressed to. Each pitch drive unit 2a, 2b, 2c translates the received position commands into motor control commands. As a function of the received motor control commands a closed control loop in each pitch drive unit 2a, 2b, 2c controls a power converter (not shown in Fig. 1). The power converter in the end generates an armature current and where applicable a shunt current to supply an armature winding and a shunt winding of a DC motor, in the following due to its function called pitch motor 3a, 3b, 3c. The power converter controls the voltages, respectively as a function of the applied voltages the electrical currents supplied to the pitch motors 3a, 3b, 3c. The magnitude and polarity of these supply currents determines in the end the rotational speed, the rotational direction and the torque of each pitch motor 3a, 3b, 3c. A rectifier (not shown in Fig. 1) for example as a part of each pitch drive unit 2a, 2b, 3c is connected to the AC power lines and provides a DC power, in this example at a nominal operation voltage of 565V, to each of the power converters of each pitch drive unit 2a, 2b, 2c. In Figure 1 the lines carrying control commands are represented by thin lines and the lines supplying electrical power are represented by thick lines 80, respectively 90.

In the example shown in Figure 1 in case the power supply from the AC grid 8 fails, each drive unit 2a independently from the other drive units 2b, 2c may be supplied by an individual backup power supply 4a, 4b, 4c. Various designs are known in prior art how to connect the backup power supply to the drive units. One possibility shown in Figure 1 is the connection of each backup power supply with a decoupling diode 5a, 5b, 5c to each power converter inside the drive units 2a, 2b, 2c. The backup power supplies 4a, 4b, 4c individually may be charged by emergency power chargers (not shown in Fig. 1) from each pitch drive unit 2a, 2b, 2c. Typically, the backup power supply 4a. 4b. 4c now-a-days comprises an ultra-capacitor or a lithium ion battery.

The emergency power supply may provide power at an initial voltage, for example 400V, which is sufficiently high to complete an emergency action from the most far position of the rotor blade from the feathering position, but for reasons of cost optimization the emergency power supply voltage may be chosen at a level that is lower than the nominal operation voltage of the converter. In case of a failure of the AC power grid 8, the supply voltage provided by the rectifier will collapse. Once the voltage provided by the rectifier has fallen below the voltage provided by the power backup 4a, 4b, 4c, the decoupling diodes 5a, 5b, 5c will enter into a conductive state and power is eventually supplied from the power backup 4a, 4b, 4c.

Common power backups for emergency operation mode are re-chargeable lead batteries or ultra-capacitors. In case the converter fails, the voltage of the power backup may be connected for example to the power converters of the pitch drive units 2a, 2b, 2c thus enabling the power converters to supply the pitch motors 3a, 3b, 3c with electrical energy, enabling the pitch motors 3a, 3b, 3c to continue to turn until the charge propelled by the motor is in a secure position, which may be detected by an end-limit switch (not shown).

Figure 2 shows another schematic diagram of a multiple axis pitch system in which the converter of the pitch drive units 2a, 2b, 2c are supplied by a centralised DC power module 9. Figure 1 and Figure 2 use identical reference signs for similar devices. The DC power module 9 is supplied with AC power from an AC grid 8 and distributes a DC voltage of, for example, 420V DC to converters of pitch drive units 2a, 2b, 2c. Similarly, to the pitch system shown in Figure 1, each pitch drive unit 2a, 2b, 2c is backed up by a separate backup power supply 4a, 4b, 4c. In this prior art example the pitch drive units 2a, 2b, 2c are supplied with direct voltage from the DC power module 9, and the backup power supplies 4a, 4b, 4c are directly coupled to the converter of the pitch drive units 2a, 2b, 2c. In this case of direct coupling there is no need for a decoupling diode or an emergency power charger. As a consequence of direct coupling the voltage of the backup power supply follows the voltage of the DC power module 9.

In case of a failure of the AC power grid 8, the power is supplied from the backup power supplies 4a, 4b, 4c directly to the power converter of each pitch drive unit 2a, 2b, 2c allowing the converter to continue operating the pitch drive motors 3a, 3b, 3c in their normal way. However, in case the backup power supplies 4a, 4b, 4c are ultra-capacitors, they dis-charge and the backup voltage decreases continuously. However, the capacity of an ultra-capacitor used in the backup power supply 4a, 4b, 4c would have been chosen such that the energy in the backup power supply lasts long enough to propel the pitch drive motors 3a, 3b, 3c into the feathering position of the wind turbine. When the converter cannot compensate the falling supply voltage, the rotational speed of the pitch motors 3a, 3b, 3c will decrease with time and it will take the pitch drive motors 3a, 3b, 3c longer to turn the rotor blades of the wind turbine into the feathering position.

Figure 3 shows in more detail a DC converter 20 as used in a pitch drive unit 2a, 2b, 2c for supplying a DC pitch motor 3 having an armature winding 31 with a first armature winding end Al and a second armature winding end Bl, a series winding 32 with a first series winding end Dl and a second series winding end D2, and a shunt winding 33 with a first shunt winding end Fl and a second shunt winding end F2. All pitch drive units 2a, 2b, 2c in a multiple axis pitch system usually are identical and also the power converters are identical. Figure 3 shows a prior art pitch control unit in which the converter is supplied with a positive input voltage ZK+ and a negative input voltage ZK-from an AC or DC power supply 90. This AC or DC power supply 90 can be the central power supply 9 shown in Figure 2 or an individual power supply integrated in each pitch drive unit 2a, 2b, 2c. A battery or an ultra-capacitor Bat is connected with its positive emergency power supply terminal Bat+ directly to the positive input voltage ZK+ and with its negative emergency power supply terminal Bat - to the negative input supply voltage ZK-. Thus in case the power supply from the power grid 8 fails, the power will be supplied without interruption from the emergency power supply Bat. In case the converter 20 is supplied with AC current decoupling diodes 51, 52 decouple the emergency power supply from the power converter 20. This decoupling diodes 51, 52 are not required when each power converter 20 is decoupled from the power grid 8 by an individual DC power supply 20 if provided in each pitch drive unit 2a, 2b, 2c.

The converter comprises a microprocessor-based pulse with modulation control module 21 which receives control signals from a wind turbine controller 6. The microprocessor-based pulse width modulation control module 21 controls a first pair of transistors 211, 212, a second pair of transistors 213, 214, and a third pair of transistors 215, 216. The first pair of transistors 211, 212, the second and the third pair of transistors 215, 216 are connected to the positive input voltage ZK+ and the negative input voltage ZK-. Thus the first pair of transistors 211, 212 and the third pair of transistors 215, 216 can be operated as an H bridge for providing a positive current flow from a positive output voltage at an armature power supply terminal U through the armature winding 31 and a negative output voltage at a series power supply terminal W, or a current with a reversed direction when providing a negative output voltage at the armature power supply terminal U and a positive output voltage at the series power supply terminal W. The second pair of transistors 213, 214 forms half an H bridge for providing a current through the shunt winding 32 in always the same direction by providing a positive shunt output voltage at the shunt power supply terminal V. For this purpose the shunt power output terminal V is connected to a first shunt winding terminal Fl of the shunt winding 33 and the second shunt winding terminal F2 is connected with the negative supply voltage ZK-. In contrast hereto the armature power output terminal U is connected to the first armature winding end Al and the series power output V is connected to the second series winding end D2. The second armature winding end B2 and the first series winding end Dl may be connected directly with each other to close the circuit of the armature winding 31 and the series winding 32. In case the chosen motor is not a compound motor and has no series winding 32 the armature power output terminal U would be connected to the first armature winding end Al and the series power output terminal V would be connected to the second armature winding end B2. A first VDR resistor 291 connected between the first armature winding end Al and the second armature winding end B2 protects the armature winding 31 when the motor in generator mode from voltage spikes. Similarly a second VDR resistor 292 connects the first shunt winding end Fl and the second shunt winding end F2. The so-called clamping voltage, i.e. the voltage above which the VDR resistors start to go into a conductive state is higher than the supply voltage of the power converter 20, for example 900 Volts.

If the DC motor 3 is a compound motor with a series winding 32, then switching a reverse polarity to the first armature winding terminal Al and the second series winding terminal D2 also reverses the magnetic field of the series winding 32. This is not ideal, as the reversed magnetic field has an opposite orientation to the magnetic field of the shunt winding 31. Depending on the build of the motor it still may work with reducedperformance. .For better performance when the motor is operated in reverse direction the series power terminal W is connected to a first terminal 341 of an optional flux bridge 34, the second armature winding end B2 is connected to a second terminal 342 of the flux bridge 342, the first series winding end Dl is connected to a third terminal 343 of the flux bridge 34, and the second series winding D2 is connected to a fourth terminal 344 of the flux bridge 34. The flux bridge 34 basically is a bridge rectifier that allows the current to flow always in the same direction through the series winding 32, irrespective what the polarity of the armature power U and the series power voltage W is. With the flux bridge 34 in place the orientation of the magnetic field of the series winding always stays the same as the orientation of the magnetic field of the shunt winding. In case the first pair of transistors 211, 212 produces a positive output voltage U and the third pair of transistors 213, 214 produces a negative output voltage the pitch motor will turn in a forward direction, i.e. by definition turning the rotor blades towards the feathering position. In case the motor shall rotate in reverse direction the first pair of transistors 211, 212 produces a negative output voltage U and the third pair of transistors 213, 214 produces a positive output voltage, thus reversing the magnetic field of the armature winding 31, but the flux bridge 34 allows a current I se ries to flow always in the same direction of the series winding 32, irrespective in which direction the armature current Iarmature is flowing through the armature winding 31. Thus the magnetic field of the series winding 32 will always have the same orientation as the magnetic field of the shunt winding 33, so that flux components do only superimpose constructively.

As the emergency power supply is connected to the power supply of the converter 20 the power converter is supplied with electrical energy in case the power supply from the power grid 8 fails. However, this architecture only works in case of a failure in the power supply of the power grid 8. In case there is an error in the DC converter, for example if one of the transistors is damaged, motor may not be supplied correctly with current and may fail to operate as expected. Therefore the pitch drive units 2a, 2b, 2c had been modified in the past to be able in case of a failure of the converter to isolate the converter 20 from the pitch motor 3 and to supply the pitch motor 3 directly by the emergency power supply 4.

Fig. 4 shows the schematics of a first prior art pitch drive unit 2a with an installation of first, second, third, fourth, fifth, and sixth contactors SI, S2, S3, S4, S5, S6 used as disconnecting means and connecting means for providing an pitch drive unit with emergency power supply capability. The contactors SI, S2, S3, S4, S5, S6 are controlled by first, second, third, fourth, fifth, and sixth control signals CI, C2, C3, C4, C5, C6 generated by contactor control means 22. The first control signal CI controls the switching state of the first contactor SI, the second control signal C2 controls the switching state of the second contactor S2, the third control signal C3 controls the switching state of the third contactor S3, the fourth control signal C4 controls the switching state of the fourth contactor S4, the fifth control signal C5 controls the switching state of the fifth contactor S5, and the sixth control signal C6 controls the switching state of the sixth contactor S6. The contactor control means 22 has a signal input for a pitch system mode signal which tells the contactor control means 22 whether the pitch drive 2 should be operated in normal operation mode or in emergency operation mode. The contactor control means accordingly generates as a function of the commanded mode the control signals CI, C2, C3, C4, C5, C6. The control signals CI, C2, C3, C4, C5, C6 will close or open contacts of the connectors SI, S2, S3, S4, S5, S6 as explained in detail further below. The contactor control means 22 also evaluates the signal of a limit switch which indicates when a rotor blade has advanced to a feathering position.

In normal operation mode the first contactor SI connects the armature power supply terminal U with the first armature winding Al, the shunt power supply terminal V with the first shunt winding end Fl, and the series power supply terminal W with the first series winding end Dl, respectively the appropriate input of the flux bridge 34. In emergency mode the first control signal CI is shut off and the contacts of the first contactor SI all will be opened and thereby interrupt the connection between the armature power supply terminal U and the first armature winding Al, the shunt power supply terminal V and the first shunt winding end Fl, and the series power supply terminal W and the first series winding end Dl, respectively the appropriate flux bridge 34 input.

In emergency operation mode the third contactor S3 connects the first armature winding end Al with the positive pole Bat+ of the emergency power supply Bat and the fourth contactor S4 connects the first terminal 341 of the flux bridge 34 with the negative pole bat- of emergency power supply Bat. This allows in emergency mode a armature current to flow from the positive pole Bat+ to flow through the armature winding 31 and directed by the flux bridge 34 to flow through the series winding 32 to the negative pole Bat- of the emergency power supply Bat. In this prior art example the third contactor S3 and the fourth contactor S4 are switched at the same time and therefore the third control signal C3 and the fourth control signal C4 are combined into one signal C3/C4. In normal operation mode the contacts of this third contactor S3 and the fourth contactor S4 are open and thus do not influence the normal operation mode.

The armature current flowing from the positive pole Bat+ of the emergency power supply Bat may be reduced by a starting resistor R. For this purpose the contactor control means 22 is configured during a first few seconds of emergency mode to open the contact of the second contactor S2 such that the current flowing from the positive pole Bat+ of the emergency power supply Bat through the starting resistor R is limited by the resistance of the starting resistor R. This allows a smooth start of the pitch motor. After a few seconds in emergency mode the contactor control means 22 is configured to close by means of the second control signal C2 the contact of the second contactor S2 thus shortcutting the starting resistor R. Now the full current can flow through the armature winding 31.

With the beginning of the emergency operation mode contactor control means 21 is further configured to close the fifth contactor S5 thereby connecting the first shunt winding end Fl with the positive pole Bat+ of the emergency power supply Bat. At the same time the sixth contactor S6 is closed thus connecting the second shunt winding end F2 with the negative pole Bat- of the emergency power supply Bat. This closes the current flow from the positive pole Bat+ of the emergency power supply Bat through the shunt winding 33 to the negative pole Bat- of the emergency power supply Bat. In this prior art example the fifth contactor S5 and the sixth contactor S6 are switched at the same time and therefore the fifth control signal C5 and the sixth control signal C6 are combined into one signal C5/C6. In normal operation mode both the fifth contactor S5 and the sixth contactor S6 have open contacts and do not interfere with the power supply from the power converter 20.

The contactor control circuit 22 thus interrupts in emergency mode the power supply from the power converter 20 and allows a smoother start of the pitch motor by inserting a starting resistor R in the armature supply. However, this is only a coarse method and not perfectly smooth. Further it does not account for a falling power supply voltage of the emergency power supply, especially when the emergency power supply is a capacitor, respectively a super capacitor. In addition to these issues contactors are bulky. A further concern is that the lifetime expectance of the contactors might be found lower than the other components, so that they can cause service costs outside the regular service intervals.

These and other problems are solved by the claims of the invention.

In one aspect of the invention a DC motor which is supplied in a non-emergency mode from a power converter and in an emergency mode from an emergency power control device. The emergency power control device comprises a connection arrangement of at least one of a connection means or a disconnecting means, the connecting means are adapted to connect in an emergency mode at least one of a armature winding, a shunt winding, or a serial winding of the DC motor to an emergency power supply. The disconnecting means are adapted in an emergency mode to disconnect the emergency power control device from the power converter. At least one of the connection means or the disconnecting means are semiconductors, particularly power transistors, particularly insulated gate bipolar transistors.

In prior art contactors, which are electromagnetic operated mechanical switches have been used to connect by wires an emergency power supply with a power converter and a DC motor. The wiring is time consuming, the size of the contactors is quite big and the lifetime expectance of mechanical switches may be lower than the planned lifetime of the drive. By substituting the connection means and the disconnecting means with appropriate semiconductors the size of the installation is smaller and the components may be integrated in one module. In a another aspect of the invention the insulated gate bipolar transistor has a diode with its cathode connected to the collector of the insulated gate bipolar transistor, or the insulated gate bipolar transistor is a reverse blocking insulated gate bipolar transistor.

Insulated gate bipolar transistors allow to handle the massive currents of high power DC motors. Reverse blocking insulated gate bipolar transistor provide a high collector emitter blocking voltage, which particularly important with high power DC motors which are operated with 400 volts supply voltage and above. In case appropriate reverse blocking insulated gate transistors are not available a diode with a high blocking voltage may be connected with its cathode to the collector of an insulated gate bipolar transistor to improve the collector emitter blocking voltage of the insulated gate bipolar transistor.

In another aspect of the invention the transistor comprises a pair of a first transistor and a second transistor, wherein the emitter of the first transistor is connected to the collector of the second transistor and the collector of the first transistor is connected to the emitter of the second transistor, respectively the first transistor is connected with its collector to a cathode of a first diode and the collector of the second transistor is connected to a cathode of a second diode, and wherein the anode of the first diode is connected to the emitter of the second transistor and the emitter of the first transistor is connected to the anode of the second diode.

The insulated gate transistor may arranged in a full H-bridge, for example for supplying an armature current for the armature coil and in a half H-bridge for supplying a shunt current for a shunt coil of a DC motor.

In another aspect of the invention a pulse width modulated signal switches the semiconductor between an on-state and an off-state for controlling the current supplied by the semiconductors.

The insulated gate bipolar transistors can be used for pulse width modulation of the armature current and the shunt current. For this purpose the pulse width modulation signal preferably is generated a hardware circuit arrangement, such as a pulse width modulator. Although a hardware circuit with a simple design may not allow a perfect control of the armature current or the shunt current, it is still an improvement compared to simply connecting the armature coil and the shunt coil directly and permanently to the emergency supply.

A typical DC compound pitch motor, i.e. a DC motor with a armature winding, a series winding and a shunt winding with a nominal power of 6 KW would draw at a nominal voltage of 400 V an armature current of 35 A and a shunt current of 0.8 A producing 32Nm torque at a nominal speed of 1800 rpm. Such a motor would be operable down to a supply voltage of 200 V. When such a DC motor would be connected without limiting the armature current, due to the missing back electromagnetic force a rush-in current of approximately 200A would occur. In order to prevent this high rush-in current when the DC motor starts from standstill, or even to further limit the current below the nominal armature current, the duty cycle of the armature modifier, i.e. the ratio of the time the armature modifier is switched on in relation to a full switched on / switched off cycle would be set by the pulse width modulated signal to 10%. With this typical pitch motor the rush-in current is limited to 20A. After the initial period of two to three seconds, the motor is up to its nominal speed and the back EMF is established. When the duty cycle of the armature modifier is set now to 100% the back EMF limits the armature current to 35 A. That means the armature modifier after the initial period can stay switched on all the time until the motor has driven the rotor blade into the feathering position. When reaching the feathering position a limit switch is activated and signals to the pulse width modulator to switch off the armature current, or in other words, the limit switch signal causes to set the duty cycle of the armature switch to 0%.

In this example the initial duty cycle of the armature current was set to 10%, which is a compromise between a powerful startup of the motor and avoiding jerks that could damage the motor. Actually, sometimes a small jerk is even desired in cases where the charge may have been blocked by friction or other causes.

In another aspect of the invention a first semiconductor is connected in-between the emergency power supply line and the armature winding terminal of the DC motor, and the pulse width ratio of a first pulse width modulated signal controls the current supplied by the first semiconductor to the armature of the DC motor such that in an initial time period the current supplied to the armature of the DC motor is lower than in a time period following the initial time period. A first pulse width modulator that is used to modify the duty cycle of the armature current therefore is called in the following an armature pulse width modulator. By initially reducing the armature current the DC motor will have a gentle run-up. Depending on the characteristics of each individual motor the initial phase may be set to two to three seconds. After the initial period the armature current may be allowed its maximum magnitude. Alternatively or in addition to this aspect of the invention a second semiconductor is connected in-between the emergency power supply line and the shunt winding terminal of the DC motor, and the pulse width ratio of a second pulse width modulated signal controls the current supplied by the second semiconductor such that in an initial time period the current supplied to the shunt winding is higher than in a time period following the initial time period. The second pulse width modulator that is used to control the duty cycle of the shunt current therefore is called in the following a shunt current pulse width modulator.

Conversely to the armature current the shunt current is at its highest value in the beginning of the emergency period and is reduced over time to compensate for the falling voltage of the emergency power supply that is discharged mainly by the armature current. The falling shunt current reduces the magnetic field of the DC motor and as consequence less voltage is induced in the armature winding. This decreases the back electromotive force, from here on abbreviated to back EMF, is reduced and allows a larger current to flow through the armature coil. As larger armature current means increased driving torque the speed. Thus, the driving torque increases despite the motor slowing down. The capacity of the emergency power supply usually is chosen with some margin to be sufficient to drive a rotor blade from the farthest position to the feathering position in a certain time. Such full feathering run with emergency power supply may take for a 5 MW wind turbine for example 20 seconds, so that for such a wind turbine the time period in which the shunt current is reduced from its maximum value to its minimum value equals basically this time. In this time typically the voltage of an emergency power supply has fallen for example from 400 Volts to 200 Volts.

In the initial phase of the emergency mode the duty cycle of the shunt switch is set by the shunt pulse width modulator to 100%. For the DC motor as described above, thus the maximum possible shunt current of 0.8A would flow at 400V through the shunt winding. Due to the discharge of the emergency power supply the voltage of the emergency power supply continuously decreases, especially when ultra-capacitors are used as an emergency power source. As the shunt resistance does not experience a back EMF, the shunt currant at 200 V would also have fallen to 0.4A. The armature current, due to the reduced back EMF would have increased, but not enough to provide the same torque as during normal operation. In order to run sufficiently powerful at a decreased armature supply voltage of 200V the magnetic field of the shunt winding can be weakened. The value to what magnitude the shunt current has to be reduced depends on the characteristics of the motor design and can be determined by tests. If we assume that the typical DC pitch motor we are looking at needs at 200 V a reduction of the shunt current from 0.4 A to 0.3 A then it is obvious that the duty cycle of the shunt current modifier at 200V should aim at 0.3 A / 0.4 A = 75%. The duty cycle of the shunt current modifier, respectively the current pulse width modulation ratio can be set in a shunt current initial phase to 100% and in a second shunt current phase following the shunt current initial phase, to 75%. The reduced shunt current will then allow the armature current to rise to approximately 70 A, so that the nominal torque and the nominal speed can be achieved.

In another aspect of the invention the pulse width ratio of the pulse width modulated signal is controlled as a function of the time passed since the emergency power control device was set into an emergency power mode. Although using the time since the emergency mode started may not be perfect parameter to control the armature current modifier, it is a simple solution and has proven to work in most cases. In another aspect of the invention the pulse width ratio of the second pulse width modulated signal is controlled as a function of the time passed since the emergency power control device was set into emergency power mode. Although using the time since the emergency mode started may not be perfect parameter to control the shunt current modifier, it is a simple solution and has proven to work in most cases.

In normal operation mode the use of sensors allows to operate the DC motor always under optimized conditions, for example for speed, torque, and smoothness. The idea of the emergency control device is to keep the emergency control device as simple as possible, so that it is utmost reliable. For most applications the relation between the actions of the DC motor in emergency mode is predictable enough so that the control of the armature current and the shunt current can be approximated as a time dependent function.

In another aspect of the invention the pulse width ratio of the first pulse width modulated signal is controlled such that the current supplied to the armature winding of the DC motor gradually increases over time.

In a simplified version the duty cycle of the armature current modifier may be ramped during the start-up period in several intermediary steps or continuously from 10% to 100%. In a simplified version of the armature modifier the first pulse width modulator may ramp up the armature current from 0% to 100%, but a little jerk at start up, caused by an initial value, may help to start moving the rotor blade in case the rotor blade is jammed. The initial value may be 10% or even bigger, in case the everyday praxis shows that a higher initial value may be advantageous to overcome rotor blade jams.

In another aspect of the invention the pulse width ratio of the pulse width modulated signal is controlled such that the current supplied to the shunt winding of the DC motor gradually decreases over time.

Although switching between two different values for the armature current and the shunt current already improves the reaction of the DC motor in emergency mode, ideally a gradual increase of the armature current and a gradual decrease of the shunt current smoothens operation of the DC motor and the propelled charge. Gradually in this context means in more than one step, and includes continuously. Ideally an optimal shunt current can be determined in tests for a number of different voltages in-between the nominal supply voltage and the minimum supply voltage of the DC motor. Thus the ideal duty cycle can be calculated for the determined voltages and be stored in a look-up table, so that for an actual voltage of the emergency power supply the optimum duty cycle could be interpolated from the tabled values. In praxis it turned out that a coarse approximation by continuously reducing the shunt current dusty cycle from 100% to 75% over 20 seconds, the expected time the pitch motor would have run down the emergency supply voltage from 400 V to 200V is sufficient to maintain an almost constant torque of the pitch motor for turning a rotor blade back to the feathering position. The person skilled in the art knows that the shunt current duty cycle depends on the parameters of each type of DC motor and therefore would determine the respective duty cycle for each DC motor type in a test arrangement.

Depending on a specific application it may be sufficient to control only the armature current or only the shunt current of a DC motor. Especially high power DC motors may require both.

In most applications a time dependent control of the armature current and the shunt current would allow a sufficiently smooth operation of the DC motor in emergency mode. However if a more precise control is needed in another aspect of the invention the emergency power control device measures continuously the voltage of the emergency power supply and adjusts the pulse width ratio of the pulse width modulated signal to compensate for a decreasing voltage of the emergency power supply. In another aspect of the invention at least one of the connection means is a semiconductor and the disconnecting means for disconnecting the power converter is a fuse or a magnetic circuit breaker.

The interrupting means are used to disconnect the emergency power control device, the emergency power supply, and the DC motor from the power converter. This is particularly important when the failure due to which the emergency power mode is activated, is due to a failure of the power converter. In this case it may happen that faulty elements of the power converter may cause additional currents flowing into the emergency power control device or into the power converter. Therefore these currents can be interrupted by the semiconductor interrupting means. However, under cost aspects, spending semiconductors with high current properties may be too expensive. It has turned out that it may more cost effective to allow the high currents, which than will burn a fuse or activate a magnetic circuit breaker. As a situation, like a feathering run of a wind turbine is anyway a serious condition which requires service personal to physically visit the installation to decide if parts have to be changed, before the installation can be set back to normal operation, the costs for changing the fuses or to reset a magnetic circuit breaker are minimal.

Another advantage of uses is that the thermal charge inside the emergency power control device is reduced in comparison to contactors or even magnetic circuit breakers. The voltage drop caused by the contact resistance of a contactor is significantly higher than the voltage drop of a fuse. As the armature current for high power motors is significantly high the thermal power generated by the contact losses sums up to several watts. Insofar fuses as disconnecting means also reduce the heat that has to be dissipated.

In another aspect of the invention the DC motor is a DC motor with a series winding with a first series winding end and a second series winding end and wherein a flux bridge is connected with a first flux bridge terminal to the first series winding end, with a second flux bridge terminal to the second series winding end, with a third flux bridge terminal connected to the second armature winding end, and wherein the at least one connecting means is adapted to connect a forth flux bridge terminal to the emergency power supply. In another aspect of the invention one terminal of a resistor with a negative temperature coefficient is connectable by the semiconductor to the emergency power supply and the other terminal of the resistor with the negative temperature coefficient is connected the first end of the armature winding. This arrangement allows the continuous control over time of the armature current without the need of a pulse width controlled semiconductor. The NTC resistor has the known property to have a high resistance at normal operation temperatures. That means that in the initial phase the NTC resistor limits the armature current. The longer the armature current flows through the NTC resistor the more the NTC resistor is heat up by the armature current and its resistance decreases. Ideally the NTC resistor is chosen to be heat up within two to three seconds to allow an unlimited armature current to flow through the NTC resistor.

In another aspect of the invention a voltage dependent resistor (VDR) is connected in emergency power mode with one terminal by the transistor to the emergency power supply line and with its other terminal to the second end of the shunt winding. A voltage dependent resistor is known to have a variable resistance that depends on the voltage applied. At the initial phase of the emergency mode the voltage across the voltage dependent resistor is high and accordingly its resistance is low, allowing a high shunt current to flow. Over time, when the emergency power supply voltage decreases, the voltage across the voltage dependent resistor decreases and accordingly the shunt current flowing through the voltage dependent resistor also decreases. Thus the voltage dependent resistor allows to control the shunt current as a function of the voltage of the emergency power supply. In another aspect of the invention the components of the emergency power control device are arranged in a housing that is separate to a housing of the power converter or a housing of the motor.

This allows easy retrofitting of an emergency power supply as all components, apart from the battery perhaps, fit into a relatively small housing and no separate components have to be installed one after another. This saves installation time and installation space.

Especially the option to group of all electrical components on one printed circuit board avoids wiring errors and increases reliability of the emergency power supply arrangement.

Insofar, retrofitting an existing emergency power supply arrangement with separate components, especially substituting less reliable contactors by a single emergency power control device could be considered as a beneficial option.

In another aspect of the invention housing of the emergency power control device, the housing of the power converter, and the emergency power supply are arranged in one cabinet.

Due to the compact arrangement that the use of the semiconductors allows, the emergency power control device can be so small that it fits into a filing cabinet that already accommodates the power converter.

In another aspect of the invention the housing of the emergency power control device provides an external first input terminal for being connected to a first output terminal of a power converter and an external first output terminal for being connected to the first end of the armature, wherein the external first input terminal and the external first output terminal are internally connected by disconnecting means. In a further or an additional aspect of the invention the housing of the emergency power control device provides an external second input terminal for being connected to a second output terminal of a power converter and an external second output terminal for being connected to the first end of the shunt winding, wherein the external third input terminal and the third external output terminal are internally connected by disconnecting means. In a further or an additional aspect the housing of the emergency power control device provides an external third input terminal for being connected to a third output terminal of a power converter and an external third output terminal for being connected to the second end of the armature, wherein the external third input terminal and the external second output terminal are internally connected by disconnecting means. In a further or an additional aspect of the invention the housing of the emergency power control device provides an external fourth input terminal for being connected to a fourth output terminal of a power converter and an external fourth output terminal for being connected to the second end of the shunt winding, wherein the external fourth input terminal and the external fourth output terminal are internally connected by disconnecting means. In a further or an additional aspect of the invention the housing provides an external seventh input terminal for being connected to the positive pole of the emergency power supply. In a further or an additional aspect of the invention the housing provides an external eighth input terminal for being to the negative pole of the emergency power supply.

This allows for an easy installation as wires that are already present for a connection of a DC motor to a power converter can be cut in two and the resulting ends can be connected to the respective terminals of the emergency power control device.

In another aspect of the invention a method of installing an emergency power control device comprises at least one of the steps of cutting in two at least one of supply wires connecting the armature power supply of the power converter with the armature winding end of the motor; the shunt power supply of the power converter with the shunt winding end of the motor; the series power supply of the power converter with the second series winding end; common ground of the power converter with the second series winding end; connecting the ends of the cut wire that lead to the power connector with the respective input terminals of the power converter; connecting the ends of the cut wire that lead to the first armature winding end, the first shunt winding end, the serial winding end, the second shunt winding end to the respective first output terminals of the emergency power control device; connecting the positive pole of an emergency power supply to the first battery input terminal of the emergency power control device; connecting the negative pole of an emergency power supply to the second battery input terminal of the emergency power control device; connecting the first battery output terminal to the power converter; connecting the common ground input output terminal to the power converter. In another aspect of the invention the emergency power control device is installed in a wind turbine, particularly in the pitch drive of a wind turbine.

The invention is now described by way of examples. The drawings show: Figure 1 A prior art backup concept for a wind turbine

Figure 2 Another prior art backup concept for a wind turbine with a centralized AC/DC power supply

Figure 3 Details of a prior art power converter for a pitch drive of a wind turbine

Figure 4 Details of a prior art power converter and an arrangement of contactors for allowing an emergency mode in case of a failure of the power converter

Figure 5 an emergency power control device connected inserted between a power converter and a DC motor.

Figure 6 an emergency power control device with a NTC resistor as a armature current modifier and a VDR transistor as a shunt current modifier.

Figure 7 an emergency power control device comprising a first pulse width modulator and a second pulse width modulator. Figure 8 a armature current modifier comprising an arrangement of operation amplifiers

Figure 9 a shunt current modifier comprising an arrangement of operation amplifiers

Figure 10 IGBTs

Figure 11 an emergency power control device comprising fuses as interrupting means

Figure 12 the outer appearance of an emergency power control device Figure 13 a wind turbine

Figure 13 shows a side view of a horizontal axis wind turbine 100 according to the invention. The wind turbine 100 is used for converting a wind's kinetic energy into electrical energy. A tower 101, supporting a nacelle 102 and a rotor 103, 104a, 104b, is fixed to the ground. Evidently the invention is not limited to on-shore installations, where the tower is fixed to the ground but could also be used in connection with so- called off-shore installations where the tower is fixed to a structure in the sea or a structure floating in the sea. The rotor 103, 104a, 104b substantially comprises a hub 103 with three rotor blades 104a, 104b extending outwards with respect to the hub 103, from their root end, which is revolvably connected by a toothed ring to the hub 103.

The wind turbine 100 of this embodiment comprises three rotor blades 104a, 104b whereby in Fig. 13 only two rotor blades 104a, 104b are visible. The third rotor blade is not visible as it happens to be concealed by the hub 103. The rotor 103, 104a, 104b is rotationally connected to the nacelle 102 by a substantially horizontally orientated generator shaft 108. A yaw drive (not shown) is used to rotate the nacelle 102 around its axis TA in order to keep the rotor 103, 104a, 104b facing into the wind as the wind direction changes. An electric current generator 109 coupled by the generator shaft 108 to the rotor 103, 104a, 104b produces electrical energy which may be fed into an energy distributing net (not shown).

The speed at which the rotor 103, 104a, 104b rotates must be controlled for efficient power generation and to keep the stress on structure and components of the wind turbine 100 within design limits. Each rotor blade 104a, 104b therefore can be pivoted by a pitch drive unit 105a, 105b. As the wind turbine 100 in this example has three rotor blades 104a, 104b, there are three pitch drive units 105a, 105b. Similarly to the third rotor blade, which is concealed by the hub 103, the third pitch drive unit is not shown in Fig. 13. The three pitch drive units 105a, 105b are controlled by one common pitch system controller 106. Each pitch drive unit 105a, 105b is connected to an input of a gear box (not shown). An output pinion (not shown) of each gear box is in constant mesh with the toothed ring (not shown) of each rotor blade 104a, 104b. The

combination of pitch drive 105a, 105b, gear box and toothed ring turns each rotor blade 104a, 104b around a rotor blade axis BA. By turning the rotor blades 104a, 104b around their axis BA the angle of attack of the rotor blades 104a, 104b to the wind can be set to an angle substantially between 0 and 90 degrees. The angle of attack can be chosen thus that the rotor blades 104a, 104b even with strong wind produce no lift at all, or produce lift as a function of the wind speed. The produced lift is transformed into a rotation of the hub 103 around a rotor axis RA and eventually by the generator 109 into electrical energy. A turbine controller 107 sends command to the pitch system controller 106 for continuously setting the pitch angle of each rotor blade 105a, 105b individually, or commanding to turn the rotor blades 104a, 104b into the feathering position. Pitch angles and yaw angle of the nacelle eventually control the rotation speed of the rotor 103, 104a, 104b and thus also the amount of energy produced by the generator 109.

The only efficient way to stop the rotation of the rotor 103, 104a, 104b is known as feathering, i.e. to increase the pitch angle of the rotor blades 104a, 104b so that they are orientated parallel to the airflow. As feathering is critical for stopping the rotor 103, 104a, 104b during emergency shutdowns, the pitch drives 5a, 5b usually are supplied by an emergency power source (not shown in Fig. 13) allowing feathering of the rotor blades 104a, 104b even when power supply from the power grid is interrupted. An emergency power control device 1 installed preferably at or at least close to each pitch drive 105a, 105b or the pitch system controller 107 enables the wind turbine 100 to drive the pitch drives 105a, 105b into the feathering position in case the wind turbine is not powered any longer from an external source such as a power grid.

There are different types of DC motors which are used for the pitch drives 205a, 205b, such as a compound motor with a shunt winding 33, which has a first shunt winding end connected to a first shunt winding terminal Fl and a second shunt winding end, connected to a second shunt winding terminal F2, an armature winding 31, which has a first armature winding end, connected to a first armature winding terminal Al and a second armature winding end, connected to a second armature winding terminal B2 , and a series winding 33, which has a first series winding end, connected to a first series winding terminal Dl and second series winding end, connected to a second series winding terminal D2, as shown for example in Fig. 5. For simple applications, where the DC motor 2 mainly turns only in one direction, the second armature winding end and the first series winding end may be permanently connected and may not even be accessible without dismantling the motor 3. The invention is explained in connection with the more complex compound DC motor, but is evident that the invention is equally applicable to pure series DC motors or pure shunt DC motors by omitting, or not connecting for example a shunt winding.

A converter 20 provides power for the armature winding 31, the shunt winding 33 and/or the series winding 32 that can be controlled to run the motor at a defined speed and/or torque and/or turning direction to a commanded position.

In case the external power source fails, and there are no provisions for an emergency power supply, the motor 3 will stop substantially at its current position, unless the motor is actuated by its charge. For applications where it is crucial that the motor is still operable for a short time period after a power failure, for example to allow to actuate a charge into a pre-defined, safe position, emergency power supplies have been provided in the past, either at the input of the power converter 20 or have been connected internally to circuitry of the power converter 20. Particularly, when the charge is heavy or has to be actuated in a sensitive way, the emergency power supply should not be directly connected to the shunt field coil 31, the armature 31 and the series field coil 32. An abrupt change of the voltage applied to the armature may result in a hard jerk which can add damage to the motor or the charge.

The invention proposes a way in which a drive system comprising a power converter 2 and a DC motor 3, which have not yet been equipped with an emergency power supply, can be easily modified to allow, in an appropriate way, to control the motor 3 during an emergency action.

Figure 5 shows in a first embodiment a circuit diagram of an emergency power control device 1 which is inserted between the power converter 20 and the DC motor 3. Figures 12a, 12b shows the housing of such an emergency power control device 1 in which the described circuit elements are implemented on a single circuit board (not shown). The emergency power control device 1 provides on one side of the housing an emergency mode signal input E, an armature input terminal U' and an armature output terminal U", a series input terminal V and a series output terminal V", a shunt input terminal W and a shunt output terminal W", a first emergency input battery terminal Bat'+ and a first emergency output battery terminal Bat"+, a second emergency input terminal Bat'-, a common ground input terminal ZK'- and a common ground input terminal ZK"-. For the purpose of easy retrofitting the input terminals ZK'+, U', V, W, and ZK'- preferably are provided on a first side 11 or faceplate of the housing as shown in Figure 12a, and the output terminals ZK"+, U", V", W", ZK"- are provided at a second side 12 of the housing or a second faceplate of the housing, that is opposite to the first side 11 of the housing. This allows to cut the wire 51, 52, 53, 54 and reconnect them, without the need to extend them, on both sides of the emergency power control device 1.

The person skilled in the art will appreciate that some terminal may not be provided, or others may be provided in addition, depending on the specific application. For example in connection with a series motor the emergency power control device 1 may not provide a shunt input terminal V and no shunt output terminal V". The emergency power control device 1 allows a simple retrofitting of a drive with an emergency power supply which had so far no emergency power supply at all, or only an emergency power supply that powered the converter 20, but did not provide emergency powering capabilities in case a failure occurs in the converter 2 itself.

For retrofitting the emergency power control device 1 a first wire 51, which connects the armature power supply terminal U of the power converter 20 with the armature winding end Al of the motor 3 is cut in two, resulting in a first armature wire end 51a and a second armature wire end 51b. In this embodiment the first armature wire end 51a denotes the wire end of that half of the first wire 51 that goes to the armature power supply terminal U of the power converter 20. The second armature wire end 51b denotes the wire end of that half of the first wire 51 that goes to the armature winding end Al of the motor 3. The first wire end 51a is then connected to the armature input terminal U' of the emergency power control device 1 and the second armature wire end 51b is then connected to the armature output terminal U" of the emergency power control device 1. Further a second wire 52 which connects the shunt power supply terminal V of the power converter 2 with the first shunt winding end Fl of the motor 3 is also cut in two, resulting in a first shunt wire end 52a and a second shunt wire end 52b. In this embodiment the first shunt wire end 52a denotes the wire end of that half of the second wire 52 that goes to the shunt power supply terminal V of the power converter 20. The second shunt wire end 52b denotes the wire end of that half of the second wire 52 that goes to the first shunt winding end Fl of the motor 3. The first shunt wire end 52a is connected to the shunt input terminal V of the emergency power control device 1 and the second shunt wire end 52b is connected to the shunt output terminal V" of the emergency power control device 1.

Similarly, a third wire 53 which connects the series power supply terminal W of the power converter 2 with the second series winding end D2, respectively the input of the flux bridge 34 of the motor 3, is also cut in two, resulting in a first series wire end 53a and a second series wire end 53b. In this embodiment the first series wire end 53a denotes the wire end of that half of the third wire 53 that goes to the series power supply terminal W of the power converter 2. The second series wire end 53b denotes the wire end of that half of the third wire 52 that goes to the second series winding end D2 of the motor 3, respectively to the flux bridge 34 input of motor 3. The first series wire end 53a is connected to the series input terminal W of the emergency power control device 1 and the second series wire end 53b is connected to the series output terminal W" of the emergency power control device 1. In case the emergency power control device 1 is retrofitted to a drive which had no emergency power supply a positive pole + of an emergency power supply 4 to the emergency power control device 1 and a second emergency power input terminal Bat- for connecting the negative pole of the emergency power supply 4 to the emergency power control device 1. The emergency power supply 4 is sufficiently dimensioned to supply the motor 3 in a worst scenario condition long enough with electrical power so that from whatever actual position of the motor 3, the motor 3 will always make it to the pre-defined, safe position. The time that it takes the motor to proceed from the actual position to the pre-defined position is called in the following the emergency phase. As will be explained in more detail later, when the power converter 20 fails to deliver power to the motor 3 the emergency power control device 1 is switched either automatically in emergency power supply mode or is switched actively in emergency power supply mode. The period of time, which starts when the emergency power control device 1 changes to emergency mode, is called in the following "initial phase" of the emergency mode. The motor after the initial phase the motor is allowed accelerate until it is running at a pre-defined maximum speed. Once the motor has arrived at the maximum speed the speed is preferably kept constant until the motor 3 has arrived at the pre-defined position. The period of time that starts when the motor has arrived at its maximum speed and lasts until the motor is in the predefined position is called in the following the "constant phase". Depending on the application, the initial phase and the final phase may last a few seconds. If the charge is already close to the pre-defined position, the initial phase may be reduced to almost zero and the constant phase is never attained.

In this, and the following embodiments, which need quite substantial power the emergency power supply 4 is of significant size. For practical reasons the emergency power supply 4 therefore is not arranged inside the emergency power control device 1. However, applications may exist, particularly for smaller motors, where the emergency power supply 4 may be placed inside of the emergency power control device 1. In all embodiments, the emergency power control device 1 comprises at least one of an armature current modifier, and a shunt modifier. The armature current modifier connects the first armature terminal Al to the positive emergency input terminal Bat+ and allows to control the armature current I ar mature supplied to the armature winding 31 of the motor 3. The armature current modifier is adapted to provide in the beginning of an emergency phase the armature current Iarmature at a reduced current level which ideally increases over time. The emergency power control device 1 also may comprise disconnecting means for disconnecting the power converter 20 in case the wind turbine enters into an emergency mode. In an embodiment shown in Fig. 6 the disconnecting means are implemented as a first transistor pair composed of a first transistor Tl and a second transistor T2, a third transistor T3, a second transistor pair composed of a fourth transistor T5 and a fifth transistor T5, and a sixth transistor T6. The first transistor Tl, the second transistor T2, the third transistor T3, the fourth transistor T5, the fifth transistor T5, and the sixth transistor T6 are termed from hereon for easier reference as the disconnecting transistors Tl, T2, T3, T4, T5, T6. An emergency control circuit 23 generates disconnecting control signals Kl, K2, K3, K4, K5, K6 for controlling the switching status of the disconnecting transistors Tl, T2, T3, T4, T5, T6. In normal operation mode the disconnecting control signals Kl, K2, K3, K4, K5, K6 set all the disconnecting transistors Tl, T2, T3, T4, T5, T6 in a conductive state. The first pair of transistors Tl, T2 connects the armature input terminal U' of the emergency power control device 1 with the armature output terminal U" of the emergency power control device 1. The third transistor T3 connects the series input terminal V of the emergency power control device 1 with the series output terminal V" of the emergency power control device 1. The second pair of transistors T4, T5 connects the shunt input terminal W of the emergency power control device 1 with the shunt output terminal W" of the emergency power control device 1. The first emergency input battery terminal Bat'+ is wired permanently to the first emergency output battery terminal Bat"+ and the second emergency input terminal Bat'- is connected permanently to common ground input terminal ZK'-. The sixth transistor T6 connects in normal operation mode the common ground input terminal ZK'- of the power emergency device 1 with the common ground output terminal ZK"- of the power emergency device 1. As soon as the pitch drive is signalled to be in emergency mode, the disconnecting control signals Kl, K2, K3, K4, K5, K6 set all the disconnecting transistors Tl, T2, T3, T4, T5, T6 in a non-conductive state. This means that the first pair of transistors Tl, T2 isolates the armature input terminal U' of the emergency power control device 1 from the armature output terminal U" of the emergency power control device 1 ; the third transistor T3 isolates the series input terminal V of the emergency power control device 1 from the series output terminal V" of the emergency power control device 1 ; the second pair of transistors T4, T5 isolates the shunt input terminal W of the emergency power control device 1 from the shunt output terminal W" of the emergency power control device 1; and the sixth transistor T6 isolates in normal operation mode the common ground input terminal ZK'- of the power emergency device 1 from the common ground output terminal ZK"- of the power emergency device 1. The disconnecting transistors Tl, T2, T3, T4, T5, T6 thus inhibit any current to flow from the power converter 20 into the emergency power control device 1, and consequently inhibit in emergency mode any current from the power converter 20 to the armature winding 31, the series winding 32, or the shunt winding 33. In emergency mode only currents generated by the emergency power control device 1 are enabled to control the DC motor 3.

The emergency power control device 1 further comprises an armature power modifier and a shunt current modifier. The armature current modifier of the first embodiment comprises a negative temperature coefficient thermistor (NTC thermistor) NTC, which is connected with a first terminal to the first armature winding end Al and with its second terminal to a third pair of transistors, composed of a seventh transistor T7 and a eight transistor T8. As a function of a seventh control signal K7 and an eighth control signal K8 the fourth pair of transistors T7, T9 connect or disconnect the NTC resistor from the positive emergency power input Bat'-, and consequently from the positive pole Bat+ of the emergency power supply 4. A fourth transistor pair, composed of a ninth transistor T09 and a tenth transistor T10 connects in emergency mode the shunt output terminal W" with the negative emergency power input terminal Bat'-. The fourth transistor pair T9, T10 is controlled by a ninth control signal K9 and a tenth control signal K10 of the emergency control circuit 23.

In normal operation mode the seventh control signal K7, the eighth control signal K8, the ninth control signal K9, and the tenth control signal K10 generated by the emergency control circuit 23 set the third transistor pair T7, T8 and the fourth transistor pair T9, T10 into non-conductive state, i.e. no current can flow from the emergency power input terminal Bat'+ through the NTC resistor NTC, or from the first input 341 of the flux bridge 34 to common ground ZK-. As long as no current is flowing through the NTC thermistor NTC the temperature of the NTC thermistor NTC follows naturally the ambient temperature and his resistance is kept at a high value. In the event the emergency signal E signals the emergency control circuit 23 that the pitch drive unit is now in an emergency mode, the emergency control circuit 23 activates the seventh control signal K7 and the eighth control signal K8 thus setting the third transistor pair T7, T8 and the fourth transistor pair T9, T10 into a conductive state, connecting the NTC resistor NTC to the emergency power supply 4, and the first terminal 341 of the flux bridge 34 to common ground, respectively the negative supply voltage of the emergency power supply 4. Once the emergency power supply is switched on a relatively small armature current I ar mature flows through the NTC resistor TC and the armature winding 31 back to the negative pole of the emergency power supply 4. Over time, the current flowing through the NTC thermistor NTC heats up the NTC thermistor NTC and the resistance of the NTC thermistor NTC continuously decreases over time. Consequently, the current flowing through the armature winding 31 increases over time. Thus, the motor 3 is allowed gently increasing speed and torque. NTC thermistors NTC are available in a wide range of parameters and the person skilled in the art will know which NTC thermistor NTC to choose for a given motor 3 to achieve the desired effect. For a typical pitch motor as described above the person skilled in the art would chose a NTC resistor NTC which after two to three seconds would have gained its lowest resistance.

As a complement to the armature current modifier, the emergency power control device 1 may further comprise a shunt current modifier which connects the positive emergency power supply input Bat+ to the first shunt winding end Fl for controlling the shunt current Ishunt flowing through the shunt winding 33. In this embodiment, the shunt field modifier is implemented as a voltage dependent resistor VDR which at a low voltage has a high electrical resistance that decreases as the voltage is raised. The shunt current modifier further comprises an eleventh transistor Ti l, which when the pitch drive is in emergency mode is set by an eleventh control signal Kl l of the emergency control circuit 23 into conductive state. In conductive state the eleventh transistor Ti l connects the voltage dependent transistor VDR to the positive pole Bat+ of emergency power supply 4. The other terminal of the voltage dependent resistor VDR is connected to the first shunt winding end Fl . The second shunt winding end F2 is connect in emergency mode by a twelfth transistor T12 to the negative emergency power input terminal Bat'-. The twelfth transistor T12 is controlled by a twelfth control signal K12 of the emergency control circuit 23. In the beginning of the emergency mode the emergency power supply provides a high voltage. Ideally the voltage dependent transistor VDR is chosen such that the voltage across the voltage dependent transistor VDR is sufficiently high to set the voltage dependent transistor VDR to a relatively low resistance, thus allowing a high current flow through the shunt winding 33. Over time, when the supply voltage of the emergency supply 4 decreases also the voltage over the voltage dependent resistor VDR decreases and consequently its resistance increases, thus allowing even less current to flow through the shunt winding 33. Thus over time the magnetic shunt field is reduced and allows the DC motor or maintain its speed and torque despite the falling voltage level of the emergency power supply 4.

The components that form the emergency power control device may be arranged as indicated in figure 5 in a separate housing. This has the advantage that the emergency power control device 1 can be retro-fitted in existing motor systems by cutting the lines that connect the power converter 2 with the terminals of the motor 3 in two. The input and output terminals of the emergency power control device 1 may be located inside the separate housing to protect the terminals against being touched. In case the power converter 2 is in a housing of a switch cabinet (not shown) and there is space inside the housing of the switch cabinet the terminals of the emergency power control device 1 may be provided openly at the outside of the separate housing of the emergency power control device 1. In another aspect of the invention, the components of the emergency power control device 1 may be even added inside a housing of the power converter 2, if there is sufficient space inside the power converter housing.

The embodiment shown in Figure 6, uses on purpose only passive components for the armature current modifier and the shunt current modifier. Especially in applications where a high safety level has to be achieved, the use of long time approved passive components may be the preferred way of implementing the emergency power control device 1.

The emergency power supply 4 may be permanently connected to the emergency power control device 1, in which case, when the power converter 2 is working regularly, the emergency power supply 4 may be charged through the VDR resistor 11. Alternatively, a dedicated charger (not shown) may charge the emergency power supply 4. In case the power supply of the power converter 2 fails, for example one or more of the transistors are short-circuited or permanently interrupted, the voltages of the first output terminal V and the third output terminal U have collapsed, the higher voltage of the emergency power supply 4 automatically takes over the power supply of the armature current modifier 12 and the series current modifier 11. In another aspect of the invention, the emergency power supply 4 may be disconnected from the emergency power control device 1 by a switch (not shown) which may be located outside the emergency power control device 1 or inside the emergency power control device 1 and which is voltage controlled. Once a voltage sensor (not shown) would detect a power failure of the power converter 2, the switch is closed and connects the emergency power supply 4 to the emergency power input terminal Bat+.

Figure 7 shows another embodiment which differs from the embodiment of Figure 6 in that the armature current modifier is implemented by a first pulse width modulator PWM 1 controlling the seventh and eight transistor T7, T8 and the and the shunt current modifier is implemented as a second pulse width modulator PWM2 controlling the eleventh transistor Ti l . Same signs are used in Figure 6 and 7 to indicate same elements. Particularly the disconnecting means, which in emergency mode will disconnect the emergency power control device 1 from the power converter 20 are identically implemented by disconnecting transistors Tl, T2, T3, T4, T5, T6.

The third pair of transistors T7, T8 connects the positive emergency power supply terminal Bat+ with the armature output terminal U" and the fourth pair of transistors T9, T10 connects the shunt output terminal W" with the second emergency input terminal Bat'-. In normal mode the third transistor pair T7, T8 and the fourth transistor pair T9, T10 are all in a non-conductive state and therefore do not disturb the normal operation mode. In emergency mode the disconnector transistors disconnect the power converter 20 from the emergency supply device 1 and the armature current and the shunt current are controlled exclusively by the emergency control circuit 23.

During an emergency mode the emergency control circuit 23 will set the ninth transistor T9 and the tenth transistor T10 by a ninth control signal K9 a tenth control signal KIO permanently in conductive state such to allow any current flowing through the armature winding 31 to complete its flow to the negative pole Bat- of the emergency supply4. The first pulse width modulator PWM 1 is controlled by a first pulse width control logic, which is part of the first pulse width modulator PWM 1 and therefore not shown in Fig. 7. In case the emergency power control device 1 is in emergency mode, the first pulse width control logic is triggered by an eleventh control signal Kl l. The first pulse width modulator PWM 1 then generates a first pulse width modulated signal Gl, which controls the gate of the seventh transistor T7, so that the duty cycle of the armature current flowing via the armature output terminal U" into the first armature winding end Al in an initial phase of the emergency mode has a lower duty cycle than in a later phase. Thus, in the initial phase the seventh transistor T7 is mainly switched off and let pass only very little armature current I ar mature from the positive pole Bat+ of the emergency power supply 4 to the armature winding 31 of the motor 3 and via the ninth transistor T9 back to the negative pole of the emergency power supply 4. Over time, the control logic of the first pulse width modulator PWM1 controls the first pulse width modulator PWM 1 to increase the duty cycle of the seventh transistor T7 until after a pre-defined time, the output signal of the first pulse width modulator PWM 1 is permanently switched on, i.e. the duty cycle is 100%, if the motor 3 has not reached the pre-defined position within this time already. In case the seventh transistor T7 does not invert the input signal at his gate, the duty cycle of the armature current is fairly identical to the pulse width ratio of the first pulse width modulated signal Gl produced by the first pulse width modulator PWM 1. In case the seventh transistor T7 inverts the first pulse width modulated signal it is obvious that the first pulse width modulated signal has to be created complementary to the desired duty cycle of the armature current. In the present embodiment, the shunt current modifier has been also substituted by a second pulse width modulator PWM2 controlled by a second pulse width controller (not shown in Fig. 7) and a twelfth transistor T12, which is controlled by a twelfth control signal K12. In normal mode the eleventh transistor Ti l and the twelfth transistor T12 are all in a non-conductive state and therefore do not disturb the normal operation mode. In emergency mode the disconnector transistors disconnect the power converter 20 from the emergency supply device 1 and the shunt current is controlled exclusively by the emergency control circuit 23. During an emergency mode the emergency control circuit 23 will set the twelfth transistor T12 by a twelfth control signal K12 permanently in conductive state such to allow any current flowing through the shunt winding 33 to complete its flow to the negative pole Bat- of the emergency supply 4.

The second pulse width modulator PWM2 produces a second pulse width modulated signal G2 for controlling the eleventh transistor Ti l . The eleventh transistor Ti l connects the positive emergency power supply terminal Bat+ and the series output terminal V" of the emergency power control device 1 and the twelfth transistor T12 connects the common ground input terminal ZK'- with the second emergency input terminal Bat'-. In case a shunt winding 33 is connected to the series output terminal V" the duty cycle of the eleventh transistor Ti l controls the shunt current of the shunt winding 33. In contrast to the first pulse width modulator PWM 1, the second pulse width modulator PWM2 controls with the second pulse width ratio of the second pulse width modulated signal G2 the duty cycle of the shunt current to be in an initial phase of the emergency mode at a very high level, for example about 100%. The second pulse width controller causes the duty-cycle of the shunt current to be reduced with the falling supply voltage or, alternatively over time. Again, the shunt current profile to be created by the second pulse with modulated signal G2 depends on the motor and the application. For example, for a DC motor with a power of 6 kW driving a rotor blade of a wind turbine into the feathering position, the duty cycle of the shunt current may be reduced from 100% to 75% when the supply voltage of the emergency power supply has fallen down to half its initial value, or if the second pulse width modulator PWM2 is time controlled, over the time the motor 3 has turned the rotor blade from an extreme position to the feathering position.

The first pulse width controller PWM 1 allows to define by means of the first pulse with modulated signal Gl an individual armature current profile, and likewise the second pulse width controller PWM2 allows to define by means of the second pulse with modulated signal G2an individual shunt current profile. Preferably, the first pulse width controller and the first pulse width modulator PWM 1 are implemented with hardware circuits. The avoidance of a microprocessor and software for generating the armature current profile and the shunt current profile allows a high degree of reliability for safety critical applications. Figure 8 shows as an example, a hardware circuit that is entirely composed of a first operational amplifier OPl, a second operational amplifier OP2, a third operational amplifier OP3, a fourth operational amplifier OP4, a fifth operational amplifier OP5, a first resistor Rl, a second resistor R2, a third resistor R3, a fourth resistor R4, a fifth resistor R5, a sixth resistor R6, a first capacitor CI, and a second capacitor C2. One terminal of the first resistor Rl forms the input E of the first pulse with modulator 1. The other terminal of the first resistor 1 is connected to the inverting input of operational amplifier OPl . Between the output of the first operational amplifier OPl and the inverting input of the first operational amplifier OPl lies the first capacitor CI . The non-inverting input of the first operational amplifier OPl is connected to common ground. In this configuration, the first operational amplifier OPl, the first resistor Rl and the first capacitor CI form a first integrator. The second resistor R2 connects the output of the first operational amplifier to the inverting input of the second operational amplifier OP2. The third resistor R3 forms a feedback resistor which is connected between the output of the second operational amplifier OP2 and the inverting input of the second operational amplifier OP2. The output signal of the second operational amplifier OP2 depends on the input signal E. As long as the input signal is on common ground potential, the first integrator OPl, Rl, CI produces an output signal that is equivalent to common ground potential. In emergency mode, when the input signal is on a pre-defined constant level, the output signal of the integrator rises constantly. The sixth resistor R6, the second capacitor C2 and the fourth operational amplifier OP4 form a second integrator. The output signal of this second integrator is fed back to the fourth resistor R4, which is connected to the inverting input of the third operational amplifier OP3. The fifth resistor R5 connects the inverting input of the third operational amplifier OP3 and the output of the third operational amplifier OP3 and thus forms with the fourth resistor R4 and the third operational amplifier OP3 an inverting amplifier. The resistance values of the fourth resistor R4 and the fifth resistor R5 are chosen so that the third operational amplifier OP3 overdrives the third operational amplifier OP3 and thus the arrangement of the fourth resistor R4, the fifth resistor R5 and the third operational amplifier OP3 forms a Schmitt-trigger. Thus, the second integrator OP4, R6, C2, the output signal of which is fed back to the Schmitt-trigger OP3, R4, R5 produces an output signal in the form of a triangular signal. As this triangular signal is input to the inverting input of the fifth operational amplifier OP5, in emergency mode, when the input signal of the fifth operational amplifier on its non-inverting input is rising slowly, the fifth operational amplifier OP5 produces the first pulse with modulated signal Gl . As indicated in Figure 8, the pulse with modulated signal can be amplified by a driver circuit DC1 and eventually control the eighth transistor T8. Figure 9 shows an example of a hardware circuit that produces a pulse with modulated signal G2 independent of the emergency battery voltage Ubat. The emergency supply voltage Ubat is fed into a voltage divider which is formed by a seventh resistor R7 and an eighth resistor R8. The output signal of the voltage divider R7, R8 is fed into the non- inverting input of a sixth operational amplifier OP6. An output divider formed by a ninth resistor R9 and a tenth resistor RIO feeds back the output signal of the sixth operational amplifier OP6 to the inverting input of the sixth operational amplifier OP6. Similar to the circuit of Figure 8, an eleventh resistor Rl l, a twelfth resistor R12, a seventh operational amplifier OP7, a thirteenth resistor R13, a third capacitor C3, and an eighth operational amplifier OP8 form a signal generator with a second triangular signal. The second triangular signal is fed into an inverting input of the ninth operational amplifier OP9 and the output signal of the sixth operational amplifier OP6 is fed to the non-inverting input of the ninth operational amplifier OP9. The ninth operational amplifier OP9 compares the emergency battery voltage Ubat with the second triangular signal and produces the second pulse with modulated signal G2, which drives via a second drive circuit DC2, the ninth transistor T9.

Figure 10 shows a replacement arrangement for the transistors Tl to T12 in case reverse blocking IGBT's are not available for the required reverse voltages and currents. In such a replacement arrangement, a first anode of a first diode Zl can be connected to the emitter of an IGBT and the cathode of the first diode Zl can be connected to the collector of the IGBT. A cathode of a second diode Z2 can be connected to the collector of the IGBT so that the anode of the second diode Z2 forms the collector input of this replacement circuit. Figure 10b shows the equivalent symbol of a reverse blocking IGBT, which has the first Diode Zl and the second Diode Z2 integrated with the IGBT chip. Figure 10c shows the way a pair of reverse blocking insulated gate bipolar transistors IGBT1, IGBT2, are connected to form a bi-directional conducting Reverse Blocking IGBT, as they are used for the first transistor pair Tl, T2, the second transistor pair T4, T5, the third transistor pair T8, T7, and the ninth transistor pair T9, T10. The collector of the first transistor IGBT1 is connected with the emitter of the second transistor IGBT2 and the emitter of the first transistor IGBT1 is connected to the collector of the second transistor IGBT2. This arrangement enables a current to flow from the collector of the first transistor IGBT1 to the emitter of the first transistor IGBT1 and in the opposite direction to flow from the collector of the second transistor IGBT2 to the emitter of the second transistor IGBT2. Figure 11 shows an embodiment in which the input terminals of the positive emergency power supply Bat+, the first input terminal V, the third input terminal U and the fourth input terminal W are each protected by fuses 15, 16, 17, 18. This allows to substitute the transistors by the fuses 15, 16, 17, 18.

The initial value of the pulse with ratio and the minimal value of the pulse with ratio may be set by little switches which allow to select different resistor values for example the third resistor R3 and the ninth resistor R9. By varying the resistance of these resistors the time constant of the first pulse width modulator PWM 1 and the amplification of the second pulse width modulator PWM2 may be adapted to motors with different power rating and different torque versus speed characteristics.

Various aspects of the invention have been described in the above embodiments. The invention covers especially an emergency power control device 1 for a DC motor 3 comprising at least one of an armature current modifier PWM 1, T7 for supplying in an emergency mode an armature winding of the DC motor 3 from emergency power supply 4 whereby the armature current modifier PWM 1, T7 is configured to control the power supplied from the emergency power supply 4 to the armature 31 such that the power increases continuously over time; a shunt winding current modifier PWM2, Ti l for supplying in an emergency mode a shunt winding 33 of the DC motor 3 by the emergency power supply 4 whereby the shunt winding current modifier PWM2 is configured to control the power supplied from the emergency power supply 4 to the shunt winding 33 such that the power supplied to the shunt winding 33 decreases continuously over time.

List f reference signs

1 emergency power control device

11 first side of emergency power control device 12 second side of emergency power control device

100 wind turbine

101 tower

102 nacelle

103 hub

104a, 104b rotor blades

105a, 105b pitch drive unit

107 turbine controller

106 pitch system controller

108 generator

BA rotor blade axis

RA rotor axis

2a, 2b, 2c pitch drive unit

20 DC converter

21 pitch drive control circuit

211, 212 first pair of transistors

213, 214 second pair of transistors

215, 216 third pair of transistors

22 contactor control circuit

23 emergency control circuit

3, 3a, 3b, 3c pitch drive motor

31 armature winding

32 series winding

33 shunt winding

34 flux bridge

341 first flux bridge terminal

342 second flux bridge terminal

343 third flux bridge terminal

344 fourth flux bridge terminal Al first armature winding end

Bl second armature winding end

Dl first series winding end

D2 second series winding end

Fl first shunt winding end

F2 second shunt winding end

4, 4a, 4b, 4c emergency power supply

40a, 40b, 40c emergency power supply charging supply lines 40 emergency power supply charger

5a, 5b, 5c, 501, 502 decoupling diodes

51 armature supply wire

51a, 51b first and second armature wire end

52 shunt supply wire

52b, 52b first and second shunt supply wire end

53 series supply wire

53a, 53b first and second series supply wire end

54 Common ground supply wire

54a, 54b first and second common ground supply wire end

6 wind turbine controller 7 pitch system controller

8 power grid

80 power supply line 9 DC power module

90 power supply line