POWER SUPPLY ARRANGEMENT OF A CONVEYING SYSTEM

The invention relates to the handling of braking power in a conveying system.

In a conveying system power is supplied to the motor for moving the conveying apparatus. Power supply to the motor generally occurs by means of a frequency converter. When braking a conveying apparatus with motor braking, power also returns from the motor to the frequency converter. Especially in low-powered systems the returning power is generally consumed as heat in a separate power resistor of large size. In higher-powered systems the braking power of the motor is normally returned to the network by means of a very expensive and complex network inverter-rectifier.

Publication US4545464 presents an elevator system in which the braking power returning from the motor is supplied to the electrification of the elevator system.

The purpose of this invention is to solve the aforementioned problems as well as the problems disclosed in the description of the invention below. One object of the invention is to disclose an arrangement for controlling the braking power of a conveying system that is more versatile than prior art.

The power supply arrangement of a conveying system according to the invention is characterized by what is disclosed in the characterization part of claim 1. The method according to the invention for controlling the power supply in a conveying system is characterized by what is disclosed in the characterization part of claim 5. Other features of the invention are characterized by what is disclosed in the other claims. Some inventive embodiments are also discussed in the descriptive section of the present application. The inventive content of the application can also be defined differently than in the claims presented below. The inventive content may also consist of several separate inventions, especially if the invention is considered in the light of expressions or implicit sub-tasks or from the point of view of advantages or categories of advantages achieved. In this case, some of the ug

2 attributes contained in the claims below may be superfluous from the point of view of separate inventive concepts.

The power supply arrangement of the conveying system according to the invention comprises a controller of the movement of the conveying apparatus, which is fitted to adjust the movement of the conveying apparatus according to a determined movement reference; and also a frequency converter with intermediate circuit, which is connected between the power source of the of the conveying system and the motor that moves the conveying apparatus; and which frequency converter comprises a rectifying bridge, which is connected to the power source of the conveying system. The power supply arrangement comprises a controllable network inverter-rectifier, which is connected between the intermediate circuit of the frequency converter and the power source of the conveying system, for supplying power from the intermediate circuit to the power source. A controllable brake chopper is fitted in connection with the main circuit of the frequency converter, for connecting a power resistor to the main circuit of the frequency converter in an electrically conductive manner. The power supplied via the network inverter-rectifier is limited to the determined limit value for power supply by the control of the network inverter-rectifier. That part of the power flow passing from the motor to the intermediate circuit, which exceeds the limit value for the power supply of the network inverter-rectifier, is determined; and the controller of the brake chopper is fitted to control at least one controllable switch of the brake chopper, for consuming in the power resistor the part of the power flow passing from the motor to the intermediate circuit that exceeds the limit value for the power supply of the network inverter- rectifier.

In one embodiment of the invention the power supply arrangement comprises a controllable single-phase network inverter-rectifier, which is connected between the intermediate circuit of the frequency converter and a phase of the electricity network. In this case power is supplied to the motor that moves the conveying apparatus from the phases of the electricity network, but power is returned in motor braking back only to one phase of the electricity network with a single- ug

3 phase network inverter-rectifier. The limited power return capability can thus be improved by adding a brake chopper to the arrangement, with which brake chopper the part of the power flow that exceeds the limit value for the power supply of the single-phase network inverter-rectifier is consumed in the power resistor as heat.

In the method for controlling the power supply in a conveying system: a controller of the movement of the conveying apparatus is fitted to the conveying system; a frequency converter is fitted between the power source of the conveying system and the motor that moves the conveying apparatus; a network inverter-rectifier is fitted between the intermediate circuit of the frequency converter and the power source of the conveying system, for supplying power from the intermediate circuit to the power source; a brake chopper is fitted in connection with the main circuit of the frequency converter; the power supplied via the network inverter-rectifier is limited to the determined limit value for power supply; that part of the power flow passing from the motor to the intermediate circuit, which exceeds the limit value for the power supply of the network inverter-rectifier is determined; and at least one controllable switch of the brake chopper is controlled, for consuming in the power resistor the part of the power flow passing from the motor to the intermediate circuit that exceeds the limit value for the power supply of the network inverter-rectifier.

The conveying system referred to in the invention can be, for instance, an elevator system, an escalator system, a travelator system, a drum drive elevator system, a crane system, a vehicle system or a conveyor system for conveying goods or raw materials. The term conveying apparatus refers to the part of a conveying system, with which passengers, goods or raw materials are moved.

The elevator system according to the invention can be with machine room or without machine room. The elevator system can also be provided with a counterweight or can be an elevator system without a counterweight.

One network inverter-rectifier according to the invention comprises a changeover switch and a choke. The aforementioned network inverter-rectifier ug

4 can be fitted to the intermediate circuit of the power supply apparatus of the motor via diodes connected to its positive and negative intermediate circuit busbar. The network inverter-rectifier according to the invention can also operate without the aforementioned diodes, but the diodes ensure that power flowing from the network to the motor of the conveying system is not possible as a result of e.g. malfunctioning of the network inverter-rectifier. Mechanical controllable switches, such as relays or contactors, or semiconductor switches such as IGBT transistors, can be used instead of the diodes.

In one embodiment of the invention a controllable switch, which is fitted to close when the intermediate circuit voltage has reached a pre-determined limit value, is fitted in series with at least one choke. The pre-determined limit value can be, for instance, 350 volts.

In one embodiment of the invention the network inverter-rectifier control comprises a first and a second limit value of intermediate circuit voltage, of which the first limit value is greater than the second limit value. The network inverter-rectifier is fitted to start the power supply from the intermediate circuit to the power source of the conveying system after the intermediate circuit voltage has exceeded the first limit value. The network inverter-rectifier is fitted to stop the power supply from the intermediate circuit to the power source of the conveying system after the intermediate circuit voltage has fallen below the second limit value. In other words, in this case the first and the second limit value form hysteresis limits for the starting and the stopping of the power supply of the network inverter-rectifier.

In one embodiment of the invention the control of the brake chopper comprises a third and a fourth limit value of intermediate circuit voltage, of which the third limit value is greater than the fourth limit value. The brake chopper is fitted to start the electricity supply through the power resistor after the intermediate circuit voltage has exceeded the third limit value. The brake chopper is fitted to stop the electricity supply through the power resistor after the intermediate circuit voltage has fallen below the fourth limit value. In this case the third and ug

5 the fourth limit value form hysteresis limits for the starting and the stopping of the electricity supply of the power resistor. In one embodiment of the invention the aforementioned fourth limit value of the intermediate circuit voltage is greater than the aforementioned first limit value of intermediate circuit voltage.

In one embodiment of the invention the power flow occurring from the motor that moves the conveying apparatus to the frequency converter is determined ^v on the basis of the measured loading of the conveying apparatus.

With the invention at least one of the following advantages, among others, is achieved:

When the power supplied via the network inverter-rectifier is limited to the determined limit value for power supply, the network inverter-rectifier can be made smaller than prior art. In this case it can also be integrated if necessary into the frequency converter.

Since it is possible with the power supply arrangement according to the invention to supply the braking energy of the motor that moves the conveying apparatus moved back to the mains network, the efficiency ratio of the conveying system improves.

When the controller of the brake chopper is fitted to control at least one controllable switch of the brake chopper, for consuming in the power resistor the part of the power flow passing from the motor to the intermediate circuit that exceeds the limit value for the power supply of the network inverter-rectifier, the power resistor can be dimensioned to be smaller than prior art. In this case in one embodiment of the invention it is possible to use a power resistor, which is connected in a thermally conductive manner to a heat sink of the frequency converter. In one embodiment of the invention a power resistor is used only with essentially maximum loading and/or in an overloading situation of the conveying system, and otherwise the power flow passing from the motor to the intermediate circuit is directed in its entirety to the power source of the conveying system. In one embodiment of the invention the power resistor has a ug

6 separate heat sink, which is fitted in the same flow channel of the cooling air as the heat sink connected in a thermally conducting manner to the power semiconductors of the frequency converter.

By means of the power supply arrangement according to the invention it is possible to reduce the maximum value of the current passing from the intermediate circuit of the frequency converter to the electricity network. The aforementioned current can also be controlled to be sinusoidal, in which case the harmonics of the network current diminish.

When the movement reference of the conveying apparatus during motor braking is determined using as the determination criteria both the limit value for the power supplied by the network inverter-rectifier and also the power handling capacity of the power resistor, the movement and the conveying capacity of the conveying apparatus can be optimized according to the loading of the conveying apparatus.

When the movement reference of the conveying apparatus during motor braking that is to be used during a functional nonconformance of the power source of the conveying system is determined using essentially just the power handling capacity of the power resistor as the determination criterion, the conveying apparatus can be used with limited movement with motor braking also during a functional nonconformance of the power source. For example, it is possible to drive the elevator car in the event of an electricity outage in the light direction at a limited speed. In this case the elevator car can be moved closer to the nearest suitable exit floor with motor braking, in which case the passengers are able to leave the elevator car.

In the following, the invention will be described in more detail by the aid of a few examples of its embodiments with reference to the attached drawings, wherein

Fig. 1 presents one power supply arrangement of a conveying system according to the invention ug 7

Fig. 2 presents a second power supply arrangement of a conveying system according to the invention

Fig. 3 presents an elevator system according to the invention

Fig. 4 presents the power flow of a conveying system according to the invention

Fig. 5 presents the movement references of a conveying apparatus

Fig. 1 presents a power supply arrangement of a conveying system, in which the power of the motor 8 that moves the conveying apparatus is adjusted with a frequency converter 3 with intermediate circuit, according to the control commands of the controller 1 of the movement of the conveying apparatus. A three-phase network inverter-rectifier 11 is fitted in parallel with the rectifying bridge 4 of the frequency converter. The direct voltage part of the network inverter-rectifier is connected to the intermediate circuit 6,6' of the frequency converter and the alternating voltage part is connected to the phases of the electricity network 7. The alternating voltage part in the network inverter-rectifier 11 comprises a three-phase choke 20, via which the network inverter-rectifier is connected to the electricity network 7. In addition, capacitors (not shown in figure) are connected between the phases of the electricity network. The distortion of the network current caused by the network inverter-rectifier is reduced with the choke and with the capacitors. The rectifying bridge 4 of the frequency converter is made from diodes, whereas the network inverter-rectifier

11 comprises controllable IGBT transistors, with which the power supply from the intermediate circuit to the electricity network is adjusted. The network inverter-rectifier 11 is made of components with a current endurance that is markedly smaller than the current endurance of the rectifying bridge 4 of the frequency converter and of the motor bridge 5. The power supplied to the electricity network via the network inverter-rectifier 11 is limited to the limit value

12 for power supply. The limit value for power supply is determined on the basis of the current endurance of the IGBT transistors of the network inverter-rectifier 1 1 . ug

8

A brake chopper 9 is fitted in connection with the intermediate circuit of the frequency converter. The IGBT transistor of the brake chopper 9 and also the serial circuit of the power resistor 10 are connected between the positive 6 and the negative 6' intermediate circuit busbar. When the IGBT transistor conducts, the power resistor 10 consumes the electrical power of the intermediate circuit as heat. The power resistor 10 is e.g. a flat thick-film resistor or a carbon-film resistor, which is fixed in a thermally conducting manner to a heat sink. The heat sink of the resistor is fitted on the exhaust air side in the same flow channel of the cooling air as the heat sink of the power semiconductors of the frequency converter.

The controller 9' of the brake chopper determines the power flow passing from the motor 8 to the intermediate circuit 6,6' on the basis of the measurement of the intermediate circuit voltage. When the power flow passing from the motor to the intermediate circuit exceeds the limit value 12 for the power supply of the network inverter-rectifier, the intermediate circuit voltage starts to increase. The controller 9' of the brake chopper controls the IGBT transistor of the brake chopper in response to the increase in intermediate circuit voltage, in which case the part of the power flow that exceeds the limit value 12 for the power supply is consumed as heat in the power resistor.

The power supply arrangement presented in Fig. 2 differs from that described in the embodiment of Fig. 1 in that the network inverter-rectifier 7 is single-phase. The alternating voltage part of the network inverter-rectifier 11 is connected to one of the three phases of the electricity network 6. The direct-voltage part of the network inverter-rectifier comprises two capacitors connected in series, and the electricity network 7 comprises a neutral wire, which is connected to the point of contact of the capacitors. The diodes 18, 19 are also fitted between the direct-voltage part of the network inverter-rectifier and the intermediate circuit 6,6' of the frequency converter, which diodes prevent power flow from the direct-voltage part to the intermediate circuit. The same type of fitting of the diodes can also be made between the direct-voltage part of the three-phase Ug

9 network inverter-rectifier 11 and the frequency converter 3 in the embodiment of Fig. 1

Fig. 3 presents an elevator system into which a power supply arrangement according to the invention is fitted. In the elevator system the elevator car 2 and the counterweight are supported by means of elevator ropes passing via the traction sheave of the elevator motor 8 in a manner that is, in itself, prior art. The power supply arrangement comprises a controllable network inverter- rectifier 11 according to the invention, which is connected between the intermediate circuit 6,6' of the frequency converter of the elevator system and the electricity network. A brake chopper 9 is fitted in connection with the main circuit of the frequency converter 3. The controller 9' of the brake chopper is fitted to control at least one controllable switch of the brake chopper, for consuming in the power resistor 10 the part 13 of the power flow passing from the motor to the intermediate circuit that exceeds the limit value 12 for the power supply of the network inverter-rectifier. The power handling capacity of the power resistor 10 is dimensioned to the determined limit value 14 for the power to be handled.

The loading of the motor 8 that moves the elevator car 2 is determined on the basis of the imbalance between the elevator car and the counterweight. In this embodiment of the invention the imbalance is at its greatest with an empty elevator car or with a fully loaded elevator car. The elevator motor supplies power to the frequency converter 3 during motor braking. In motor braking the force effect of the elevator motor is in the opposite direction to the movement of the elevator car.

One power supply arrangement of an elevator system according to the invention also comprises a determination of the operating status of the electricity network 7. In this case the power supply of the network inverter- rectifier 11 is fitted to be disconnected when a functional nonconformance of the electricity network 7, such as a reduction of the voltage of the electricity network or a voltage cut, is detected. The speed reference of the elevator car during ug

10 motor braking that is to be used during a functional nonconformance of the electricity network 7 is determined using essentially just the power handling capacity 14 of the power resistor as the determination criterion. The speed of the elevator car is limited during a functional nonconformance such that the power flow returning from the elevator motor 8 to the intermediate circuit 6, 6' of the frequency converter can be consumed in its entirety in the power resistor 10. The speed of the elevator car is in this case limited during motor braking, especially during a large imbalance between the elevator car and the counterweight.

Fig. 4 presents the power flow as a function of time in one elevator system according to the invention. During acceleration of the elevator car power is supplied from the frequency converter to the elevator motor. The force effect of the elevator motor during even speed is in the opposite direction to the movement of the elevator car, in which case power flows from the elevator motor to the frequency converter. The flowing power is supplied in this case in its entirety back to the electricity network via the network inverter-rectifier 11. When the elevator car starts to brake the power flow from the elevator motor to the frequency converter increases, exceeding the limit value 12 for the maximum power supply of the network inverter-rectifier. In this case the part 13 of the power flow that exceeds the limit value of power supply is consumed as heat in the power resistor 10 connected to the main circuit of the frequency converter.

Fig. 5 presents some speed references during motor braking of one elevator system according to the invention. When the imbalance between the elevator car and the counterweight is small, the speed reference is determined according to the nominal speed 17 of the elevator system. As the imbalance increases, the deceleration of the elevator car decreases 15, in which case the power flow from the elevator motor to the frequency converter decreases correspondingly. The speed reference 16 during a functional nonconformance of the electricity network is fitted to limit the movement of the elevator car, in Ug

11 which case the power flowing from the elevator motor to the frequency converter can be consumed in its entirety in the power resistor 10.

The invention is not limited solely to the embodiments described above, but instead many variations are possible within the scope of the inventive concept defined by the claims below.

If a direct-current motor is used as the motor of the conveying apparatus, the main circuit of the motor bridge can be arranged as an H-bridge circuit.

The motor that moves the conveying apparatus can be a rotating motor or also a linear motor, in which case the moving rotor can be fixed directly to the conveying apparatus.

The power source of the conveying system can be e.g. an electricity network, a generator, a fuel cell, and/or a UPS power source. In this case the alternating- electricity source can be e.g. single-phase or three-phase.

The part of the power returning to the frequency converter during motor braking can be used also for the power needs of the electrification of the conveying system.

Movement of the conveying apparatus refers to e.g. the speed, acceleration and length of movement of the conveying apparatus.

The movement reference of the conveying apparatus can be formed e.g. from a plurality of consecutive reference values. On the other hand the reference can also be described as a continuous reference curve in relation to time.

The controller of the movement of the conveying apparatus, the controller of the brake chopper and/or the controller of the network inverter-rectifier can be integrated into some other controller of the conveying system.

The power flow passing from the motor that moves the conveying apparatus to the intermediate circuit of the frequency converter can be determined e.g. on the basis of the measurements of the current and/or voltage of the motor.