DEVICE FOR ADJUSTING THE POWER OF THE CAPACITORS USED FOR REACTIVE POWER COMPENSATION IN AN ELECTRONICALLY-CONTROLLED

WAY

Technical Field

The present invention relates to a device adjusting, in an electronically-controlled way, the capacitive reactive power provided to the network by the power capacitors which are used for reactive power compensations in three phase power plants.

State of the Art In our day, there are systems manufactured for compensation. Generally in these systems, power capacitors which are proportional to the reactive power are used in order to meet the reactive power. Another system is SVC (Static VAR [volt-ampere reactive] compensator) system. This system operates by using a fixed capacitor and by using a shunt reactor adjusted according to the capacitor power. Existing applications generally use two methods:

The First Method: Traditional capacitor switching method (stepped method). The Second Method: static VAR compensator (SVC) method, where a thyristor- controlled reactor is added to the first method.

In the first method, the interference can only be as much as the smallest capacitor in the system and it cannot reach the intermediate values. For example, the capacitor values in the steps are:

0,25 kVAR mono-phase (one for each phase, in total 3),

-0,5 kVAR mono-phase (one for each phase, in total 3),

-1 kVAR three-phase,

-2,5 kVAR three-phase,

-5 kVAR three-phase capacitors,

Reactive power is 7 kVA. In this situation, the relay can only use the capacitors with 5 kVAR + 2,5 kVAR but cannot meet the real value. Moreover, this method cannot compensate for the instability in the phases. In order to compensate for the instability, there is a need to add an extra capacitor into the circuit. This increases the cost.

In the second SVC system, the result is more successful. But there is a need to add a SVC driver, a SVC relay and a shunt reactor. The cost thereof is very higher compared to the first method. Moreover, there are volume and weight problems in this system increased relative to the power of the shunt reactor.

On the other hand, there is no system in the prior art similar to the device of the present invention. There are only thyristor-switched reactors and phase-angle adjusted reactor applications and products.

The disadvantages of the existing methods are given below:

Limited and insufficient: rough and unsuccessful compensation interference: Naturally, each step of a capacitor steps in or out completely in stepped methods. The interference is performed as available or not in the circuit for each capacitor step. This leads to an unsuccessful compensation when there is a need for intermediate values apart from the number and power of the steps.

Higher cost, size and weight:

An absolute solution cannot be provided with the rough values originating from the stepped nature of the first method. The second method should be added. In the second system, as there is a need for a reactor, a reactor driver and a suitable relay the cost, size and weight increase very much.

More step need for unbalanced loads:

In the plants where unbalanced loads are drawn between the phases, each phase needs to be compensated differently. In this way with traditional methods, more capacitors, more contactors, more fuses and more harmonic filters are needed in the plants and facilities with unbalanced loads. This problem can be solved by high cost solutions in the existing applications. It causes the products to have more step number like 18 steps, 24 steps and 36 steps instead of 12 steps suitable for this purpose.

The problems caused by or cannot be solved properly by the existing methods are as follows:

1 . Overloading of the electrical distribution and transmission lines for electric power manufacturers and distributors

2. Penalty payment of reactive power besides the consumption amount for the electric consumers and plant and facility owners

3. Loading of the internal lines for the electric consumers and plant and facility owners

4. Increase in the installation costs for the electric consumers and plant and facility owners

5. High maintenance costs for the electric consumers and plant and facility owners

6. Decrease in energy quality and therefore problems in the stabilization of the machines during operation for the electric consumers and plant and facility owners

7. Manufacture with high cost for the compensation system manufacturers

8. A large number of parts, therefore high labor costs for the compensation system manufacturers

9. Difficulty in manufacture, transportation and handling relative to the weight and sizes for the compensation system manufacturers

Consequently, there is a need for development in the related technical field because of the disadvantages mentioned above and the insufficiency of the existing solutions.

Object of the Invention

The object of the invention is to overcome the above mentioned disadvantages which are created by inspiring from the existing situations.

The device of the present invention provides a solution for all the technical problems mentioned above and for the shortcomings of the traditional methods in the market by performing the near-ideal compensation with less part number when compared to the existing technique. The solution provided by said device performs near-ideal compensation by a method different than the existing one. An ideal compensation means compensation which meets the reactive power needed for the plant-facility separately, completely and instantly for each phase. For this reason, only one capacitor with sufficient power should be divided into infinite number of steps for each phase and interference should be performed to the plant for the speed of the network frequency in an ideal compensation. As it is not possible to divide into infinite number in practice, the capacitor power should be divided into thousands of steps thanks to the device of the present invention.

The device of the present invention operates separately for each phase. In the device, there is only one capacitor for each phase and there are three mono-phase capacitors in total. Each capacitor is divided into thousands of steps electronically by software. In an application where the device is tested and operated, the capacitor power is divided into 3125 steps for each phase and 9375-stepped-compensation is performed in total. Change in the number of the steps cannot be the subject of another invention and it can be changed according to the application. Each capacitor in the present invention is switched 50 times in a second simultaneously with the network frequency (50Hz in Turkey and Europe) at a value suitable for the plant.

In brief, the object of the present invention is to divide any power capacitor electronically into thousands of steps. In order to realize this, we use IGBT (Insulated Gate Bipolar Transistor) semi-conductors and microcontrollers which are cutting-edge technology of the power electronic.

The digital values of the present invention and the reactive power control relay software used may vary according to the applications and to the person who performs the application.

The AC power capacitor of the present invention can be controlled by power diodes + IGBT power electronics circuit, the voltage remaining thereon can be changed at each alternans of the network and the power of the capacitor can be adjusted instantly. The energy which is stored on AC power capacitor and which is re-discharged can be adjusted and controlled periodically like opening and closing a valve. AC power capacitor can be controlled by means of software via semiconductors and the adjusted energy can be stored. Thus, total energy storage capacity of the capacitor does not need to be activated completely but the desired amount can be used; therefore a power-adjusted capacitor is obtained. Comparably, the opening-cutting down operation is performed by the IGBT and power diodes which serve as a valve; the hand which controls the valve is the reactive power control relay and software. Here the part which stores and returns the energy is the power capacitor because of the current thereof controlled by the valve. Therefore, the power capacitor exceeds the condition "whether it is activated completely or it is deactivated" as is in the traditional methods in the state of art. The need for a large number of steps in traditional methods is eliminated and only one capacitor is sufficient per one phase.

In order to realize the objects mentioned above, a device is developed which can adjust, in an electronically-controlled way, the capacitive reactive power provided (compensated, met with capacitive one against the inductive one) to the network by the power capacitors which are used for reactive power compensations in three phase power plants, which can store and discharge the energy instantly. Said device comprises: for each phase of the network:

IGBT-A which is a transistor serving as a controller in the positive direction of the AC current in order to control the reactive energy amount stored on the power capacitor and/or drawn by the power capacitor,

IGBT-B which is a transistor serving as a controller in the negative direction of the AC current in order to control the reactive energy amount stored on the power capacitor and/or drawn by the power capacitor,

- the following power diodes which performs a blockage in the reverse direction in order to use IGBT-A and IGBT-B and which enable connecting IGBT-A and

IGBT-B to AC voltage:

o Diode A which does not conduct current to IGBT-A in the reverse direction

o Diode B which does not conduct current to IGBT-B in the reverse direction IGBT driver-A which converts the weak digital signal from the reactive power control relay (R) with microcontroller into an amplitude to be applied to the IGBT- A and which applies it to IGBT-A,

IGBT driver-B which converts the weak digital signal from the reactive power control relay with microcontroller into an amplitude to be applied and which applies it to IGBT-B,

- and in order to provide the desired amount of the reactive power of the power capacitor into the circuit by interrupting the current of the power capacitor at each alternans of each period of the network at an absolute voltage value of the target power capacitor, said reactive power control relay common for all of the phases; o which measures reactive power and electrical parameters of the system to which the device is connected at each period of the network;

o which provides switching of IGBT-A and IGBT-B via the software on the microcontroller therein;

o which calculates the target voltage for the interruption point of the power capacitor current via the software on said microcontroller in order to reach the target power, wherein the reactive power needed by the system is the target power; and

o which calculates the triggering timing of IGBT-A and IGBT-B which provides the calculated target voltage via the software on said microcontroller for the determined and needed reactive power;

o which is connected to said IGBT driver-A and said IGBT driver-B.

The structural and characteristic features and all of the advantages of the present invention can be understood more clearly thanks to the drawings and the detailed description given with reference to the these drawings and therefore, the assessment should be performed by taking these drawings and detailed description into account.

DRAWINGS WHICH HELP UNDERSTANDING OF THE INVENTION

Figure 1 shows the circuit diagram of the device according to the present invention. Description of Part References

11 . IGBT-A

12. IGBT-B

D1 . Diode-A

D2. Diode-B

C. Power capacitor

51 . IGBT driver-A

52. IGBT driver-B

R. Reactive power control relay

x: connection part to which an on-off signal is transmitted

The drawings do not necessarily be scaled and unnecessary elements to understand the invention may be ignored. In addition, the elements with at least substantially the same or having at least substantially functions are shown with the same number.

Detailed Description of the Invention

In this detailed description, preferred embodiments of device of the invention are explained for better understanding of the subject.

The device of the invention has been developed for three phase power plants. The device operates with the same logic for each phase (phase R, phase S, phase T). The operating logic of the first phase (for example, phase R) was described by referring the elements thereof. The operating logic of the other two phases (phase S and phase T) was the same as that of first phase. Thus, only the operation of the first phase was disclosed. The other phases operates with the same logic by increasing the same elements. The device of the invention comprises: for every phase (R, S and T): one IGBT-A (11 ),

one IGBT-B (I2), - one diode-A (DI ),

- one diode-B (D2),

- one power capacitor (C),

- one IGBT driver-A (SI ),

- one IGBT driver-B (S2); and for every phases a common reactive power control relay (R). Said elements were described in conjunction with their properties and functions. - IGBT-A (11 ) is a transistor serving as a controller in the positive direction of the AC current in order to control the reactive energy amount stored on the power capacitor and/or drawn by the power capacitor. IGBT-A (11 ) is a modern control member used in power electronics and provides an electronic switching function.

IGBT-B (12) serves as a controller in the negative direction of the AC current in order to control the reactive energy amount stored on the power capacitor and/or drawn by the power capacitor. IGBT-B (12) is a modern control member used in power electronics and provides an electronic switching function.

- With respect to Diode-A (D1 ) and Diode-B (D2): IGBT-A (11 ) and IGBT-B (I2) are unidirectional power switching members operating at a DC voltage and current. In the device of the invention diode-A (D1 ) and diode-B (D2) were used, which perform a blockage in the reverse direction in order to use

IGBT-A and IGBT-B and which enable connecting IGBT-A and IGBT-B to AC voltage. The function of Diode-A (D1 ) is not to conduct current to IGBT- A (11 ) in the reverse direction. DC member serves as a connection to AC voltage. The technical characteristic of Diode-A (D1 ) is not to conduct current in the reverse direction. The function of Diode-B (D2) is not to conduct current to IGBT-B (I2) in the reverse direction. DC member serves as a connection to AC voltage. The technical characteristic of Diode-B (D2) is not to conduct current in the reverse direction. - With respect to power capacitor (C): In the prior arts, full power was enabled by contactors or electronic switching processes (generally by thyristors), or power capacitor was never enabled. The reactive energy amount which is stored on the power capacitor (C) and is transmitted to the network via the power capacitor (C) can be controlled owing to the device of the invention. The function of the power capacitor is to store and discharge instant reactive power. Capacitors are able to store and discharge the reactive power as long as the electronic switches are turned on. Determining the reactive power amount is not a function of the capacitor. The function of the capacitor is to store and discharge the reactive energy. Operation of all the elements together allows this energy to be adjustable. Technically, these capacitors are able to store electric energy as much as their capacities and to discharge the stored energy, thus providing compensation of the inductive reactive energy. The power capacitor (C) of the invention has also this characteristic. The power capacitor is connected to E (Emitter) end of IGBT- A and to C (Collector) end of IGBT-B.

IGBT driver-A (S1 ) and IGBT driver-B (S2) are the driver circuits which are required to control IGBT-A (11 ) and IGBT-B via weak signals of a microcontroller contained in the reactive power relay (R). IGBT driver-A (S1 ) and IGBT driver-B (S2) connects IGBT-A (11 ) and IGBT-B to the reactive power control relay (R). IGBT driver-A (S1 ) and IGBT driver-B (S2) generates the insulation voltage and the needed supply voltage internally. IGBT driver-A (S1 ) and IGBT driver-B (S2) convert the weak digital signal from the reactive power control relay (R) with microcontroller into an amplitude to be applied to IGBT-A (11 ) or IGBT-B (I2); generate their supplies with one supply obtained from the reactive power control relay (R) in an insulated manner; and enable an electrical insulation. The connection of IGBT-driver-A (S1 ) and IGBT driver-B (S2) to IGBT-A (11 ) and IGBT-B (I2), respectively is as follows: For example, for phase R (the connections for the other two phases, namely phase S and phase T, are the same as phase R): The connection of IGBT driver-A (S1 ) to IGBT-A (11 ) is performed via G (Gate), E (Emitter), C (Collector) ends of IGBT-A (11 ). Similarly, the connection of IGBT driver-B (S2) to IGBT-B (I2) is performed via G (Gate), E (Emitter), C (Collector) ends of IGBT-B (I2). The connection G (Gate) and E (Emitter) is sufficient to allow IGBT (IGBT-A (11 ) and IGBT-B (I2)) to turn on or off, whereas additional functions such as a thermal or short-circuit protection are provided via the connection C (Collector). - Although there are different types of reactive power relay (R) in the present methods, IGBT-A (11 ) and IGBT-B are switched when required and as needed owing to specifity of the microcontroller software to the device of the invention. The function of the reactive control relay (R) is to generate control signals such that they will be specific to the compensation needs of the plant.

In the device of the invention, for every phase two digital signals (2 on-off signals for one phase, total 6 on-off signals for three phases) output from the reactive power relay (R), with respect to the connection parts to which an on-off signal is transmitted. For phase R (in phase S and T the same method and operation logic apply), of these two signals from the reactive power relay (R) one is connected to input ends of IGBT driver- A (S1 ) and the other is connected to input ends of IGBT driver-B (S2). Two connection points are present in the inputs of IGBT driver-A (S1 ) and IGBT driver-B (S2). One for each is joined and connected to "+" (positive) supply connection point of driver circuit supply voltage from the reactive power control relay (R). The other "-" (negative) input ends are connected to on-off signal outputs from the relay. As the object of the device of the invention is to drive IGBT-A (11 ) and IGBT-B (I2), this connection may be achieved in a different way. For example, an "on" situation may be achieved by a "+" (positive) signal from the reactive power relay (R) instead of a "-" (negative) signal by joining "-" (negative) connections instead of "+" (positive) ones.

Electric parameters of the network can be measured in each period via the reactive power control relay (R). Reactive power required for compensation of the system is determined by reactive power control relay (R) depending on the reactive power, phase voltage parameters and in accordance with compensation target adjustments. This power required is the target reactive power. Thanks to the device of the invention, power capacitor (C) is adjusted such that it meets capacitive reactive requirements formed on inductive loads (a more ideal solution than the present methods of the prior art is provided by adding additional reactor to our method even in inductive requirements being a requirement in capacitive loads).

According to this reactive power determined by the reactive power control relay (R) times of IGBT driving signals is again determined by the target voltage calculated by the active power control relay (R). The target reactive power, the target voltage and switching and interruption signal timings which will bring the power capacitor (C) to this voltage and will cease it when reached are measured and calculated by the reactive power control relay (R) in each period of the network. IGBT driving signals are produced in these times calculated in each period by the reactive power control relay (R). There are two IGBT driving signals for each phase. One of the IGBT driving signals is in positive current direction flowing from the AC network to the power capacitor (C), and the other is in negative current direction from the power capacitor (C) to the AC network. In positive direction current, Diode-A (D1 ) and IGBT-A (11 ) components are active. In negative direction current, Diode-B (D2) and IGBT-B (I2) components are active. IGBT driver-A (S1 ) or IGBT driver-B (S2) are used as signal amplifier and converter in order to apply the IGBT driving signals from the reactive power control relay (R) to the relevant IGBT. The target voltage is an absolute value its operation is symmetrical in working principle of the device of the invention. The voltage consists of positive and negative alternans; for example if it is 125 Volts, "+125Volts" in positive alternans and "-125 Volt" in negative alternans is the target voltage. The meaning of the operation of the target voltage in working principle of the device is that the location of the point in which energy stored on power capacitor (C) will be interrupted upon reaching to which voltage, i.e. current of power capacitor (C) will be interrupted. Another meaning is that the location of the point in which energy stored on power capacitor (C) will be discharged, i.e. current of power capacitor (C) will be interrupted. From the opposite dimension, it is the point on which the power capacitor (C) current will start. The power capacitor (C) current is controlled to be initiated at the point when the voltage of the network has the voltage value of charging of the capacitor (C). The current is passed through the power capacitor (C) until the networks is again on the opposite direction point of the target voltage point. The target voltage period may change in each period. And at the point of the target voltage required in the period of change, the charging of the power capacitor (C) is interrupted the charging and response is provided to the required within 20 msecs at most.

As a summary, the power capacitor may be adjusted with the automatic control by means of the device of the invention. Thousands of capacitor power is produced from a power capacitor (C) of a fixed power. In the working principle of the invention, while "the capacitor power" is the maximum power limit, "zero" is the minimum power limit. Thousands of capacitive power values are obtained between "zero" and "capacitor power" value. Thanks to the device of the invention, the energy stored in and discharged from the power capacitor (C) is provided in desired amounts, for each period and with power switches (IGBT-A (11 ), IGBT-B (I2), diode-A (D1 ), diode-B (D2), IGBT driver-A (S1 ), IGBT driver-B (S2)). Amount of stored and discharged energy is indirectly related to the voltage point of the network at which power capacitor (C) current is interrupted and continued on reaching to the same voltage point. With periodical switching of power electronic semiconductors, i.e. IGBT-A (11 ) and IGBT-B (12), the power capacitor (C) is enabled in desired point, and disabled in desired point. Thusly, capacitive reactive effect of the power capacitor (C) to the system for each period may be adjusted with tens of thousands steps.

Working principle of the device of which components are explained above is as follows:

- The reactive power and the electrical parameters of the system to which the device will be attached are measured in each period of the network by the reactive power control relay (R).

- The reactive power required by the system is determined by adjustments and measurements of the reactive power control relay (R) in each period of the network.

- The reactive power required by the system is the target power.

- The target voltage is calculated for the point of interruption of the current of the power capacitor (C) by means of an installed software within the microcontroller inside the reactive power control relay (R) for reaching a the target power.

IGBT triggering timings are calculated to enable the calculated target voltage by means of the installed software within the microcontroller inside the reactive power control relay (R) for the determined and required reactive power.

- The signals activating (switching with closed circuit) and deactivating (interruption of the current with open circuit) IGBT-A (11 ) and IGBT-B (I2) at predetermined times are from the reactive power control relay (R) by the microcontroller in each period of the AC electrical network. The signals from the reactive power control relay (R) are provided to the IGBT-A (11 ) and IGBT-B (I2) by being converted to an adequate amplitude and power by IGBT driver-A (S1 ) and IGBT driver-B (S2).

After the half of the negative alternans of the network and until the half of the positive alternans (10 milliseconds for 50 Hz network), the ones with positive direction current from IGBT branches, i.e. diode-A (D1 ) and IGBT-A (11 ), in the other process of the period the ones with negative direction current from IGBT branches, i.e. diode-B (D2) and IGBT-B (I2) are controlled (the points of the processes on which the power capacitor (C) is enabled and disabled is determined with the target voltage).

All these procedure steps are repeated in network frequency, the power capacitor (C) current is interrupted in each alternans of each period of the network in absolute voltage value (positive voltage value for the positive alternans, negative voltage value for negative alternans), it is thusly enabled that desired amount of the reactive power of the power capacitor (C) is enabled (thusly, "all power enabled" and "disabled" method of the prior art is surpassed, and a novel working principle in which enabling and disabling of the power capacitor (C) power in an adjusted manner).