Control system for asymmetric and instantaneous grid static var generator

Abstract

The control system for the asymmetric and instantaneous power grid static var generator comprises a control system body, the control system body is further provided with a main control unit, and the main control unit comprises a constant voltage subunit, a transient state control subunit, a reactive power control subunit, a reactive power voltage control subunit, a harmonic control subunit, a negative sequence voltage control subunit and a remote control subunit. After asymmetric and transient voltage signals sampled by the control system body are processed, harmonic components in the signals are filtered out, meanwhile, three-phase positive sequence voltage signals are extracted to serve as reference signals, the control system body samples reactive current, negative sequence voltage, voltage out-of-limit and the like according to the positive sequence signals, and then the reactive current, the negative sequence voltage, the voltage out-of-limit and the like are obtained. The SVG power device is controlled to emit trigger pulse impact according to different control strategy modules of the SVG power compensation device, the control efficiency is improved, on the other hand, the signal processing speed of the whole control system body is improved, the compensation speed of the SVG dynamic reactive power compensation equipment controlled by the control system body is ensured, and the service life of the SVG dynamic reactive power compensation equipment is prolonged. And a good dynamic compensation effect can be obtained in the transient process of the power grid.

Description

Technical Field

[0001] The invention relates to the technical field of electric power application, in particular to a control system for an asymmetric, instantaneous power grid static reactive generator. Background Art

[0002] In the power supply system, asymmetric load (asymmetric load refers to the three-phase power load with initial phase difference or amplitude difference, or both, in the three-phase AC power system) will cause the three-phase asymmetry of the grid voltage, which will lead to unstable grid operation, increase the additional loss of equipment, reduce the efficiency and life of electrical equipment, and even cause safety hazards. For example, single-phase electrified railways and AC welding, if no power compensation device is installed, will produce a relatively large negative sequence current; negative sequence current will cause many protection and automatic devices in the power system that use negative sequence current as the starting element to malfunction, and because the phase sequence of negative sequence and positive sequence current is opposite, the additional electric force generated after the power enters the rotating motor will cause vibration and additional loss of the motor, and the negative sequence current will also affect the power output capacity of the power generation equipment. In addition, when hydropower, thermal power and other power generation are transmitted over long distances or offshore wind power is transmitted via long cables, the reactance and resistance of the transmission line will cause reactive loss and voltage drop, which will affect the transmission efficiency and stability, or the instantaneous power transmission of large-capacity transformers without load will cause instantaneous fluctuations in the power grid. All of the above require dynamic reactive power compensation via power compensation devices.

[0003] In the prior art, power compensation devices generally perform dynamic reactive compensation through SVC (static VAR compensator, a device used for dynamic reactive compensation in power systems, which improves the voltage stability and power quality of the power grid by quickly adjusting reactive power) and SVG (static VAR generator, also a device used for dynamic reactive compensation in power systems, which performs dynamic reactive compensation through power semiconductor bridge converters, can emit or absorb reactive power, and the output can be changed to control specific parameters in the power system). Among them, SVG has the advantages of fast response speed, low harmonic content, strong reactive regulation ability, safe operation, small footprint and good low voltage characteristics in terms of dynamic reactive compensation compared to SVC, and has more applications. However, due to technical limitations, when the three-phase grid voltage is asymmetrical, the inaccurate reference DC signal voltage collected by the sensor of the existing SVG dynamic reactive power compensation equipment will cause inaccurate sampling for its control system, which will affect the compensation effect of the power supply line. In addition, for SVG, the imbalance of the three-phase voltage will also cause one of the phases to be unable to be put into the signal end of the control system because the sampled DC signal voltage is too large. In severe cases, it will cause instability of the control system, which will also have an adverse effect on the compensation effect of the power supply line. Summary of the invention

[0004] In order to overcome the drawbacks of the existing SVG-based power compensation device due to technical limitations as described in the background, the present invention provides a control system that is used in conjunction with the SVG power compensation device to process the front-stage signal of the control system body, and the control system body samples reactive current, negative sequence voltage, voltage over-limit, etc. according to the positive sequence signal, and controls the power device of the SVG to send trigger pulses through different control strategy modules of the SVG power compensation device, thereby improving the control efficiency and ensuring the speed at which the control system body controls the compensation of the SVG dynamic reactive compensation equipment, so as to obtain a good dynamic compensation effect during the transient state of the power grid, and is used for a control system for asymmetric and instantaneous static reactive generators of the power grid.

[0005] The technical solution adopted by the present invention to solve its technical problem is:

[0006] The control system for asymmetric and instantaneous static reactive power generator of power grid includes a control system body, a control signal output end of the control system body and a control signal input end of an SVG power compensation device are connected via a wire, a sensor of the control system body and a three-phase power line are connected via a wire, a control strategy of a basic control software unit of the control system body itself is defined as a bottom-level control algorithm based on the constant current of the SVG power compensation device to ensure that the voltage source converter module of the SVG power compensation device can work normally, and an auxiliary control unit of the control system body itself includes a power grid overvoltage control subunit and a power grid low voltage control subunit; the characteristic is that when the control system body is working, the sensor samples the power grid current. The voltage signal is processed by passive filtering, and the positive-sequence three-phase balanced voltage is extracted as the basic voltage for the control system body to control the operation of the SVG power compensation device; the control system body also has a main control unit, which includes a constant voltage control subunit, a transient control subunit, a reactive power control subunit, a reactive power and voltage control subunit, a harmonic control subunit, a negative-sequence voltage control subunit, and a remote control subunit; when the constant voltage control subunit is working, the voltage regulator working mode based on the combination of voltage deviation and current adjustment rate is controlled, and the set voltage deviation is determined by its own reference voltage and the voltage feedback of the controlled power line collected by the sensor; when the transient control subunit is working When the grid fault signal collected by the sensor causes the voltage at the access point to drop suddenly but not less than 0.2pu, the SVG power compensation device directly outputs the rated capacitive current to support the grid voltage. When the voltage recovers to 0.8pu, the SVG power compensation device resumes the conventional steady-state control mode. When the reactive power control subunit is working, the control system body detects the load current, calculates the load reactive current, and then makes a difference between the target reactive current set by the control system body and the load reactive current and takes a negative value, that is, the reactive current given value of the inner loop control of the SVG power compensation device itself is obtained. When the reactive power and voltage control subunit is working, when the voltage at the sensor detection point is within the allowable range, the SVG power compensation device resumes the normal steady-state control mode. The device compensates for the reactive power of the detection point. Once the voltage at the detection point exceeds the limit, the SVG power compensation device reduces its own reactive characteristics to control the voltage within the allowable range. When the harmonic control subunit is working, the SVG power compensation device suppresses the load harmonics on the basis of reactive compensation, and only the SVG power compensation device needs to output a constant harmonic current. The negative sequence voltage control subunit compensates for the voltage imbalance problem of the substation by delta-connecting the SVG power compensation device. The remote control subunit enables the SVG power compensation device to receive external control instructions, change the SVG control target, and realize automatic scheduling of reactive power or voltage, so as to optimize the reactive power distribution of the entire system.

[0007] Furthermore, in the constant voltage control subunit, the voltage regulation rate is implemented by a current feedback method.

[0008] Furthermore, in the transient control subunit, when the grid voltage is higher than 1.15pu, the SVG power compensation device directly outputs the rated inductive current to reduce the grid voltage, and when it returns to normal, the SVG power compensation device returns to the conventional steady-state control mode.

[0009] Furthermore, in the reactive power control subunit, when the SVG power compensation device adopts power factor control, the control system body calculates the current active power of the SVG power compensation device, calculates the required reactive power according to the target power factor, and the reactive power is used as the reactive power control target, and subsequent control is consistent with the reactive power control.

[0010] Furthermore, in the harmonic control subunit, the dual goals of compensating reactive current and harmonic current can be achieved simultaneously.

[0011] Furthermore, in the negative sequence voltage control subunit, its working process is: collecting the grid line voltage, calculating its negative sequence voltage, subtracting the negative sequence voltage from 0, and the deviation passes through the PI regulator as the negative sequence reactive current instruction within the angle of the SVG power compensation device.

[0012] Furthermore, the remote control subunit includes the following working modes: reactive power control of the SVG power compensation device body, voltage control of the SVG power compensation device access point, and reactive power control of the SVG power compensation device access point. According to the above control working modes, a trigger pulse of the SVG power compensation device body is issued to control the conduction of the IGBT of the SVG power compensation device body, so as to realize the reactive output corresponding to the control strategy to the load.

[0013] Compared with the prior art, the present invention has the following beneficial effects: the present invention cooperates with the SVG power compensation device to process the front-stage signal of the control system body. Specifically, the asymmetric and transient voltage signals sampled by the control system body are processed, the harmonic components therein are filtered out, and the three-phase positive sequence voltage signal is extracted as the reference signal. The control system body then samples the reactive current, negative sequence voltage, voltage over-limit, etc. according to the positive sequence signal. Then, according to the different control strategy modules of the SVG power compensation device, the power device of the SVG is controlled to send a trigger pulse, thereby improving the control efficiency. On the other hand, the speed of processing signals of the entire control system body is improved, and the speed of the control system body controlling the compensation of the SVG dynamic reactive compensation device is ensured, so that a good dynamic compensation effect can be obtained in the transient process of the power grid, and the compensation effect of the SVG dynamic reactive compensation device is prevented from being affected by the inaccurate reference voltage. Based on the above, the present invention has a good application prospect. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0015] Figure 1 It is a schematic block diagram of the application of the constant voltage control subunit of the present invention.

[0016] Figure 2 Schematic diagram of the U-I characteristic curve of the constant voltage control SVG of the present invention.

[0017] Figure 3 Schematic diagram of the transient control characteristic curve of SVG of the present invention.

[0018] Figure 4 Schematic diagram of output waveform of SVG during transient control of the present invention.

[0019] Figure 5 A schematic block diagram of the application of the reactive power control subunit of the present invention.

[0020] Figure 6 A schematic block diagram of the application of the harmonic control subunit of the present invention.

[0021] Figure 7 A schematic block diagram of the application of the negative sequence voltage control subunit of the present invention. DETAILED DESCRIPTION

[0022] A control system for asymmetric and instantaneous static reactive generators of power grids comprises a control system body, a control signal output end of the control system body and a control signal input end of an SVG power compensation device are connected via a wire, a sensor of the control system body and a three-phase power line are connected via a wire, a control strategy of a basic control software unit of the control system body itself is defined as a bottom-level control algorithm based on the constant current of the SVG power compensation device to ensure that the voltage source converter module of the SVG power compensation device can work normally, and an auxiliary control unit of the control system body itself comprises a power grid overvoltage control subunit and a power grid low voltage control subunit; when the control system body is working, the sensor samples the power grid voltage signal, performs passive filtering processing on the signal, and extracts the positive sequence three-phase balanced voltage as the basic voltage for the control system body to control the SVG power compensation device to work; the control system body also has a main control unit, which comprises a constant voltage control subunit, a transient control subunit, a reactive power control subunit, a reactive power voltage control subunit, a harmonic control subunit, a negative sequence voltage control subunit, and a remote control subunit. In the application of constant voltage control subunit, SVG power compensation device generally adopts constant voltage control subunit as a strategy to stabilize the voltage of power supply system. Specifically, the control system body adopts voltage regulator based on voltage deviation and current adjustment rate as the voltage and current output adjustment device. The voltage deviation is determined by the reference voltage set by the constant voltage control subunit itself and the controlled voltage feedback output to the power load. The adjustment rate is realized by current feedback method. Its block diagram is as follows: Figure 1As shown. The working process of the voltage regulator is: compare the control variable measured by the sensor with its own reference voltage reference value to obtain the voltage deviation, and use the SVG power compensation device feedback current calibration value multiplied by the adjustment rate to correct the voltage deviation. The corrected deviation passes through the SVG power compensation device's PI controller as the given value of the SVG power compensation device's inner loop reactive current control, thereby achieving the purpose of stabilizing the system voltage. The U-I characteristic curve of the constant voltage control SVG is shown in Figure 2 shown.

[0023] In the application of the transient control subunit, when a grid fault causes the voltage at the access point of the power supply line to drop suddenly but not less than 0.2pu, the SVG power compensation device directly outputs the rated capacitive current to support the grid voltage. When the voltage recovers to 0.8pu, the SVG power compensation device restores the steady-state control method strategy. Similarly, when the grid voltage is higher than 1.15pu, the SVG power compensation device directly outputs the rated inductive current to reduce the grid voltage. When it returns to normal, the SVG power compensation device restores the steady-state control strategy. Specifically, since the SVG power compensation device has an extremely fast response speed, when the power supply system experiences a voltage drop or surge, the SVG power compensation device can quickly support (suppress) the power supply system voltage and improve the transient stability of the power supply system. Figure 3 is the SVG transient control characteristic curve; Figure 4 Output waveform of SVG transient control.

[0024] In the reactive power control (power factor control) subunit application, the control subsystem of the SVG power compensation device detects the load current (usually obtained by subtracting the grid current from the output current of the SVG power compensation device), calculates the reactive current of the load, and subtracts the set target reactive current from the load reactive current and takes the negative value as the reactive current set value of the inner loop control of the SVG power compensation device. The control block diagram is as follows: Figure 5 As shown. When the SVG power compensation device adopts power factor control, the control subsystem of the SVG power compensation device itself calculates the active power data of the current power supply system, and calculates the reactive power data of the required load according to its own set target power factor. The reactive data is used as the control target of the load reactive control, and the subsequent control is consistent with the load reactive control. In the application of the reactive power and voltage control subunit, when the point voltage of the transmission line detection point is within the allowable range, the SVG power compensation device compensates the reactive power data of the detection point. Once the voltage of the detection point exceeds the limit, the SVG power compensation device reduces part of the reactive characteristics to control the voltage within the allowable range.

[0025] In the application of harmonic control subunit, the working principle of the active filter type medium voltage SVG power compensation device using direct current control is as follows: Figure 6 As shown. From the figure, we can get formula (1), that is, the power supply current is the load current and compensation current The phase sum; Assuming the load current Contains fundamental positive sequence current (including fundamental positive sequence reactive current and fundamental positive sequence active current ), fundamental negative sequence current Harmonic current As shown in formula (2).

[0026]

[0027] To make the power supply current If the fundamental positive sequence reactive power and fundamental negative sequence current are not contained in the current, the output current of the SVG power compensation device needs to be controlled. Satisfies equation (3); thus, the power supply current only contains fundamental positive sequence active power and harmonic current, as shown in equation (4).

[0028]

[0029] Therefore, in order to achieve the compensation purpose, the key is to control the output current of the SVG power compensation device. Satisfies formula (3). From the description of the working principle of the SVG power compensation device, it can be seen that if the SVG power compensation device is to suppress the load harmonics on the basis of reactive power compensation, it is only necessary to make the SVG power compensation device output the corresponding harmonic current. Therefore, in this sense, the SVG power compensation device can simultaneously achieve the dual goals of compensating reactive current and harmonic current; specifically, the input signal of the SVG power compensation device can be power, voltage, current, etc., and the line active power is generally selected as the input signal of the SVG damping controller.

[0030] In the application of negative sequence voltage control subunit, the unbalanced output voltage of some substations can be compensated by the delta connection SVG power compensation device, such as Figure 7 As shown in the figure, assuming that the voltage on the power supply side Us is unbalanced, the SVG power compensation device generates a negative sequence current , forming a negative sequence voltage drop on the line impedance, thereby making the voltage at the access point balanced; the specific control block diagram is as follows Figure 1 The working process is as follows: collecting the grid line voltage, calculating its negative sequence voltage, making a difference between the negative sequence voltage and 0, and the deviation passes through the PI regulator as the negative sequence reactive current instruction of the SVG power compensation device.

[0031] In the application of remote control subunit, the so-called remote control means that the SVG power compensation device can receive external control instructions, change the control target of the SVG power compensation device, realize automatic scheduling of reactive power or voltage, and optimize the reactive power distribution of the entire power supply system. Specifically, the remote control system controls the SVG power compensation device in different ways according to the different access systems, which generally include the following methods. (1) Reactive power control of the SVG power compensation device itself: that is, the remote control system regards the SVG power compensation device as a reactive source, and the SVG power compensation device controls its own reactive power within the reactive power target given by the remote control system. (2) Voltage control of the SVG power compensation device access point: The SVG power compensation device is the main voltage regulation device in the area. The remote control system gives the SVG power compensation device the current target voltage value according to the requirements of the control system itself. The SVG power compensation device controls the voltage of the power supply area near the given target through the voltage control strategy. (3) Reactive power control at the access point of the SVG power compensation device: The SVG power compensation device is the main reactive power regulation device in the area. The remote control system gives the reactive power of the area controlled by the SVG power compensation device according to the needs of the control system. The SVG power compensation device controls the reactive power of the area near the given target through the reactive power control strategy. In actual situations, if a voltage surge or sag occurs during remote control, the SVG power compensation device will be separated from remote control and enter the transient control strategy, unless there are special requirements that do not allow the SVG power compensation device to perform transient control. According to the above control strategy,

[0032] Send out a trigger pulse of the SVG power compensation device body, control the IGBT of the SVG power compensation device body to turn on, and realize the reactive power output corresponding to the control strategy to the load.

[0033] In summary, the present invention cooperates with the SVG power compensation device to process the front-stage signal of the control system body. Specifically, the asymmetric and transient voltage signals sampled by the control system body are processed, the harmonic components therein are filtered out, and the three-phase positive-sequence voltage signal is extracted as the reference signal. The control system body then samples the reactive current, negative-sequence voltage, voltage over-limit, etc. according to the positive-sequence signal. Then, according to different control strategy modules of the SVG power compensation device, the power device of the SVG is controlled to send a trigger pulse, thereby improving the control efficiency. On the other hand, the speed of signal processing of the entire control system body is improved, and the speed of compensation of the SVG dynamic reactive compensation device controlled by the control system body is ensured, so that a good dynamic compensation effect can be obtained during the transient process of the power grid, and the compensation effect of the SVG dynamic reactive compensation device is prevented from being affected by the inaccuracy of the reference voltage.

[0034] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It is obvious to those skilled in the art that the present invention is limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims are included in the present invention. Any figure mark in the claims should not be regarded as limiting the claim involved.

[0035] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in the embodiments may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A control system for an asymmetric, instantaneous power grid static VAR generator, comprising a control system body, a control signal output end of the control system body and a control signal input end of an SVG power compensation device connected via a wire, a sensor of the control system body and a three-phase power line connected via a wire, a control strategy definition of a basic control software unit of the control system body itself is based on a constant current of the SVG power compensation device to ensure that the voltage source converter module of the SVG power compensation device can work normally, and an auxiliary control unit of the control system body itself includes a power grid overvoltage control subunit and a power grid low voltage control subunit; characterized in that, When the control system is working, the sensor samples the grid voltage signal, performs passive filtering on the signal, and extracts the positive sequence three-phase balanced voltage as the basic voltage for the control system to control the SVG power compensation device. The control system also has a main control unit, which includes a constant voltage control subunit, a transient control subunit, a reactive power control subunit, a reactive power voltage control subunit, a harmonic control subunit, a negative sequence voltage control subunit, and a remote control subunit. When the constant voltage control subunit is working, it controls the working mode of the voltage regulator based on the combination of voltage deviation and current adjustment rate, and the set voltage deviation is determined by its own reference voltage and the voltage feedback of the controlled power line collected by the sensor. When the transient control subunit is working, when the grid fault signal collected by the sensor causes the access When the voltage at the point drops suddenly but is not less than 0.2pu, the SVG power compensation device directly outputs the rated capacitive current to support the grid voltage. When the voltage recovers to 0.8pu, the SVG power compensation device resumes the conventional steady-state control mode. When the reactive power control subunit is working, the control system body detects the load current, calculates the load reactive current, and then makes a difference between the target reactive current set by the control system body and the load reactive current and takes a negative value, that is, the reactive current given value of the inner loop control of the SVG power compensation device itself is obtained. When the reactive power and voltage control subunit is working, when the voltage at the sensor detection point is within the allowable range, the SVG power compensation device compensates for the reactive power of the detection point. Once the voltage at the detection point exceeds the limit, the SVG power compensation device reduces its own reactive characteristics to control the voltage within the allowable range. When the harmonic control subunit is working, the SVG power compensation device suppresses the load harmonics on the basis of reactive power compensation, and the SVG power compensation device only needs to output a constant harmonic current; The negative sequence voltage control subunit compensates for the voltage imbalance problem of the substation by delta-connecting the SVG power compensation device; the remote control subunit is an SVG power compensation device that can receive external control instructions, change the SVG control target, and realize automatic scheduling of reactive power or voltage, so as to optimize the reactive power distribution of the entire system.

2. The control system for an asymmetric, instantaneous power grid static VAR generator according to claim 1, characterized in that: In the constant voltage control subunit, the voltage regulation rate is realized by current feedback method.

3. The control system for an asymmetric, instantaneous power grid static VAR generator according to claim 1, characterized in that: In the transient control subunit, when the grid voltage is higher than 1.15pu, the SVG power compensation device directly outputs the rated inductive current to reduce the grid voltage. When it returns to normal, the SVG power compensation device resumes the conventional steady-state control mode.

4. The control system for an asymmetric, instantaneous power grid static VAR generator according to claim 1, characterized in that: In the reactive power control subunit, when the SVG power compensation device adopts power factor control, the control system body calculates the current active power of the SVG power compensation device and calculates the required reactive power according to the target power factor. The reactive power is used as the reactive power control target, and the subsequent control is consistent with the reactive power control.

5. The control system for an asymmetric, instantaneous power grid static VAR generator according to claim 1, characterized in that: In the harmonic control subunit, the dual goals of compensating reactive current and harmonic current can be achieved simultaneously.

6. The control system for an asymmetric, instantaneous power grid static VAR generator according to claim 1, characterized in that: In the negative-sequence voltage control subunit, the working process is: collect the grid line voltage, calculate its negative-sequence voltage, make a difference between the negative-sequence voltage and 0, and the deviation passes through the PI regulator as the negative-sequence reactive current instruction within the angle of the SVG power compensation device.

7. The control system for an asymmetric, instantaneous power grid static VAR generator according to claim 1, characterized in that: The remote control subunit includes the following working modes: reactive power control of the SVG power compensation device body, voltage control of the SVG power compensation device access point, and reactive power control of the SVG power compensation device access point. According to the above control working modes, a trigger pulse of the SVG power compensation device body is issued to control the conduction of the IGBT of the SVG power compensation device body, so as to realize the reactive power output corresponding to the control strategy to the load.

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