A control method applied to a voltage compensation device of a hybrid distribution network

Abstract

The application provides a control method applied to a hybrid power distribution network voltage compensation device, including a control module, a three-phase multi-winding transformer and an UPFC, the multi-winding transformer is responsible for coarse adjustment of large capacity in a power distribution network voltage compensation process, and the UPFC is responsible for fine adjustment of small capacity; the control module includes an electromagnetic part control strategy sub-module, a power electronic part control strategy sub-module and a compensation component generation sub-module; in the control method, the compensation component generation sub-module provides a compensation voltage component for the electromagnetic part control strategy sub-module and the power electronic part control strategy sub-module; the electromagnetic part control strategy sub-module calculates the number of required compensation taps according to the compensation voltage component, and controls a tap switch of the voltage compensation device to access a corresponding tap position; the application can solve the problem of cooperative control of the electromagnetic part and the power electronic part, simultaneously compensates for three-phase imbalance existing in the power distribution network, so as to realize multifunctionalization of the hybrid power distribution network voltage compensation device.

Description

Technical Field

[0001] This invention relates to the field of electronic equipment technology, and in particular to a control method for a voltage compensation device in a hybrid power distribution network. Background Technology

[0002] With the development of technology, the role of modern power distribution networks has evolved from simply distributing electricity to a platform encompassing multiple functions such as power transmission, distribution, storage, and trading, while also undertaking the responsibility of absorbing distributed energy resources. However, the generation capacity and load of distributed energy resources exhibit random characteristics, leading to frequent voltage fluctuations in the distribution network. This can even result in voltage amplitude exceeding limits both upwards and downwards within a single day, severely impacting the quality of power supply. Therefore, it is necessary to employ appropriate voltage compensation devices to compensate for voltage fluctuations in the distribution network.

[0003] Compared to conventional electromagnetic and power electronic voltage compensation devices, hybrid voltage compensation devices combine the advantages of both, achieving both cost minimization and efficiency maximization through reasonable capacity configuration. However, current control methods only support individual electromagnetic and power electronic voltage compensation devices. Therefore, research is needed on control methods for hybrid voltage compensation devices to enable their coordinated operation. Summary of the Invention

[0004] This invention proposes a control method for voltage compensation devices in hybrid distribution networks, which can solve the problem of coordinated control of electromagnetic and power electronic components, and can also compensate for the three-phase imbalance problem in the distribution network, thereby realizing the multi-functionality of the voltage compensation device in hybrid distribution networks.

[0005] The present invention adopts the following technical solution.

[0006] A control method for a voltage compensation device applied to a hybrid power distribution network, wherein the voltage compensation device includes a control module, a three-phase multi-winding transformer, and a UPFC (Upgraded Voltage Controller). The multi-winding transformer is responsible for coarse adjustment of large capacity voltage compensation in the power distribution network process, while the UPFC is responsible for fine adjustment of small capacity voltage compensation. The control module includes an electromagnetic control strategy submodule, a power electronic control strategy submodule, and a compensation component generation submodule. In the control module control method, the compensation component generation submodule provides compensation voltage components to the electromagnetic and power electronic control strategy submodules. The electromagnetic control strategy submodule calculates the required number of compensation levels based on the compensation voltage components, and then controls the tap changer of the voltage compensation device to connect to the corresponding tap level.

[0007] The power electronics control strategy submodule achieves precise compensation through closed-loop control. Its working method includes front-stage control and back-stage control. The goal of the front-stage control is to keep the intermediate DC bus voltage constant and compensate for the three-phase imbalance. The goal of the back-stage control is the difference between the compensation voltage component provided by the compensation component generation submodule and the voltage component compensated by the electromagnetic part.

[0008] When the voltage compensation device is connected to a hybrid distribution network, let D... a D b and D c These represent the tap positions of the three-phase tap changer; v ar v br and v cr These represent the rated phase voltage values ​​of a three-phase distribution network; v a1 v b1 and v c1 These represent the phase voltages of the three-phase distribution network upstream of the compensation point; v a2 v b2 and v c2 These represent the phase voltages of the three-phase distribution network downstream of the compensation point; i a1 i b1 and i c1 These represent the currents in the three-phase distribution network upstream of the compensation point; v d1 v q1 v 01 i d1 i q1 i 01 These represent the d-axis, q-axis, and 0-axis components of the phase voltage and current at the compensation point after Parker transformation, respectively; v dc1 v dc2 and v dcr These represent the voltages of capacitors C1 and C2, and the reference value of the DC bus voltage of the three-phase rectifier, respectively; i a i b and i c These represent the AC side current of the three-phase rectifier; ω0t represents v a1 The phase of the abc to dq0 transformation is the Parker transformation, and the transformation from dq0 to abc transformation is the inverse Parker transformation; SPWM stands for sinusoidal pulse width modulation.

[0009] Then G n The transfer functions of notch filters with center frequencies of 50Hz and 100Hz are shown in the following formulas.

[0010]

[0011] Where ω0 and ω c This indicates the grid angular frequency and the notch filter bandwidth;

[0012] G1 and G2 are proportional-integral controllers, and their transfer functions are shown in the following equation.

[0013]

[0014] Where k px and k ix (x = 1, 2) represents the proportionality coefficient and the integral coefficient;

[0015] G3 and G4 are proportional-quasi-resonant controllers, and their transfer functions are shown in the following equation.

[0016]

[0017] Where k px and k rx (x=3,4) represents the proportional coefficient and the resonance coefficient; K1 represents the turns ratio between the primary winding and the secondary winding connected to the three-phase rectifier in a multi-winding transformer; LM is the limiter;

[0018] When generating the compensation components, the control module first converts v... ar v br and v cr With v a1 v b1 and v c1 Subtracting them gives the difference v. ae v be and v ce Secondly, v ae v be and v ce The peak value divided by N+1 and rounded off gives D. a D b and D c Where N is the number of tap positions in each phase of a multi-winding transformer;

[0019] Based on the D obtained above a D b and D c By combining the relationship between the peak value of the phase voltage before the compensation point and the peak value of the rated voltage, the corresponding tap changer position can be selected.

[0020] The voltage compensation device is connected to the medium-voltage distribution network requiring voltage compensation via the excitation winding of the UPFC in a star connection. Specifically, each phase of the voltage compensation device has two excitation windings on its secondary side, one of which is connected to the input terminal of the three-phase rectifier, and the other winding is a winding with a tap. The three-phase secondary windings connected to the three-phase rectifier are connected in a star configuration. Three single-phase inverters are connected to the DC bus of the three-phase rectifier and distributed to the three-phase distribution network. The output terminal of each phase inverter is connected in series with the tapped secondary winding of each phase in the multi-winding transformer of the voltage compensation device, and then connected in parallel to the primary side of a single-phase transformer. The secondary side of this transformer is connected to the distribution network in series.

[0021] Compared with the prior art, the present invention has the following advantages and technical effects:

[0022] This invention enables the coordinated operation of hybrid power distribution network voltage compensation devices, and can also compensate for three-phase imbalance in the power distribution network, thereby realizing the multi-functionality of the device. Attached Figure Description

[0023] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0024] Appendix Figure 1 This is a schematic diagram of the overall control strategy of the present invention;

[0025] Appendix Figure 2 This is a schematic diagram of the topological structure of the object to which this invention is applied;

[0026] Appendix Figure 3 This is a schematic diagram of the AC current waveform of the rectifier in the first group of experiments according to the embodiments of the present invention;

[0027] Appendix Figure 4 This is a schematic diagram of the phase voltage and current waveforms at the compensation point in the first group of experiments according to an embodiment of the present invention;

[0028] Appendix Figure 5 This is a schematic diagram of the phase voltage and current waveforms at the compensation point in the first set of experiments of this invention.

[0029] Appendix Figure 6 This is a schematic diagram of the AC current waveform of the rectifier in the second set of experiments according to an embodiment of the present invention;

[0030] Appendix Figure 7 This is a schematic diagram of the phase voltage and current waveforms at the compensation point in the second set of experiments according to an embodiment of the present invention.

[0031] Appendix Figure 8 This is a schematic diagram of the phase voltage and current waveforms at the compensation point in the second set of experiments of this invention. Detailed Implementation

[0032] As shown in the figure, a control method for a voltage compensation device applied to a hybrid distribution network includes a control module, a three-phase multi-winding transformer, and a UPFC. The multi-winding transformer is responsible for coarse adjustment of large capacity voltage compensation in the distribution network process, while the UPFC is responsible for fine adjustment of small capacity voltage compensation. The control module includes an electromagnetic control strategy submodule, a power electronic control strategy submodule, and a compensation component generation submodule. In the control module control method, the compensation component generation submodule provides compensation voltage components to the electromagnetic and power electronic control strategy submodules. The electromagnetic control strategy submodule calculates the required number of compensation levels based on the compensation voltage components and then controls the voltage compensation device's level switches to connect to the corresponding tap levels.

[0033] The power electronics control strategy submodule achieves precise compensation through closed-loop control. Its working method includes front-stage control and back-stage control. The goal of the front-stage control is to keep the intermediate DC bus voltage constant and compensate for the three-phase imbalance. The goal of the back-stage control is the difference between the compensation voltage component provided by the compensation component generation submodule and the voltage component compensated by the electromagnetic part.

[0034] When the voltage compensation device is connected to a hybrid distribution network, let D... a D b and D c These represent the tap positions of the three-phase tap changer; v ar v br and v cr These represent the rated phase voltage values ​​of a three-phase distribution network; v a1 v b1 and v c1 These represent the phase voltages of the three-phase distribution network upstream of the compensation point; v a2 v b2 and v c2 These represent the phase voltages of the three-phase distribution network downstream of the compensation point; i a1 i b1 and i c1 These represent the currents in the three-phase distribution network upstream of the compensation point; v d1 v q1 v 01 i d1 i q1 i 01 These represent the d-axis, q-axis, and 0-axis components of the phase voltage and current at the compensation point after Parker transformation, respectively; v dc1 v dc2 and v dcr These represent the voltages of capacitors C1 and C2, and the reference value of the DC bus voltage of the three-phase rectifier, respectively; i a i b and i cThese represent the AC side current of the three-phase rectifier; ω0t represents v a1 The phase of the abc to dq0 transformation is the Parker transformation, and the transformation from dq0 to abc transformation is the inverse Parker transformation; SPWM stands for sinusoidal pulse width modulation.

[0035] Then G n The transfer functions of notch filters with center frequencies of 50Hz and 100Hz are shown in the following formulas.

[0036]

[0037] Where ω0 and ω c This indicates the grid angular frequency and the notch filter bandwidth;

[0038] G1 and G2 are proportional-integral controllers, and their transfer functions are shown in the following equation.

[0039]

[0040] Where k px and k ix (x = 1, 2) represents the proportionality coefficient and the integral coefficient;

[0041] G3 and G4 are proportional-quasi-resonant controllers, and their transfer functions are shown in the following equation.

[0042]

[0043] Where k px and k rx (x=3,4) represents the proportional coefficient and the resonance coefficient; K1 represents the turns ratio between the primary winding and the secondary winding connected to the three-phase rectifier in a multi-winding transformer; LM is the limiter;

[0044] When generating the compensation components, the control module first converts v... ar v br and v cr With v a1 v b1 and v c1 Subtracting them gives the difference v. ae v be and v ce Secondly, v ae v be and v ce The peak value divided by N+1 and rounded off gives D. a D b and D c Where N is the number of tap positions in each phase of a multi-winding transformer;

[0045] Based on the D obtained abovea D b and D c By combining the relationship between the peak value of the phase voltage before the compensation point and the peak value of the rated voltage, the corresponding tap changer position can be selected.

[0046] The voltage compensation device is connected to the medium-voltage distribution network requiring voltage compensation via the excitation winding of the UPFC in a star connection. Specifically, each phase of the voltage compensation device has two excitation windings on its secondary side, one of which is connected to the input terminal of the three-phase rectifier, and the other winding is a winding with a tap. The three-phase secondary windings connected to the three-phase rectifier are connected in a star configuration. Three single-phase inverters are connected to the DC bus of the three-phase rectifier and distributed to the three-phase distribution network. The output terminal of each phase inverter is connected in series with the tapped secondary winding of each phase in the multi-winding transformer of the voltage compensation device, and then connected in parallel to the primary side of a single-phase transformer. The secondary side of this transformer is connected to the distribution network in series.

[0047] Example:

[0048] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0049] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0050] Figure 1 The diagram illustrates the overall control strategy of this invention, including the compensation component generation submodule shown in the upper left, the electromagnetic part control strategy submodule shown in the upper right, and the power electronic part control strategy submodule shown in the lower half, where D... a D b and D c These represent the tap positions of the three-phase tap changer; v ar v br and v cr These represent the rated phase voltage values ​​of a three-phase distribution network; v a1 v b1 and v c1 These represent the phase voltages of the three-phase distribution network upstream of the compensation point; v a2 v b2 and v c2 These represent the phase voltages of the three-phase distribution network downstream of the compensation point; i a1 i b1and i c1 These represent the currents in the three-phase distribution network upstream of the compensation point; v d1 v q1 v 01 i d1 i q1 i 01 These represent the d-axis, q-axis, and 0-axis components of the phase voltage and current at the compensation point after Parker transformation, respectively; v dc1 v dc2 and v dcr These represent the voltages of capacitors C1 and C2, and the reference value of the DC bus voltage of the three-phase rectifier, respectively; i a i b and i c These represent the AC side current of the three-phase rectifier; ω0t represents v a1 The phase of the abc to dq0 transformation is the Parker transformation, and the transformation from dq0 to abc transformation is the inverse Parker transformation; SPWM stands for sinusoidal pulse width modulation.

[0051] Then G n The transfer functions of notch filters with center frequencies of 50Hz and 100Hz are shown in the following formulas.

[0052]

[0053] Where ω0 and ω c This indicates the grid angular frequency and the notch filter bandwidth;

[0054] G1 and G2 are proportional-integral controllers, and their transfer functions are shown in the following equation.

[0055]

[0056] Where k px and k ix (x = 1, 2) represents the proportionality coefficient and the integral coefficient;

[0057] G3 and G4 are proportional-quasi-resonant controllers, and their transfer functions are shown in the following equation.

[0058]

[0059] Where k px and k rx (x=3,4) represents the proportional coefficient and the resonance coefficient; K1 represents the turns ratio between the primary winding and the secondary winding connected to the three-phase rectifier in a multi-winding transformer; LM is the limiter;

[0060] When generating the compensation components, the control module first converts v... ar v br and vcr With v a1 v b1 and v c1 Subtracting them gives the difference v. ae v be and v ce Secondly, v ae v be and v ce The peak value divided by N+1 and rounded off gives D. a D b and D c Where N is the number of tap positions in each phase of a multi-winding transformer;

[0061] Based on the D obtained above a D b and D c By combining the relationship between the peak value of the phase voltage before the compensation point and the peak value of the rated voltage, the corresponding tap changer position can be selected.

[0062] Figure 2 This diagram illustrates the topology of the object to which this invention is applied. The excitation winding is connected in a star configuration to the medium-voltage distribution network requiring voltage compensation. Each phase's secondary winding comprises two windings, one connected to the input of the rectifier and the other a tapped winding. The three-phase secondary windings of the three-phase rectifier are connected in a star configuration. Three single-phase inverters are connected to the DC bus of the three-phase rectifier and distributed to the three-phase distribution network. The output of each inverter is connected in series with the tapped secondary winding of each phase in the multi-winding transformer, and then connected in parallel to the primary winding of a single-phase transformer. The secondary winding of this transformer is connected to the distribution network in series.

[0063] To verify the compensation effect of the device, a simulation model of a medium-voltage distribution network was built using MATLAB / Simulink simulation software. The effectiveness of the control method provided by this invention is verified through two sets of comparative experiments. The first set only performs phase voltage compensation of the distribution network, while the second set performs both phase voltage compensation and three-phase imbalance compensation.

[0064] The results of the first group of experiments are as follows: Figures 3 to 5 As shown, from Figure 3 It can be seen that the current on the AC side of the rectifier is three-phase balanced. This is because three-phase imbalance compensation was not performed in this experiment. Figure 3 The peak current shown is -64A, which is due to Figure 2 The standard specifies that the positive direction of the AC current on the rectifier side is from the rectifier to the transformer. However, in this experiment, the rectifier operates in rectification mode, therefore the current is negative. Figure 4It can be observed that without compensation, the peak voltage of the distribution network is only 6670V, lower than the rated peak voltage of 8165V, while the peak currents of the three-phase distribution network are 87.9A, 79.8A, and 75.8A respectively, indicating a clear imbalance in the three-phase load; from Figure 5 It can be seen that after compensation by the hybrid distribution network voltage compensation device, the peak voltage of the distribution network has been restored to the rated value, thus verifying the effectiveness of the device and control method.

[0065] The results of the second group of experiments are as follows: Figures 6 to 8 As shown, this group of experiments added three-phase imbalance compensation control, from Figure 6 It can be observed that the current on the AC side of the rectifier is in a three-phase unbalanced state. This is due to the three-phase unbalance compensation control implemented by the rectifier. Figure 7 The peak currents of the three-phase distribution network changed to 83.8A, 80.9A, and 78.5A respectively. Compared with the first group, it can be seen that the three-phase load imbalance of the distribution network has been improved, thus verifying the effectiveness of the three-phase imbalance compensation control in the control method proposed in this invention. The incomplete compensation of the three-phase imbalance is due to the rectifier capacity limitation. Furthermore, similar to the first group of experiments, from... Figure 8 It can be seen that after compensation by the hybrid distribution network voltage compensation device, the voltage peak of the distribution network also returned to the rated value, which once again verified the effectiveness of the device and control method.

[0066] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the embodiments described. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

[0067] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A control method applied to a voltage compensation device for a hybrid distribution network, characterized in that: The voltage compensation device comprises a control module, a three-phase multi-winding transformer and a UPFC, the multi-winding transformer is responsible for coarse adjustment of large capacity in the voltage compensation process of the power distribution network, and the UPFC is responsible for fine adjustment of small capacity; the control module comprises an electromagnetic part control strategy sub-module, a power electronic part control strategy sub-module and a compensation component generation sub-module; in the control method of the control module, the compensation component generation sub-module provides compensation voltage components for the electromagnetic part control strategy sub-module and the power electronic part control strategy sub-module; The electromagnetic part control strategy sub-module calculates the number of required compensation taps according to the compensation voltage components, and then controls the tap switch of the voltage compensation device to access the corresponding tap. The power electronic part control strategy sub-module realizes accurate compensation in a closed loop control mode, and the working method thereof comprises front-stage control and rear-stage control, the target of the front-stage control is constant intermediate DC bus voltage and three-phase unbalance compensation, and the target of the rear-stage control is the difference between the compensation voltage components provided by the compensation component generation sub-module and the voltage components compensated by the electromagnetic part; When the voltage compensation device is connected to the hybrid distribution network, let D a , D b and D c represent the tap positions of the three-phase tap changer; let v ar , v br and v cr represent the phase voltage ratings of the three-phase distribution network; let v a1 , v b1 and v c1 represent the phase voltages of the three-phase distribution network in front of the compensation point; let v a2 , v b2 and v c2 represent the phase voltages of the three-phase distribution network behind the compensation point; let i a1 , i b1 and i c1 represent the currents of the three-phase distribution network in front of the compensation point; let v d1 , v q1 , v 01 , i d1 , i q1 , i 01 represent the d-axis, q-axis and 0-axis components of the phase voltages and currents in front of the compensation point after the Park transformation; let v dc1 , v dc2 and v dcr represent the voltages of the capacitors C1 and C2 and the DC bus voltage reference value of the three-phase rectifier; let i a , i b and i c represent the AC side currents of the three-phase rectifier; let ω0t represent the phase of v a1 ; the transformation from abc to dq0 is the Park transformation, and the transformation from dq0 to abc is the inverse Park transformation; SPWM represents the sinusoidal pulse width modulation. G n represents a notch filter with a center frequency of 50 Hz and 100 Hz, whose transfer function is given by the following equation, where ω0and ω c represent the grid angle frequency and the notch bandwidth; G1 and G2 are proportional-integral controllers, and the transfer functions thereof are as follows, where k px and k ix represent proportionality and integration coefficients, where x = 1,2; G3 and G4 are proportional-quasi-resonant controllers, and the transfer functions thereof are as follows, where k px and k rx represent the proportionality coefficient and the resonance coefficient, where x = 3, 4; The control module, when generating the compensation component, first, subtracts v ar , v br and v cr from v a1 , v b1 and v c1 respectively to obtain difference values v ae , v be and v ce ; secondly, divides the peak values of v ae , v be and v ce by N+1 and rounds them to obtain D a , D b and D c , wherein N is the number of tap positions in each phase of the multi-winding transformer. According to the above obtained D a , D b and D c , and in combination with the size relationship between the peak value of the previous phase voltage of the compensation point and the rated voltage peak value, the corresponding tap switch gear position can be selected.

2. The control method for the voltage compensation device applied to the hybrid distribution network according to claim 1, characterized in that: The voltage compensation device is connected to the medium-voltage power distribution network requiring voltage compensation through the field winding of the UPFC in a star connection mode, and the specific connection mode is as follows: the secondary side of each phase of the voltage compensation device comprises two field windings, one of which is connected to the input end of the three-phase rectifier, and the other winding is a tap-changing winding; the three-phase secondary side windings connected to the three-phase rectifier are connected in a star mode, the DC bus of the three-phase rectifier is connected to three single-phase inverters and is distributed to the three-phase power distribution network, respectively, the output end of each phase of the inverter is connected in series with the tap-changing secondary side winding of each phase of the multi-winding transformer of the voltage compensation device, and then is connected in parallel to the primary side of a single-phase transformer, and the secondary side of the transformer is connected to the power distribution network in a series mode.

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