Fault voltage support method for renewable energy distribution network based on SVG inter-phase active power exchange

Abstract

The method for supporting fault voltage of a new energy distribution network based on active power exchange between phases of SVG provided by the present invention first calculates the active power and reactive power compensation required by the fault phase and the active power required to be provided by the non-fault phase and the reactive power compensation required by the non-fault phase according to the bus voltage drop of the grid connection point, the output power of the new energy inverter at the grid connection point, and the resistance and inductance of the grid line, wherein the active power required by the fault phase is equal to the active power required to be provided by the non-fault phase; then calculates the output current reference value of each phase of SVG according to the active power and reactive power compensation required by the fault phase and the active power required to be provided by the non-fault phase and the reactive power compensation required by the non-fault phase; finally, determines the SVG three-phase bridge arm control signal and the zero-sequence bridge arm control signal according to the output current reference value of each phase of SVG and in combination with the voltage-current dual closed-loop control method, so as to drive the switch tubes of each bridge arm of SVG, thereby realizing the three-phase output current control of the grid.

Description

Technical Field

[0001] The present invention relates to the field of electrical engineering technology, and in particular to a fault voltage support method for a new energy distribution network based on SVG inter-phase active power exchange. Background Art

[0002] Under the background of new power system construction, a large number of new energy sources such as photovoltaic and wind power are connected to the distribution network through inverters. Affected by factors such as operating environment, equipment defects, and line aging, the distribution network often fails, among which the single-phase or two-phase asymmetric failure rate is the highest. When an asymmetric fault occurs in the power grid and causes the bus voltage at the inverter grid connection point to drop, it will directly affect the inverter's operating performance. In the worst case, it will cause the inverter output current to be distorted and the output power to drop significantly. In the worst case, it will directly cause the inverter to be disconnected from the grid, making it impossible to realize the grid-connected power generation of new energy, which seriously hinders the improvement of the new energy consumption capacity.

[0003] In order to solve the problem that single-phase faults in the distribution network can easily cause the new energy inverter to be disconnected from the grid, the existing solutions are mainly divided into two categories. One is to modify the control strategy of the new energy inverter to enable it to have a low voltage ride-through function, but this type of technology cannot guarantee that the new energy inverter operates in the maximum active power output mode; the other is to use the reactive power compensation device to generate reactive power to support the bus voltage at the inverter grid connection point, but the line resistance in the distribution network is large and cannot be ignored. It is difficult to achieve the best support effect for the bus voltage at the grid connection point by simply relying on the reactive power generated by the reactive power compensation device. A certain amount of active power support needs to be provided. However, under the existing control technology conditions, the reactive power compensation device cannot directly generate active power, and therefore cannot directly achieve the best support effect for the bus voltage at the grid connection point. Summary of the invention

[0004] The purpose of the present invention is to provide a fault voltage support method for a new energy distribution network based on SVG inter-phase active power exchange, which achieves the best support effect on the fault phase voltage by exchanging active power between the non-fault phase and the fault phase of the power grid, thereby ensuring that the new energy inverter operates in the maximum active power output mode.

[0005] In order to solve the above technical problems, the present invention adopts the following technical methods: a method for supporting fault voltage of a new energy distribution network based on active power exchange between phases of SVG. When a fault occurs in the distribution network, the non-fault phase injects active power into the fault phase through SVG, and SVG emits reactive power to provide reactive power support for each phase, so as to support the voltage of the fault phase;

[0006] The fault voltage support method for a new energy distribution network based on SVG interphase active power exchange includes:

[0007] Step S1, according to the bus voltage drop of the grid connection point, the output power of the new energy inverter at the grid connection point, and the resistance and inductance of the grid line, calculate the active power and reactive power compensation required by the fault phase, as well as the active power required to be provided by the non-fault phase and the reactive power compensation required by itself, wherein the active power required by the fault phase is equal to the active power required to be provided by the non-fault phase;

[0008] Step S2, calculating the output current reference value of each phase of the SVG according to the active power and reactive power compensation required by the faulty phase obtained in step S1, and the active power required to be provided by the non-faulty phase and the reactive power compensation required by the non-faulty phase;

[0009] Step S3, according to the output current reference value of each phase of SVG obtained in step S2, and in combination with the voltage-current dual closed-loop control method, determine the SVG three-phase bridge arm control signal and the zero-sequence bridge arm control signal, and drive the switch tubes of each bridge arm of SVG according to the obtained control signal, so as to realize the three-phase output current control of the power grid.

[0010] Furthermore, in step S1:

[0011] The calculation expression of the active power required by the fault phase is as follows:

[0012] (1)

[0013] (2)

[0014] (3)

[0015] (4)

[0016] (5)

[0017] In the formula, is the active power required by the fault phase, where x =a, b, c, respectively indicating the A phase, B phase or C phase where the fault occurs; is the rated value of the effective value of the grid bus phase voltage; is the equivalent resistance on the grid side; is the equivalent reactance on the grid side, , is the equivalent inductance on the grid side; It is the effective value of the output phase current of the new energy inverter; Output power for new energy inverter; is the effective value drop ratio of the fault phase voltage, ; is the reactive power compensation amount of the fault phase;

[0018] The calculation method of the active power required by the non-fault phase is as follows:

[0019] 1) If it is a single-phase fault, the active power required by the other two non-faulty phases is half of the active power required by the faulty phase;

[0020] 2) If it is a two-phase asymmetric fault, the active power required by the non-faulty phase is the sum of the active powers required by the two faulty phases.

[0021] Furthermore, in step S1, the reactive power compensation required for the faulty phase and the non-faulty phase is respectively calculated by the effective value of the corresponding phase bus voltage and After making the difference, it is obtained through the proportional-integral controller.

[0022] Furthermore, the process of calculating the output current reference value of each phase of SVG in step S2 is as follows:

[0023] 1) Using a dual second-order generalized integrator phase-locked loop to measure the three-phase voltage at the grid connection point , , Perform phase locking to obtain the bus voltage phase angle ;

[0024] 2) The active power required by the faulty phase and the reactive power required by the non-faulty phase obtained in step S1 , , , the reactive power compensation required for the fault phase and the non-fault phase , , , and bus voltage phase angle , and bus voltage effective value , , , calculate the current reference value of SVG output , , .

[0025] Furthermore, the process of determining the SVG three-phase bridge arm control signal in step S3 is as follows:

[0026] 1) The current reference value of the SVG output obtained in step S2 , , and bus voltage phase angle ,right , , Clark transformation, positive and negative sequence separation, inverse Clark transformation and Park transformation are performed in sequence to obtain the positive sequence d-axis reference value of the current output by SVG , Current positive sequence q axis reference value , Current negative sequence d-axis reference value , Current negative sequence q axis reference value , current zero sequence reference value ;

[0027] 2) According to the bus voltage phase angle The sampled SVG output current , , Clark transformation, positive and negative sequence separation, inverse Clark transformation and Park transformation are performed in sequence to obtain the positive sequence d-axis value of the current output by SVG , Current positive sequence q-axis value , Current negative sequence d-axis value , current negative sequence q axis value , current zero sequence value ;

[0028] 3) SVG adopts voltage-current dual closed-loop control;

[0029] Voltage outer loop: The collected SVG DC side voltage After the notch filter and the reference value The difference is obtained by PI controller ;

[0030] Current inner loop:

[0031] ① , , , , and The positive sequence current is sent to the positive sequence current control loop for positive sequence current tracking control and output of positive sequence voltage modulation wave , , ;

[0032] ② , , , and The negative sequence current is sent to the negative sequence current control loop for negative sequence current tracking control and output of negative sequence voltage modulation wave , , ;

[0033] 4) The positive sequence voltage modulation wave obtained above , , and negative sequence voltage modulation wave , , The three-phase bridge arm control signals of SVG are obtained by adding them respectively and performing sinusoidal pulse width modulation.

[0034] Preferably, in step S3, the current zero-sequence reference value Multiply by -3 and add to the SVG zero-sequence bridge arm current The difference is sent to the proportional controller and then pulse width modulated to obtain the SVG zero-sequence bridge arm control signal.

[0035] The method for supporting fault voltage of a new energy distribution network based on active power exchange between phases of SVG provided by the present invention first calculates the active power and reactive power compensation required by the fault phase after detecting that the busbar of the grid connection point drops due to a fault, then calculates the active power required to be provided by the non-fault phase and the reactive power compensation required by itself, and on this basis calculates the current reference value of each phase of SVG, and uses voltage-current dual closed-loop control to achieve tracking control of the current reference value, finally achieving active power exchange between the non-fault phase and the fault phase and the best supporting effect on the fault phase voltage, while ensuring that the new energy inverter operates in the maximum active power output mode. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a schematic diagram of the topology of the new energy distribution network in the present invention;

[0037] Figure 2 A block diagram of generating an SVG output current reference value in the present invention;

[0038] Figure 3 A block diagram of processing SVG output current and its reference value in the present invention;

[0039] Figure 4 It is a block diagram of the voltage-current dual closed-loop control of SVG in the present invention;

[0040] Figure 5 It is a system simulation waveform diagram in an implementation mode of the present invention that does not adopt the method involved in the present invention;

[0041] Figure 6 It is a system simulation waveform diagram after adopting the method involved in the present invention in an implementation manner of the present invention. DETAILED DESCRIPTION

[0042] In order to facilitate the understanding of those skilled in the art, the present invention is further described below in conjunction with embodiments and drawings. The contents mentioned in the implementation modes are not intended to limit the present invention.

[0043] The new energy distribution network topology involved in the present invention is as follows Figure 1 As shown, the grid bus includes three phases ABC and the neutral line N, and the grid side is the line impedance (including the equivalent inductance and equivalent resistance ) and grid voltage , , , where the equivalent impedance of the grid-side load is taken into account in the line impedance; photovoltaic, wind turbine and other new energy sources are connected to the grid bus through inverters, and the new energy inverter generally works in a power factor of 1 mode; SVG with a three-phase four-wire structure is also connected to the grid bus, where the DC side of SVG is a voltage-stabilizing capacitor And the second single tuned filter (shown in the dotted box in the figure) in parallel form, is the DC voltage of SVG.

[0044] based on Figure 1 The new energy distribution network topology shown in the figure, the new energy distribution network fault voltage support method based on SVG inter-phase active power exchange provided by the present invention, the core of which is: when a fault occurs in the distribution network, the non-fault phase injects active power into the fault phase through SVG, and SVG emits reactive power to provide reactive power support for each phase, so as to achieve support for the fault phase voltage. Specifically:

[0045] Step S1: When a single-phase asymmetric fault occurs in the power grid, the voltage of the corresponding phase of the power grid bus will drop. In this embodiment, the fault of phase C is taken as an example, and the rated value of the effective value of the power grid bus phase voltage is After the fault occurs, the effective value of the phase voltage of the power grid bus C phase drops to (in is the effective value drop ratio of the fault phase voltage, ), at this time, in order to support the bus voltage of phase C, a certain amount of active power and reactive power needs to be injected. The calculation expression of the active power that needs to be injected into phase C is as follows:

[0046] (1)

[0047] (2)

[0048] (3)

[0049] (4)

[0050] (5)

[0051] In the formula, is the active power required by the fault phase, where , indicating that the faulty phase C occurs; is the rated value of the effective value of the grid bus phase voltage; is the equivalent resistance on the grid side, is the equivalent reactance on the grid side, , is the equivalent inductance on the grid side. and It is variable, but can be obtained according to existing public technologies (such as literature Asiminoaei L, Teodorescu R, Blaabjerg F, et al. Implementation and test of an online embedded grid impedance estimation technique for PVinverters. IEEE Transactions on Industrial Electronics, 2005, 52(4): 1136-1144.); It is the effective value of the output phase current of the new energy inverter; Output power for new energy inverter; is the reactive power compensation of the fault phase, where: , indicating that the faulty phase C occurs. The reactive power compensation is determined by the C phase bus voltage Calculated effective value (RMS) and After making the difference, it is obtained through the proportional integral controller, such as Figure 2 As shown, the reactive power compensation amount that needs to be injected into phase A and phase B is , It is also obtained in a similar way, but the active power that needs to be injected into phase A and phase B is , The calculation expression is:

[0052] (6)

[0053] The above formula (6) shows that the active power required by the fault phase C is provided by the non-fault phases A and B. Figure 1 The dashed arrow in the middle represents the flow direction of active power in the circuit at this time.

[0054] It should be noted that the above active power , , and reactive power compensation , , The calculation is based on the C phase fault as an example. When a two-phase asymmetric fault occurs, the active power of each fault phase can be calculated according to equations (1)-(5). The active power of the non-fault phase is the sum of the active powers of the two fault phases. Their reactive powers are calculated from the effective value of the bus voltage of the phase and combined with The difference is obtained through the proportional integral controller (PI).

[0055] Step S2, such as Figure 2 As shown, according to the obtained , , , , , and , bus voltage effective value , , Calculate the current reference value of SVG output , , , and its calculation method can be found in public literature (for example, literature: Yang Hang. Distribution network fault-tolerant control technology based on photovoltaic reactive power depth regulation [D]. Southeast University, 2022. DOI: 10.27014 / d.cnki.gdnau.2022.003116.); In addition, since the three-phase bus voltage is unbalanced after the fault occurs, a dual second-order generalized integrator phase-locked loop (DSOGI-PLL) is used to adjust the three-phase voltage of the grid connection point. , , Phase lock The specific algorithm of DSOGI-PLL can be found in the public document "Liu Feng. Research on three-phase phase-locked loop under unbalanced power grid [D]. University of Electronic Science and Technology of China, 2013".

[0056] Step S3:

[0057] like Figure 3 As shown, according to the above obtained SVG output current reference value , , and ,right , , Data processing is performed to obtain the positive sequence d-axis reference value of the current output by SVG , Current positive sequence q axis reference value , Current negative sequence d-axis reference value , Current negative sequence q axis reference value , current zero sequence reference value The data processing process involves Clark transformation, positive and negative sequence separation, inverse Clark transformation and Park transformation, which can be found in public literature (for example, literature: Yang Hang. Fault-tolerant control technology of distribution network based on photovoltaic reactive power deep regulation [D]. Southeast University, 2022. DOI: 10.27014 / d.cnki.gdnau.2022.003116.).

[0058] At the same time, Figure 3 As shown, according to The sampled SVG output current , , Perform the same data processing in sequence to obtain the positive sequence d-axis value of the current output by SVG , Current positive sequence q-axis value , Current negative sequence d-axis value , current negative sequence q axis value , current zero sequence value .

[0059] Next, SVG adopts voltage-current dual closed-loop control, such as Figure 4 As shown in the figure, the voltage outer loop is a DC voltage control loop, which collects the DC side voltage of SVG. After the notch filter (the center frequency of the notch filter is set to 2 times the fundamental frequency) and the reference value The difference is obtained by PI controller The current inner loop of SVG includes a positive sequence current control loop and a negative sequence current control loop, and both implement current tracking control in dq coordinates. and The sum of is taken as the positive sequence d-axis current reference value, As positive sequence q-axis current reference values, they are related to the current , and At the same time, positive sequence current tracking control is realized, and positive sequence voltage modulation wave is output , , ; As the negative sequence d-axis current reference value, As negative sequence q-axis current reference values, they are related to the current , and At the same time, negative sequence current tracking control is realized, and negative sequence voltage modulation wave is output , , The positive sequence current control loop and negative sequence current control loop involved in this process are existing mature technologies, which can be found in public literature and will not be described here.

[0060] Finally, if Figure 4 As shown, the positive sequence voltage modulation wave obtained above is , , and negative sequence voltage modulation wave , , The three-phase bridge arm control signal of SVG is obtained by adding them respectively and modulating the sine pulse width. The control signal can drive the abc three-phase bridge arm switch tube of SVG to realize the abc three-phase output current control. In addition, the current zero sequence reference value Multiply by -3 and add to the SVG zero-sequence bridge arm current The difference is sent to the proportional controller and then pulse width modulated to obtain the SVG zero-sequence bridge arm control signal, which can drive the zero-sequence bridge arm switch tube of SVG to realize abc three-phase output current control.

[0061] Next, this embodiment uses a 380V / 50Hz distribution network as an example to perform system simulation. The rated value of the effective value of the phase voltage of the distribution network is 220V, and the three-phase line impedance of the power grid is set to 2mH+0.1Ω. Figure 5 It can be seen that at 3s, the effective value of the grid voltage dropped to 80% due to a fault on the grid side phase C. Since no measures were taken, the fault phase voltage remained at 80%. Figure 6 It can be seen that after the fault voltage support method proposed in the present invention is adopted, the voltage of phase C drops at 3s, but quickly recovers to the rated value, which proves the effectiveness and superiority of the fault voltage support method proposed in the present invention.

[0062] The above embodiments are preferred implementation schemes of the present invention. In addition, the present invention may also be implemented in other ways. Any obvious replacement without departing from the concept of the present technical solution is within the protection scope of the present invention.

[0063] In order to make it easier for ordinary technicians in the field to understand the improvements of the present invention over the prior art, some drawings and descriptions of the present invention have been simplified, and for the sake of clarity, some other elements are omitted in this application document. Ordinary technicians in the field should realize that these omitted elements may also constitute the content of the present invention.

Claims

1. A fault voltage support method for a new energy distribution network based on SVG interphase active power exchange, characterized in that: When a fault occurs in the distribution network, the non-fault phase injects active power into the fault phase through the SVG, and the SVG emits reactive power to provide reactive power support for each phase to support the voltage of the fault phase. The method includes: Step S1, according to the bus voltage drop of the grid connection point, the output power of the new energy inverter at the grid connection point, and the resistance and inductance of the grid line, calculate the active power and reactive power compensation required by the fault phase, as well as the active power required to be provided by the non-fault phase and the reactive power compensation required by itself, wherein the active power required by the fault phase is equal to the active power required to be provided by the non-fault phase; The calculation expression of the active power required by the fault phase is as follows: （1） （2） （3） （4） （5） In the formula, is the active power required by the fault phase, where x =a, b, c, respectively indicating the A phase, B phase or C phase where the fault occurs; is the rated value of the effective value of the grid bus phase voltage; is the equivalent resistance on the grid side; is the equivalent reactance on the grid side, , is the equivalent inductance on the grid side; It is the effective value of the output phase current of the new energy inverter; Output power for new energy inverter; is the effective value drop ratio of the fault phase voltage, 0< k <1; is the reactive power compensation amount of the fault phase; The calculation method of the active power required by the non-fault phase is as follows: 1) If it is a single-phase asymmetric fault, the active power required by the other two non-faulty phases is half of the active power required by the faulty phase; 2) If it is a two-phase asymmetric fault, the active power required by the non-faulty phase is the sum of the active powers required by the two faulty phases; The reactive power compensation required for the fault phase and the non-fault phase is calculated by the effective value of the corresponding phase bus voltage and After making the difference, it is obtained by proportional integral controller; Step S2, calculating the output current reference value of each phase of the SVG according to the active power and reactive power compensation required by the faulty phase obtained in step S1, and the active power required to be provided by the non-faulty phase and the reactive power compensation required by the non-faulty phase; 1) Using a dual second-order generalized integrator phase-locked loop to measure the three-phase voltage at the grid connection point Perform phase locking to obtain the bus voltage phase angle ; 2) The active power required by the faulty phase and the reactive power required by the non-faulty phase obtained in step S1 , the reactive power compensation required for the fault phase and the non-fault phase , and bus voltage phase angle , and bus voltage effective value , calculate the current reference value of SVG output ; Step S3, according to the output current reference value of each phase of SVG obtained in step S2, and in combination with the voltage-current dual closed-loop control method, determine the SVG three-phase bridge arm control signal and the zero-sequence bridge arm control signal, and drive the switch tubes of each bridge arm of SVG according to the obtained control signal, so as to realize the three-phase output current control of the power grid.

2. The fault voltage support method for a new energy distribution network based on SVG interphase active power exchange according to claim 1 is characterized in that: The process of determining the SVG three-phase bridge arm control signal in step S3 is as follows: 1) The current reference value of the SVG output obtained in step S2 and bus voltage phase angle ,right Clark transformation, positive and negative sequence separation, inverse Clark transformation and Park transformation are performed in sequence to obtain the positive sequence d-axis reference value of the current output by SVG , Current positive sequence q axis reference value , Current negative sequence d-axis reference value , Current negative sequence q axis reference value , current zero sequence reference value ; 2) According to the bus voltage phase angle The sampled SVG output current Clark transformation, positive and negative sequence separation, inverse Clark transformation and Park transformation are performed in sequence to obtain the positive sequence d-axis value of the current output by SVG , Current positive sequence q-axis value , Current negative sequence d-axis value , current negative sequence q axis value , current zero sequence value ; 3) SVG adopts voltage-current dual closed-loop control; Voltage outer loop: The collected SVG DC side voltage After the notch filter and the reference value The difference is obtained by PI controller ; Current inner loop: ① and The positive sequence current is sent to the positive sequence current control loop for positive sequence current tracking control and output of positive sequence voltage modulation wave ; ② and The negative sequence current is sent to the negative sequence current control loop for negative sequence current tracking control and output of negative sequence voltage modulation wave ; 4) The positive sequence voltage modulation wave obtained above and negative sequence voltage modulation wave The three-phase bridge arm control signals of SVG are obtained by adding them respectively and performing sinusoidal pulse width modulation.

3. The fault voltage support method for a new energy distribution network based on SVG interphase active power exchange according to claim 2 is characterized in that: In step S3, the current zero sequence reference value Multiply by -3 and add to the SVG zero-sequence bridge arm current The difference is sent to the proportional controller and then pulse width modulated to obtain the SVG zero-sequence bridge arm control signal.

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