Networking cascade star connection SVG (static var generator), control method of networking cascade star connection SVG and computer equipment

Abstract

The invention belongs to the technical field of SVG control, and particularly relates to a networking cascade star connection SVG, a control method thereof and computer equipment. When an asymmetric metallic grounding fault or a non-metallic grounding fault of an alternating current system occurs, a final unbalanced voltage compensation value is generated from at least one aspect of sub-module voltage and power grid voltage and current; the two aspects are respectively intended to perform compensation in consideration of a sub-module voltage imbalance condition caused by a fault (generating an internal potential of a negative sequence dq axis component based on the sub-module voltage according to a sub-module voltage mean value of each phase) and perform compensation in consideration of a power grid voltage and current imbalance condition caused by the fault (the internal potential of the negative sequence dq axis component based on the sub-module voltage is generated according to the sub-module voltage mean value of each phase). A zero-sequence voltage instruction based on the power grid voltage and the power grid current is generated according to the power grid voltage and the power grid current), the SVG can complete reactive power support when an asymmetric fault occurs on the alternating current side in the fault period, and locking cannot occur.

Description

Technical Field

[0001] The invention belongs to the technical field of SVG control, and in particular relates to a networked cascade star-connected SVG and a control method and computer equipment thereof. Background Art

[0002] A grid-type static VAR generator (SVG) topology structure in the prior art is as follows: Figure 1 As shown, the grid-type high-voltage direct-mounted energy storage usually adopts the form of H-bridge cascade, and the three-phase chain links can be connected in a star shape, such as Figure 1 When a power grid fails, the grid-connected cascaded SVG can compensate for the reactive power and negative sequence current of the system.

[0003] In actual power systems, three-phase chain SVGs are required to be able to operate normally under grid fault conditions. When an asymmetric non-metallic or metallic grounding fault occurs in the AC system, such as a single-phase grounding or a two-phase short circuit, the fault will cause an imbalance in the DC voltage between the three-phase cascade chains, and even cause the submodule capacitor voltage to be overvoltage or undervoltage, which in turn causes the overvoltage capacitor of one phase to trigger overvoltage protection, and the modulation of the undervoltage phase to be saturated. At this time, the SVG cannot operate normally, resulting in insufficient reactive support for the grid fault, and unable to support the grid through the fault period, and ultimately a fault ride-through failure occurs. Summary of the invention

[0004] The object of the present invention is to provide a network-building cascade star-connected SVG and a control method and computer device thereof, so as to solve the problem that when an asymmetric fault occurs in an AC system, the SVG cannot operate normally, resulting in insufficient reactive power support for the power grid and causing failure of fault crossing.

[0005] In order to solve the above technical problems, the present invention provides a control method for cascading star-connected SVGs, comprising the following steps:

[0006] 1) When an asymmetric fault occurs in the AC system, an internal potential based on the negative-sequence dq-axis component of the submodule voltage and / or a zero-sequence dq-axis voltage command based on the grid voltage and current is generated;

[0007] The internal potential of the negative sequence dq axis component based on the submodule voltage is generated in the following manner: a negative sequence dq axis current command is obtained according to the average value of the submodule voltage of each phase, and then the internal potential of the negative sequence dq axis component based on the submodule voltage is obtained according to the negative sequence dq axis current command;

[0008] The method for generating the zero-sequence dq axis voltage command based on the unbalanced grid voltage and current is as follows: the positive-sequence dq axis voltage components and the positive-sequence dq axis current components are obtained according to the grid voltage and the grid current, and the zero-sequence dq axis voltage command is obtained according to the positive-sequence dq axis voltage components and the positive-sequence dq axis current components;

[0009] 2) Generate a final unbalanced voltage compensation value according to the generated result of step 1), and superimpose the final unbalanced voltage compensation value on the modulation wave of SVG to generate a control signal of SVG to control SVG.

[0010] Furthermore, the final unbalanced voltage compensation value instruction is the sum of the internal potential response of the negative-sequence dq-axis component of the submodule voltage and the zero-sequence dq-axis voltage instruction.

[0011] Furthermore, the method for obtaining the negative-sequence dq-axis current command according to the average value of the sub-module voltage of each phase is as follows: the average value of the sub-module voltage of each phase is subjected to Clarke transformation to obtain the dq-axis voltage; the difference between 0 and the d-axis voltage is made and the obtained difference is adjusted and controlled to obtain the negative-sequence d-axis current command; the difference between 0 and the q-axis voltage is made and the obtained difference is adjusted and controlled to obtain the negative-sequence q-axis current command.

[0012] Furthermore, the method of obtaining the internal potential of the negative-sequence dq-axis component based on the submodule voltage according to the negative-sequence dq-axis current command is: the negative-sequence dq-axis current command is respectively adjusted and controlled to obtain the internal potential of the negative-sequence dq-axis component based on the submodule voltage accordingly.

[0013] Furthermore, the way to obtain the zero-sequence dq-axis voltage command according to the positive-sequence dq-axis voltage components and the positive-sequence dq-axis current components is as follows:

[0014]

[0015] In the formula, A=-U dp I dn -U dn I dp +U qp I qn +U qn I qp , B=U qn I dp +U dn I qp +U qp I dn +U dp I qn ; U dp , U qp , U dn , U qn I represents the positive sequence d-axis voltage component, the positive sequence q-axis voltage component, the negative sequence d-axis voltage component, and the negative sequence q-axis voltage component respectively; dp ,I qp ,I dn ,I qn Respectively represent the positive sequence d-axis current component, the positive sequence q-axis current component, the negative sequence d-axis current component, and the negative sequence q-axis current component; Vd0_ref 、V q0_ref Respectively represent the zero-sequence dq axis voltage instructions.

[0016] Furthermore, the modulation wave of SVG is generated by adopting dq decoupling control of voltage outer loop and current inner loop to generate the modulation wave of SVG, and the command and feedback of d-axis voltage outer loop are DC voltage command U dcref , the average voltage of all submodules in the three-phase link U dcave The command and feedback of the AC voltage outer loop are AC voltage amplitude command V mref , AC voltage feedback V m .

[0017] Furthermore, when the system operates normally, an internal potential based on the negative-sequence dq-axis component of the submodule voltage is generated, and a control signal of the SVG is generated according to the internal potential based on the negative-sequence dq-axis component of the submodule voltage to control the SVG.

[0018] To solve the above technical problem, the present invention further provides a computer device, including a processor, wherein the processor executes a computer program to implement the steps of the control method for networking cascade star-connected SVG introduced above.

[0019] To solve the above technical problems, the present invention also provides a networked cascaded star-connected SVG, including an SVG controller, the SVG controller including a processor, the processor executing a computer program to implement the steps of the control method of the networked cascaded star-connected SVG introduced above.

[0020] The present invention is an improved invention, and the beneficial effects of the above technical solution are as follows: for star-connected SVG, when an asymmetric metallic grounding or non-metallic grounding fault occurs in the AC system, the final unbalanced voltage compensation value is generated from at least one aspect of the submodule voltage and the grid voltage and current, and then the generated unbalanced voltage compensation value is superimposed on the modulation wave of the SVG so that the SVG can complete reactive support. Among them, considering the submodule voltage is specifically based on the mean value of the submodule voltage of each phase to generate the internal potential based on the negative sequence dq axis component of the submodule voltage, and this aspect intends to compensate for the unbalanced submodule voltage caused by the fault; considering the grid voltage and current is specifically based on the unbalanced voltage and current caused by the grid fault to generate the zero sequence dq axis voltage instruction based on the grid voltage and current, and this aspect intends to compensate for the unbalanced grid voltage and current caused by the fault. Both aspects can achieve a certain degree of compensation effect from different perspectives. The use of appropriate sub-module voltage unbalance compensation strategy during fault period enables SVG to complete reactive power support during asymmetric fault on the AC side without lockout. This solves the problem of insufficient reactive power support for grid faults caused by inability of static VAR generator to operate normally due to overvoltage or undervoltage of sub-module capacitor voltage during unbalanced fault period. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a topological structure diagram of a star-type network static reactive generator in the prior art;

[0022] Figure 2 It is a circuit diagram of an H-bridge submodule connected in series on each phase link of a star-type network-forming static VAR generator;

[0023] Figure 3 It is a control block diagram of the star-connected SVG generating the final unbalanced voltage instruction in the "control method embodiment of the network-connected cascaded star-connected SVG" of the present invention;

[0024] Figure 4 It is a control block diagram of the angle ωt generated based on virtual synchronous control adopted in the "control method embodiment of networked cascaded star-connected SVG" of the present invention;

[0025] Figure 5 It is a control block diagram of the star-connected SVG generating the final modulation wave in the "control method embodiment of the network-constructing cascaded star-connected SVG" of the present invention. DETAILED DESCRIPTION

[0026] The core idea of ​​the present invention is that, for a star-connected SVG, when an asymmetric metallic grounding or non-metallic grounding fault occurs in the AC system, a final unbalanced voltage compensation value is generated by taking into account at least one aspect of the submodule voltage and the grid voltage and current. These two aspects are intended to compensate for the submodule voltage imbalance caused by the fault and the grid voltage and current imbalance caused by the fault, respectively. During the fault period, the SVG can complete the reactive support of the asymmetric fault on the AC side without locking.

[0027] For star-connected SVG, the method of generating the internal potential of the negative-sequence dq-axis component based on the submodule voltage is as follows: the negative-sequence dq-axis current command is obtained according to the average value of the submodule voltage of each phase, and then the internal potential of the negative-sequence dq-axis component based on the submodule voltage is obtained according to the negative-sequence dq-axis current command; the method of generating the zero-sequence dq-axis voltage command based on the unbalanced grid voltage and current is as follows: the positive-sequence dq-axis voltage components and the positive-sequence dq-axis current components are obtained according to the grid voltage and the grid current, and the zero-sequence dq-axis voltage command is obtained according to the positive-sequence dq-axis voltage components and the positive-sequence dq-axis current components.

[0028] Based on the above invention concept, a control method for cascading star-connected SVG, a computer device and a cascading star-connected SVG of the present invention can be realized. In order to make the purpose, technical solution and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0029] Example of a control method for building a network cascade star connection SVG:

[0030] The topology of the mesh-type SVG in this embodiment is the same as that in the prior art. Figure 1 As shown, SVG adopts star connection, and multiple submodules are connected in series on each phase link. Figure 2 The H-bridge submodule shown. Of course, the topology of each submodule can be selected from other topological structures in the prior art.

[0031] When an asymmetric fault occurs in the AC system, the compensation strategy for the unbalanced submodule voltage in the case of an asymmetric fault in the AC system includes a zero-sequence voltage unbalance compensation strategy based on the submodule voltage generation (for generating the internal potential E of the negative sequence dq axis component) dn 、E qn ) and a zero-sequence voltage injection strategy based on the unbalanced grid voltage and current during a fault (for generating a zero-sequence dq-axis voltage command V based on the unbalanced grid voltage and current d0_ref 、V q0_ref ).

[0032] The zero-sequence voltage unbalance compensation strategy based on submodule voltage generation is as follows: Figure 3 As shown in the upper part, the average voltage U of each phase submodule is collected dca_av , U dcb_av , U dcc_av , Clarke transform is performed on the average voltage of each phase submodule to generate the d-axis voltage V dc_d and q-axis voltage V dc_q ; Use 0 to subtract the d-axis voltage V dc_d and q-axis voltage V dc_q , and perform PI control on the obtained difference (other controls, such as PID control, can be selected according to actual conditions), that is, use PI control to control V dc_d With V dc_q Control to 0, so as to obtain the negative sequence d-axis current command I dnref With the negative sequence q axis current command I qnref ; Then, the negative sequence d axis current command I dnref With the negative sequence q axis current command I qnref Perform PI control (other controls such as PID control can be selected according to actual conditions) to generate the internal potential E of the negative sequence dq axis component dn 、E qn .

[0033] The zero-sequence current injection strategy based on the unbalanced grid voltage and current generation during the fault period is as follows: Figure 3 As shown in the lower part, the grid voltage u is collected a_ac 、u b_ac 、u c_ac And the grid current i a_ac 、i b_ac 、i c_ac , decouple and transform the angle ωt generated by virtual synchronous control to generate the positive and negative sequence dq axis voltage components U dp , U qp , U dn , U qn And the positive and negative sequence dq axis current components I dp ,I qp ,I dn ,I qn ; Then, according to the positive and negative sequence dq axis voltage and current components and formula (1), the zero sequence dq axis voltage command V based on the unbalanced grid voltage and current is generated. d0_ref 、V q0_ref .

[0034]

[0035] In the formula, A=-U dp I dn -U dn I dp+U qp I qn +U qn I qp , B=U qn I dp +U dn I qp +U qp I dn +U dp I qn .

[0036] The angle ωt is thetaP, which is the angle of the potential inside the network cascade SVG. It can be generated by virtual synchronous control. The generation method is as follows: Figure 4 As shown in the figure, P ref is the active power command, P e is the active power exchanged between the SVG and the grid, w g is the angular frequency of the power grid, K D is the damping coefficient.

[0037] Since the dq axis components of voltage and current based on dq rotating coordinates can be used for PI control under star connection, the zero-sequence dq axis voltage command V generated based on the unbalanced grid voltage and current is d0_ref 、V q0_ref The internal potential E directly superimposed on the negative sequence dq axis component dn 、E qn Thus, the final unbalanced voltage compensation value E is obtained. d_n0 、E q_n0 , the final zero-sequence voltage command E d_n0 、E q_n0 Superimposed on the modulation wave of SVG generated by the steady-state strategy to obtain the final modulation wave v abc The final modulation wave is compared with the carrier wave to generate the SVG control signal (i.e. PWM) to control the SVG. Among them, the steady-state strategy is as follows Figure 5 As shown in the figure, it is the dq decoupling control strategy of the voltage outer loop and the current inner loop. The command and feedback of the d-axis voltage outer loop are the DC voltage command U dcref , the average voltage of all submodules in the three-phase link U dcave , the instruction and feedback of the q-axis voltage outer loop are respectively the AC voltage amplitude instruction V mref , AC voltage feedback V m .

[0038] In this embodiment, the final unbalanced voltage compensation value is obtained based on the two strategies mentioned above, and the corresponding final unbalanced voltage compensation value is the superposition of the output results of the two strategies. Considering the actual situation, only one of the strategies can be used to generate the final unbalanced voltage compensation value. Both methods can solve the problem of voltage imbalance of the asymmetric fault submodule of the AC system to a certain extent.

[0039] When the system is operating normally, the zero-sequence voltage imbalance compensation strategy based on the submodule voltage generation can be used to generate the final voltage compensation value, and the final voltage compensation value is superimposed on the modulation wave of the SVG generated by the steady-state strategy (using the same Figure 5 The same steady-state strategy) is used to generate the control signal of SVG to control SVG.

[0040] Computer equipment example:

[0041] A computer device embodiment of the present invention includes a memory, a processor, an internal bus, and a computer program stored in the memory. The processor and the memory communicate and exchange data with each other through the internal bus. The processor executes the computer program to implement the steps of the method described in the "Control Method Embodiment for Networking Cascaded Star Connection SVG" of the present invention. The processor can be a processing device such as a microprocessor MCU, a programmable logic device FPGA, etc.; the memory can be various memories that use electrical energy to store information, such as RAM, ROM, etc., or it can be a memory that uses other methods.

[0042] SVG implementation example of cascading star connection:

[0043] A network-building cascade star-connected SVG embodiment of the present invention has a topology as follows: Figure 1 As shown, multiple submodules are arranged in series on each phase link, and each submodule can be an H-bridge submodule. In addition, an SVG controller is also included, and the SVG controller includes a processor, and the processor executes a computer program to implement the steps of the method described in the "Control Method Embodiment for Networking Cascaded Star Connection SVG". The processor can be a processing device such as a microprocessor MCU, a programmable logic device FPGA, etc.

[0044] In summary, according to the different fault depths of metallic grounding and non-metallic grounding of the power grid, the present invention can adopt a suitable sub-module voltage unbalance compensation strategy during the fault period so that the SVG can complete the reactive power support during the asymmetric fault on the AC side without lockout, thereby improving the imbalance problem of the DC voltage between the three chains caused by the unbalanced grid voltage and current of the SVG during the grid fault, and solving the problem of the static VAR generator being unable to operate normally due to the overvoltage or undervoltage problem of the sub-module capacitor voltage during the unbalanced fault period, and the insufficient reactive power support for the grid fault.

[0045] Specific implementation methods are given above, but the present invention is not limited to the described implementation methods. The basic idea of ​​the present invention lies in the above basic scheme. For ordinary technicians in this field, it does not take creative work to design various deformed models, formulas, and parameters according to the teachings of the present invention. Changes, modifications, substitutions, and variations of the implementation methods without departing from the principles and spirit of the present invention still fall within the scope of protection of the present invention.

Claims

1. A control method for SVG with cascaded star connection, characterized in that: The steps include: 1) When an asymmetric fault occurs in the AC system, an internal potential based on the negative-sequence dq-axis component of the submodule voltage and / or a zero-sequence dq-axis voltage command based on the grid voltage and current is generated; The internal potential of the negative sequence dq axis component based on the submodule voltage is generated in the following manner: a negative sequence dq axis current command is obtained according to the average value of the submodule voltage of each phase, and then the internal potential of the negative sequence dq axis component based on the submodule voltage is obtained according to the negative sequence dq axis current command; The method for generating the zero-sequence dq axis voltage command based on the unbalanced grid voltage and current is as follows: the positive-sequence dq axis voltage components and the positive-sequence dq axis current components are obtained according to the grid voltage and the grid current, and the zero-sequence dq axis voltage command is obtained according to the positive-sequence dq axis voltage components and the positive-sequence dq axis current components; 2) Generate a final unbalanced voltage compensation value according to the generated result of step 1), and superimpose the final unbalanced voltage compensation value on the modulation wave of SVG to generate a control signal of SVG to control SVG.

2. The control method of the networked cascade star connection SVG according to claim 1, characterized in that: The final unbalanced voltage compensation value is the sum of the internal potential response of the negative-sequence dq-axis component of the submodule voltage and the zero-sequence dq-axis voltage command.

3. The control method for SVG of network cascade star connection according to claim 1 or 2, characterized in that: The method for obtaining the negative-sequence dq-axis current command according to the average value of the submodule voltage of each phase is as follows: the average value of the submodule voltage of each phase is subjected to Clarke transformation to obtain the dq-axis voltage; the difference between 0 and the d-axis voltage is made and then the obtained difference is adjusted and controlled to obtain the negative-sequence d-axis current command; the difference between 0 and the q-axis voltage is made and then the obtained difference is adjusted and controlled to obtain the negative-sequence q-axis current command.

4. The control method for SVG of network cascade star connection according to claim 1 or 2, characterized in that: The method of obtaining the internal potential of the negative-sequence dq-axis component based on the submodule voltage according to the negative-sequence dq-axis current command is: the negative-sequence dq-axis current command is respectively adjusted and controlled to obtain the internal potential of the negative-sequence dq-axis component based on the submodule voltage accordingly.

5. The control method of the networked cascade star connection SVG according to claim 1 or 2, characterized in that: The way to obtain the zero-sequence dq-axis voltage command according to the positive and negative sequence dq-axis voltage components and the positive and negative sequence dq-axis current components is: In the formula, A=-U dp I dn -U dn I dp +U qp I qn +U qn I qp , B=U qn I dp +U dn I qp +U qp I dn +U dp I qn ; U dp , U qp , U dn , U qn I represents the positive sequence d-axis voltage component, the positive sequence q-axis voltage component, the negative sequence d-axis voltage component, and the negative sequence q-axis voltage component respectively; dp ,I qp ,I dn ,I qn Respectively represent the positive sequence d-axis current component, the positive sequence q-axis current component, the negative sequence d-axis current component, and the negative sequence q-axis current component; V d0_ref 、V q0_ref Respectively represent the zero-sequence dq axis voltage instructions.

6. The control method of the networked cascade star connection SVG according to claim 1 or 2, characterized in that: The modulation wave of SVG is generated by using the dq decoupling control of the voltage outer loop and the current inner loop to generate the modulation wave of SVG, and the command and feedback of the d-axis voltage outer loop are respectively the DC voltage command U dcref , the average voltage of all submodules in the three-phase link U dcave , the instruction and feedback of the q-axis voltage outer loop are respectively the AC voltage amplitude instruction V mref , AC voltage feedback V m .

7. The control method of the networked cascade star connection SVG according to claim 1 or 2, characterized in that: When the system is operating normally, an internal potential based on the negative-sequence dq-axis component of the submodule voltage is generated, a voltage compensation value is generated according to the internal potential based on the negative-sequence dq-axis component of the submodule voltage, and the voltage compensation value is superimposed on the modulation wave of the SVG to generate a control signal of the SVG to control the SVG.

8. A computer device comprising a processor, characterized in that: The processor executes the computer program to implement the steps of the method according to any one of claims 1 to 7.

9. A networked cascade star-connected SVG, comprising an SVG controller, wherein the SVG controller comprises a processor, characterized in that: The processor executes the computer program to implement the steps of the method according to any one of claims 1 to 7.

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