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

Abstract

The invention belongs to the technical field of SVG (Static Var Generator) control, and particularly relates to a networking cascade angular 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 zero-sequence current instruction is generated from at least one aspect of sub-module voltage and power grid voltage and current; the two aspects aim to compensate by considering the voltage imbalance condition of the sub-module caused by the fault and to compensate by considering the voltage and current imbalance condition of the power grid caused by the fault, so that the SVG can complete reactive power support during the asymmetric fault of the alternating current side in the fault period, and locking is avoided.

Description

Technical Field

[0001] The invention belongs to the technical field of SVG control, and in particular relates to a network-building cascaded angular connection SVG and a control method and computer equipment thereof. Background Art

[0002] A grid-type static VAR generator (SVG) topology in the prior art is shown in Figure 1(a). Grid-type high-voltage direct-mounted energy storage is usually in the form of H-bridge cascade, and the three-phase chain links can be connected in an angular manner. When a grid fault occurs, the grid-type cascade static VAR generator can compensate for the reactive power and negative sequence current of the system.

[0003] In actual power systems, the three-phase chain static VAR generator needs 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 unbalanced grid voltage and current caused by the grid fault will cause an imbalance in the DC voltage between the three-phase cascade H-bridge chains, and even cause overvoltage or undervoltage of the submodule capacitors, resulting in saturation of the modulation system of the undervoltage phase and triggering of overvoltage protection of the overvoltage phase capacitor. At this time, the static VAR generator cannot operate normally, and the SVG is insufficient to support the grid fault reactive power and cannot support the grid through the fault period, and ultimately a fault ride-through failure occurs. Summary of the invention

[0004] The purpose of the present invention is to provide a grid-connected cascaded triangle-connected SVG and a control method and computer device thereof, so as to solve the problem of failure of fault crossing due to insufficient reactive support to the power grid caused by the inability of SVG to operate normally when an asymmetric fault occurs in the AC system.

[0005] In order to solve the above technical problems, the present invention provides a control method for connecting SVG by meshing cascaded angles, comprising the following steps:

[0006] 1) When an asymmetric fault occurs in the AC system, a zero-sequence injection current i based on the submodule voltage is generated 0_ref1 and / or zero sequence injection current i based on unbalanced grid voltage and current 0_ref2 ;

[0007] i 0_ref1 The generation method is as follows: the negative sequence dq axis current command is obtained according to the average value of the sub-module voltage of each phase, and then the i is obtained according to the negative sequence dq axis current command. 0_ref1 ;

[0008] i 0_ref2The generation method is as follows: according to the grid voltage and grid current, the positive and negative sequence dq axis voltage components and the positive and negative sequence dq axis current components are obtained; according to the positive and negative sequence dq axis voltage components and the positive and negative sequence dq axis current components, the zero sequence dq axis current components are obtained; according to the zero sequence dq axis current components, i 0_ref2 ;

[0009] 2) Generate zero-sequence current command i according to the result of step 1) 0_ref , using i 0_ref A control signal of the SVG is generated to control the SVG.

[0010] Furthermore, the generated i 0_ref for i 0_ref1 and i 0_ref2 The sum.

[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, according to the negative sequence dq axis current command, i 0_ref1 The method is: i 0_ref1 =I qnref cos(thetaP)+I dnref sin(thetaP), where I dnref and I qnref They represent the negative-sequence dq-axis current commands respectively, and thetaP represents the angle of the potential inside the network cascade SVG.

[0013] Furthermore, the zero-sequence dq-axis current component is obtained according to the positive-sequence dq-axis voltage component and the positive-sequence dq-axis current component 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 Iqn ; 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 They 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 respectively; I d0_ref ,I q0_ref Represent the zero-sequence dq-axis current components respectively.

[0016] Furthermore, according to the zero-sequence dq-axis current component, i 0_ref2 The method is: i 0_ref2 =I0sin(thetaP0+thetaP), where I0 represents the amplitude of the zero-sequence current and is obtained based on the zero-sequence dq-axis current component, thetaP0 represents the initial angle of the zero-sequence current and is obtained based on the zero-sequence dq-axis current component, and thetaP represents the angle of the potential within the network cascade SVG.

[0017] Furthermore, using i 0_ref The method of generating the SVG control signal is to add the active current command and reactive current command of each phase and then superimpose them respectively. 0_ref The current command of each phase is obtained, and the current command of each phase is subtracted from the current feedback of each phase, and then the obtained difference is adjusted and controlled to obtain the output value of each phase; and the control signal of SVG is generated according to the output value of each phase.

[0018] Furthermore, the control signal of the SVG is generated according to the output value of each phase by respectively superimposing the voltage feedforward value of each phase on the output value of each phase, and generating the control signal of the SVG according to the superimposed result.

[0019] Furthermore, thetaP is obtained through virtual synchronous control.

[0020] Furthermore, when the system is operating normally, a zero-sequence injection current i based on the submodule voltage is generated. 0_ref1 And as the zero-sequence current command i 0_ref , using i 0_ref A control signal of the SVG is generated to control the SVG.

[0021] In order to solve the above technical problem, the present invention also provides a computer device, including a processor, wherein the processor executes a computer program to implement the steps of the control method for meshing cascaded angular connections SVG introduced above.

[0022] In order to solve the above technical problems, the present invention also provides a meshed cascaded angular connection 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 meshed cascaded angular connection SVG introduced above.

[0023] The present invention is an improved invention, and the beneficial effect of the above technical solution is as follows: for the angle-connected SVG, when an asymmetric metallic grounding or non-metallic grounding fault occurs in the AC system, the final zero-sequence current instruction is generated by considering at least one aspect of the submodule voltage and the grid voltage and current. Among them, considering the submodule voltage is specifically based on the average value of the submodule voltage of each phase to generate a zero-sequence injection current based on the submodule voltage, wherein the unbalanced submodule voltage is due to the exchange imbalance between the three-phase link and the active power, and the unbalanced active power is generated by the negative-sequence current. To eliminate the imbalance, the zero-sequence current can be used to balance the imbalance generated by the negative-sequence current. Therefore, it is necessary to generate a negative-sequence dq-axis current instruction first, and then convert it into a zero-sequence component to obtain a zero-sequence injection current based on the submodule voltage. This aspect aims to take into account the unbalanced submodule voltage caused by the fault for compensation; considering the grid voltage and current is specifically based on the unbalanced voltage and current caused by the grid fault to generate a zero-sequence injection current based on the unbalanced grid voltage and current. This aspect aims to take into account the unbalanced grid voltage and current caused by the fault for compensation. 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

[0024] FIG. 1( a ) is a topological structure diagram of a angular grid-type static VAR generator in the prior art;

[0025] FIG. 1( b ) is a circuit diagram of an H-bridge submodule connected in series on each phase link of a angular grid-type static VAR generator;

[0026] Figure 2 It is a control block diagram of generating a final zero-sequence current instruction by the angle-connected SVG in the "control method embodiment of the grid-connected cascade angle-connected SVG" of the present invention;

[0027] Figure 3 It is a control block diagram of the zero-sequence current imbalance compensation strategy based on submodule voltage generation adopted in the "control method embodiment of network-connected cascaded angular connection SVG" of the present invention;

[0028] Figure 4It is a control block diagram of the angle ωt generated based on virtual synchronous control adopted in the "control method embodiment of networked cascaded angular connection SVG" of the present invention;

[0029] Figure 5 It is a control block diagram of the zero-sequence current injection strategy based on the generation of unbalanced grid voltage and current during a fault period adopted in the "Control method embodiment of grid-connected cascaded angular connection SVG" of the present invention. DETAILED DESCRIPTION

[0030] The core idea of ​​the present invention is that, when an asymmetric metallic grounding or non-metallic grounding fault occurs in the AC system, a final zero-sequence current instruction 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.

[0031] For the delta-connected SVG, the method for generating the zero-sequence injection current based on the submodule voltage is as follows: a negative-sequence dq-axis current instruction is obtained according to the average value of the submodule voltage of each phase, and then the zero-sequence injection current based on the submodule voltage is obtained according to the negative-sequence dq-axis current instruction; the method for generating the zero-sequence injection current based on the unbalanced grid voltage and current is as follows: positive-sequence dq-axis voltage components and positive-sequence dq-axis current components are obtained according to the grid voltage and the grid current, zero-sequence dq-axis current components are obtained according to the positive-sequence dq-axis voltage components and the positive-sequence dq-axis current components, and zero-sequence injection current based on the unbalanced grid voltage and current is obtained according to the zero-sequence dq-axis current component.

[0032] Based on the above invention concept, a control method for cascading angular connection SVG, a computer device and a cascading angular connection 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.

[0033] Example of a control method for connecting SVG with cascaded angles:

[0034] The topology of the mesh-type SVG of this embodiment is the same as that in the prior art, as shown in FIG1(a), the SVG is connected in an angular shape, and a plurality of submodules are connected in series on each phase link, each submodule is an H-bridge submodule, and its circuit is shown in FIG1(b). Of course, the topology of each submodule can select other topological structures in the prior art.

[0035] 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 current unbalanced compensation strategy based on the submodule voltage generation (for generating a zero-sequence injection current i based on the submodule voltage). 0_ref1 ) and a zero-sequence current injection strategy based on the unbalanced grid voltage and current during a fault (for generating a zero-sequence injection current i based on the unbalanced grid voltage and current) 0_ref2 ).

[0036] The zero-sequence current unbalance compensation strategy based on submodule voltage generation is as follows: Figure 2 , Figure 3 As shown, 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 the obtained difference is subjected to PI control (i.e. proportional integral control, other control methods can be selected according to actual conditions, such as proportional integral differential PID control), that is, PI control is used 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 ; Let the zero-sequence injection current based on the submodule voltage be i 0_ref1 =I qnref cos(ωt)+I dnref sin(ωt). The angle ωt is thetaP, which is the angle of the potential in the network cascade SVG. This angle can be used to perform park transformation of voltage and current from the abc coordinate system to the dq coordinate system. 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] Among them, the unbalanced submodule voltage is caused by the unbalanced exchange of the three-phase link and the active power. The unbalanced active power is generated by the negative-sequence current and voltage. To eliminate the unbalanced power, the zero-sequence current can be used to balance the unbalanced power generated by the negative-sequence current. Therefore, it is necessary to obtain the negative-sequence current command first, and generate the final zero-sequence current command value (i.e., the zero-sequence injection current i based on the submodule voltage) according to the relationship between the zero-sequence current and the negative-sequence current. 0_ref1 ).

[0038] The zero-sequence current injection strategy based on the unbalanced grid voltage and current during the fault period is as follows: Figure 2 As shown, 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 d axis current component I is generated d0_ref and the zero-sequence q-axis current component I q0_ref ; Then the zero-sequence dq-axis current component I d0_ref ,I q0_ref The square root of these two parameters is used to obtain the amplitude of the zero-sequence current I0. According to the zero-sequence dq-axis current component I d0_ref and I q0_ref The initial angle thetaP0 of the zero-sequence current can be obtained. The initial angle thetaP0 plus the angle ωt generated by the virtual synchronous control is taken as its sine value and then multiplied by the amplitude of the zero-sequence current to obtain the zero-sequence injection current i based on the unbalanced grid voltage and current. 0_ref2 , i.e. i 0_ref2 =I0sin(thetaP0+thetaP).

[0039]

[0040] In the formula, A=-U dp I dn -U dn I dp +U qp I qn +U qn Iqp , B=U qn I dp +U dn I qp +U qp I dn +U dp I qn .

[0041] Furthermore, Figure 2 As shown, the zero-sequence injection current i based on the submodule voltage 0_ref1 and zero-sequence injection current i based on unbalanced grid voltage and current 0_ref2 Add together to get the final zero-sequence current command i 0_ref .

[0042] Then according to the final zero-sequence current command i 0_ref To generate a three-phase modulation wave, the specific process is as follows Figure 5 As shown, the reactive current command i of each phase ab_qref 、i bc_qref 、i ca_qref Respectively with the zero-sequence current command i 0_ref Add them together, and then correspond to the active current instructions of each phase (I dref sinθ a ,I dref sinθ b ,I dref sinθ c ) are added together to obtain the final current command, where I dref Indicates active current command, through the DC voltage command U dcref The average voltage of all submodules in the three-phase link is U dcave The difference between the two is used for PI control (other controls such as PID control can be selected according to actual conditions) to obtain, θ a ,θ b ,θ c The angle ωt (thetaP) generated by virtual synchronous control is obtained as thetaP, thetaP-2π / 3, thetaP+2π / 3 respectively; the final current command and the actual current feedback i ab 、i bc 、i ca The inner loop control is performed by making a difference, and the output of the inner loop control is then added with the voltage feedforward value u of each phase accordingly. ab_ff 、u bc_ff 、u ca_ff Generate a three-phase modulation wave, and then compare it with the carrier wave to output the final PWM signal (i.e., the control signal of SVG) used to control SVG. ab_ff 、u bc_ff 、uca_ff The three-phase AC voltage sampling standard value is multiplied by the modulation index. The modulation index is the AC phase voltage peak value divided by the DC voltage value of the bridge arm. The DC voltage value of the bridge arm is the rated number of sub-modules of the bridge arm multiplied by the rated voltage of the sub-module.

[0043] In this embodiment, the final zero-sequence current command i is obtained. 0_ref The method is based on the two strategies mentioned above to generate the corresponding zero-sequence current command i 0_ref =i 0_ref1 +i 0_ref2 Considering the actual situation, only one of the strategies can be used to generate the zero-sequence current command i 0_ref For example, only the zero-sequence current unbalance compensation strategy based on the submodule voltage generation is used to generate i 0_ref1 , and i 0_ref1 As the final zero-sequence current command i 0_ref , or only the zero-sequence current injection strategy based on the unbalanced grid voltage and current during the fault period can be used to generate i 0_ref2 , and i 0_ref2 As the final zero-sequence current command i 0_ref Both methods can solve the problem of voltage imbalance of the asymmetric fault submodule of the AC system to a certain extent. Moreover, these two methods are subsequently based on the final zero-sequence current command i 0_ref The method of generating three-phase modulation waves is the same.

[0044] In the case of normal system operation, the zero-sequence current unbalance compensation strategy based on submodule voltage generation can be used to generate i 0_ref1 , and i 0_ref1 As the final zero-sequence current command i 0_ref To generate SVG control signals to control SVG.

[0045] Computer equipment example:

[0046] 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 Angular 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.

[0047] Example of SVG for cascading grid polygon connections:

[0048] An embodiment of the present invention of a meshed cascaded angular connection SVG has a topology as shown in FIG1(a), and multiple submodules are arranged in series on each phase link, and each submodule can be an H-bridge submodule as shown in FIG1(b). In addition, it also includes an SVG controller, which includes a processor, and the processor executes a computer program to implement the steps of the method described in the "control method embodiment of meshed cascaded angular connection SVG". The processor can be a processing device such as a microprocessor MCU, a programmable logic device FPGA, etc.

[0049] 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.

[0050] 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 angular connections, characterized in that: The steps include: 1) When an asymmetric fault occurs in the AC system, a zero-sequence injection current i based on the submodule voltage is generated 0_ref1 and / or zero sequence injection current i based on unbalanced grid voltage and current 0_ref2 ; i 0_ref1 The generation method is as follows: the negative sequence dq axis current command is obtained according to the average value of the sub-module voltage of each phase, and then the i is obtained according to the negative sequence dq axis current command. 0_ref1 ; i 0_ref2 The generation method is as follows: according to the grid voltage and grid current, the positive and negative sequence dq axis voltage components and the positive and negative sequence dq axis current components are obtained; according to the positive and negative sequence dq axis voltage components and the positive and negative sequence dq axis current components, the zero sequence dq axis current components are obtained; according to the zero sequence dq axis current components, i 0_ref2 ; 2) Generate zero-sequence current command i according to the result of step 1) 0_ref , using i 0_ref A control signal of the SVG is generated to control the SVG.

2. The control method for SVG of meshed cascaded angular connections according to claim 1, characterized in that: Generated i 0_ref for i 0_ref1 and i 0_ref2 The sum.

3. The control method of the SVG for cascading meshed angular connections 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 meshed cascaded angular connections according to claim 1 or 2, characterized in that: According to the negative sequence dq axis current command, i 0_ref1 The method is: 0_ref1 =I qnref cos(thetaP)+I dnref sin(thetaP), where I dnref and I qnref They represent the negative-sequence dq-axis current commands respectively, and thetaP represents the angle of the potential inside the network cascade SVG.

5. The control method of the SVG for cascading meshed angular connections according to claim 1 or 2, characterized in that: The way to obtain the zero-sequence dq-axis current component according to the positive-sequence dq-axis voltage component and the positive-sequence dq-axis current component 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 They 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 respectively; I d0_ref ,I q0_ref Represent the zero-sequence dq-axis current components respectively.

6. The control method for meshed cascaded angular connection SVG according to claim 1 or 2, characterized in that: According to the zero-sequence dq-axis current component, i 0_ref2 The method is: 0_ref2 =I0sin(thetaP0+thetaP), where I0 represents the amplitude of the zero-sequence current and is obtained based on the zero-sequence dq-axis current component, thetaP0 represents the initial angle of the zero-sequence current and is obtained based on the zero-sequence dq-axis current component, and thetaP represents the angle of the potential within the network cascade SVG.

7. The control method of the meshed cascaded angular connection SVG according to claim 1 or 2, characterized in that: Use i 0_ref The method of generating the SVG control signal is to add the active current command and reactive current command of each phase and then superimpose them respectively. 0_ref Obtaining the current command of each phase, subtracting the current command of each phase from the current feedback of each phase, and then adjusting and controlling the obtained difference to obtain the output value of each phase; The control signal of SVG is generated according to the output value of each phase.

8. The control method of the SVG for cascading meshed angular connections according to claim 7, characterized in that: The method of generating the control signal of SVG according to the output value of each phase is: superimposing the voltage feedforward value of each phase on the output value of each phase respectively, and generating the control signal of SVG according to the superimposed result; the voltage feedforward of each phase is the AC voltage sampling per unit value of each phase multiplied by the modulation index, the modulation index is the peak value of the AC phase voltage divided by the DC voltage value of the bridge arm, and the DC voltage value of the bridge arm is the rated number of sub-modules of the bridge arm multiplied by the rated voltage of the sub-module.

9. The control method of the SVG for cascading meshed angular connections according to claim 4, characterized in that: thetaP is obtained through virtual synchronization control.

10. The control method of the SVG for cascading meshed angle connections according to claim 1 or 2, characterized in that: When the system is operating normally, a zero-sequence injection current i based on the submodule voltage is generated. 0_ref1 And as the zero-sequence current command i 0_ref , using i 0_ref A control signal of the SVG is generated to control the SVG.

11. 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 10.

12. A SVG for cascading grids, 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 10.

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