A control method of a static var generator with capability of maintaining grid strength of a virtual synchronous generator

Abstract

The application provides a control method of a static var generator with the capability of maintaining the grid strength of a virtual synchronous generator, and relates to the electrical technical field.The core of the method is that the static var generator increases a control link of a current or voltage instruction value on the basis of traditional double-loop control, the control link calculates the grid inductance parameter in real time according to the operation state of the virtual synchronous generator and the grid strength, flexibly regulates and controls the instruction value of the static var generator, the static var generator combines the instruction value to carry out current loop control, coordinate transformation and PWM modulation, and finally outputs corresponding voltage and current, when the system is disturbed, the static var generator adjusts the reactive power output by changing the instruction value, so that the short-circuit ratio before and after the system is disturbed remains unchanged, thereby maintaining the grid strength of the grid connection point of the virtual synchronous generator, supporting the stable operation of the virtual synchronous generator, and improving the grid connection stability of the virtual synchronous generator.

Description

Technical Field

[0001] This invention relates to the field of electrical technology, and in particular to a control method for a static reactive power generator capable of maintaining the grid connection strength of a virtual synchronous generator. Background Technology

[0002] With the continuous development of society, the demand for and dependence on energy are constantly increasing, and new energy sources such as wind and solar power have received widespread attention. As large-scale new energy sources are integrated into the power grid, their safe and stable operation is of great significance to grid connection.

[0003] To ensure the stable operation of grid-connected inverters for renewable energy sources and improve the damping and inertial support of renewable energy grid-connected systems, virtual synchronous generator (VSG) technology is widely used in the power control of inverters in renewable energy power generation systems. Current research on VSG stability mainly focuses on its intrinsic parameter design, model optimization, control improvement, and parameter adaptation. However, renewable energy resources are mainly concentrated in the "Three Norths" region of my country, where the power grid architecture is weak. Large-scale integration of renewable energy into the common connection point (PCC) causes the PCC to exhibit weak grid characteristics. When a VSG is connected to a weak grid, the large equivalent reactance consumes a significant amount of reactive power, making the PCC prone to voltage and reactive power instability.

[0004] To address the instability issue of VSGs under weak grid conditions, renewable energy power plants typically install reactive power compensation devices at the PCC point to stabilize the PCC voltage and ensure stable VSG operation. Static var generators (SVGs) offer advantages such as rapid reactive power compensation, error regulation, and flexible control, improving voltage and reactive power balance in weak grid systems. Therefore, the reactive power compensation characteristics of SVGs can be utilized to enhance the operating characteristics of VSGs.

[0005] Some literature takes renewable energy grid-connected converters as the research object, considering the power transmission characteristics of renewable energy grid-connected converters when SVG and static var compensator perform reactive power compensation at the PCC point.

[0006] Some literature takes direct-drive wind turbines as the research object, establishes linearized models of grid-connected converters and SVG for direct-drive wind turbines, and analyzes the subsynchronous oscillation characteristics and interaction between wind turbines and SVG.

[0007] Some literature takes doubly-fed wind turbines as the research object, derives the dynamic response process of doubly-fed wind turbines and static var generators under system disturbances, and reveals the interaction principle between doubly-fed wind farms and static var generators.

[0008] The aforementioned literature mainly focuses on wind turbine generators in its analysis, neglecting the impact of the grid-connected inverter's own control strategy on the system. When the grid-connected inverter adopts VSG control, the research on the SVG's operational characteristics of VSG is still insufficient. Summary of the Invention

[0009] The technical problem to be solved by the present invention is to provide a control method for a static reactive power generator with the ability to maintain the grid connection strength of a virtual synchronous generator. The method flexibly adjusts the command value of the static reactive power generator according to the operating status of the virtual synchronous generator and the grid strength, so as to maintain the stable operation of the virtual synchronous generator in a weak grid and improve the stability of the new energy grid connection system.

[0010] To solve the above-mentioned technical problems, the present invention adopts the following technical method: a control method for a static reactive power generator capable of maintaining the grid connection strength of a virtual synchronous generator, wherein the static reactive power generator is connected in parallel with the virtual synchronous generator, and the control of the static reactive power generator includes the following steps:

[0011] Step S1: Acquire the current signal value I of the virtual synchronous generator. v Grid connection point voltage V pcc And the power angle δ, to calculate the active power P output by the virtual synchronous generator. e ;

[0012] Step S2: Acquire the output current I of the static var generator. s and grid voltage V g Based on the control method of the static var generator, the grid inductance X is calculated. g ;

[0013] Step S3: Based on the active power P obtained in step S1 e The grid inductance X obtained in step S2 g And the system short-circuit ratio (SCR) of the virtual synchronous generator in parallel with the static reactive power generator during normal operation, and calculate the command value of the static reactive power generator;

[0014] Step S4: Input the command value into the static var generator for dual-loop control. The static var generator outputs the corresponding voltage and current to maintain the grid strength at the virtual synchronous generator connection point.

[0015] Furthermore, in step S1, the active power P output by the virtual synchronous generator is calculated using the following formula (1). e .

[0016] P e =I v V pcc cosδ (1)

[0017] Furthermore, in step S2, the control methods of the static reactive power generator include constant voltage control and constant current control.

[0018] If the static var generator adopts a constant voltage control method, the grid inductance X g The following formula (2) is used for calculation:

[0019]

[0020] If the static reactive power generator adopts constant current control, the grid inductance X g The following formula (3) is used for calculation.

[0021]

[0022] Furthermore, under constant voltage control mode, the static var generator command value calculated in step S3 is the grid connection point voltage reference value V. pccref The reference value of the grid connection point voltage V pccref The following formula (4) is used for calculation.

[0023]

[0024] Furthermore, under constant voltage control mode, in step S4, the grid connection point voltage reference value V is... pccref Input to the static var generator:

[0025] First, the voltage loop within it will convert the grid connection point voltage V pcc With grid connection point voltage reference value V pccref By comparison, the voltage error dq component α is obtained. d α q Then PI control is performed, and the output current reference signal i is generated. sdref i sqref According to the following formula (5);

[0026]

[0027] Among them, K vp K vi These are the proportional-integral parameters of the voltage loop; V dcref V dc These are the reference and actual values ​​of the DC side voltage of the static var generator, respectively.

[0028] The actual current is then compared with the reference current by the internal current loop to obtain the current error dq component β. d β q Then, PI control is applied, and cross-coupling compensation is used to output the dq component E of the static var generator terminal voltage. sd Esq According to the following formula (6);

[0029]

[0030] Among them, i sd i sd i represents the dq component of the output current of the static var generator; sdref i sdref K represents the dq component of the reference current of the static var generator. cp K ci These are the proportional-integral parameters of the current loop under constant voltage control; ω pll L is the angular frequency output by the static var generator. s The filter inductor for the static var generator;

[0031] Finally, the dq component E of the static reactive power generator terminal voltage is... sd E sq After inverse dq / abc transformation to the three-phase coordinate system, a static reactive power generator is driven by a PWM modulator to generate corresponding voltage and current, thus increasing the grid connection point voltage V. pcc With grid connection point voltage reference value V pccref Equal to maintain the grid strength at the virtual synchronous generator connection point.

[0032] Alternatively, in constant current control mode, the static var generator command value calculated in step S3 is its current reference value I. sref The current reference value I sref The following formula (7) is used for calculation.

[0033]

[0034] Furthermore, in the constant current control mode, in step S4, the current reference value I is... sref Input to the static var generator:

[0035] First, the actual current is compared with the current reference value I by its internal current loop. sref By comparison, the current error dq component β is obtained. d β q Then, PI control is applied, and cross-coupling compensation is used to output the dq component E of the static var generator terminal voltage. sd E sq According to the following formula (8);

[0036]

[0037] Among them, i sd i sd i represents the dq component of the output current of the static var generator;dref i dref Current reference value I sref dq components; K si K sp These are the proportional-integral parameters of the current loop under constant current control mode; ω pll L is the angular frequency output by the static var generator. s The filter inductor for the static var generator;

[0038] Then the dq component E of the static var generator terminal voltage. sd E sq After inverse dq / abc transformation to the three-phase coordinate system, a static reactive power generator is driven by a PWM modulator to generate corresponding voltage and current, thus increasing the grid connection point voltage V. pcc With grid connection point voltage reference value V pccref Equal to maintain the grid strength at the virtual synchronous generator connection point.

[0039] This invention provides a control method for a static var generator (SVA) capable of maintaining the grid connection strength of a virtual synchronous generator (VSR). In this method, the VSR is connected in parallel with the static var generator. Based on traditional dual-loop control, the static var generator adds a control loop for current or voltage command values. This control loop aims to calculate the grid inductance parameters in real time based on the operating status of the VSR and the grid strength (detecting the active power, power angle, and grid connection point voltage of the VSR), and then flexibly adjust the command value of the static var generator. The static var generator then combines the command value with current loop control, coordinate transformation, and PWM modulation to ultimately output the corresponding voltage and current. When the system is disturbed, the static var generator adjusts the reactive power output by changing the command value, keeping the short-circuit ratio unchanged before and after the disturbance, thereby maintaining the grid strength at the VSR connection point and supporting the stable operation of the VSR, thus improving the grid connection stability of the VSR. Attached Figure Description

[0040] Figure 1 This is a system structure diagram of the virtual synchronous generator in parallel static reactive power generator in this invention (the command value generation part in the diagram takes the voltage command value generation method as an example);

[0041] Figure 2 This is a schematic diagram of the dual-loop control principle of the static reactive power generator under constant voltage control in an embodiment of the present invention.

[0042] Figure 3 This is a schematic diagram of the dual-loop control principle of the static reactive power generator under constant current control in an embodiment of the present invention.

[0043] Figure 4The waveform diagram of the operating parameters of the system when the control method of the static reactive power generator involved in this invention is not adopted;

[0044] Figure 5 The waveform diagram shows the operating parameters of the system when the control method of the constant voltage static var generator involved in this invention is adopted.

[0045] Figure 6 The waveform diagram shows the operating parameters of the system when the control method of the constant current static reactive power generator involved in this invention is adopted. Detailed Implementation

[0046] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to embodiments and accompanying drawings. The content mentioned in the embodiments is not intended to limit the present invention.

[0047] like Figure 1 As shown, the present invention relates to a virtual synchronous generator connected in parallel with a static var generator. The control system of the virtual synchronous generator includes an active power loop, as shown in equation (9), and a reactive power loop, as shown in equation (10). The virtual synchronous generator simulates mechanical input changes by changing the active power reference value, adding damping and inertia elements, calculating the three-phase modulation wave and PWM modulator, and finally outputting the corresponding voltage and current. The static var generator adds a control loop for current or voltage command values ​​based on the traditional dual-loop control. This control loop aims to calculate the grid inductance parameters in real time according to the operating status of the virtual synchronous generator and the grid strength (detecting the active power, power angle and grid connection point voltage of the virtual synchronous generator), and then flexibly adjust the command value of the static var generator. The static var generator then combines the command value to perform current loop control, coordinate transformation and PWM modulation, and finally outputs the corresponding voltage and current. When the system is disturbed, the static var generator adjusts the reactive power output by changing the command value, so that the short-circuit ratio before and after the disturbance remains unchanged, thereby maintaining the grid strength at the grid connection point of the virtual synchronous generator, supporting the stable operation of the virtual synchronous generator and improving the grid connection stability of the virtual synchronous generator.

[0048]

[0049] E m =V0+D q (Q set -Q e (10)

[0050] Where J is the virtual inertia coefficient, δ is the power angle of the virtual synchronous generator, and P... ref P is the reference value for the actual active power of the virtual synchronous generator. e ω represents the active power output of the virtual synchronous generator. g Let ω be the angular frequency of the grid voltage, D be the damping coefficient, Δω be the deviation of the virtual rotational speed, and E be the angular frequency of the grid voltage.m V0 represents the amplitude of the output voltage of the virtual synchronous generator; D represents the amplitude of the rated voltage of the virtual synchronous generator. q Q is the reactive power droop factor. set Q is the reference value for the reactive power output of the virtual synchronous generator. e This represents the reactive power output of the virtual synchronous generator.

[0051] The invention is described in detail below, such as Figure 1 As shown, a control method for a static var generator capable of maintaining the grid connection strength of a virtual synchronous generator is described. The static var generator is connected in parallel with the virtual synchronous generator, and the control of the static var generator includes the following steps:

[0052] Step S1: Acquire the current signal value I of the virtual synchronous generator. v Grid connection point voltage V pcc And the power angle δ, the active power P output by the virtual synchronous generator is calculated according to the following formula (1). e .

[0053] P e =I v V pcc cosδ (1)

[0054] Step S2: Acquire the output current I of the static var generator. s and grid voltage V g Based on the control method of the static var generator, the grid inductance X is calculated. g .

[0055] The control methods for static var generators include constant voltage control and constant current control.

[0056] If the static var generator adopts a constant voltage control method, the grid inductance X g The following formula (2) is used for calculation:

[0057]

[0058] If the static reactive power generator adopts constant current control, the grid inductance X g The following formula (3) is used for calculation.

[0059]

[0060] Step S3: Based on the active power P calculated in step S1 e The grid inductance X calculated in step S2 g The system short-circuit ratio (SCR) of the virtual synchronous generator in parallel with the static var generator during normal operation is used to calculate the command value of the static var generator.

[0061] Under constant voltage control mode, the calculated static var generator command value is the grid connection point voltage reference value V. pccref The reference value of the grid connection point voltage V pccref The following formula (4) is used for calculation.

[0062]

[0063] Under constant current control mode, the calculated static var generator command value is its current reference value I. sref The current reference value I sref The following formula (7) is used for calculation.

[0064]

[0065] Step S4: Input the command value into the static var generator for dual-loop control. The static var generator outputs the corresponding voltage and current to maintain the grid strength at the virtual synchronous generator connection point.

[0066] like Figure 2 As shown, under constant voltage control mode, the grid connection point voltage reference value V is... pccref Input to the static var generator:

[0067] First, the voltage loop within it will convert the grid connection point voltage V pcc With grid connection point voltage reference value V pccref By comparison, the voltage error dq component α is obtained. d α q Then PI control is performed, and the output current reference signal i is generated. sdref i sqref According to the following formula (5).

[0068]

[0069] Among them, K vp K vi These are the proportional-integral parameters of the voltage loop; V dcref V dc These are the reference and actual values ​​of the DC side voltage of the static var generator, respectively.

[0070] The actual current is then compared with the reference current by the internal current loop to obtain the current error dq component β. d β q Then, PI control is applied, and cross-coupling compensation is used to output the dq component E of the static var generator terminal voltage. sd E sq According to the following formula (6).

[0071]

[0072] Among them, i sd i sd i represents the dq component of the output current of the static var generator; sdref i sdref K represents the dq component of the reference current of the static var generator. cp K ci These are the proportional-integral parameters of the current loop under constant voltage control; ω pll L is the angular frequency output by the static var generator. s This is the filter inductor for the static var generator.

[0073] Finally, the dq component E of the static reactive power generator terminal voltage is... sd E sq After inverse dq / abc transformation to the three-phase coordinate system, a static reactive power generator is driven by a PWM modulator to generate corresponding voltage and current, thus increasing the grid connection point voltage V. pcc With grid connection point voltage reference value V pccref equal.

[0074] Under normal conditions, the active power transmitted by the virtual synchronous generator to the grid satisfies the following relationship (V... pcc Use V pccref After substitution, the relationship is the same as in Formula 2, and the active power of the virtual synchronous generator remains unchanged at all times.

[0075]

[0076] In addition, under normal conditions, the system short-circuit ratio satisfies the following relationship (V pcc Use V pccref After substitution, the relationship is the same as in Formula 4, and the system short-circuit ratio remains unchanged before and after the time interval.

[0077]

[0078] When a disturbance occurs in the system, the grid inductance, grid connection voltage, active power, and power angle of the virtual synchronous generator all change instantaneously. The static var generator (SVA) then rapidly calculates the grid inductance parameters in real time based on the operating parameters at that moment, flexibly adjusts the grid connection voltage reference value of the SVA, and outputs the corresponding voltage to ensure that the grid connection voltage V... pcc The adaptive changes allow the system's short-circuit ratio and the active power of the virtual synchronous generator to quickly return to normal values, restoring the system to normal operation and continuing stable operation.

[0079] Therefore, it can be seen that under the control method of constant voltage static reactive power generator, the grid strength at the virtual synchronous generator connection point can be kept very stable.

[0080] like Figure 3 As shown, under constant current control mode, the current reference value I is... sref Input to the static var generator:

[0081] First, the actual current is compared with the current reference value I by its internal current loop. sref By comparison, the current error dq component β is obtained. d β q Then, PI control is applied, and cross-coupling compensation is used to output the dq component E of the static var generator terminal voltage. sd E sq According to the following formula (8);

[0082]

[0083] Among them, i sd i sd i represents the dq component of the output current of the static var generator; dref i dref Current reference value I sref dq components; K si K sp These are the proportional-integral parameters of the current loop under constant current control mode; ω pll L is the angular frequency output by the static var generator. s The filter inductor for the static var generator;

[0084] Then the dq component E of the static var generator terminal voltage. sd E sq After inverse dq / abc transformation to the three-phase coordinate system, a static reactive power generator is driven by a PWM modulator to generate corresponding voltage and current, thus increasing the grid connection point voltage V. pcc With grid connection point voltage reference value V pccref equal.

[0085] Under normal conditions, the active power transmitted by the virtual synchronous generator to the grid satisfies the following relationship (V... pcc Use V pccref After substitution, the relationship is the same as in Formula 3, and the active power of the virtual synchronous generator remains unchanged at all times.

[0086]

[0087] In addition, under normal conditions, the system short-circuit ratio satisfies the following relationship (V pcc Use V pccref After substitution, the relationship is the same as in Formula 5, and the system short-circuit ratio remains unchanged before and after the time interval.

[0088]

[0089] When a disturbance occurs in the system, the grid inductance, grid connection voltage, active power, and power angle of the virtual synchronous generator all change instantaneously. The static var generator quickly calculates the grid inductance parameters in real time based on the operating parameters at this moment, flexibly adjusts the current reference value of the static var generator, and outputs the corresponding current to keep the grid connection voltage V... pcc The adaptive changes allow the system's short-circuit ratio and the active power of the virtual synchronous generator to quickly return to normal values, restoring the system to normal operation and continuing stable operation.

[0090] Therefore, it can be seen that under the control method of constant current static reactive power generator, the grid strength at the virtual synchronous generator connection point can be kept very stable.

[0091] To verify the correctness of the control method of this invention, a system was built in MATLAB / Simulink as follows: Figure 1 The main simulation parameters of the virtual synchronous generator grid connection simulation model shown are shown in Table 1.

[0092] Table 1 Simulation Parameters

[0093]

[0094]

[0095] like Figure 4 As shown, the system inductance changes at 1.5s, the system short-circuit ratio decreases, and the system becomes unstable due to the small reactive power compensation of the static reactive power generator.

[0096] like Figure 5 As shown, the system inductance changes at 1.5s. By altering the reactive power output of the static var generator using the control method of this invention, the system recovers stable operation after a transient process. Simulation results demonstrate that the constant-voltage static var generator control method of this invention can dynamically adjust the voltage command value of the static var generator according to the operating state of the virtual synchronous generator, thus maintaining system stability.

[0097] like Figure 6 As shown, the system inductance changes at 1.5s. By altering the reactive power output of the static var generator using the control method of this invention, the system recovers stable operation after a transient process. Simulation results demonstrate that the control method of the constant current static var generator of this invention can dynamically adjust the current command value of the static var generator according to the operating state of the virtual synchronous generator, thus maintaining system stability.

[0098] The above embodiments are preferred implementations of the present invention. In addition, the present invention can be implemented in other ways. Any obvious substitutions without departing from the concept of the present technical solution are within the protection scope of the present invention.

[0099] To facilitate understanding by those skilled in the art of the improvements of this invention over the prior art, some of the accompanying drawings and descriptions have been simplified, and for clarity, some other elements have been omitted from this application. Those skilled in the art should realize that these omitted elements may also constitute the content of this invention.

Claims

1. A control method for a static var generator capable of maintaining the grid connection strength of a virtual synchronous generator, wherein the static var generator is connected in parallel with a virtual synchronous generator, characterized in that: Controlling the static var generator includes the following steps: Step S1: Acquire the current signal value of the virtual synchronous generator. I v Grid connection point voltage V pcc and the angle of attack δ Calculate the active power output of the virtual synchronous generator. P e ; Step S2: Acquire the output current of the static var generator. I s and grid voltage V g Based on the control method of the static var generator, the grid inductance is calculated. X g The control methods for static var generators include constant voltage control and constant current control. If the static var generator adopts a constant voltage control method, the grid inductance... X g The following formula (2) is used for calculation: （2） If the static reactive power generator adopts constant current control, the grid inductance... X g The following formula (3) is used for calculation: （3） Step S3: Based on the active power obtained in step S1 P e The grid inductance obtained in step S2 X g And the system short-circuit ratio when the virtual synchronous generator parallel static var generator is operating normally. SCR Calculate the command value of the static var generator; Under constant voltage control mode, the static var generator command value calculated in step S3 is the grid connection point voltage reference value. V pccref The reference value of the grid connection point voltage V pccref The following formula (4) is used for calculation: （4） Under constant current control mode, the static reactive power generator command value calculated in step S3 is its current reference value. I sref This current reference value I sref The following formula (7) is used for calculation: （7） Step S4: Input the command value into the static var generator for dual-loop control. The static var generator outputs the corresponding voltage and current to maintain the grid strength at the virtual synchronous generator's grid connection point.

2. The control method for a static reactive power generator with the ability to maintain the grid connection strength of a virtual synchronous generator according to claim 1, characterized in that: In step S1, the active power output of the virtual synchronous generator is calculated using the following formula (1). P e ; （1）。 3. The control method for a static reactive power generator with the ability to maintain the grid connection strength of a virtual synchronous generator according to claim 2, characterized in that: In constant voltage control mode, step S4 involves setting the grid connection point voltage reference value. V pccref Input to the static var generator: First, the voltage loop within it will convert the grid connection point voltage. V pcc Reference value of grid connection point voltage V pccref By comparison, the voltage error dq component is obtained. α d , α q Then PI control is performed to output the current reference signal. According to the following formula (5); （5） in, These are the proportional-integral parameters of the voltage loop; V dcref , V dc These are the reference and actual values ​​of the DC side voltage of the static var generator, respectively. The actual current is then compared with the reference current by the internal current loop to obtain the current error dq component. β d , β q Then, PI control is applied, and cross-coupling compensation is used to output the dq component of the static var generator terminal voltage. E sd , E sq According to the following formula (6); （6） in, The dq component is the output current of the static var generator. The dq component is the reference current of the static var generator. K cp , K ci These are the proportional-integral parameters of the current loop under constant voltage control mode; ω pll The angular frequency output by the static var generator; L s The filter inductor for the static var generator; Finally, the dq component of the static reactive power generator terminal voltage is... E sd , E sq After inverse dq / abc transformation to the three-phase coordinate system, a static var generator is driven by a PWM modulator to generate corresponding voltage and current, thus adjusting the grid connection point voltage. V pcc Reference value of grid connection point voltage V pccref Equal to maintain the grid strength at the virtual synchronous generator connection point.

4. The control method for a static reactive power generator with the ability to maintain the grid connection strength of a virtual synchronous generator according to claim 3, characterized in that: In constant current control mode, the current reference value is set in step S4. I sref Input to the static var generator: First, its internal current loop compares the actual current with the current reference value. I sref By comparison, the current error dq component is obtained. β d , β q Then, PI control is applied, and cross-coupling compensation is used to output the dq component of the static var generator terminal voltage. E sd , E sq According to the following formula (8); （8） in, The dq component is the output current of the static var generator. Current reference value I sref The dq component; These are the proportional-integral parameters of the current loop under constant current control mode; ω pll The angular frequency output by the static var generator; L s The filter inductor for the static var generator; Then the dq component of the static var generator terminal voltage E sd , E sq After inverse dq / abc transformation to the three-phase coordinate system, a static var generator is driven by a PWM modulator to generate corresponding voltage and current, thus adjusting the grid connection point voltage. V pcc Reference value of grid connection point voltage V pccref Equal to maintain the grid strength at the virtual synchronous generator connection point.

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