CN116191456A - VSG power decoupling control method based on dynamic diagonal matrix compensation matrix - Google Patents

Abstract

The invention discloses a VSG power decoupling control method based on a dynamic diagonal matrix compensation matrix, wherein the topological structure of the VSG comprises a VSG main circuit and a VSG control circuit, the VSG main circuit comprises a direct-current voltage source, a three-phase bridge type inverter circuit, an LC filter and an alternating-current power grid, and the VSG control circuit comprises an active power control loop, a reactive power control loop and a voltage control loop; according to the invention, through estimating the power angle parameter in the active power control loop, dynamic tracking of the static working point of the system by the diagonal matrix compensation matrix is realized, the VSG power decoupling effect is improved, and the method is suitable for frequent change of the power grid frequency and frequent switching of micro-source load.

Description

VSG power decoupling control method based on dynamic diagonal compensation matrix

Technical Field

The invention relates to the field of virtual synchronous motor control, and in particular to a VSG power decoupling control method based on a dynamic diagonal array compensation matrix.

Background Art

Microgrids are an important way for future smart distribution networks to achieve self-healing, user-side interaction and demand response. Through interactive supplementation with large power grids, they can alleviate the impact of a large number of distributed power sources on the power grid. However, compared with the synchronous generators of traditional large power grids, the power electronic inverters of microgrids have defects such as small capacity, low output impedance, and lack of system inertia. With the continuous increase in the penetration rate of distributed power sources, the stability problem of the power grid has become increasingly severe. At the same time, unlike the inductive line impedance of the large power grid, the line impedance of the distribution network where the microgrid is located mostly presents resistive or resistive-inductive characteristics, which leads to strong coupling between the active and reactive power output of the inverter, reducing the accuracy of the inverter power output and the control effect of power sharing between micro sources.

To address the problem of strong coupling between active and reactive power output by the inverter, current power decoupling algorithms mainly include the following three:

(1) Virtual impedance method: This method adjusts the impedance of the micro-source system by subtracting the voltage drop of the additional output current on the virtual inductor on the input side of the voltage loop. This method can reduce the resistance-to-inductance ratio of the micro-source system impedance to a certain extent. By adjusting the virtual impedance parameters, the characteristics of the system impedance can be flexibly changed, providing a more ideal solution for power decoupling. It has a clear physical meaning and is easy to implement. It is currently the most widely used decoupling method. However, in order to obtain the inductive system impedance in a resistive line environment, a larger virtual inductor is required, which aggravates the drop of the bus voltage and brings harmonic problems, seriously affecting the power control and stable operation of the microgrid;

(2) Anti-droop control method: This method is different from the output characteristics of traditional synchronous generators. It pairs active output with voltage and reactive output with frequency, thus realizing the decoupling control of active and reactive power in a low-voltage resistive environment. However, this scheme is only applicable to the case where the line resistance is much larger than the inductance. In resistive and inductive lines, virtual impedance must still be introduced to ensure the decoupling effect. At the same time, since the equivalent droop formula of the system is changed, the micro power source under this scheme cannot be directly connected to the distribution network containing traditional power generation forms such as diesel generators and steam turbines.

(3) Diagonal matrix compensation method: By using the decoupling idea of diagonalizing the objective function and introducing a compensation matrix, the purpose of eliminating the coupling component is finally achieved. This method can achieve complete decoupling of active and reactive power without changing the hardware circuit. However, since the diagonal matrix is subject to the precise acquisition of the system operating point, and microgrids are mostly on the distribution network side, load switching will inevitably lead to frequent fluctuations in the micro-source operating point. If the system operating point changes, the decoupling effect of this scheme will be greatly affected.

Summary of the invention

In order to overcome the deficiencies in the prior art and improve the output response characteristics of the inverter, the present invention is based on the control technology of a virtual synchronous generator (virtual synchronous generator). By simulating the rotor motion equation of the synchronous generator, the inverter is equipped with the ability to damp power oscillations. On this basis, a VSG power decoupling control method based on a dynamic diagonal array compensation matrix is proposed to address the problem of power coupling. The control method proposed by the present invention can reduce the influence of line impedance with a high resistance-to-inductance ratio on the output power of the inverter in a weak power grid environment. In addition, when the system operating point changes, the inverter can dynamically track the operating point and change its own key parameters to ensure the control effect of power decoupling.

The purpose of the present invention can be achieved by the following technical solutions:

A VSG power decoupling control method based on a dynamic diagonal array compensation matrix, wherein the topological structure of the VSG includes a VSG main circuit and a VSG control circuit, wherein the VSG main circuit includes a DC voltage source, a three-phase bridge inverter circuit, an LC filter, a filter inductor, and an AC power grid, wherein the VSG control circuit includes an active power control loop, a reactive power control loop, and a voltage control loop, wherein the VSG control loop collects the voltage and current at the output side of the LC filter to calculate the active power and reactive power of the VSG, wherein the active power loop controls the active power and frequency of the virtual synchronous generator, wherein the reactive power loop controls the reactive power and voltage of the virtual synchronous generator, and the terminal voltage is adjusted by a voltage regulator and a reactive power adjustment module; by estimating the power angle parameters in the active power control loop, the diagonal array compensation matrix is dynamically tracked to the static operating point of the system, thereby improving the power decoupling effect of the VSG and adapting to frequent changes in the grid frequency and frequent switching of micro-source loads;

The VSG power decoupling control method specifically comprises the following steps:

S1: Set the command values of active power, reactive power and terminal voltage, measure the real-time current and voltage signals on the inverter side, and calculate the instantaneous value of active power and reactive power according to the equal amplitude transformation formula;

S2: Acquiring a reference voltage command signal of the voltage control loop, including generating an active power loop output angle through the active power control loop, and generating a reactive power loop output voltage amplitude through the reactive power control loop;

S3: performing voltage closed-loop control on the reference voltage command signal to generate a PWM wave to drive the inverter circuit switch to turn on or off;

S4: According to the VSG grid-connected equivalent circuit, the complex power of the grid-connected point is obtained using the power system flow calculation formula;

S5: using a small signal analysis method to obtain active power disturbance, reactive power disturbance and a system decoupling matrix; the decoupling matrix describes the relationship between the active power disturbance and the reactive power disturbance and the voltage disturbance and the power angle disturbance respectively;

S6: adopting a diagonal matrix compensation method, introducing a decoupling compensation matrix, and converting the matrix to be decoupled into a diagonal matrix;

S7: According to the characteristics of the static operating point change when the grid-connected side load is frequently switched, several straight lines are selected to estimate the power angle after the static operating point changes, and a power angle estimation curve is obtained.

Furthermore, the calculation process of the instantaneous active power value _Pe and the instantaneous reactive power value _Qe is as shown in formula (S-1):

In formula (S-1), _ud and _ud are the components of the real-time voltage signal input voltage of the inverter side in the dq coordinate system, and _id and _id are the components of the real-time current signal of the inverter side in the dq coordinate system;

The calculation process of _ud and _uq is as shown in formula (S-2):

The calculation process of i _d and i _q is as shown in formula (S-3):

In equations (S-2) to (S-3), _ua , _ub , and _uc represent the measured real-time voltage outputted from the LC filter side, and _ia , _ib , and _ic represent the measured real-time current outputted from the LC filter side.

Furthermore, the calculation process of obtaining the reference voltage command signal of the voltage control loop is as shown in formula (S-4):

The calculation process of the active power loop output angle δ and the reactive power loop output voltage amplitude _Em is as shown in formula (S-5):

In formula (S-5), J represents the moment of inertia, D represents the damping coefficient, _Pref represents the reference power, _ωn represents the reference angular frequency, ω represents the actual angular frequency, _Ucn represents the no-load electromotive force, _Qref represents the reactive power command value, _Dq represents the voltage regulation coefficient, _Un represents the rated value of the machine-end voltage, and _Uc represents the actual output value of the machine-end voltage;

The VSG active power loop outputs the phase information of the command voltage, and the reactive power loop outputs the amplitude information of the command voltage. The two are combined to obtain the input command signal of the voltage loop, and then the voltage loop controller can track the voltage command signal.

Due to the influence of line impedance, the output power of VSG may be coupled, that is, if the active output instruction or the reactive output instruction is changed alone, the corresponding reactive output or active output will also change, affecting the accuracy of power control; therefore, it is necessary to improve the control strategy of VSG to remove the coupling between powers.

Furthermore, during the stable operation of the system, according to the VSG grid-connected equivalent circuit, using the power system flow calculation formula, considering the situation when the line is resistive and inductive, the calculation process of obtaining the complex power S of the grid-connected point is as shown in formula (S-6):

In formula (4), _Es represents the actual output voltage amplitude of VSG, _Ug represents the grid voltage amplitude, _δs represents the actual output power angle of VSG, α represents the line impedance angle, _δs represents the actual output power angle of VSG, and _Zline represents the line impedance.

无功功率扰动量

的计算过程如式(S-7)：Furthermore, according to the grid-connected equivalent circuit of the virtual synchronous generator, the small signal analysis method is used to analyze the small signal equivalent model of the system and obtain the active power disturbance

Reactive power disturbance

The calculation process is as follows:

表示电压扰动量，

表示功角扰动量；In formula (S-7),

represents the voltage disturbance,

represents the power angle disturbance;

Write equation (S-7) into a matrix form as shown in equation (S-8):

其中K₁₁和K₁₂作为耦合分量，是功率耦合的原因所在；Then the system to be decoupled matrix

Among them, K ₁₁ and K ₁₂ are coupling components, which are the cause of power coupling;

According to the traditional diagonal matrix compensation matrix decoupling method, the decoupling compensation matrix is obtained, which can make the active power only controlled by the power angle and the reactive power only controlled by the voltage; therefore, the diagonal matrix compensation method is adopted to transform the matrix T to be decoupled into a diagonal matrix by introducing the decoupling compensation matrix, thereby realizing power decoupling.

Furthermore, a decoupling compensation matrix G _c is introduced, as shown in formula (S-9):

The calculation process of converting the matrix to be decoupled _Gc into a diagonal matrix is as shown in formula (S-10):

The calculation process of the decoupling compensation matrix _Gc is as shown in formula (S-11):

However, when the actual VSG is working, due to the frequent switching of the grid-connected load, the static working point will change, and the output of each inverter will also change. If the decoupling compensation matrix of formula (S-11) is continued to be decoupled, the compensated matrix T matrix to be decoupled will become as shown in formula (S-12):

In formula (S-12), K _g11 , K _g12 , K _g21 , and K _g22 are the proportional coefficients when the static operating point changes to another steady state, and δ _s2 is the power angle when the static operating point changes to another steady state. It can be seen from formula (S-12) that when the static operating point changes, the compensated T matrix is no longer a diagonal matrix, the decoupling effect will weaken, or even fail.

According to the operating characteristics of frequent switching of grid-connected loads, the dynamic diagonal array compensation matrix can automatically track the changes of the static working point. The compensated reactive power is no longer affected by the coupling effect of the power angle, ensuring the decoupling effect.

According to formula (S-12), (E _s ,δ _s ) is the value of the static operating point. Since the coupling effect of voltage is no longer considered, only the power angle is estimated. As long as the value of the changed power angle is given, the value of the decoupling matrix can be calculated. In order to solve this problem, it is necessary to re-estimate the changed power angle.

Furthermore, the selection rules of several straight lines can be described as formula (S-13):

H＝[(K _ci ,[P _i ,P _i+1 ])](S-13)

In formula (S-13), K _ci represents the slope of the i-th power angle estimation curve, _Pi represents the active power of the i-th power angle estimation curve, [ _Pi , Pi ₊₁ ] represents the active power range used by the i-th estimation curve, and when the output power is in the power range [ _Pi , Pi ₊₁ ] of the i-th power angle estimation curve in H, the actual power angle curve D will switch to the i-th power angle estimation curve.

Furthermore, the actual power angle curve D can be described as follows:

_Pe = _Pemax sinδ(S-14)

In formula (S-14), _Pemax represents the maximum value of VSG output power;

Furthermore, the obtained power angle estimation curve can be described as formula (S-15):

Δδ=(δ _i+1 -δ _i )=K _ci ΔP=K _ci (P _i+1 -P _i ) (S-15)

Compared with the prior art, the present invention has the following beneficial effects:

(1) When the grid load is frequently switched on and off and the system operating point changes, a dynamic decoupling strategy based on the diagonal array compensation method is used to design the dynamic decoupling strategy, which can output the reactive power distribution load accurately and avoid the impact of underload and overload under load switching.

(2) The proposed control strategy can dynamically track the operating point to achieve power decoupling under different static operating points. Therefore, it has a certain positive effect on improving the stability and anti-interference ability of new energy grid-connected power generation. The feasibility of the proposed control strategy is verified through simulation and experimental results.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a topological structure and overall control block diagram of a VSG of the present invention;

Figure 2 is the VSG grid-connected equivalent circuit;

Figure 3 shows the power decoupling control strategy for the VSG diagonal array compensation matrix;

Figure 4 shows the dynamic power decoupling control of power angle estimation linearization;

Figure 5 shows the power response waveforms under different control strategies;

Figure 6 is a diagram showing the effects of different control strategies under frequent load switching;

FIG7 is a current waveform diagram and FFT analysis diagram;

Figure 8 shows the reactive power output waveform under different control strategies.

DETAILED DESCRIPTION

The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments in the invention, all other embodiments obtained by ordinary technicians in this field without creative work, any modifications, equivalent substitutions, improvements, etc., should be included in the protection scope of the present invention.

A VSG power decoupling control method based on a dynamic diagonal array compensation matrix, as shown in FIG1 , the topological structure of the VSG includes a VSG main circuit and a VSG control circuit, the VSG main circuit includes a DC voltage source, a three-phase bridge inverter circuit, an LC filter, a filter inductor, and an AC power grid, the VSG control circuit includes an active power control loop, a reactive power control loop, and a voltage control loop, the VSG control loop collects the voltage and current at the output side of the LC filter to calculate the active power and reactive power of the VSG, the active power loop controls the active power and frequency of the virtual synchronous generator, the reactive power loop controls the reactive power and voltage of the virtual synchronous generator, and the terminal voltage is adjusted by a voltage regulator and a reactive power adjustment module; by estimating the power angle parameters in the active power control loop, the diagonal array compensation matrix is dynamically tracked to the static operating point of the system, the VSG power decoupling effect is improved, and the frequent changes in the grid frequency and the frequent switching of micro-source loads are adapted;

The VSG power decoupling control method specifically comprises the following steps:

S1: Set the command values of active power, reactive power and terminal voltage, measure the real-time current and voltage signals on the inverter side, and calculate the instantaneous value of active power and reactive power according to the equal amplitude transformation formula;

S2: Acquiring a reference voltage command signal of the voltage control loop, including generating an active power loop output angle through the active power control loop, and generating a reactive power loop output voltage amplitude through the reactive power control loop;

S3: performing voltage closed-loop control on the reference voltage command signal to generate a PWM wave to drive the inverter circuit switch to turn on or off;

S4: According to the VSG grid-connected equivalent circuit, the complex power of the grid-connected point is obtained using the power system flow calculation formula;

S5: using a small signal analysis method to obtain active power disturbance, reactive power disturbance and a system decoupling matrix; the decoupling matrix describes the relationship between the active power disturbance and the reactive power disturbance and the voltage disturbance and the power angle disturbance respectively;

S6: adopting a diagonal matrix compensation method, introducing a decoupling compensation matrix, and converting the matrix to be decoupled into a diagonal matrix;

S7: According to the characteristics of the static operating point change when the grid-connected side load is frequently switched, several straight lines are selected to estimate the power angle after the static operating point changes, and a power angle estimation curve is obtained.

The calculation process of the instantaneous active power value _Pe and the instantaneous reactive power value _Qe is as shown in formula (S-1):

In formula (S-1), _ud and _ud are the components of the real-time voltage signal input voltage of the inverter side in the dq coordinate system, and _id and _id are the components of the real-time current signal of the inverter side in the dq coordinate system;

The calculation process of _ud and _uq is as shown in formula (S-2):

The calculation process of i _d and i _q is as shown in formula (S-3):

In equations (S-2) to (S-3), _ua , _ub , and _uc represent the measured real-time voltages on the inverter side, and _ia , _ib , and _ic represent the measured real-time currents on the inverter side.

The calculation process of obtaining the reference voltage command signal of the voltage control loop is as shown in formula (S-4):

The calculation process of the active power loop output angle δ and the reactive power loop output voltage amplitude _Em is as shown in formula (S-5):

In formula (S-5), J represents the moment of inertia, D represents the damping coefficient, _Pref represents the reference power, _ωn represents the reference angular frequency, ω represents the actual angular frequency, _Ucn represents the no-load electromotive force, _Qref represents the reactive power command value, _Dq represents the voltage regulation coefficient, _Un represents the rated value of the machine-end voltage, and _Uc represents the actual output value of the machine-end voltage;

The VSG active power loop outputs the phase information of the command voltage, and the reactive power loop outputs the amplitude information of the command voltage. The two are combined to obtain the input command signal of the voltage loop, and then the voltage loop controller can track the voltage command signal.

Due to the influence of line impedance, the output power of VSG may be coupled, that is, if the active output instruction or the reactive output instruction is changed alone, the corresponding reactive output or active output will also change, affecting the accuracy of power control; therefore, it is necessary to improve the control strategy of VSG to remove the coupling between powers.

As shown in FIG2 , during the stable operation of the system, according to the VSG grid-connected equivalent circuit, using the power system flow calculation formula, considering the situation when the line is resistive and inductive, the calculation process of obtaining the complex power S of the grid-connected point is as shown in formula (S-6):

In formula (4), _Es represents the actual output voltage amplitude of VSG, _Ug represents the grid voltage amplitude, _δs represents the actual output power angle of VSG, α represents the line impedance angle, _δs represents the actual output power angle of VSG, and _Zline represents the line impedance.

无功功率扰动量

的计算过程如式(S-7)：Use small signal analysis method to analyze the small signal equivalent model of the system and obtain the active power disturbance

Reactive power disturbance

The calculation process is as shown in formula (S-7):

表示电压扰动量，是主要影响有功功率耦合因素的量；

表示功角扰动量，主要影响无功功率耦合因素的量；另外，电压对于有功的变化影响可以忽略不计，而功角对于有功的影响是功率耦合的主要原因；In formula (S-7),

It represents the voltage disturbance amount, which is the amount that mainly affects the active power coupling factor;

It represents the power angle disturbance, which mainly affects the reactive power coupling factor. In addition, the influence of voltage on active power can be ignored, while the influence of power angle on active power is the main reason for power coupling.

Write equation (S-7) into a matrix form as shown in equation (S-8):

其中K₁₁和K₁₂作为耦合分量，是功率耦合的原因所在；K₁₁、K₁₂、K₂₁、K₂₂是系统待解耦矩阵T的系数，在功角值确定的情况下，比例系数是固定的。Then the system to be decoupled matrix

Among them, K ₁₁ and K ₁₂ are coupling components, which are the cause of power coupling; K ₁₁ , K ₁₂ , K ₂₁ , and K ₂₂ are coefficients of the system matrix T to be decoupled. When the power angle value is determined, the proportional coefficient is fixed.

According to the traditional diagonal matrix compensation matrix decoupling method, the decoupling compensation matrix is obtained, which can make the active power only controlled by the power angle and the reactive power only controlled by the voltage; therefore, the diagonal matrix compensation method is adopted to transform the matrix T to be decoupled into a diagonal matrix by introducing the decoupling compensation matrix, thereby realizing power decoupling.

The decoupling compensation matrix G _c is introduced, as shown in formula (S-9):

The calculation process of converting the matrix to be decoupled _Gc into a diagonal matrix is as shown in formula (S-10):

The calculation process of the decoupling compensation matrix _Gc is as shown in formula (S-11):

As shown in FIG3 , according to (S-11), a small signal equivalent model with a diagonal compensation matrix added can be obtained.

However, when the actual VSG is working, due to the frequent switching of the grid-connected load, the static working point will change, and the output of each inverter will also change. If the decoupling compensation matrix of formula (S-11) is continued to be decoupled, the compensated matrix T matrix to be decoupled will become as shown in formula (S-12):

In formula (S-12), K _g11 , K _g12 , K _g21 , and K _g22 are the proportional coefficients when the static operating point changes to another steady state, and δ _s2 is the power angle when the static operating point changes to another steady state. It can be seen from formula (S-12) that when the static operating point changes, the compensated T matrix is no longer a diagonal matrix, the decoupling effect will weaken, or even fail.

According to the operating characteristics of frequent switching of grid-connected loads, the dynamic diagonal array compensation matrix can automatically track the changes of the static working point. The compensated reactive power is no longer affected by the coupling effect of the power angle, ensuring the decoupling effect.

According to formula (S-12), (E _s ,δ _s ) is the value of the static operating point. Since the coupling effect of voltage is no longer considered, only the power angle is estimated. As long as the value of the power angle after the change is given, the value of the decoupling matrix can be calculated. In order to solve this problem, it is necessary to re-estimate the power angle after the change. For the nonlinear power angle, the linearization idea can be adopted to divide it so that it presents linear characteristics in a small area. Therefore, a straight line is used instead of a curve in a small range to estimate the power angle.

As shown in FIG4 , curve D is the actual power angle curve, curves A, B, and C are power angle estimation curves described by formula (S-15), a(δ ₀ , P ₀ ) is the initial steady-state operating point, point b is a point closer to point a, and the slope of straight line A represents the slope between curves ab. When the system operates between points ab, the power angle can be estimated. Similarly, when the system operates at point bc, the power angle can be estimated by using straight line B to represent the slope between curves bc.

The specific selection scheme of the power angle curve is to select multiple groups of straight lines with different slopes to replace the curve, forming several power angle estimation curves with different slopes. The selection rule can be described as formula (S-13):

H＝[(K _ci ,[P _i ,P _i+1 ])](S-13)

In formula (S-13), K _ci represents the slope of the i-th power angle estimation curve, _Pi represents the active power of the i-th power angle estimation curve, [ _Pi , Pi ₊₁ ] represents the active power range used by the i-th estimation curve, and when the output power is in the power range [ _Pi , Pi ₊₁ ] of the i-th power angle estimation curve in H, the actual power angle curve D will switch to the i-th power angle estimation curve.

The actual power angle curve D can be described as formula (S-14):

_Pe = _Pemax sinδ(S-14)

In formula (S-14), _Pemax represents the maximum value of VSG output power;

The obtained power angle estimation curve can be described as formula (S-15):

Δδ=(δ _i+1 -δ _i )=K _ci ΔP=K _ci (P _i+1 -P _i ) (S-15).

In order to verify the effectiveness and feasibility of the proposed dynamic power decoupling control strategy, a VSG with an active power of 10kW and a reactive power of 5kVar was built in Matlab/Simulink.

First, verify the coupling phenomenon of traditional VSG under microgrid. As shown in Figure 5, the power response waveforms under different control strategies are described. From Figure 5-a (traditional VSG output power diagram), it can be seen that the traditional VSG control strategy has two power coupling processes. The first is when the frequency drops to 49.8HZ, the reactive power changes from 5000Var to 3500Var, which shows the existence of system power coupling; the second is when the load increases by 6kW, the reactive power changes from 3500Var to 2000Var, which further shows that the change of the static working point will affect the reactive power, indicating the existence of coupling phenomenon under frequent load switching. Secondly, verify the effectiveness of static decoupling. From Figure 5-b (diagonal array compensation matrix VSG output power), it can be seen that compared with the traditional VSG control strategy, the control strategy based on the diagonal array compensation matrix can adapt to small disturbances such as the decrease in grid frequency, improve the stability of the grid-connected inverter, and can safely and reliably realize distributed grid-connected power generation. However, with the frequent switching of the load, the decoupling control strategy based on the diagonal array compensation matrix will continue to produce coupling phenomenon. Finally, the VSG dynamic decoupling control strategy is verified. From Figure 5-c (dynamic diagonal compensation matrix VSG output power), it can be seen that the dynamic decoupling control strategy can achieve power decoupling after frequency drop and frequent load switching.

In order to simulate the characteristics of frequent switching of the grid-connected load, the grid-connected load is set to change frequently. The load is 10kW at 0-0.4s, 4000kW at 0.4-0.8s, 22kW at 0.8-1.2s, 7kW at 1.2-1.6s, and 16kW at 1.6-2.0s. The waveform is shown in Figure 6. It can be seen that the decoupling control strategy based on the dynamic diagonal array compensation matrix can always maintain the reactive power at 5000Var, while the coupling effect of the traditional VSG control is the most serious. The VSG based on the diagonal array compensation matrix is alleviated compared with the traditional VSG, but compared with the dynamic diagonal array decoupling control strategy, the coupling phenomenon still exists.

In order to verify the correctness of the theoretical analysis results, a DSP+RT-Lab semi-physical experimental platform was built, and the experimental parameters were consistent with the simulation parameters. Figure 7-a is the a-phase current change waveform based on the dynamic diagonal array compensation matrix. The change process of the current waveform is gentle and there is no large impact; Figure 7-b is the total harmonic distortion (THD) of the current when the current is from 0.7s to 0.75s, which is 2.56%, which meets the grid requirements; Figure 7-c is the current when the current is from 1.4s to 1.45s, the THD of the current is 3.32%, which meets the grid requirements.

As shown in Figure 8, it is the reactive power output waveform under different control strategies. Q1 is the traditional VSG control, and Q2 is the power decoupling control strategy based on the dynamic diagonal array compensation matrix. The experimental results verify that the traditional VSG will always have power coupling when the system load changes, while the dynamic power decoupling control strategy can automatically adjust the coupling component and realize real-time decoupling under different working conditions.

Claims (9)

1. A VSG power decoupling control method based on a dynamic diagonal array compensation matrix, characterized in that the topological structure of the VSG includes a VSG main circuit and a VSG control circuit, the VSG main circuit includes a DC voltage source, a three-phase bridge inverter circuit, an LC filter and an AC power grid, and the VSG control circuit includes an active power control loop, a reactive power control loop and a voltage control loop. By estimating the power angle parameters in the active power control loop, the diagonal array compensation matrix is used to dynamically track the static operating point of the system, thereby improving the VSG power decoupling effect and adapting to frequent changes in grid frequency and frequent switching of micro-source loads. The VSG power decoupling control method specifically comprises the following steps: S1: Set the command values of active power, reactive power and terminal voltage, measure the real-time current and voltage signals on the inverter side, and calculate the instantaneous values of active power and reactive power; S2: Acquiring a reference voltage command signal of the voltage control loop, including generating an active power loop output angle through the active power control loop, and generating a reactive power loop output voltage amplitude through the reactive power control loop; S3: performing voltage closed-loop control on the reference voltage command signal to generate a PWM wave to drive the inverter circuit switch to turn on or off; S4: According to the VSG grid-connected equivalent circuit, the complex power of the grid-connected point is obtained using the power system flow calculation formula; S5: using a small signal analysis method to obtain active power disturbance, reactive power disturbance and a system decoupling matrix; the decoupling matrix describes the relationship between the active power disturbance and the reactive power disturbance and the voltage disturbance and the power angle disturbance respectively; S6: adopting a diagonal matrix compensation method, introducing a decoupling compensation matrix, and converting the matrix to be decoupled into a diagonal matrix; S7: According to the characteristics of the static operating point change when the grid-connected side load is frequently switched, several straight lines are selected to estimate the power angle after the static operating point changes, and a power angle estimation curve is obtained. 2. According to the VSG power decoupling control method based on the dynamic diagonal array compensation matrix of claim 1, it is characterized in that the calculation process of the instantaneous value of active power _Pe and the instantaneous value of reactive power _Qe is as shown in formula (1):

In formula (1), _ud and _q are the components of the real-time voltage signal input voltage of the inverter side in the dq coordinate system, and _id and _q are the components of the real-time current signal of the inverter side in the dq coordinate system. 3. According to the VSG power decoupling control method based on the dynamic diagonal compensation matrix of claim 2, it is characterized in that the calculation process of obtaining the reference voltage command signal of the voltage control loop is as follows:

The calculation process of the active power loop output angle δ and the reactive power loop output voltage amplitude _Em is as shown in formula (3):

In formula (3), J represents the moment of inertia, D represents the damping coefficient, _Pref represents the reference power, _ωn represents the reference angular frequency, ω represents the actual angular frequency, _Ucn represents the no-load electromotive force, _Qref represents the reactive power command value, _Dq represents the voltage regulation coefficient, _Un represents the rated value of the machine-end voltage, and _Uc represents the actual output value of the machine-end voltage. 4. According to the VSG power decoupling control method based on the dynamic diagonal array compensation matrix of claim 3, it is characterized in that the calculation process of obtaining the complex power S of the grid connection point is as follows:

In formula (4), _Es represents the actual output voltage amplitude of VSG, _Ug represents the grid voltage amplitude, _δs represents the actual output power angle of VSG, α represents the line impedance angle, and _Zline represents the line impedance. 5. According to claim 4, the VSG power decoupling control method based on the dynamic diagonal array compensation matrix is characterized in that the active power disturbance is obtained by using a small signal analysis method.

Reactive power disturbance

The calculation process is as follows:

In formula (5),

represents the voltage disturbance,

represents the power angle disturbance; Write equation (5) into a matrix form as shown in equation (6):

Then the system to be decoupled matrix

6. The VSG power decoupling control method based on the dynamic diagonal array compensation matrix according to claim 5 is characterized by introducing a decoupling compensation matrix G _c , as shown in formula (7):

The calculation process of converting the matrix to be decoupled _Gc into a diagonal matrix is as shown in formula (8):

The calculation process of the decoupling compensation matrix _Gc is as shown in formula (9):

7. The VSG power decoupling control method based on the dynamic diagonal compensation matrix according to claim 6 is characterized in that the selection rule of the plurality of straight lines can be described as formula (10): H＝[(K _ci ,[P _i ,P _i+1 ])] (10) In formula (10), K _ci represents the slope of the i-th power angle estimation curve, [P _i ,P _i+1 ] represents the active power range used by the i-th estimation curve, and when the output power is in the power range [P _i ,P _i+1 ] of the i-th power angle estimation curve in H, the actual power angle curve D will switch to the i-th power angle estimation curve. 8. The VSG power decoupling control method based on the dynamic diagonal array compensation matrix according to claim 7 is characterized in that the actual power angle curve D can be described as formula (11): P _e =P _emax sinδ (11) In formula (11), _Pemax represents the maximum value of VSG output power. 9. The VSG power decoupling control method based on the dynamic diagonal array compensation matrix according to claim 8 is characterized in that the acquired power angle estimation curve can be described as formula (12): Δδ=(δ _i+1 -δ _i )=K _ci ΔP=K _ci (P _i+1 -P _i ) (12) In formula (12), _Pi represents the active power of the i-th power angle estimation curve.

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