A method for grid connection of energy storage converter based on virtual synchronous generator control

Abstract

The present application relates to a kind of energy storage converter grid-connected method based on virtual synchronous generator control, compared with prior art, response ability of the defect in the prior art energy storage converter grid-connected control technology is weak, power control precision and stability are insufficient, controller robustness is poor.The present application includes the following steps: design the adaptive rule of virtual inertia and damping coefficient in VSG controller active loop;Adaptive adjustment is carried out;Design the VSG power decoupling controller based on super-local model cooperative control;Power smooth following and the effective decoupling control of active power and reactive power.The present application provides a kind of energy storage grid-connected converter operating process has the inertia and damping characteristics of synchronous generator, when grid-connected active power or grid-connected frequency disturbance occurs, frequency fluctuation can be inhibited by the adaptive adjustment of virtual inertia and damping coefficient, and has good power decoupling control ability.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of new energy grid-connected power generation, in particular to a kind of energy storage converter grid-connected method based on virtual synchronous generator control. BACKGROUND

[0002] In recent years, China has made remarkable progress in the field of distributed renewable energy such as wind power and photovoltaic, and the grid-connected penetration rate of these energies has gradually increased, bringing the volatility and intermittency characteristics of renewable energy generation, which seriously threatens the safe and stable operation of the power system. Especially in the case of load change and renewable energy generation fluctuation, the frequency and voltage stability of the power grid faces great challenges.

[0003] Energy storage grid operation is through power electronic equipment to interact with the grid, and large-scale renewable energy generation and energy storage grid operation gradually makes the grid evolve into a low-inertia, under-damped system dominated by power electronic converters. This transformation poses challenges to traditional power system control methods, especially in terms of frequency and power regulation capabilities. Therefore, virtual synchronous generator (VSG) control, which simulates the characteristics of synchronous generators, increases inertia and damping, and improves the frequency stability of the grid, has emerged.

[0004] Currently, existing energy storage converter grid-connected systems based on VSG control simulate the mechanical equation and droop characteristics of synchronous generators, not only providing active power, reactive power and frequency support for the grid, but also effectively addressing the problem of insufficient inertia and damping of power electronic converters. These systems have to some extent suppressed the fluctuations in grid frequency and improved the stability of grid operation. However, VSG control with fixed virtual inertia and damping coefficients cannot achieve rapid and accurate frequency recovery when the grid frequency deviates from the nominal value, resulting in a lag in system response. In addition, the line impedance in medium and low voltage distribution networks often exhibits resistive and inductive characteristics, which can cause active power and reactive power to be coupled during VSG control grid operation, affecting the dynamic and steady-state control performance of VSG control, and further affecting the stability and safe and reliable operation of the power system.

[0005] Considering the impact of virtual inertia and damping coefficients on system dynamic performance, it is urgent to design an adaptive control law related to the output angular frequency deviation and angular frequency change rate of VSG control, which can have more flexible and efficient response in grid operation. At the same time, the actual line impedance characteristics may cause coupling between active power and reactive power control, so it is also necessary to break through the power decoupling technology of VSG control to achieve continuous safe and stable operation of the system.

[0006] Given the adverse effects of fixed virtual inertia and damping coefficient design, as well as power coupling issues, on grid connection of energy storage converters, there is an urgent need to develop a new method for grid connection of energy storage converters based on virtual synchronous generator (VSG) control. This new method can dynamically adjust the virtual inertia and damping coefficient to adapt to real-time changes in the grid when there are disturbances in the grid-connected active power or grid frequency. Furthermore, it can effectively reduce the coupling effect between the active and reactive power of the VSG, optimize the frequency and active power regulation capabilities of the power system, thereby providing solid technical support for the high proportion of renewable energy grid connection and promoting the safe, stable, and sustainable development of the power system. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing energy storage converter grid connection control technologies, such as weak response to grid disturbances, insufficient power control accuracy and stability, and poor controller robustness. This invention provides an energy storage converter grid connection method based on virtual synchronous generator control to solve the above problems.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows:

[0009] A grid-connection method for an energy storage converter based on virtual synchronous generator control includes the following steps:

[0010] An adaptive rule for virtual inertia and damping coefficient in the active loop of the VSG controller was designed.

[0011] Adaptive adjustment: Based on the adaptive rules of virtual inertia and damping coefficient, the virtual inertia and damping coefficient are adaptively adjusted.

[0012] Design a VSG power decoupling controller based on hyperlocal model cooperative control;

[0013] Power smooth tracking and effective decoupling control of active and reactive power.

[0014] The adaptive rules for virtual inertia and damping coefficient in the active loop of the designed VSG controller include the following steps:

[0015] The adaptive rules for virtual inertia and damping coefficient in the active loop of the VSG controller are set as follows:

[0016]

[0017] In the formula, w, w n w d , These represent the angular frequency of the energy storage converter connected to the grid, the rated angular frequency of the energy storage converter connected to the grid, the frequency deviation of the energy storage converter connected to the grid, and the rate of change of angular frequency during the grid connection process, respectively. ΔP is the power deviation at the grid connection point, and P... refP is the active power reference value for the virtual synchronous generator. e The actual active power of the virtual synchronous generator is denoted by ; D is the VSG damping coefficient, and J is the VSG virtual inertia.

[0018] When the active power is disturbed, the angular frequency ω is set at ω n Damped oscillations occur up and down.

[0019] When w>w n hour,

[0020] when If the value is greater than 0, the virtual inertia J is increased to suppress the growth of angular frequency w.

[0021] when If the value is less than 0, the virtual inertia J is reduced to induce w to recover to w. n ;

[0022] When w <w n hour,

[0023] when If the value is less than 0, the virtual inertia J is increased to suppress the reverse growth of the angular frequency w.

[0024] when If the value is less than 0, the virtual inertia J is reduced to induce w to recover to w. n ;

[0025] When w>w n hour,

[0026] when If the value is greater than 0, the damping coefficient D is increased to accelerate the decay of the angular frequency ω oscillation.

[0027] when If the value is less than 0, the damping coefficient D is reduced to avoid excessive energy dissipation;

[0028] When w <w n hour,

[0029] when If the value is less than 0, the damping coefficient D is increased to accelerate the decay of the reverse oscillation at angular frequency ω.

[0030] when If the value is less than 0, the damping coefficient D is reduced to avoid excessive energy dissipation.

[0031] The adaptive adjustment includes the following steps:

[0032] The VSG virtual inertia J and damping coefficient D are adaptively adjusted, and their expressions are as follows:

[0033]

[0034] Where: J0 represents the initial value of the virtual inertia, k1 represents the adaptive adjustment coefficient of the virtual inertia, D0 is the initial value of the damping coefficient, k2 represents the adaptive adjustment coefficient of the damping coefficient, J is the VSG virtual inertia, D is the VSG damping coefficient, and w d and |w d | represents the absolute value of the angular frequency deviation of the energy storage converter connected to the grid. Let be the rate of change of angular frequency deviation during the grid connection process of the energy storage converter, and e be an exponential function;

[0035] The rotor motion equation in the active loop of the VSG controller is set as follows:

[0036]

[0037] Substituting equation (2) into the rotor motion equation of (3), we get:

[0038]

[0039] In the formula, w n ω and ω are the rated angular frequency and the grid-connected angular frequency of the energy storage converter, respectively. P ref P is the active power reference value for VSG. e D is the actual power of the VSG, and D is the damping coefficient of the VSG.

[0040] Let ΔP be the difference between the reference value and the actual value of active power, which is the power deviation at the grid connection point; w d The angular frequency deviation of the energy storage converter connected to the grid;

[0041] Through derivation, we obtain:

[0042]

[0043] For w d Find the derivative of and solve for it. Then we have:

[0044]

[0045] When the system is in steady state, the angular frequency deviation w of the energy storage converter connected to the grid is... d =0, the denominator of equation (6) is zero, the equation is invalid, therefore its denominator is rationalized as:

[0046]

[0047] Equation (7) represents the rate of change of the power deviation ΔP at the grid connection point and the angular frequency deviation during the grid connection process of the energy storage converter when the active power is disturbed. The dynamic relationship between them;

[0048] When active power is disturbed, the VSG controller adjusts the VSG virtual inertia and damping coefficient in the active power loop to reduce angular frequency fluctuations.

[0049] The design of the VSG power decoupling controller based on hyperlocal model cooperative control includes the following steps:

[0050] Because the line impedance is not purely inductive, the transmitted active power is controlled not only by the power angle δ but also by the voltage amplitude E. That is, there is strong coupling between active and reactive power. The small-signal model near the steady-state operating point δ0 and E0 is expressed as:

[0051]

[0052] From equation (8), we know that

[0053] If δ0≠0, that is, k′ pe ≠0,k′ qδ ≠0, the phase of the grid voltage is the reference phase, δ0 and E0 are the stable operating points of the power angle and voltage amplitude, and Z g U is the line impedance between the grid connection point and the power grid. g θ is the grid voltage amplitude, θ is the line impedance angle, and ΔP is the line impedance angle. e The active power deviation, ΔQ e For reactive power deviation, sin and cos are sine and cosine trigonometric functions, Δδ is the power angle deviation, ΔE is the voltage amplitude deviation, and k is the reactive power deviation. pδ k is the active power coefficient for the power angle deviation. qδ The reactive power coefficient of the power angle deviation, k pe k is the active power coefficient for voltage amplitude deviation. qe Reactive power factor of voltage amplitude deviation;

[0054] Even if the line impedance is purely inductive, i.e., θ = 90° and Z g =X g There is still coupling between active power and reactive power;

[0055] Extract k from equation (8) pe and k qδ Dividing the two, we get:

[0056]

[0057] In equation (9), E0 is the stable operating point of the voltage amplitude, and X gThe line impedance between the grid connection point and the grid is inductive and equal to the grid voltage amplitude under steady state. In VSG control, the influence of the power angle on reactive power is much greater than the influence of the voltage amplitude. That is, the coupling effect of active power change on reactive power is greater, while the influence of reactive power change on active power is negligible.

[0058] First, the reactive power output of the VSG is measured, and then low-pass filtered to ensure that the bandwidth of the VSG power control loop is much smaller than the bandwidth of its voltage and current control loop. Then:

[0059]

[0060] In the formula: Q em ω represents the reactive power after passing through the low-pass filter. c Here, is the cutoff frequency of the low-pass filter, s is the Laplace operator, and Q... e This represents the actual reactive power.

[0061] The time-domain small-signal model of equation (10) is:

[0062]

[0063] Where: ΔQ em This refers to the reactive power deviation caused by changes in active power. The derivative of reactive power deviation;

[0064] Based on equations (8) and (11), the voltage amplitude fluctuation when reactive power deviation exists is taken as the compensation voltage, and the dynamic equation of reactive power deviation of the VSG power decoupling controller is established as follows:

[0065]

[0066] In the formula, E comp This is the voltage compensation amount output by the VSG power decoupling controller.

[0067] The power decoupling controller is designed to decouple the active and reactive power of the VSG, meaning that when the active power command changes abruptly, the reactive power deviation remains at zero. To achieve this, the macro variable ψ... e Designed as follows:

[0068]

[0069] In the formula, Let λ1 be the expected reactive power deviation, λ2 be the proportional coefficient, and ∫e be the integral of e.

[0070] Design the dynamic evolution equations for collaborative control, and have

[0071]

[0072] In the formula, T e The reactive power deviation convergence time parameter. For the macro variable ψ in equation (14) e Differentiate;

[0073] The derived cooperative control law E of the VSG power decoupling controller output comp for:

[0074]

[0075] The cooperative control law E output by the VSG power decoupling controller comp As a voltage compensation combined with the VSG reactive power control loop, power decoupling is achieved;

[0076] For a system with a single input and a single output, the algebraic differential equation is as follows:

[0077]

[0078] In the formula, t is the time variable, u and y are the system input and output respectively, E is a differentiable function, and y (n) It is the nth derivative of the system output, u (b) It is the b-th derivative of the system input, y (a) It is the b-th derivative of the system output.

[0079] Equation (16) can be written in hyperlocal model form, and we have:

[0080] y (n) (t)=F(t)+αu(t) (17)

[0081] In the formula, y (n) (t) is the nth derivative of the system output at time t, where n represents the system order, usually taken as 1, α is the scaling factor of the system input, the constantly updated variable F(t) represents the known part, unknown part and various possible disturbances of the system, and the estimation of variable F(t) is determined by using the system input and output data, u(t) is the system input at time t;

[0082] Based on the dynamic equation of reactive power deviation of the VSG power decoupling controller, in order to eliminate its sensitive dependence on line impedance and power angle changes, a hyperlocal model of VSG reactive power deviation is established, and we have:

[0083]

[0084] In the formula, a n F is a proportional parameter, Δa is the error voltage coefficient, and F est E represents the known and unknown parts. compThis refers to the voltage compensation value output by the VSG power decoupling controller. The derivative of reactive power deviation, ΔQ em ω represents the reactive power deviation caused by changes in active power. c Z is the cutoff frequency of the low-pass filter. g U is the line impedance between the grid connection point and the power grid. g denoted as the grid voltage amplitude, sin and cos are sine and cosine trigonometric functions, Δδ is the power angle deviation, δ0 and E0 are the stable operating points of the power angle and voltage amplitude, and θ is the line impedance angle.

[0085] F est Online estimation: Based on the VSG reactive power deviation hyperlocal model, for F est Perform online estimation.

[0086] The F est The online estimation includes the following steps:

[0087] Assume F est It is a constant over a relatively short period of time. The frequency domain expression of equation (18) is:

[0088]

[0089] In the formula, ΔQ e0 Let represent the initial value of reactive power deviation, s be the Laplace transform operator, and a n E is a proportional parameter. comp ΔQ is the voltage compensation value output by the VSG power decoupling controller. em This refers to the reactive power deviation caused by changes in active power.

[0090] Differentiating both sides of the equation with respect to s eliminates the influence of the initial value, resulting in:

[0091]

[0092] In the formula, For ΔQ em Differentiate in the frequency domain For E comp Differentiate in the frequency domain;

[0093] To avoid noise amplification due to differentiation when measuring reactive power, both sides of the equation are multiplied by . s -2 ,have to:

[0094]

[0095] The estimation is based on algebraic identification, transforming equation (21) into a time-domain form, within the sampling interval [0, T]. F F is obtained from the inner [element]. est The estimated value is:

[0096]

[0097] In the formula, For the known and unknown parts F at time t est The estimated value, T s To control the cycle, T F =n F T s Let E be the length of the sliding window, t be the time variable, and E be the value of E. comp (t) and ΔQ em (t) represent the voltage compensation and reactive power deviation at time t, respectively. F The length of the sliding window;

[0098] The estimate obtained by equation (22) Substituting this into equation (18), a hyperlocal model of the reactive power deviation of the VSG is established, and expressed as:

[0099]

[0100] In the formula, T is the derivative of reactive power deviation. F E is the length of the sliding window. comp E represents the voltage compensation value output by the VSG power decoupling controller. comp (t) and ΔQ em (t) represents the voltage compensation and reactive power deviation at time t, where t is a time variable;

[0101] Based on the designed cooperative control VSG power decoupling controller based on the reactive power deviation hyperlocal model, the generated cooperative control law is as follows:

[0102]

[0103] in, The estimation is performed using the algebraic identification method in step 54), where λ1 is the proportionality coefficient, λ2 is the integral coefficient, and ∫e is the integral of e. T e This is the reactive power deviation convergence time parameter.

[0104] The steps of power smooth tracking and effective decoupling control of active and reactive power are as follows: In grid-connected mode, the active power is calculated using the current and voltage at the grid connection point and used as the input of the active power loop of the VSG controller. After adjustment by the virtual inertia and damping coefficient adaptive rules, the active power smooth tracking is achieved. Based on the reactive power calculated at the grid connection point, it is used as the input of the VSG power decoupling controller based on hyperlocal model collaborative control. The macro variables are designed with the reactive power deviation as the control objective to keep the reactive power stable and achieve robust control that is insensitive to line impedance parameters.

[0105] Beneficial effects

[0106] The present invention provides a grid-connected method for energy storage converters based on virtual synchronous generator control. Compared with the prior art, this method provides an energy storage converter that has the inertia and damping characteristics of a synchronous generator during operation. When the grid-connected active power or grid-connected frequency is disturbed, frequency fluctuations can be suppressed by adaptive adjustment of virtual inertia and damping coefficient, thereby enhancing the stability of grid-connected operation of the energy storage converter.

[0107] This invention proposes a VSG power decoupling controller based on hyperlocal model cooperative control. The manifold is designed with zero reactive power deviation as the control objective, which enables the system to achieve a more obvious power decoupling effect and realize robust control that is insensitive to line impedance parameters.

[0108] This invention uses Simulink software to build a grid-connected simulation model of an energy storage converter, and verifies the role of improved VSG control in supporting system frequency stability through system simulation research. Attached Figure Description

[0109] Figure 1 This is a flowchart of the method of the present invention;

[0110] Figure 2 The equivalent circuit diagram for a virtual synchronous generator;

[0111] Figure 3 The active loop control diagram of VSG based on adaptive dynamic virtual inertia and damping coefficient;

[0112] Figure 4 The diagram shows the VSG power decoupling reactive power loop control based on hyperlocal model cooperative control.

[0113] Figure 5 This is a dynamic schematic diagram of the grid connection angular frequency.

[0114] Figure 6 This is a schematic diagram illustrating the adaptive change of virtual inertia.

[0115] Figure 7 This is a schematic diagram illustrating the adaptive variation of the damping coefficient.

[0116] Figure 8 This is a schematic diagram comparing the decoupling performance of active and reactive power under line impedances Rg = 1Ω and Lg = 2mH.

[0117] Figure 9 This is a schematic diagram comparing the decoupling performance of active and reactive power under line impedances Rg = 3Ω and Lg = 2mH. Detailed Implementation

[0118] To provide a better understanding of the structural features and effects achieved by the present invention, a detailed description is provided below, accompanied by preferred embodiments and accompanying drawings:

[0119] like Figure 1 As shown, the grid connection method for an energy storage converter based on virtual synchronous generator control according to the present invention includes the following steps:

[0120] The first step is to design adaptive rules for the virtual inertia and damping coefficient in the active loop of the VSG controller.

[0121] For high-proportion grid-connected systems, when a large power disturbance occurs, the system's low inertia can cause a significant frequency deviation, leading to the grid disconnection from the main power grid. Figure 2 This is the equivalent circuit diagram for grid connection of a VSG-controlled energy storage converter.

[0122] (1) Set the adaptive rules for virtual inertia and damping coefficient in the active loop of the VSG controller as follows:

[0123]

[0124] In the formula, w, w n w d , These represent the angular frequency of the energy storage converter connected to the grid, the rated angular frequency of the energy storage converter connected to the grid, the frequency deviation of the energy storage converter connected to the grid, and the rate of change of angular frequency during the grid connection process, respectively. ΔP is the power deviation at the grid connection point, and P... ref P is the active power reference value for the virtual synchronous generator. e Let represent the actual active power of the virtual synchronous generator, D be the damping coefficient of the VSG, and J be the virtual inertia of the VSG.

[0125] (2) Set the angular frequency ω at which the active power is disturbed. n Damped oscillations occur up and down.

[0126] A1) When w>w n hour,

[0127] when If the value is greater than 0, the virtual inertia J is increased to suppress the growth of angular frequency w.

[0128] when If the value is less than 0, the virtual inertia J is reduced to induce w to recover to w. n ;

[0129] A2) When w <w n hour,

[0130] when If the value is less than 0, the virtual inertia J is increased to suppress the reverse growth of the angular frequency w.

[0131] when If the value is less than 0, the virtual inertia J is reduced to induce w to recover to w. n ;

[0132] A3) When w>w n hour,

[0133] when If the value is greater than 0, the damping coefficient D is increased to accelerate the decay of the angular frequency ω oscillation.

[0134] when If the value is less than 0, the damping coefficient D is reduced to avoid excessive energy dissipation;

[0135] A4) When w <w n hour,

[0136] when If the value is less than 0, the damping coefficient D is increased to accelerate the decay of the reverse oscillation at angular frequency ω.

[0137] when If the value is less than 0, the damping coefficient D is reduced to avoid excessive energy dissipation.

[0138] The second step is to perform adaptive adjustment: based on the adaptive rules of virtual inertia and damping coefficient, the virtual inertia and damping coefficient are adaptively adjusted.

[0139] By setting flexible virtual inertia and damping coefficients in the active power loop of the VSG controller, timely adjustments can be made to power disturbances in the power grid, thereby enhancing grid connection stability. Figure 3 The active loop control diagram of VSG based on adaptive dynamic virtual inertia and damping is shown.

[0140] (1) The virtual inertia J and damping coefficient D of the VSG are adaptively adjusted, and their expressions are as follows:

[0141]

[0142] Where: J0 represents the initial value of the virtual inertia, k1 represents the adaptive adjustment coefficient of the virtual inertia, D0 is the initial value of the damping coefficient, k2 represents the adaptive adjustment coefficient of the damping coefficient, J is the virtual inertia of the VSG, D is the damping coefficient of the VSG, and w d and |w d | represents the absolute value of the angular frequency deviation of the energy storage converter connected to the grid. Let be the rate of change of angular frequency deviation during the grid connection process of the energy storage converter, and e be an exponential function.

[0143] (2) Set the rotor motion equation in the active loop of the VSG controller as follows:

[0144]

[0145] B1) Substituting equation (2) into the rotor motion equation (3), we get:

[0146]

[0147] In the formula, w n ω and ω are the rated angular frequency and the grid-connected angular frequency of the energy storage converter, respectively. P ref P is the active power reference value for VSG. e This is the actual power output by the VSG.

[0148] B2) Let the difference between the reference value and the actual value of active power be ΔP, which is the power deviation at the grid connection point; w d For the frequency deviation of the energy storage converter connected to the grid;

[0149] Through derivation, we obtain:

[0150]

[0151] B3) For w d Find the derivative of and solve for it. Then we have:

[0152]

[0153] B4) When the system is in steady state, the angular frequency deviation w of the energy storage converter connected to the grid. d =0, the denominator of equation (6) is zero, the equation is invalid, therefore its denominator is rationalized as:

[0154]

[0155] Equation (7) is the rate of change of the angular frequency deviation between the active power disturbance ΔP and the grid connection process of the energy storage converter. The dynamic relationship between them;

[0156] When active power is disturbed, the VSG controller adjusts the adaptive dynamic virtual inertia and damping coefficient in the active power loop to reduce angular frequency fluctuations.

[0157] The third step is to design a VSG power decoupling controller based on hyperlocal model cooperative control.

[0158] When a VSG-controlled energy storage converter is connected to the grid, the line impedance in medium and low voltage distribution networks often exhibits resistive-inductive characteristics. This leads to active and reactive power coupling during grid-connected operation, affecting the dynamic and steady-state control performance of the VSG control. A VSG power decoupling controller based on hyperlocal model cooperative control is designed to achieve robust control that is insensitive to line impedance parameters.

[0159] (1) Since the line impedance is not purely inductive, the transmitted active power is controlled not only by the power angle δ, but also by the voltage amplitude E. That is, there is strong coupling between the power. The small-signal model near the steady-state operating point δ0 and E0 is:

[0160]

[0161] From equation (8), we know that

[0162] If δ0≠0, that is, k′ pe ≠0,k′ qδ ≠0, such as Figure 2 The equivalent circuit diagram of the grid-connected energy storage converter based on VSG control is shown. The phase of the grid voltage is the reference phase, and δ0 and E0 are the stable operating points of the power angle and voltage amplitude, respectively. g U is the line impedance between the grid connection point and the power grid. g θ is the grid voltage amplitude, θ is the line impedance angle, and ΔP is the line impedance angle. e The active power deviation, ΔQ e For reactive power deviation, sin and cos are sine and cosine trigonometric functions, Δδ is the power angle deviation, ΔE is the voltage amplitude deviation, and k is the reactive power deviation. pδ k is the active power coefficient for the power angle deviation. qδ The reactive power coefficient of the power angle deviation, k pe k is the active power coefficient for voltage amplitude deviation. qe Reactive power factor of voltage amplitude deviation;

[0163] (2) Although the line impedance is not purely inductive, i.e., θ = 90° and Z g =X g There is still coupling between active and reactive power;

[0164] Extract k from equation (8) pe and k qδ Dividing the two, we get:

[0165]

[0166] In equation (9), E0 is the stable operating point of the voltage amplitude, and X g Since the line impedance between the grid connection point and the grid is inductive and equal to the grid voltage amplitude under steady state, in VSG control, the influence of the power angle on reactive power is much greater than the influence of the voltage amplitude. That is, the coupling effect of active power change on reactive power is greater, while the influence of reactive power change on active power is negligible.

[0167] (3) First, measure the reactive power output of the VSG, then perform low-pass filtering to make the bandwidth of the VSG power control loop much smaller than the bandwidth of its voltage and current control loop. Then:

[0168]

[0169] In the formula: Q em ω represents the reactive power after passing through the low-pass filter. c Here, is the cutoff frequency of the low-pass filter, s is the Laplace operator, and Q... e This represents the actual reactive power.

[0170] The time-domain small-signal model of equation (10) is:

[0171]

[0172] Where: ΔQ em This refers to the reactive power deviation caused by changes in active power. The derivative of reactive power deviation;

[0173] Based on equations (8) and (11), the voltage amplitude fluctuation when reactive power deviation exists is taken as the compensation voltage, and the dynamic equation of reactive power deviation of the VSG power decoupling controller is established as follows:

[0174]

[0175] In the formula, E comp This is the voltage compensation amount output by the VSG power decoupling controller.

[0176] The power decoupling controller is designed to achieve power decoupling of the VSG, meaning that the reactive power deviation remains zero when the active power command changes abruptly. To achieve this, the macro variable ψ... e Designed as follows:

[0177] ψ e =λ1e+λ2∫e (13)

[0178] In the formula, Let λ1 be the expected reactive power deviation, λ2 be the proportional coefficient, and ∫e be the integral of e.

[0179] (4) Design the dynamic evolution equations for collaborative control, and have

[0180]

[0181] In the formula, T e The reactive power deviation convergence time parameter. For the macro variable ψ in equation (14) e Differentiate;

[0182] The derived cooperative control law E of the VSG power decoupling controller output comp for:

[0183]

[0184] The cooperative control law E output by the VSG power decoupling controller comp As a voltage compensation combined with the VSG reactive power control loop, power decoupling is achieved;

[0185] However, the generated cooperative control law is based on the known line impedance and the system being in steady state. But the actual line impedance is difficult to estimate, and the operating conditions of microgrids based on VSG control can change at any time. Therefore, there is an urgent need to study a model-free scheme that eliminates the dependence on system parameters for the control law. Figure 4 This is a control diagram for the VSG power decoupling reactive power loop based on hyperlocal model collaborative control.

[0186] (5) For a controller system with a single control input and a single output, the algebraic differential equation is as follows:

[0187]

[0188] In the formula, t is the time variable, u and y are the input and output of the controller system, respectively, E is a differentiable function, and y (n) It is the nth derivative of the controller system output, u (b) It is the b-th derivative of the controller system input, y (a) It is the b-th derivative of the controller system output.

[0189] Equation (16) can be written in the form of a hyperlocal model, and we have:

[0190] y (n) (t)=F(t)+αu(t) (17)

[0191] In the formula, y (n)(t) is the nth derivative of the controller system output at time t, where n represents the system order, usually taken as 1, α is the scaling factor of the system input, the constantly updated variable F(t) represents the known part of the system, the unknown part, and various possible disturbances, and the estimation of variable F(t) is determined by using the system's input and output data, u(t) is the input of the controller system at time t.

[0192] (6) Based on the dynamic equation of reactive power deviation of the VSG power decoupling controller, in order to get rid of its sensitive dependence on line impedance and power angle changes, a hyperlocal model of VSG reactive power deviation is established, and we have:

[0193]

[0194] In the formula, a n F is a proportional parameter, Δa is the error voltage coefficient, and F est E represents the known and unknown parts. comp This refers to the voltage compensation value output by the VSG power decoupling controller. The derivative of reactive power deviation, ΔQ em ω represents the reactive power deviation caused by changes in active power. c Z is the cutoff frequency of the low-pass filter. g U is the line impedance between the grid connection point and the power grid. g Let be the grid voltage amplitude, sin and cos be the sine and cosine trigonometric functions, Δδ be the power angle deviation, δ0 and E0 be the stable operating points of the voltage amplitude of the power angle, and θ be the line impedance angle.

[0195] (7)F est Online estimation: Based on the VSG reactive power deviation hyperlocal model, for F est Perform online estimation.

[0196] C1) Assume F est It is a constant over a relatively short period of time. The frequency domain expression of equation (18) is: (This represents the estimated value in the frequency domain.)

[0197]

[0198] In the formula, ΔQ e0 This represents the initial output, s is the Laplace transform operator, and a n E is a proportional parameter. comp ΔQ is the voltage compensation value output by the VSG power decoupling controller. em This refers to the reactive power deviation caused by changes in active power.

[0199] C2) Differentiating both sides of the equation with respect to s simultaneously eliminates the influence of the initial output, resulting in:

[0200]

[0201] In the formula, For ΔQ em Differentiate in the frequency domain For E comp Differentiate in the frequency domain;

[0202] C3) To avoid noise amplification due to differentiation when measuring reactive power, both sides of the equation are multiplied by . s -2 ,have to:

[0203]

[0204] C4) Based on the algebraic identification method, the estimation is performed, transforming equation (21) into a time-domain form, within the sampling interval [0,T]. F F is obtained from the inner [element]. est The estimated value is:

[0205]

[0206] In the formula, For the known and unknown parts F at time t est The estimated value, T s To control the cycle, T F =n F T s Let E be the length of the sliding window, t be the time variable, and E be the value of E. comp (t) and ΔQ em (t) represents the voltage compensation and reactive power deviation T at time t, respectively. F The length of the sliding window;

[0207] C5) The estimate obtained by equation (21) Substituting this into equation (18), a hyperlocal model of the reactive power deviation of the VSG is established, and expressed as:

[0208]

[0209] In the formula, T is the derivative of reactive power deviation. F E is the length of the sliding window. comp E represents the voltage compensation value output by the VSG power decoupling controller. comp (t) and ΔQ em (t) represents the voltage compensation and reactive power deviation at time t, where t is a time variable;

[0210] C6) Based on the designed cooperative control VSG power decoupling controller based on the reactive power deviation hyperlocal model, the output cooperative control law is:

[0211]

[0212] in, The estimation is performed using the algebraic identification method in step 54), where λ1 is the proportionality coefficient, λ2 is the integral coefficient, and ∫e is the integral of e. T e This is the reactive power deviation convergence time parameter.

[0213] The stability of a grid-connected energy storage converter system based on VSG control is proven using Lyapunov's stability theorem. The Lyapunov function is defined as follows:

[0214]

[0215] In the formula, V is the variable of the Lyapunov function, and ψ e The macro variable defined in equation (13).

[0216] The derivative of the Lyapunov function is:

[0217]

[0218] From equation (26), it can be seen that as long as T is satisfied... e A value greater than 0 ensures that the designed macrovariable ψ is guaranteed. e It can stabilize to 0, and ψ e The linear combination of proportional-integral form of reactive power deviation is used to prove that the proposed VSG power decoupling controller based on hyperlocal model cooperative control is globally stable.

[0219] The fourth step is power smooth tracking and effective decoupling control of active and reactive power: In grid-connected mode, the active power is calculated using the current and voltage at the grid connection point and used as the input to the active power loop of the VSG controller. Through the adaptive rules of virtual inertia and damping coefficient, active power smooth tracking is achieved. Based on the reactive power calculated at the grid connection point, it is used as the input to the VSG power decoupling controller based on hyperlocal model collaborative control. The macro-variable function is designed with the reactive power deviation as the control objective to keep the reactive power stable and achieve robust control that is insensitive to line impedance parameters.

[0220] To verify the effectiveness of the proposed new grid connection method for energy storage converters based on VSG control, a Simulink simulation model was built using Matlab software.

[0221] First, the initial active power setpoint is set to 2kW, which abruptly increases to 5kW at t=1.5s. The grid-connected angular frequency dynamics are as follows: Figure 5 As shown, the virtual inertia and damping coefficient adapt to changes in dynamic angular frequency.Figure 6 and Figure 7 As shown.

[0222] Then, the initial active power setpoint is set to 0kW and the reactive power to 0var. At time t = 2s, the active power abruptly increases to 10kW, while the reactive power remains at 0var. To compare the performance of the power decoupling controller, this invention uses the root mean square error (RMSE) of the reactive power deviation to measure the effectiveness of different control strategies. The dynamic comparison of the active and reactive power decoupling performance of the VSG output is shown below, with line impedance Rg = 1Ω and Lg = 2mH. Figure 8 As shown, the dynamic comparison of the decoupling performance of active and reactive power output of VSG under line impedance Rg = 3Ω and Lg = 2mH is as follows: Figure 9 As shown.

[0223] exist Figure 5 In the diagram, the upper line represents the grid-connected angular frequency w(VSG) of the energy storage converter under conventional VSG grid-connected control, while the lower line represents the grid-connected angular frequency w(Improved VSG) of the energy storage converter using the method designed in this invention. Figure 6 In the diagram, the upper line represents the adaptively adjustable VSG virtual inertia self-J and D designed in this invention, while the lower line represents the traditional fixed VSG virtual inertia constant-J and D. Figure 7 In the diagram, the upper line represents the adaptively adjustable VSG damping coefficient (self-J, D) designed in this invention, while the lower line represents the conventionally fixed VSG damping coefficient (constant-J, D). Figure 8 In the middle, from left to right, are: the line impedance R g =1Ω, L g Under the condition of 2mH, VSG power decoupling is achieved through undecoupled and coordinated control based on a hyperlocal model; Figure 9 In the middle, in the line impedance R g =3Ω, L g From left to right under the 2mH operating condition: undecoupled and VSG power decoupling achieved through cooperative control based on a hyperlocal model. When sudden changes in active power cause grid frequency fluctuations, the energy storage converter grid connection method based on virtual synchronous generator control designed in this invention can achieve adaptive adjustment of virtual inertia and damping coefficient. Compared with traditional VSG control, it enjoys the technical advantages of smaller frequency fluctuations and faster frequency return speed.

[0224] pass Figure 8 and Figure 9In comparison of reactive power RMSE, the VSG power decoupling controller based on hyperlocal model of the present invention has a smaller RMSE and enjoys better power decoupling performance than the traditional VSG grid-connected control.

[0225] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention. The scope of protection claimed by the appended claims and their equivalents is defined.

Claims

1. A grid-connection method for an energy storage converter based on virtual synchronous generator control, characterized in that, Includes the following steps: 11) Design adaptive rules for virtual inertia and damping coefficient in the active loop of the VSG controller; 12) Perform adaptive adjustment: Based on the adaptive rules of virtual inertia and damping coefficient, adaptively adjust the virtual inertia and damping coefficient; 13) Design a VSG power decoupling controller based on hyperlocal model cooperative control; 14) Power smooth tracking and effective decoupling control of active and reactive power: In grid-connected mode, the active power is calculated using the current and voltage at the grid connection point and used as the input of the active power loop of the VSG controller. After adjustment by the virtual inertia and damping coefficient adaptive rules, the active power smooth tracking is achieved. Based on the reactive power calculated at the grid connection point, it is used as the input of the VSG power decoupling controller based on superlocal model cooperative control. The macro variables are designed with the reactive power deviation as the control objective to keep the reactive power stable and achieve robust control that is insensitive to line impedance parameters.

2. The grid connection method for an energy storage converter based on virtual synchronous generator control according to claim 1, characterized in that, The adaptive rules for virtual inertia and damping coefficient in the active loop of the designed VSG controller include the following steps: 21) Set the adaptive rules for virtual inertia and damping coefficient in the active loop of the VSG controller as follows: In the formula, w, w n w d , These represent the angular frequency of the energy storage converter connected to the grid, the rated angular frequency of the energy storage converter connected to the grid, the frequency deviation of the energy storage converter connected to the grid, and the rate of change of angular frequency during the grid connection process, respectively. ΔP is the power deviation at the grid connection point, and P... ref P is the active power reference value for the virtual synchronous generator. e The actual active power of the virtual synchronous generator is denoted by D; the damping coefficient of the VSG is denoted by J; and the virtual inertia of the VSG is denoted by J. 22) Set the angular frequency ω to be at ω when the active power is disturbed. n Damped oscillations occur up and down. 221) When w > w n hour, when If the value is greater than 0, the virtual inertia J is increased to suppress the growth of angular frequency w. when If the value is less than 0, the virtual inertia J is reduced to induce w to recover to w. n ; 222) When w <w n hour, when If the value is less than 0, the virtual inertia J is increased to suppress the reverse growth of the angular frequency w. when If the value is less than 0, the virtual inertia J is reduced to induce w to recover to w. n ; 223) When w > w n hour, when If the value is greater than 0, the damping coefficient D is increased to accelerate the decay of the angular frequency ω oscillation. when If the value is less than 0, the damping coefficient D is reduced to avoid excessive energy dissipation; 224) When w <w n hour, when If the value is less than 0, the damping coefficient D is increased to accelerate the decay of the reverse oscillation at angular frequency ω. when If the value is less than 0, the damping coefficient D is reduced to avoid excessive energy dissipation.

3. The grid connection method for an energy storage converter based on virtual synchronous generator control according to claim 1, characterized in that, The adaptive adjustment includes the following steps: 31) Adaptive adjustment of the VSG virtual inertia J and damping coefficient D is given by the following expression: Where: J0 represents the initial value of the virtual inertia, k1 represents the adaptive adjustment coefficient of the virtual inertia, D0 is the initial value of the damping coefficient, k2 represents the adaptive adjustment coefficient of the damping coefficient, J is the VSG virtual inertia, D is the VSG damping coefficient, and w d and |w d | represents the absolute value of the angular frequency deviation of the energy storage converter connected to the grid. Let be the rate of change of angular frequency deviation during the grid connection process of the energy storage converter, and e be an exponential function; 32) Set the rotor motion equation in the active loop of the VSG controller as follows: 321) Substituting equation (2) into the rotor motion equation of (3), we get: In the formula, w n ω and ω are the rated angular frequency and the grid-connected angular frequency of the energy storage converter, respectively. P ref P is the active power reference value for VSG. e This is the actual power of the VSG; 322) Let the difference between the reference value and the actual value of active power be ΔP, which is the power deviation at the grid connection point; Through derivation, we obtain: 323) For w d Find the derivative of and solve for it. Then we have: 324) When the system is in steady state, the angular frequency deviation w of the energy storage converter connected to the grid d =0, the denominator of equation (6) is zero, the equation is invalid, therefore its denominator is rationalized as: Equation (7) represents the rate of change of the power deviation ΔP at the grid connection point and the angular frequency deviation during the grid connection process of the energy storage converter when the active power is disturbed. The dynamic relationship between them; When active power is disturbed, the VSG controller adjusts the VSG virtual inertia and damping coefficient in the active power loop to reduce angular frequency fluctuations.

4. The grid connection method for an energy storage converter based on virtual synchronous generator control according to claim 1, characterized in that, The design of the VSG power decoupling controller based on hyperlocal model cooperative control includes the following steps: 41) Due to the non-purely inductive nature of the line impedance, the transmitted active power is controlled not only by the power angle δ but also by the voltage amplitude E. That is, there is strong coupling between active and reactive power. The small-signal model near the steady-state operating point δ0 and E0 is expressed as: From equation (8), we know that If δ0≠0, that is, k′ pe ≠0,k′ qδ ≠0, the phase of the grid voltage is the reference phase, δ0 and E0 are the power angle and voltage amplitude at the steady operating point, and Z g U is the line impedance between the grid connection point and the power grid. g θ is the grid voltage amplitude, θ is the line impedance angle, and ΔP is the line impedance angle. e For small-signal analysis, the active power small disturbance deviation, ΔQ e For small-signal analysis, the reactive power small disturbance deviation is represented by sin and cosine trigonometric functions, Δδ is the power angle deviation, ΔE is the voltage amplitude deviation, and k is the voltage amplitude deviation. pδ k is the active power coefficient for the power angle deviation. qδ The reactive power coefficient of the power angle deviation, k pe k is the active power coefficient for voltage amplitude deviation. qe Reactive power factor of voltage amplitude deviation; 42) Even if the line impedance is purely inductive, i.e., θ = 90° and Z g =X g There is still coupling between active power and reactive power; Extract k from equation (8) pe and k qδ Dividing the two, we get: In VSG control, the influence of the power angle on reactive power is much greater than the influence of voltage amplitude. That is, the coupling effect of active power change on reactive power is greater, while the influence of reactive power change on active power is negligible. 43) First, measure the reactive power output of the VSG, then perform low-pass filtering to make the bandwidth of the VSG power control loop much smaller than the bandwidth of its voltage and current control loop. Then: In the formula: Q em ω represents the reactive power after passing through the low-pass filter. c Here, is the cutoff frequency of the low-pass filter, s is the Laplace operator, and Q... e This represents the actual reactive power. The time-domain small-signal model of equation (10) is: Where: ΔQ em This refers to the reactive power deviation caused by changes in active power. The derivative of reactive power deviation; Based on equations (8) and (11), the voltage amplitude fluctuation when reactive power deviation exists is taken as the compensation voltage, and the dynamic equation of reactive power deviation of the VSG power decoupling controller is established as follows: In the formula, E comp This is the voltage compensation amount output by the VSG power decoupling controller. The power decoupling controller is designed to decouple the active and reactive power of the VSG, meaning that when the active power command changes abruptly, the reactive power deviation remains at zero. To achieve this, the macro variable ψ... e Designed as follows: ψ e =λ1ε+λ2∫ε (13) In the formula, Let λ1 be the expected reactive power deviation, λ2 be the proportional coefficient, and ∫ε be the integral of ε. 44) Design the dynamic evolution equations for cooperative control, and have In the formula, T e The reactive power deviation convergence time parameter. For the macro variable ψ in equation (14) e Differentiate; The derived cooperative control law E of the VSG power decoupling controller output comp for: The cooperative control law E output by the VSG power decoupling controller comp As a voltage compensation combined with the VSG reactive power control loop, power decoupling is achieved; 45) For a system with a single input and a single output, the algebraic differential equation is as follows: E(t,y,....y (n) ,u,....,u (τ) )=0 (16) In the formula, t is the time variable, u and y are the system input and output, respectively, E() is a differentiable function, and y ( n ) It is the nth derivative of the system output, u (τ) It is the τ-th derivative of the system input. Equation (16) can be written in hyperlocal model form, and we have: y (n) (t)=F(t)+αu(t) (17) In the formula, y (n) (t) is the nth derivative of the system output at time t, where n represents the system order, usually taken as 1, α is the scaling factor of the system input, the constantly updated variable F(t) represents the known part, unknown part and various possible disturbances of the system, and the estimation of variable F(t) is determined by using the system input and output data, u(t) is the system input at time t; 46) Based on the dynamic equation of reactive power deviation of the VSG power decoupling controller, in order to get rid of its sensitive dependence on line impedance and power angle changes, a hyperlocal model of VSG reactive power deviation is established, and we have: In the formula,

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