A sliding mode control method and system for VSG inverter power supply based on disturbance estimation

Abstract

This invention provides a sliding mode control method and system for VSG inverter power supplies based on disturbance estimation, relating to the field of VSG-based inverter control technology. In the outer loop control layer based on VSG, an active-frequency control loop with a phase angle regulator and a reactive-voltage control loop with an amplitude regulator are established. Then, a small-signal model is established for the grid-connected inverter system under VSG control, and transient stability analysis is performed using eigenvalue analysis. In the inner loop control layer based on SMC, considering the uncertainty of the VSG inverter output voltage under complex environments, a sliding mode disturbance observer is established, and disturbance estimates are fed back, thus establishing a sliding mode controller based on disturbance estimation. This invention, through the combination of inner and outer control layers, can effectively solve the problems of low inertia and weak damping characteristics in new power systems, while improving the robustness of the VSG inverter control system to uncertain disturbances, providing a certain theoretical basis and engineering application for practical inverter power supply control.

Description

Technical Field

[0001] This invention relates to the field of VSG-based inverter control technology, specifically to a sliding mode control method and system for VSG inverter power supplies based on disturbance estimation. Background Technology

[0002] Large-scale renewable energy primarily connects to the grid via power electrification interface inverters, resulting in low inertia and weak damping characteristics in the new power system. This further weakens the system's transient response performance, leading to the widespread application of Virtual Synchronous Generator (VSG) control technology, which mimics synchronous generators to give inverters similar characteristics. Currently, research mainly focuses on power frequency characteristics, virtual impedance power decoupling, adaptive damping inertia, fault ride-through methods, and multi-VSG clusters. However, most of the aforementioned VSG control research still uses traditional voltage and current dual-loop control as the underlying control strategy, supplemented by a relatively ideal linear PID control method. Although this dual-loop underlying control structure is simple to design and easy to implement, it still faces limitations such as slow response speed and poor robustness when the actual controlled system has nonlinear and strongly coupled characteristics.

[0003] Sliding mode variable structure control (SMC), as a nonlinear control method, exhibits strong robustness in dealing with uncertainties such as parameter perturbations, unmodeled dynamics, and external disturbances. Most existing work on sliding mode control related to VSG control focuses on improving voltage-current dual-loop control, failing to fully integrate the inertial support capability of VSG control with the disturbance rejection capability of sliding mode control to effectively address the disturbance rejection requirements of complex scenarios such as distributed power inverters operating on and off the grid, thus possessing certain limitations. Therefore, simultaneously considering the design of an outer-loop control layer based on VSG and an inner-loop control layer based on SMC will be more challenging and have greater practical engineering significance. Summary of the Invention

[0004] The purpose of this invention is to provide a sliding mode control method and system for VSG inverter power supply based on interference estimation, which is used to solve the problems that existing technologies have limitations in effectively dealing with the anti-interference requirements of complex scenarios such as distributed power inverters being connected to and disconnected from the grid. It can effectively solve the problems of low inertia and weak damping characteristics of new power systems, while improving the robustness of the VSG inverter control system to uncertain interference.

[0005] To achieve the above objectives, in a first aspect, the present invention provides a sliding mode control method for VSG inverter power supplies based on disturbance estimation, comprising:

[0006] Step 1: Establish a VSG-based inverter grid-connected system, which includes a VSG-based outer loop control layer, an SMC-based inner loop control layer, power calculation, inverter circuit, and grid side.

[0007] Step 2: Establish an active-frequency control loop with a phase angle regulator and a reactive-voltage control loop with an amplitude regulator in the outer loop control layer;

[0008] Step 3: Establish a small-signal model of the inverter grid-connected system in the outer loop control layer, and perform transient stability analysis using the eigenvalue analysis method;

[0009] Step 4: Establish a mathematical model of the inverter power supply in the inner loop control layer and derive the state-space equation of the inverter power supply.

[0010] Step 5: Based on the state-space equations of the inverter power supply, establish a sliding mode disturbance observer for the unknown composite disturbances in the inner loop control layer;

[0011] Step 6: Prove the stability of the sliding mode disturbance observer;

[0012] Step 7: Based on the state-space equations of the inverter power supply and the sliding mode disturbance observer, establish a sliding mode controller in the inner loop control layer;

[0013] Step 8: Verify the stability of the sliding mode controller.

[0014] According to the VSG inverter power supply sliding mode control method based on disturbance estimation provided by the present invention, step 2 specifically includes:

[0015] Based on the active-frequency control principle of the VSG (Dynamic Synchronous Generator) according to the rotor motion equation of the simulated synchronous generator, an active-frequency control loop with a phase angle adjuster is established in the outer loop control layer of the VSG. The active-frequency control loop is as follows:

[0016]

[0017] in, , ;

[0018] In the formula, , and These are virtual mechanical power, rated active power, and output active power, respectively. For virtual rotational inertia, This is the virtual damping coefficient. , These represent the angular frequency and phase of the inverter output voltage, respectively. The phase of the reference voltage, The rated angular frequency, The active power-frequency droop factor is... Indicates the phase angle adjustment amount. This represents the phase of the inverter output voltage after filtering. The phase difference of the grid voltage. and The relevant PI parameters for phase angle adjustment;

[0019] Based on the reactive power-voltage control principle of the simulated synchronous generator excitation system, a reactive power-voltage control loop with an amplitude regulator is established in the outer loop control layer of the VSG. The reactive power-voltage control loop is as follows:

[0020]

[0021] in, ;

[0022] and These are the reactive power-voltage regulation coefficient and the droop coefficient, respectively. and These are the rated reactive power and the output reactive power, respectively. , and These are the rated voltage amplitude, the inverter output voltage amplitude, and the reference voltage amplitude, respectively. This is the amplitude adjustment amount. This represents the amplitude of the inverter output voltage after filtering. The magnitude of the grid voltage. and These are the relevant PI parameters for amplitude adjustment.

[0023] According to the VSG inverter sliding mode control method based on interference estimation provided by the present invention, step 3 involves establishing a small-signal model of the inverter grid-connected system in the outer loop control layer, including:

[0024] The state equations of the main circuit of the inverter power supply are as follows:

[0025]

[0026] In the formula, For filtering resistors, For filtering inductors, For filtering capacitors, For grid-side resistance, For grid-side inductance, , The output voltage of the inverter after filtering is respectively Shaft component, output voltage Axial components, , These are the output currents of the inverter after filtering. Shaft component, output current Axial components, , The current output by the inverter Axis components, current Axial components, , The voltages on the grid side are respectively Axis components, voltage Axial components, , The voltage output by the inverter Axis components, voltage Axial components;

[0027] Linearizing the state equations of the inverter power supply main circuit, we obtain its small-signal model as follows:

[0028]

[0029] In the formula, Represents small variables that represent linearization;

[0030] Linearizing the power calculation, we obtain its small-signal model as follows:

[0031]

[0032] Linearizing the active-frequency control loop, its small-signal model is obtained as follows:

[0033]

[0034] Linearizing the reactive power-voltage control loop yields its small-signal model as follows:

[0035]

[0036] Linearizing the power grid side, its small-signal model is obtained as follows:

[0037]

[0038] The final small-signal model of the inverter grid-connected system is as follows:

[0039]

[0040] in, , and These are the state variables and the state matrix, respectively.

[0041] According to the VSG inverter power supply sliding mode control method based on disturbance estimation provided by the present invention, step 3 involves performing transient stability analysis using eigenvalue analysis, including:

[0042] The eigenvalues ​​and distribution diagram of the state matrix were obtained using Matlab software. Based on the distribution of the eigenvalues, the effects of virtual moment of inertia, virtual damping coefficient, filter resistance, and filter inductance on the transient stability of the inverter grid-connected system were analyzed.

[0043] According to the VSG inverter power supply sliding mode control method based on disturbance estimation provided by the present invention, step 4 specifically includes:

[0044] According to Kirchhoff's laws, establish The mathematical model of the inverter power supply in the coordinate system is as follows:

[0045]

[0046] in, , ;

[0047] In the formula, , For state variables, The voltage output by the inverter Axial component or Axial components, For disturbance, The output voltage of the inverter after filtering Axial component or Axial components;

[0048] Therefore, the state-space equation of the inverter power supply is derived as follows:

[0049]

[0050] in, , , , , ;

[0051] In the formula, This represents the perturbation of unknown parameters caused by the filter resistor, filter inductor, and filter capacitor. The output current of the inverter after filtering Axial component or Axial components.

[0052] According to the VSG inverter power supply sliding mode control method based on disturbance estimation provided by the present invention, step 5 specifically includes:

[0053] Define the state estimation error as:

[0054]

[0055] in, and They are respectively and The observed values, and They are respectively and The observation error;

[0056] Select the sliding surface as:

[0057]

[0058] Based on the state-space equations of the inverter power supply, a sliding mode disturbance observer is established for the unknown composite disturbance in the inner loop control layer, and the disturbance estimate is obtained; the sliding mode disturbance observer is:

[0059]

[0060] in, , ;

[0061] In the formula, For disturbance The estimated value, As an auxiliary quantity, For positive integers, It is a symbolic function.

[0062] According to the VSG inverter power supply sliding mode control method based on disturbance estimation provided by the present invention, step 6 specifically includes:

[0063] The Lyapunov function is selected as follows:

[0064]

[0065] Taking the derivative of the Lyapunov function, we get:

[0066]

[0067] if and Then, according to the derivative of the Lyapunov function, we can obtain:

[0068]

[0069] In the formula, and Let be any positive constant. It is a positive number;

[0070] Based on Lyapunov stability theory, if and only if and hour, Then we can get This completes the stability proof of the sliding mode disturbance observer.

[0071] According to the VSG inverter power supply sliding mode control method based on disturbance estimation provided by the present invention, step 7 specifically includes:

[0072] The voltage tracking error is defined as:

[0073]

[0074] Select the linear sliding surface as:

[0075]

[0076] In the formula, Here, c is the reference voltage, and c > 0.

[0077] A sliding mode controller is established based on the disturbance estimates. The sliding mode controller is as follows:

[0078]

[0079] in, For parameters, .

[0080] According to the VSG inverter power supply sliding mode control method based on disturbance estimation provided by the present invention, step 8 specifically includes:

[0081] The Lyapunov function is selected as follows:

[0082]

[0083] Taking the derivative of the Lyapunov function, we get:

[0084]

[0085] if , Substituting this into the sliding mode controller, we can obtain the following from the derivative of the Lyapunov function:

[0086]

[0087] In the formula, For parameters, ;

[0088] Based on Lyapunov stability theory, then Then, based on the voltage tracking error and the linear sliding surface, the stability of the sliding mode controller is proven.

[0089] Secondly, the present invention also provides a VSG inverter power supply sliding mode control system based on interference estimation, comprising:

[0090] The first module is used to establish a VSG-based inverter grid-connected system. The inverter grid-connected system includes a VSG-based outer loop control layer, an SMC-based inner loop control layer, power calculation, inverter circuit, and grid side.

[0091] The second module is used to establish an active-frequency control loop with a phase angle regulator and a reactive-voltage control loop with an amplitude regulator in the outer loop control layer.

[0092] The analysis module is used to establish a small-signal model of the inverter grid-connected system at the outer loop control layer and perform transient stability analysis using the eigenvalue analysis method.

[0093] The derivation module is used to establish a mathematical model of the inverter power supply in the inner loop control layer and derive the state-space equations of the inverter power supply.

[0094] The third module is used to establish a sliding mode disturbance observer for unknown composite disturbances in the inner loop control layer based on the state-space equations of the inverter power supply.

[0095] The first proof module is used to prove the stability of the sliding mode disturbance observer;

[0096] The fourth module is used to establish a sliding mode controller in the inner loop control layer based on the state-space equations of the inverter power supply and the sliding mode disturbance observer.

[0097] The second proof module is used to prove the stability of the sliding mode controller.

[0098] The technical solution of the present invention has at least the following technical effects:

[0099] This invention considers both the low inertia and weak damping characteristics of novel power systems and the robustness of traditional dual-loop control, providing a sliding mode control method and system for VSG inverters based on disturbance estimation. By combining an outer-loop control layer based on VSG and an inner-loop control layer based on SMC, it effectively addresses the disturbance rejection requirements of complex scenarios such as grid connection and disconnection of distributed power inverters. In the outer-loop control layer of VSG, an active-frequency control loop with a phase angle regulator and a reactive-voltage control loop with an amplitude regulator are established. The impact of key parameters is analyzed through small-signal transient stability, effectively achieving pre-synchronization in grid-connected scenarios. In the inner-loop control layer based on SMC, a sliding mode disturbance observer for the VSG inverter is established, and the disturbance estimate is fed back to the controlled system, i.e., the state-space equation of the inverter, completing the design of the sliding mode controller based on disturbance estimation. This effectively improves the robustness of the VSG inverter control system to uncertain disturbances, providing a theoretical basis and engineering application for practical inverter control. Attached Figure Description

[0100] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0101] In the attached diagram:

[0102] Figure 1 This is a block diagram of a VSG-based inverter grid-connected system.

[0103] Figure 2 The equivalent circuit diagram of the main circuit of the VSG inverter;

[0104] Figure 3 A distribution diagram of the system's eigenvalues;

[0105] Figure 4 virtual rotational inertia and virtual damping coefficient A schematic diagram illustrating the impact on eigenvalues;

[0106] Figure 5 For filter resistors and filter inductor A schematic diagram illustrating the impact on eigenvalues;

[0107] Figure 6 The frequency response diagrams of the traditional V / I loop and the proposed strategy control are shown with and without interference.

[0108] Figure 7 Transient analysis diagram of inverter output voltage initialization under traditional V / I loop control;

[0109] Figure 8 Transient analysis diagram of inverter output voltage initialization under the proposed strategy control;

[0110] Figure 9 The frequency response diagram is shown under the proposed strategy control with / without pre-synchronization.

[0111] Figure 10 The transient process of voltage initialization with and without pre-synchronization is shown in the figure under the control of the proposed strategy.

[0112] Figure 11 The grid-connected voltage analysis diagram is shown under the proposed strategy control without pre-synchronization.

[0113] Figure 12 The grid-connected voltage analysis diagram is shown under the proposed strategy control with pre-synchronization.

[0114] Figure 13 This is a flowchart of a sliding mode control method for VSG inverter power supplies based on disturbance estimation. Detailed Implementation

[0115] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0116] The following detailed description of some embodiments of the present invention will be provided in conjunction with the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0117] Please see Figure 13 This invention provides a sliding mode control method for VSG inverter power supplies based on disturbance estimation, comprising:

[0118] Step 1: Establish a VSG-based inverter grid-connected system. This system includes a VSG-based outer loop control layer, a sliding mode control (SMC)-based inner loop control layer, power calculation, inverter circuit, grid side, PWM modulation, and DC voltage source U. dc Loads, etc., DC voltage source U dc It provides stable DC power, which is then converted into AC power by an inverter, and the entire circuit forms an inverter circuit.

[0119] like Figure 1 As shown, the outer loop control layer (VSG control layer) based on the VSG generates the reference voltage. The signal is transmitted to the SMC-based inner loop control layer (sliding mode control layer), which generates control signals for inverter PWM modulation. . The amplitude of the voltage control signal. This refers to the phase of the voltage control signal.

[0120] Step 2: Establish an active-frequency control loop with a phase angle regulator and a reactive-voltage control loop with an amplitude regulator in the outer loop control layer;

[0121] Specifically, based on the VSG active-frequency control principle of the simulated synchronous generator rotor motion equation, an active-frequency control loop with a phase angle adjuster is established in the outer loop control layer of the VSG. This active-frequency control loop is as follows:

[0122]

[0123] in, , and These are virtual mechanical power, rated active power, and output active power, respectively. For virtual rotational inertia, This is the virtual damping coefficient. , These represent the angular frequency and phase of the inverter output voltage, respectively. The phase of the reference voltage, The rated angular frequency, The active power-frequency droop factor is... Indicates angular frequency deviation. This is the phase angle adjustment amount; , is the phase of the inverter output voltage after filtering. Phase with grid voltage difference; and These are the relevant PI parameters for phase angle adjustment.

[0124] Specifically, based on the reactive power-voltage control principle of the simulated synchronous generator excitation system, a reactive power-voltage control loop with an amplitude regulator is established in the outer loop control layer of the VSG. This reactive power-voltage control loop is as follows:

[0125]

[0126] in, and These are the reactive power-voltage regulation coefficient and the droop coefficient, respectively. and These are the rated reactive power and the output reactive power, respectively. , and These are the rated voltage amplitude, the inverter output voltage amplitude, and the reference voltage amplitude, respectively. Indicates the amplitude adjustment amount; This indicates the amplitude of the inverter output voltage after filtering. Amplitude of grid voltage difference; and These are the relevant PI parameters for amplitude adjustment.

[0127] Step 3: Establish a small-signal model of the inverter grid-connected system under VSG control in the outer loop control layer, and perform transient stability analysis using the eigenvalue analysis method;

[0128] Specifically, establish Figure 1 The equivalent circuit diagram of the main circuit in the overall system structure diagram of the VSG-based inverter grid-connected system is shown below. Then, as shown... Figure 2As shown, based on this equivalent circuit diagram, the state equations of the inverter power supply main circuit are established. Step 3 specifically includes:

[0129] S31: The state equations for the main circuit of the inverter power supply are as follows:

[0130]

[0131] Among them, subscript and Representing the corresponding quantities Axial components and Axial components, For grid-side resistance, For grid-side inductance, and These represent the output voltage and output current of the inverter after filtering, respectively. and These represent the voltage and current on the grid side, respectively. and These represent the voltage and current output by the inverter, respectively.

[0132] S32: Linearizing the state equations of the inverter power supply main circuit yields its small-signal model:

[0133]

[0134] in, Represents a small variable that represents linearization.

[0135] S33: Linearizing the power calculation yields its small-signal model as follows:

[0136]

[0137] S34: Linearizing the active-frequency control loop yields its small-signal model as follows:

[0138]

[0139] S35: Linearizing the reactive-voltage control loop yields its small-signal model as follows:

[0140]

[0141] S36: Linearizing the grid side yields its small-signal model as follows:

[0142]

[0143] S37: Combining the above steps, the small-signal model of the inverter grid-connected system under VSG control can be obtained as follows:

[0144]

[0145] in, , The subscript represents the small variable representing linearization. and Representing the corresponding quantities Axial components and Axial components, and These are the state variables and the state matrix, respectively.

[0146] Transient stability analysis is performed using eigenvalue analysis, including:

[0147] The eigenvalues ​​and distribution diagram of the state matrix were obtained using Matlab software. Based on the distribution of the eigenvalues, the effects of the virtual moment of inertia, virtual damping coefficient, filter resistor, and filter inductor on the transient stability of the inverter grid-connected system were analyzed. A detailed description will follow.

[0148] Step 4: Establish a mathematical model of the inverter power supply in the inner loop control layer and derive the state-space equation of the inverter power supply.

[0149] Specifically, step 4 includes:

[0150] S41: Considering Without coupling in the coordinate system, and combining Kirchhoff's laws, establish The mathematical model of the inverter power supply in the coordinate system is as follows:

[0151]

[0152] in , and This represents the inverter's output voltage, the inverter's filtered output voltage, and the current. Axial component or Axial components, or Due to symmetry, we will only consider the following. In the case of the shaft, we use respectively , and express , and Similarly, for ease of expression, we use... express .

[0153] S42: Let the state variable... State variables The mathematical model of the inverter power supply in step S41 can be written as:

[0154]

[0155] S43: For ease of analysis, define... The state-space equation of the inverter power supply circuit can then be obtained as follows:

[0156]

[0157] in, , , , , ;

[0158] in For disturbance, Indicated by the filter resistor Filter inductor and filter capacitor The resulting perturbation of unknown parameters.

[0159] Step 5: Based on the state-space equations of the inverter power supply, establish a sliding mode disturbance observer for the unknown composite disturbances in the inner loop control layer;

[0160] Specifically, step 5 includes:

[0161] S51: Define the state estimation error as:

[0162]

[0163] in, and They are respectively and The observed values, and They are respectively and The observation error.

[0164] S52: Select the sliding surface as:

[0165]

[0166] S53: Then, based on the state-space equations of the inverter power supply in S4, a sliding mode disturbance observer for the unknown composite disturbance can be established, and the disturbance estimate can be obtained. The sliding mode disturbance observer is:

[0167]

[0168] in, It is a disturbance The estimated value, It is a positive constant and symbolic functions The auxiliary amount.

[0169] Step 6: Prove the stability of the sliding mode disturbance observer;

[0170] Specifically, step 6 includes:

[0171] S61: Select the Lyapunov function as:

[0172]

[0173] S62: Differentiating the Lyapunov function in S61 yields:

[0174]

[0175] S63: If and ,in and Let be any positive constant, then the derivative of the Lyapunov function in S62 can be calculated as follows:

[0176]

[0177] S64: Based on the calculation results in S63, and using the Lyapunov stability theory, if and only if and hour, You can get This completes the stability proof of the sliding mode disturbance observer.

[0178] Step 7: Based on the state-space equations of the inverter power supply and the sliding mode disturbance observer, establish a sliding mode controller in the inner loop control layer;

[0179] Specifically, step 7 includes:

[0180] S71: Define voltage tracking error as:

[0181]

[0182] S72: Select the linear sliding surface as:

[0183]

[0184] In the formula, Here, c is the reference voltage, and c > 0.

[0185] S73: Then, based on the approach rate design method and combined with the disturbance estimate, the sliding mode controller can be established as follows:

[0186]

[0187] in, For parameters, .

[0188] It should be noted that the establishment of a sliding mode controller is not limited to the isorheological approach law, but can also be based on the exponential approach law. or power-law approach To achieve better control performance. , For parameters.

[0189] Step 8: Verify the stability of the sliding mode controller.

[0190] Specifically, step 8 includes:

[0191] S81: Select the Lyapunov function as:

[0192]

[0193] S82: Differentiating the Lyapunov function in S81 yields:

[0194]

[0195] S83: Consider the observation error in S5 ,in For parameters, If the parameter Substituting this into the sliding mode controller in S7, the derivative of the Lyapunov function in S82 can be calculated as follows:

[0196]

[0197] S84: Based on the calculation results in S83, and using Lyapunov stability theory, then... Then, based on the definition of voltage tracking error in S71 and the selection of the linear sliding surface in S72, the output voltage can track the reference voltage generated by the upper outer loop control layer, thus completing the stability proof of the sliding mode controller.

[0198] Based on the same inventive concept, another embodiment of the present invention provides a VSG inverter power supply sliding mode control system based on disturbance estimation. This system corresponds to the method of the foregoing embodiment and includes:

[0199] The first module is used to establish a VSG-based inverter grid-connected system. The inverter grid-connected system includes a VSG-based outer loop control layer, an SMC-based inner loop control layer, power calculation, inverter circuit, and grid side. The inverter circuit includes a DC voltage source, inverter, and filter, etc.

[0200] The second module is used to establish an active-frequency control loop with a phase angle regulator and a reactive-voltage control loop with an amplitude regulator in the outer loop control layer.

[0201] The analysis module is used to establish a small-signal model of the inverter grid-connected system at the outer loop control layer and perform transient stability analysis using the eigenvalue analysis method.

[0202] The derivation module is used to establish a mathematical model of the inverter power supply in the inner loop control layer and derive the state-space equations of the inverter power supply.

[0203] The third module is used to establish a sliding mode disturbance observer for unknown composite disturbances in the inner loop control layer based on the state-space equations of the inverter power supply.

[0204] The first proof module is used to prove the stability of the sliding mode disturbance observer;

[0205] The fourth module is used to establish a sliding mode controller in the inner loop control layer based on the state-space equations of the inverter power supply and the sliding mode disturbance observer.

[0206] The second proof module is used to prove the stability of the sliding mode controller.

[0207] The following are specific embodiments of the present invention.

[0208] Example 1

[0209] In this embodiment, transient stability analysis was performed using eigenvalue analysis based on the established small-signal model of the inverter grid-connected system under VSG control. The relevant system parameters are shown in Table 1.

[0210] Table 1. Relevant Parameter Table

[0211]

[0212] Based on the relevant parameters in Table 1, the state matrix is ​​solved using Matlab software. The eigenvalues ​​and distribution plots, such as Figure 3 As shown. By Figure 3 Analysis shows that the system's eigenvalues ​​are all distributed in the left half of the complex plane, including the eigenvalues... ~ Therefore, the system is transiently stable under appropriate disturbances.

[0213] Then, considering the complexity and flexibility of the VSG inverter power supply control system parameters, the virtual moment of inertia is analyzed based on the distribution of eigenvalues. Virtual damping coefficient Filter resistor and filter inductor The influence of parameters on the transient stability of the system, such as Figure 4 , Figure 5 As shown.

[0214] Figure 4 (a) is the moment of inertia. Increase from 0.1 to 10, Figure 4 (b) is the damping coefficient. Increasing the value from 0.1 to 25, the eigenvalue distribution is analyzed, and all values ​​lie in the left half of the complex plane, indicating that the system can maintain transient stability. Then, the eigenvalues ​​with larger variations are analyzed. , Increase Being close to the imaginary axis has a certain impact on system stability; while... Increase Moving away from the virtual axis can improve stability to some extent.

[0215] Figure 5 (a) is the filter resistor. From 0.1 Increase to 10 , Figure 5 (b) is the filter inductor. From 0.002 Increase to 0.1 Analyzing the distribution of eigenvalues, all of which lie in the left half of the complex plane, indicates that the system is transiently stable. Then, we analyze the eigenvalues ​​with larger variations. - , Increase - Moving away from the imaginary axis can improve the transient stability of the system to some extent, while... Increase - Being close to the imaginary axis has a certain impact on the transient stability of the system.

[0216] Example 2

[0217] This embodiment constructs an inverter power supply model in an isolated scenario and performs comparative simulations of VSG-based dual-loop control (referred to as "traditional V / I loop") and the VSG inverter power supply sliding mode control strategy based on disturbance estimation provided in this invention (referred to as "the proposed strategy"). The following operating conditions are set: load increases by 10kW at 0.2s; load decreases by 10kW at 0.35s; active power command increases by 30kW at 0.5s; active power command decreases by 30kW at 0.65s. To highlight the robustness of the proposed strategy to disturbances, comparisons with and without disturbances are set in the steady-state (0.4-0.45s) and transient (0.55-0.6s) periods. Then, the frequency and voltage waveforms are obtained through simulation, and voltage Fourier transform (FFT) analysis is performed on the initialization process (the transient process after system startup), as shown below. Figures 6-8 As shown.

[0218] from Figure 6 As can be seen from (a), due to the low line loss, both the traditional V / I loop control and the proposed strategy control can stabilize the system frequency near the rated frequency when there is no interference, which meets the power balance requirement. However, in the primary frequency regulation characteristics during initialization, load changes, and power command variations, the proposed strategy control exhibits a faster response speed and better transient performance than the traditional V / I loop control. Further comparative analysis is shown below. Figure 6 As shown in (b) with the addition of interference, the frequency response characteristics indicate that, under the same operating conditions and parameters, the control strategy proposed in this invention has strong robustness against composite interference.

[0219] Finally, comparative analysis Figure 7 and Figure 8 The voltage initialization transient process and its FFT analysis waveform show that the total harmonic distortion (THD) of the traditional V / I loop control and the proposed strategy control are 15.92% and 10.68%, respectively. Therefore, the VSG inverter power supply sliding mode control strategy based on disturbance estimation proposed in this invention exhibits faster response speed and stronger robustness during voltage transient processes.

[0220] Example 3

[0221] This embodiment verifies the effectiveness of the VSG inverter sliding mode control strategy based on interference estimation in the voltage fluctuation pre-synchronization grid connection process of the present invention. First, a grid-connected inverter model is built, and a comparative simulation of the proposed strategy control with and without pre-synchronization is performed, with the following operating conditions set: grid connection in 0.2s; grid voltage drops by 5% in 0.4s; grid voltage rises by 5% in 0.6s. Then, the frequency and voltage waveforms are obtained through simulation, and FFT analysis of the voltage during the grid connection process is performed as follows: Figures 9-12 As shown.

[0222] Through comparative analysis Figure 9 The frequency response curves generated by the proposed strategy control with and without pre-synchronization, as shown, indicate that after grid connection operation at 0.2s, the impact on the system from the proposed strategy control algorithm with pre-synchronization is significantly less than that from the proposed strategy control algorithm without pre-synchronization. Furthermore, during the initialization transient process and after grid connection voltage fluctuations, the frequency waveforms of the proposed strategy control algorithms with and without pre-synchronization almost overlap and both transition smoothly, demonstrating that the inverter control strategy provided by this invention has good pre-synchronization control performance during grid connection operation.

[0223] Through comparative analysis Figure 10The initial voltage response curves generated by the proposed strategy control with and without pre-synchronization are shown (since the parameters are completely identical, and phase B of the three-phase voltage is observed in both cases). It can be seen that initially, the waveforms with and without pre-synchronization are almost identical. However, with the pre-synchronization effect, the waveform with pre-synchronization gradually converges with the grid voltage, achieving the pre-synchronization effect. In contrast, the waveform without pre-synchronization shows a certain amplitude and phase angle difference with the grid voltage after the system stabilizes, thus verifying the effectiveness of pre-synchronization in the proposed strategy control. To further verify the grid-connected advantages of the proposed strategy control, voltage waveform diagrams were obtained and FFT analysis was performed, as follows... Figures 11-12 As shown.

[0224] By comparing and analyzing the grid-connected voltage waveforms generated by the proposed strategies for VSG inverters with and without pre-synchronization (e.g., ... Figure 11 (a) and Figure 12 (a) and its FFT analysis (as shown) Figure 11 (b) and Figure 12 As shown in (b), the proposed strategy without pre-synchronization resulted in a voltage THD of 2.06% during grid connection, while the voltage THD with pre-synchronization was 1.37%. This demonstrates that the VSG inverter sliding mode control strategy based on interference estimation in this invention not only has good robustness during voltage fluctuation pre-synchronization grid connection, but also effectively improves power quality.

[0225] Other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the embodiments disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein. It should be understood that the invention is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. A sliding mode control method for VSG inverter power supplies based on disturbance estimation, characterized in that, include: Step 1: Establish a VSG-based inverter grid-connected system, which includes a VSG-based outer loop control layer, an SMC-based inner loop control layer, power calculation, inverter circuit, and grid side. Step 2: Establish an active-frequency control loop with a phase angle regulator and a reactive-voltage control loop with an amplitude regulator in the outer loop control layer; Step 3: Establish a small-signal model of the inverter grid-connected system in the outer loop control layer, and perform transient stability analysis using the eigenvalue analysis method; Step 4: Establish a mathematical model of the inverter power supply in the inner loop control layer and derive the state-space equation of the inverter power supply. Step 5: Based on the state-space equation of the inverter power supply, establish a sliding mode disturbance observer for the unknown composite disturbance of the inner loop control layer; Step 6: Verify the stability of the sliding mode interference observer; Step 7: Based on the state-space equation of the inverter power supply and the sliding mode disturbance observer, establish a sliding mode controller in the inner loop control layer; Step 8: Verify the stability of the sliding mode controller; Step 4 specifically includes: According to Kirchhoff's laws, establish The mathematical model of the inverter power supply in the coordinate system is as follows: in, ; In the formula, x 1. x 2 is a state variable. u S This refers to the α-axis or β-axis component of the inverter's output voltage. d For disturbance, This refers to the α-axis or β-axis component of the inverter's filtered output voltage. R f For filtering resistors, L f For filtering inductors, C f For filtering capacitors; Therefore, the state-space equation of the inverter power supply is derived as follows: in, , ； In the formula, d 0 indicates the perturbation of unknown parameters caused by the filter resistor, filter inductor, and filter capacitor. The output current of the inverter after filtering is either the α-axis component or the β-axis component. Step 5 specifically includes: Define the state estimation error as: in, and They are respectively x 1 and x The observed value of 2, e 1 and e 2 are respectively x 1 and x 2% observation error; Select the sliding surface as: Based on the state-space equations of the inverter power supply, a sliding mode disturbance observer is established for the unknown composite disturbance of the inner loop control layer, and the disturbance estimate is obtained; the sliding mode disturbance observer is: in, ; In the formula, For disturbance d The estimated value, v As an auxiliary quantity, k 1 is a positive constant. It is a symbolic function; k 2 is a positive constant; Step 7 specifically includes: The voltage tracking error is defined as: Select the linear sliding surface as: In the formula, u r Here, c is the reference voltage, and c > 0. The sliding mode controller is established based on the interference estimate, and the sliding mode controller is as follows: in, k 3 is a parameter. k 3 > 0.

2. The VSG inverter power supply sliding mode control method based on disturbance estimation according to claim 1, characterized in that, Step 2 specifically includes: Based on the active-frequency control principle of the VSG (Dynamic Synchronous Generator) according to the rotor motion equation of the simulated synchronous generator, an active-frequency control loop with a phase angle adjuster is established in the outer loop control layer of the VSG. The active-frequency control loop is as follows: in, ; In the formula, P m , P n and P e These are virtual mechanical power, rated active power, and output active power, respectively. J Let D be the virtual moment of inertia and D be the virtual damping coefficient. These represent the angular frequency and phase of the inverter output voltage, respectively. The phase of the reference voltage, The rated angular frequency, k f The active power-frequency droop factor is... Indicates the phase angle adjustment amount. This represents the phase of the inverter output voltage after filtering. The phase difference of the grid voltage. and The relevant PI parameters for phase angle adjustment; Based on the reactive power-voltage control principle of the simulated synchronous generator excitation system, a reactive power-voltage control loop with an amplitude regulator is established in the outer loop control layer of the VSG. The reactive power-voltage control loop is as follows: in, ; K and k q These are the reactive power-voltage regulation coefficient and the droop coefficient, respectively, Q. n and Q e These are the rated reactive power and the output reactive power, E, respectively. n E v and E r These are the rated voltage amplitude, the inverter output voltage amplitude, and the reference voltage amplitude, respectively. This is the amplitude adjustment amount. This represents the amplitude of the inverter output voltage after filtering. E g The magnitude of the grid voltage. and These are the relevant PI parameters for amplitude adjustment.

3. The VSG inverter power supply sliding mode control method based on disturbance estimation according to claim 2, characterized in that, In step 3, establishing a small-signal model of the inverter grid-connected system at the outer loop control layer includes: The state equations of the inverter power supply main circuit are established as follows: In the formula, R f For filtering resistors, L f For filtering inductors, C f For the filter capacitor, R g L is the grid-side resistance. g For the grid-side inductance, U od U oq These represent the d-axis component and q-axis component of the inverter's filtered output voltage, respectively. od I oq These represent the d-axis component and q-axis component of the output current after filtering by the inverter, respectively. I fd , I fq These represent the d-axis and q-axis components of the inverter output current, respectively. gd U gq These are the d-axis component and q-axis component of the voltage on the grid side, respectively. U sd 、U sq These are the d-axis and q-axis components of the inverter output voltage, respectively. Linearizing the state equations of the inverter power supply main circuit, its small-signal model is obtained as follows: In the formula, Represents small variables that represent linearization; Linearizing the power calculation, its small-signal model is obtained as follows: Linearizing the active-frequency control loop, its small-signal model is obtained as follows: Linearizing the reactive-voltage control loop yields its small-signal model as follows: Linearizing the power grid side, its small-signal model is obtained as follows: The final small-signal model of the inverter grid-connected system is as follows: in, X S and A S These are the state variables and the state matrix, respectively.

4. The VSG inverter power supply sliding mode control method based on disturbance estimation according to claim 3, characterized in that, In step 3, transient stability analysis is performed using eigenvalue analysis, including: The eigenvalues ​​and distribution diagram of the state matrix were obtained using Matlab software. Based on the distribution of the eigenvalues, the effects of the virtual moment of inertia, virtual damping coefficient, filter resistor, and filter inductor on the transient stability of the inverter grid-connected system were analyzed.

5. The VSG inverter power supply sliding mode control method based on disturbance estimation according to claim 1, characterized in that, Step 6 specifically includes: The Lyapunov function is selected as follows: Taking the derivative of the Lyapunov function, we get: if and Then, according to the derivative of the Lyapunov function, we can obtain: In the formula, and Let k be any positive constant, and k2 be a positive constant. Based on Lyapunov stability theory, if and only if and hour, Then we can get This completes the stability proof of the sliding mode disturbance observer.

6. The VSG inverter power supply sliding mode control method based on disturbance estimation according to claim 1, characterized in that, Step 8 specifically includes: The Lyapunov function is selected as follows: Taking the derivative of the Lyapunov function, we get: if Substituting this into the sliding mode controller, we can obtain the derivative of the Lyapunov function as follows: In the formula, For parameters, ; Based on Lyapunov stability theory, then Then, based on the voltage tracking error and the linear sliding surface, the stability of the sliding mode controller is verified.

7. A sliding mode control system for a VSG inverter power supply based on disturbance estimation, characterized in that, The system employs the VSG inverter power supply sliding mode control method based on disturbance estimation as described in claim 1, wherein the system comprises: The first establishment module is used to establish a VSG-based inverter grid-connected system, which includes a VSG-based outer loop control layer, an SMC-based inner loop control layer, power calculation, inverter circuit and grid side; The second module is used to establish an active-frequency control loop with a phase angle regulator and a reactive-voltage control loop with an amplitude regulator in the outer loop control layer. The analysis module is used to establish a small-signal model of the inverter grid-connected system in the outer loop control layer and perform transient stability analysis using the eigenvalue analysis method. The derivation module is used to establish a mathematical model of the inverter power supply in the inner loop control layer and derive the state-space equation of the inverter power supply. The third module is used to establish a sliding mode disturbance observer for the unknown composite disturbance of the inner loop control layer based on the state space equation of the inverter power supply. The first proof module is used to prove the stability of the sliding mode interference observer. The fourth module is used to establish a sliding mode controller in the inner loop control layer based on the state-space equation of the inverter power supply and the sliding mode disturbance observer. The second proof module is used to prove the stability of the sliding mode controller.

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