Grid-connected distributed photovoltaic low-voltage ride-through inverter control method and system based on proxy sliding mode control

Abstract

The invention discloses a grid-connected distributed photovoltaic low-voltage ride-through inverter control method and system based on proxy sliding mode control, and the method comprises the steps: obtaining a controlled object, setting a control law of a controller, connecting the controlled object to a proxy object through the controller, carrying out the control through sliding mode control, and setting a control law of sliding mode control. The control law of the sliding mode control comprises the following steps: when the sliding surface is reached, an error signal of the sliding mode control is converged to zero; combining a control law of sliding mode control with a control law of the controller to obtain a control law based on proxy sliding mode control, and outputting a current reference value of a controlled object by the controller; the method comprises the following steps: acquiring a reactive current, performing inverter current inner loop control on the reactive current and a current reference value to obtain a voltage reference value output by an inverter, performing Park inverse change on the voltage reference value to obtain a three-phase voltage reference value, and generating a control signal through a pulse generator to control a controlled object. And the response speed and the control precision of the inverter are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of grid-connected distributed photovoltaic array inverter control, and in particular to a grid-connected distributed photovoltaic low voltage ride through inverter control method and system based on proxy sliding mode control. Background Art

[0002] Distributed photovoltaic arrays are often connected to the distribution network in a two-stage three-phase grid-connected form. This two-stage structure consists of a boost converter connected to the photovoltaic array and an inverter connected to the grid. When a fault occurs in the distribution network and causes the grid-side voltage to drop, the grid-connected photovoltaic array will be disconnected from the distribution network to achieve off-grid and self-protection. Low Voltage Ride Through (LVRT) of a grid-connected photovoltaic array means that when the voltage at the grid-connected point drops, the photovoltaic array can remain connected to the grid and even provide a certain amount of reactive power to the grid to support grid recovery until the grid returns to normal, thereby "crossing" the low voltage time (area). In recent years, the penetration rate of distributed photovoltaics has exploded, and the requirements for the low voltage ride-through capability of grid-connected distributed photovoltaic arrays have become increasingly higher. How to design a distributed photovoltaic grid-connected system control strategy to achieve safe and stable operation of distributed photovoltaic power generation clusters while having low voltage ride-through capabilities that comply with the "Technical Specifications for Photovoltaic Power Generation Grid-Connected Inverters" has become an urgent problem to be solved. During low voltage ride-through, in the voltage recovery phase after the fault is cleared, the grid-connected PV array often absorbs reactive power from the grid, resulting in unstable voltage recovery on the DC side of the PV array DC / AC inverter.

[0003] At present, the design of low voltage ride-through control strategy for grid-connected photovoltaic arrays focuses on adjusting and replacing the maximum power tracking strategy. There is no detailed consideration for the voltage recovery stage after the fault during low voltage ride-through. It only injects a corresponding amount of reactive current into the grid according to the voltage drop degree during low voltage ride-through according to the "Technical Specifications for Photovoltaic Power Grid-Connected Inverters". This results in that after the fault is cleared during the low voltage ride-through, the PID control of the grid-connected photovoltaic array inverter itself is still in a saturated state during the voltage recovery stage, the voltage recovery is slow, and it deviates from the target value unsteadily. Summary of the invention

[0004] In view of the above existing problems, the present invention is proposed.

[0005] Therefore, the present invention provides a grid-connected distributed photovoltaic low voltage ride-through inverter control method and system based on proxy sliding mode control to solve the problem that during the low voltage ride-through period, after the fault is cleared, in the voltage recovery stage, the PID control of the grid-connected photovoltaic array inverter itself is still in a saturated state, the voltage recovers slowly, and deviates unsteadily from the target value.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0007] In a first aspect, the present invention provides a method for controlling a grid-connected distributed photovoltaic low voltage ride-through inverter based on proxy sliding mode control, comprising:

[0008] Acquire a controlled object, set a control law of a controller, and connect the controlled object to a proxy object through the controller;

[0009] The proxy object is controlled by using sliding mode control, and a control law of the sliding mode control is set, wherein the control law of the sliding mode control includes that when a sliding surface is reached, an error signal of the sliding mode control converges to zero;

[0010] Combining the control law of the sliding mode control with the control law of the controller to obtain a control law based on a proxy sliding mode control, according to which the controller outputs a current reference value of the controlled object;

[0011] Acquire reactive current, obtain voltage reference value of inverter output by controlling the reactive current and current reference value according to the inverter current inner loop, perform Park inverse transformation on the voltage reference value to obtain three-phase voltage reference value, and generate control signal for the three-phase voltage reference value through a pulse generator to control the controlled object.

[0012] As a preferred solution of the grid-connected distributed photovoltaic low voltage ride through inverter control method based on proxy sliding mode control described in the present invention, wherein: setting the control law of the controller includes:

[0013] The control force of the controller is the difference between the proxy position and the controlled object position multiplied by the proportional gain of the controller plus the integral of the difference between the proxy position and the controlled object position multiplied by the integral gain of the controller plus the derivative of the difference between the proxy position and the controlled object position multiplied by the derivative gain of the controller.

[0014] As a preferred solution of the grid-connected distributed photovoltaic low voltage ride through inverter control method based on proxy sliding mode control described in the present invention, the sliding mode control includes:

[0015] The sliding surface is the weight coefficient of the sliding mode control multiplied by the derivative of the difference between the desired position and the proxy position plus the difference between the desired position and the proxy position;

[0016] When the agent's position reaches the sliding surface, the sliding surface is zero, the agent's position and velocity errors will decay exponentially to zero, and the agent converges to the desired trajectory and reaches the expected value.

[0017] As a preferred solution of the grid-connected distributed photovoltaic low voltage ride through inverter control method based on proxy sliding mode control described in the present invention, wherein: setting the control law of sliding mode control includes:

[0018] The control force of the sliding mode control is the control gain of the sliding mode control multiplied by the sign of the sliding surface;

[0019] When the sliding mode surface is reached, the error signal of the sliding mode control converges to zero, and the convergence time constant is the weight coefficient of the sliding mode control.

[0020] As a preferred solution of the grid-connected distributed photovoltaic low voltage ride through inverter control method based on proxy sliding mode control described in the present invention, the control law based on proxy sliding mode control includes:

[0021] Define auxiliary variables as:

[0022]

[0023] Modify the form of the controller and the control law of sliding mode control;

[0024] Applying the control force of the controller and sliding mode control to the agent, the equation of motion of the agent is expressed as:

[0025]

[0026] Among them, ρ and σ are auxiliary variables, x p is the agent position, x is the position of the controlled object, and x d is the desired position, K is the weight coefficient of sliding mode control, f SMC is the control force of sliding mode control, f PID is the control force of the controller, and m is the agent mass.

[0027] As a preferred solution of the grid-connected distributed photovoltaic low voltage ride through inverter control method based on proxy sliding mode control described in the present invention, it also includes:

[0028] Assume m = 0, expressed as:

[0029]

[0030] The functional relationship is defined as:

[0031]

[0032] Among them, sat(〃) is the saturation function, sgn(〃) is the sign function, y is the output, X and Y are constants, ω is the variable, and z is the input.

[0033] As a preferred solution of the grid-connected distributed photovoltaic low voltage ride through inverter control method based on proxy sliding mode control described in the present invention, it also includes:

[0034] The agent-based sliding mode control law is expressed as:

[0035]

[0036] Among them, ρ and σ are auxiliary variables, F is the control gain of sliding mode control, k d is the derivative gain of the controller, K is the weight coefficient of the sliding mode control, is the time derivative, k i is the integral gain of the controller, k p is the proportional gain of the controller.

[0037] In a second aspect, the present invention provides a grid-connected distributed photovoltaic low voltage ride-through inverter control system based on proxy sliding mode control, comprising:

[0038] A first control law setting module, used for acquiring a controlled object, setting a control law of a controller, and connecting the controlled object to a proxy object through the controller;

[0039] a second controller setting module, configured to control the proxy object using sliding mode control and set a control law of the sliding mode control, wherein the control law of the sliding mode control includes that an error signal of the sliding mode control converges to zero when a sliding surface is reached;

[0040] A combining module, used for combining the control law of the sliding mode control with the control law of the controller to obtain a control law based on a proxy sliding mode control, according to which the controller outputs a current reference value of the controlled object;

[0041] The control module is used to obtain reactive current, obtain a voltage reference value output by the inverter by controlling the reactive current and the current reference value according to the inverter current inner loop, perform a Park inverse transformation on the voltage reference value to obtain a three-phase voltage reference value, and generate a control signal for the three-phase voltage reference value through a pulse generator to control the controlled object.

[0042] In a third aspect, the present invention provides a computing device, comprising:

[0043] Memory and processor;

[0044] The memory is used to store computer executable instructions, and the processor is used to execute the computer executable instructions. When the computer executable instructions are executed by the processor, the steps of a grid-connected distributed photovoltaic low voltage ride-through inverter control method based on proxy sliding mode control are implemented.

[0045] In a fourth aspect, the present invention provides a computer-readable storage medium storing computer-executable instructions, which, when executed by a processor, implement the steps of the method for controlling a grid-connected distributed photovoltaic low-voltage ride-through inverter based on proxy sliding mode control.

[0046] Compared with the prior art, the present invention has the following beneficial effects: by introducing feedforward compensation, the present invention can quickly compensate for the mutual coupling part between the d-axis and q-axis currents output by the inverter, realize fast dynamic decoupling, thereby improving the response speed and control accuracy of the inverter. After a power grid fault occurs, especially during low voltage ride-through, the control strategy of the present application can support the smooth recovery of the voltage, avoiding the problems of slow and unstable voltage recovery that may be caused by traditional PID control. After the fault is cleared during the low voltage ride-through, the DC side voltage of the inverter is supported to be smoothly recovered, and there will be no sharp increase in voltage due to controller saturation. The DC side voltage of the inverter is stably restored to normal operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0048] Figure 1 A schematic diagram of the overall process logic of a grid-connected distributed photovoltaic low voltage ride through inverter control method based on proxy sliding mode control according to an embodiment of the present invention;

[0049] Figure 2 A DC link voltage controlled by PI in a control method for a grid-connected distributed photovoltaic low voltage ride through inverter based on proxy sliding mode control according to an embodiment of the present invention;

[0050] Figure 3 The invention discloses a DC link voltage based on proxy sliding mode control in a grid-connected distributed photovoltaic low voltage ride through inverter control method based on proxy sliding mode control according to an embodiment of the present invention. DETAILED DESCRIPTION

[0051] In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the drawings of the specification. Obviously, the described embodiments are part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary persons in the art without creative work should fall within the scope of protection of the present invention.

[0052] Example 1

[0053] Reference Figure 1 , which is an embodiment of the present invention, provides a grid-connected distributed photovoltaic low voltage ride through inverter control method based on proxy sliding mode control, comprising:

[0054] S100: Acquire the controlled object, set the control law of the controller, and connect the controlled object to the proxy object through the controller;

[0055] S200: Controlling the proxy object using sliding mode control, setting a control law of the sliding mode control, wherein the control law of the sliding mode control includes that when reaching a sliding surface, an error signal of the sliding mode control converges to zero;

[0056] S300: combining the control law of the sliding mode control with the control law of the controller to obtain a control law based on the proxy sliding mode control, and according to the control law based on the proxy sliding mode control, the controller outputs a current reference value of the controlled object;

[0057] S400: Acquire reactive current, obtain a voltage reference value output by the inverter by controlling the reactive current and the current reference value according to the inverter current inner loop, perform Park inverse transformation on the voltage reference value to obtain a three-phase voltage reference value, and generate a control signal for the three-phase voltage reference value through a pulse generator to control the controlled object;

[0058] Specifically, corresponding to the depth of voltage drop, the standard setting standard of reactive current per unit value is as follows:

[0059]

[0060] By controlling the d-axis current reference value of the DC / AC inverter output based on the proxy sliding mode controller and the obtained reactive current, the d-axis and q-axis voltage reference values ​​of the inverter output are obtained by the inverter current inner loop control. The current inner loop control formula is expressed as:

[0061]

[0062] in, is the ratio of actual voltage to rated voltage, is the reference value of reactive current, I N is the inverter rated current, is the reference value of the d and q axis voltage output by the inverter, v d 、v q is the actual d-axis and q-axis voltage of the inverter, i d * 、i q * is the reference value of the d and q axis current output by the inverter, i d 、i q is the actual d and q axis current of the inverter, K iP , K iI It is the proportional adjustment gain and integral adjustment gain of the current inner loop.

[0063] The phase angle θ generated by the phase-locked loop is used to obtain the d and q axis voltage reference values. and The Park inverse transformation is performed to obtain the three-phase voltage reference value, and the control signal is generated by the PWM pulse generator to control the DC / AC inverter to achieve the complete execution of the control strategy.

[0064] It should be noted that the strategy based on agent sliding mode control has the fast tracking characteristics of PID control under normal working conditions, and can provide smooth and over-damped response under large disturbances, so that the controller can exit the saturation state faster and more smoothly, significantly improving the recovery performance of the grid-connected photovoltaic array. Through effective control strategies, it is ensured that all the electricity generated by the photovoltaic array can be efficiently transmitted to the power grid, thereby improving the efficiency and reliability of photovoltaic power generation, maintaining the safe and stable operation of the photovoltaic array, and enhancing the robustness of the system.

[0065] In the embodiment of the present application, the above step S100 includes the following sub-step A1:

[0066] In A1: The control force of the controller is the difference between the proxy position and the controlled object position multiplied by the proportional gain of the controller plus the integral of the difference between the proxy position and the controlled object position multiplied by the integral gain of the controller plus the derivative of the difference between the proxy position and the controlled object position multiplied by the derivative gain of the controller;

[0067] Specifically, feedforward compensation is introduced to quickly compensate the d and q axis currents i output by the inverter. d 、i q The mutually coupled parts realize i d 、i q Rapid dynamic decoupling between

[0068] Measure the three-phase voltage value v abc The voltage vector rotation angle θ is obtained through the phase-locked loop MAF-PLL, and the rotation angle θ is used to calculate the three-phase voltage v abc and three-phase current i abc Perform Park transformation to obtain the DC component v in the synchronously rotating dq axis coordinate system d and v q And the DC current component i d and i q ;

[0069] The agent-based sliding mode control can be seen as an extension of the PID controller and an approximation of the sliding mode control (SMC), where the controlled object is the DC link capacitor voltage of the DC / AC inverter, which is connected to the virtual mass (agent) through the PID controller, and the PID controller generates the force f PID To keep the position error of the controlled object relative to the agent equal to zero, in addition, the force f generated by the sliding mode control SMCIt affects the position of the agent, and the sliding mode control keeps the position error between the agent position and the desired position of the controlled object equal to zero;

[0070] The main goal of the DC / AC inverter controller based on agent sliding mode control is to control the DC link voltage v during the low voltage ride-through process of the grid-connected distributed photovoltaic array. dc Equal to its reference value To maintain the DC link voltage stability, for the DC / AC inverter controller, the error is defined as:

[0071]

[0072] In agent-based sliding mode control, the PID controller has the characteristics of fast response. Its goal is to track the trajectory of a virtual object called the "agent". The control law of PID is expressed as:

[0073]

[0074] Among them, x is the position of the controlled object, x p is the proxy position, k p is the proportional gain of the PID controller, k i is the integral gain of the PID controller, k d is the derivative gain of the PID controller, v dc is the DC link voltage, is the DC link voltage reference value.

[0075] It should be noted that through effective control strategies, it is ensured that all the electricity generated by the photovoltaic array can be efficiently transmitted to the power grid, which improves the efficiency and reliability of photovoltaic power generation. By introducing feedforward compensation, rapid dynamic decoupling is achieved, thereby improving the response speed and control accuracy of the inverter.

[0076] In the embodiment of the present application, the sliding mode control in the above step S200 includes the following sub-steps B1-B2:

[0077] In B1: The sliding surface is the weight coefficient of the sliding mode control multiplied by the derivative of the difference between the desired position and the proxy position plus the difference between the desired position and the proxy position;

[0078] In B2: When the agent's position reaches the sliding surface, the sliding surface is zero, the agent's position and velocity errors will decay exponentially to zero, and the agent converges to the desired trajectory and reaches the expected value.

[0079] Specifically, the proxy object is controlled using sliding mode control to track the desired position, and the gains of the sliding mode control are selected to achieve a smooth and overdamped response under large disturbances.

[0080] The goal of sliding mode control is to make the agent's position reach the desired position, which is achieved by defining the sliding surface as:

[0081]

[0082] Where K is the weight coefficient of sliding mode control. By changing the value of K, the trajectory recovered from large input errors is adjusted. d is the desired position, x p The location of the agent.

[0083] When Agent x p When the sliding surface is reached, s = 0, the position and velocity errors of the agent will decay exponentially to zero, causing the agent to slowly converge to the desired trajectory and achieve the control target to reach the desired value.

[0084] In the embodiment of the present application, after completing steps B1-B2, the above step S200 may further include steps B3-B4:

[0085] In B3: The control force of the sliding mode control is the control gain of the sliding mode control multiplied by the sign of the sliding surface;

[0086] In B4: When the sliding mode surface is reached, the error signal of the sliding mode control converges to zero, and the convergence time constant is the weight coefficient of the sliding mode control.

[0087] Specifically, the control law of sliding mode control is defined as:

[0088]

[0089] Among them, F>0 is the control gain of sliding mode control, which is the amplitude limit of the actuator force and the current of the DC / AC inverter.

[0090] When reaching the sliding surface S PBSMC When , the error signal of sliding mode control converges to zero, and the convergence time constant is equal to K.

[0091] It should be noted that by defining the sliding surface and using the weight coefficient of the sliding mode control, the trajectory of the system recovering from the large input error can be adjusted so that the agent position can quickly and smoothly track the desired position, thereby enhancing the dynamic response capability of the system. PBSMC =0, the position and velocity errors of the agent will decay exponentially to zero, which means that the system can quickly and stably reach the expected value, improving the accuracy of control. The sliding mode control strategy can provide a smooth and over-damped response when facing large disturbances, which enhances the system's resistance to external disturbances and improves the robustness of the system.

[0092] In the embodiment of the present application, the control law based on the proxy sliding mode control in the above step S300 includes the following sub-steps C1-C5;

[0093] In C1: Define auxiliary variables as:

[0094]

[0095]

[0096] In C2: modify the form of the controller and the control law of the sliding mode control;

[0097] In C3: The control force of the controller and sliding mode control is applied to the agent, and the equation of motion of the agent is expressed as:

[0098]

[0099] Among them, ρ and σ are auxiliary variables, x p is the agent position, x is the position of the controlled object, and x d is the desired position, K is the weight coefficient of sliding mode control, f SMC is the control force of sliding mode control, f PID is the control force of the controller, and m is the agent mass.

[0100] In C4: Let m = 0, expressed as:

[0101]

[0102] The functional relationship is defined as:

[0103]

[0104] Among them, sat(〃) is the saturation function, sgn(〃) is the sign function, y is the output, X and Y are constants, ω is the variable, and z is the input.

[0105] In C5: The agent-based sliding mode control law is expressed as:

[0106]

[0107] Among them, ρ and σ are auxiliary variables, F is the control gain of sliding mode control, k d is the derivative gain of the controller, K is the weight coefficient of the sliding mode control, is the time derivative, k i is the integral gain of the controller, k p is the proportional gain of the controller.

[0108] Specifically, the control law of the modified controller and sliding mode control is expressed as:

[0109]

[0110] It should be noted that by defining variables and modifying the control law form of the controller and sliding mode control, the control force can be accurately synthesized to ensure that the agent position can quickly and accurately track the desired position. By setting the agent quality, the implementation of the controller is simplified, making the control algorithm easier to implement and adjust. The control force of the sliding mode control and the control force of the controller are combined to provide stronger robustness, so that the system can remain stable in the face of large disturbances.

[0111] The above is a schematic scheme of a grid-connected distributed photovoltaic low voltage ride through inverter control method based on proxy sliding mode control in this embodiment. It should be noted that the technical scheme of the grid-connected distributed photovoltaic low voltage ride through inverter control system based on proxy sliding mode control and the technical scheme of the grid-connected distributed photovoltaic low voltage ride through inverter control method based on proxy sliding mode control belong to the same concept. The details of the technical scheme of the grid-connected distributed photovoltaic low voltage ride through inverter control system based on proxy sliding mode control in this embodiment that are not described in detail can all be referred to the description of the technical scheme of the grid-connected distributed photovoltaic low voltage ride through inverter control method based on proxy sliding mode control.

[0112] In this embodiment, the grid-connected distributed photovoltaic low voltage ride through inverter control system based on proxy sliding mode control includes:

[0113] A first control law setting module, used for acquiring a controlled object, setting a control law of a controller, and connecting the controlled object to a proxy object through the controller;

[0114] a second controller setting module, configured to control the proxy object using sliding mode control and set a control law of the sliding mode control, wherein the control law of the sliding mode control includes that an error signal of the sliding mode control converges to zero when a sliding surface is reached;

[0115] A combining module, used for combining the control law of the sliding mode control with the control law of the controller to obtain a control law based on a proxy sliding mode control, according to which the controller outputs a current reference value of the controlled object;

[0116] The control module is used to obtain reactive current, obtain a voltage reference value output by the inverter by controlling the reactive current and the current reference value according to the inverter current inner loop, perform a Park inverse transformation on the voltage reference value to obtain a three-phase voltage reference value, and generate a control signal for the three-phase voltage reference value through a pulse generator to control the controlled object.

[0117] This embodiment further provides a computing device, which is applicable to the case of grid-connected distributed photovoltaic low voltage ride through inverter control based on proxy sliding mode control, including:

[0118] A memory and a processor; the memory is used to store computer executable instructions, and the processor is used to execute computer executable instructions to implement the control method of a grid-connected distributed photovoltaic low voltage ride-through inverter based on proxy sliding mode control as proposed in the above embodiment.

[0119] This embodiment also provides a storage medium having a computer program stored thereon, which, when executed by a processor, implements a control method for a grid-connected distributed photovoltaic low voltage ride through inverter based on proxy sliding mode control as proposed in the above embodiment.

[0120] The storage medium proposed in this embodiment and the control method for implementing a grid-connected distributed photovoltaic low-voltage ride-through inverter based on proxy sliding mode control proposed in the above embodiment belong to the same inventive concept. The technical details not described in detail in this embodiment can be referred to the above embodiment, and this embodiment has the same beneficial effects as the above embodiment.

[0121] Through the above description of the implementation methods, the technicians in the relevant field can clearly understand that the present invention can be implemented by means of software and necessary general hardware, and of course can also be implemented by hardware. Based on such an understanding, the technical solution of the present invention is essentially or the part that contributes to the prior art can be embodied in the form of a software product, and the computer software product can be stored in a computer-readable storage medium, such as a computer floppy disk, read-only memory (ReadOnly, Memory, ROM), random access memory (Random Access Memory, RAM), flash memory (FLASH), hard disk or optical disk, etc., including a number of instructions for a computer device (which can be a personal computer, server, or network device, etc.) to perform the methods of various embodiments of the present invention.

[0122] Example 2

[0123] Reference Figure 2-Figure 3 This embodiment is different from the first embodiment and provides a verification test of a grid-connected distributed photovoltaic low voltage ride through inverter control method based on proxy sliding mode control to verify and illustrate the technical effects used in this method.

[0124] Take a two-level three-phase grid-connected distributed photovoltaic array system as an example to do Simulink simulation;

[0125] The grid side is a 60Hz system with a rated voltage of 120kV. The three-phase voltage drops to 20% of the original value after 1s of operation, and recovers to the original rated voltage after 1.15s, which is used as the inducing condition of low voltage ride through of the grid-connected system. Transformer 1 has a rated capacity of 150kVA, a rated voltage of 260V / 25kV, and the resistance, reactance, and inductance converted to per unit values ​​are 0.06, 0.002, and 500 respectively; Transformer 2 has a rated capacity of 5MVA, a rated voltage of 25kV / 120kV, and the resistance, reactance, and inductance converted to per unit values ​​are 0.16, 0.005, and 500 respectively; the filter parameters are inductance 0.25mH, resistance 0.0019Ω; the line parameters are inductance 5.25mH, capacitance 0.0565μF, and resistance 0.5765Ω.

[0126] DC / DC converter parameters: the rated value, maximum value and minimum value of the DC link voltage are 500V, 700V and 300V respectively, and the DC link capacitance is 36mf.

[0127] DC / AC inverter parameters: Inverter rated at 125kVA, maximum output current 563A, maximum output voltage 320V; current inner loop proportional gain and integral gain K iP and K iI They are 0.3 and 20 respectively; the inductance is 0.25mH and the resistance is 0.002Ω.

[0128] The photovoltaic array parameters are as follows: open circuit voltage 64.2V, short circuit current 5.96A, maximum power voltage 54.7V, maximum power current 5.58A, number of parallel modules 66, series modules 5, maximum output power 100.72KW. It works under the external conditions of temperature 25℃ and light intensity 1000W / ㎡, and adopts the maximum power tracking strategy in the same way as the general photovoltaic array operation mode.

[0129] The designed sliding surface, the controlled object is the DC link capacitor voltage V of the DC / AC inverter dc The rated voltage is 500V.

[0130] In the sliding mode controller, the weight coefficient K of the sliding mode control is 0.01, k p , k i , k d The proportional gain, integral gain and derivative gain of the PID controller are 7, 800 and 0.0001 respectively. The control gain F of the sliding mode control is the amplitude limit of the actuator force and is the current i of the DC / AC inverter. d The rated value is taken as 1.25 per unit.

[0131] The control law is set as:

[0132]

[0133] in, x is the DC link voltage, x d =500V, x p The location of the agent.

[0134] The original DC voltage control method is:

[0135] PI control, parameter is K p0 , K i0 They are 700 and 800 respectively, and the control rate is:

[0136]

[0137] Comparing the two solutions, the DC link voltage during low voltage ride-through is measured. Figure 2 and Figure 3 As shown;

[0138] contrast Figure 2 and Figure 3 ,It is found that the DC link voltage surges due to the low voltage on the grid side during the 1.0-1.15s fault ,process.,After the 1.15s fault ends, when the grid voltage is normal in the subsequent ,circumstance, the DC link voltage under the PI control strategy will still surge and become unstable.,In contrast, the DC link voltage under the proxy sliding mode control ,strategy remains stable, and the DC voltage can be ,smoothly restored after the fault is cleared during the low voltage ride-through period.

[0139] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A control method for a grid-connected distributed photovoltaic low voltage ride through inverter based on proxy sliding mode control, characterized in that: include: Acquire a controlled object, set a control law of a controller, and connect the controlled object to a proxy object through the controller; The proxy object is controlled by using sliding mode control, and a control law of the sliding mode control is set, wherein the control law of the sliding mode control includes that when a sliding surface is reached, an error signal of the sliding mode control converges to zero; Combining the control law of the sliding mode control with the control law of the controller to obtain a control law based on a proxy sliding mode control, according to which the controller outputs a current reference value of the controlled object; Acquire reactive current, obtain voltage reference value of inverter output by controlling the reactive current and current reference value according to the inverter current inner loop, perform Park inverse transformation on the voltage reference value to obtain three-phase voltage reference value, and generate control signal for the three-phase voltage reference value through a pulse generator to control the controlled object.

2. The control method of a grid-connected distributed photovoltaic low voltage ride through inverter based on proxy sliding mode control according to claim 1, characterized in that: Setting the control law of the controller includes: The control force of the controller is the difference between the proxy position and the controlled object position multiplied by the proportional gain of the controller plus the integral of the difference between the proxy position and the controlled object position multiplied by the integral gain of the controller plus the derivative of the difference between the proxy position and the controlled object position multiplied by the derivative gain of the controller.

3. The control method of the grid-connected distributed photovoltaic low voltage ride through inverter based on proxy sliding mode control according to claim 2, characterized in that: Sliding mode control includes: The sliding surface is the weight coefficient of the sliding mode control multiplied by the derivative of the difference between the desired position and the proxy position plus the difference between the desired position and the proxy position; When the agent's position reaches the sliding surface, the sliding surface is zero, the agent's position and velocity errors will decay exponentially to zero, and the agent converges to the desired trajectory and reaches the expected value.

4. The control method of the grid-connected distributed photovoltaic low voltage ride through inverter based on proxy sliding mode control according to claim 3, characterized in that: Setting the control law for sliding mode control involves: The control force of the sliding mode control is the control gain of the sliding mode control multiplied by the sign of the sliding surface; When the sliding mode surface is reached, the error signal of the sliding mode control converges to zero, and the convergence time constant is the weight coefficient of the sliding mode control.

5. The control method of the grid-connected distributed photovoltaic low voltage ride through inverter based on proxy sliding mode control according to claim 4, characterized in that: The control law based on agent sliding mode control includes: Define auxiliary variables as: Modify the form of the controller and the control law of sliding mode control; Applying the control force of the controller and sliding mode control to the agent, the agent's equation of motion is expressed as: Among them, ρ and σ are auxiliary variables, x p is the agent position, x is the position of the controlled object, and x d is the desired position, K is the weight coefficient of sliding mode control, f SMC is the control force of sliding mode control, f PID is the control force of the controller, and m is the agent mass.

6. The control method of a grid-connected distributed photovoltaic low voltage ride through inverter based on proxy sliding mode control according to claim 4 or 5, characterized in that: Also includes: Assume m = 0, which is expressed as: The functional relationship is defined as: Among them, sat(·) is the saturation function, sgn(·) is the sign function, y is the output, X and Y are constants, ω is the variable, and z is the input.

7. The control method of a grid-connected distributed photovoltaic low voltage ride through inverter based on proxy sliding mode control according to claim 6, characterized in that: Also includes: The proxy-based sliding mode control law is expressed as: Among them, ρ and σ are auxiliary variables, F is the control gain of sliding mode control, k d is the derivative gain of the controller, K is the weight coefficient of the sliding mode control, is the time derivative, k i is the integral gain of the controller, k p is the proportional gain of the controller.

8. A system using the proxy sliding mode control-based grid-connected distributed photovoltaic low voltage ride through inverter control method as described in any one of claims 1 to 7, characterized in that: include: A first control law setting module, used for acquiring a controlled object, setting a control law of a controller, and connecting the controlled object to a proxy object through the controller; a second controller setting module, configured to control the proxy object using sliding mode control and set a control law of the sliding mode control, wherein the control law of the sliding mode control includes that an error signal of the sliding mode control converges to zero when a sliding surface is reached; A combining module, used for combining the control law of the sliding mode control with the control law of the controller to obtain a control law based on a proxy sliding mode control, according to which the controller outputs a current reference value of the controlled object; The control module is used to obtain reactive current, obtain a voltage reference value output by the inverter by controlling the reactive current and the current reference value according to the inverter current inner loop, perform a Park inverse transformation on the voltage reference value to obtain a three-phase voltage reference value, and generate a control signal for the three-phase voltage reference value through a pulse generator to control the controlled object.

9. An electronic device, comprising: Memory and processor; The memory is used to store computer executable instructions, and the processor is used to execute the computer executable instructions. When the computer executable instructions are executed by the processor, the steps of the grid-connected distributed photovoltaic low voltage ride-through inverter control method based on proxy sliding mode control according to any one of claims 1 to 7 are implemented.

10. A computer-readable storage medium storing computer-executable instructions, which, when executed by a processor, implement the steps of the method for controlling a grid-connected distributed photovoltaic low voltage ride-through inverter based on proxy sliding mode control as described in any one of claims 1 to 7.

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