A control method and system for grid-connected distributed photovoltaic low-voltage ride-through inverters based on proxy sliding mode control.

Abstract

This invention discloses a control method and system for a grid-connected distributed photovoltaic low-voltage ride-through inverter based on proxy sliding mode control. The method includes: acquiring the controlled object; setting the control law of the controller; connecting the controlled object to a proxy object through the controller; using sliding mode control for control; setting the control law of the sliding mode control, which includes that the error signal of the sliding mode control converges to zero when the sliding surface is reached; combining the control law of the sliding mode control with the control law of the controller to obtain a control law based on proxy sliding mode control; the controller outputs a current reference value of the controlled object; acquiring the reactive current; using the reactive current and the current reference value to obtain a voltage reference value output by the inverter according to the inverter current inner loop control; performing a Parker inverse transformation on the voltage reference value to obtain a three-phase voltage reference value; and generating a control signal through a pulse generator to control the controlled object, thereby improving the response speed and control accuracy of the inverter.

Description

Technical Field

[0001] This invention relates to the field of grid-connected distributed photovoltaic array inverter control technology, and in particular to a control method and system for grid-connected distributed photovoltaic low-voltage ride-through inverters based on proxy sliding mode control. Background Technology

[0002] Distributed photovoltaic (PV) arrays are typically connected to the distribution network in a two-stage, three-phase grid-connected configuration. This two-stage structure consists of a step-up converter connected to the PV array and an inverter connected to the grid. When a fault in the distribution network causes a voltage drop on the grid side, the grid-connected PV array disconnects from the distribution network, achieving grid disconnection and self-protection. Low Voltage Ride Through (LVRT) of a grid-connected PV array refers to the ability of the PV array to remain connected to the grid, and even provide some reactive power to the grid to support grid recovery, until the grid returns to normal, thus "traveling" through the low voltage period (area). In recent years, the penetration rate of distributed PV has exploded, placing increasingly higher demands on the LVRT capability of grid-connected distributed PV arrays. Designing control strategies for distributed PV grid-connected systems to achieve safe and stable operation of distributed PV power generation clusters while possessing LVRT capabilities compliant with the "Technical Specifications for Grid-Connected Inverters for Photovoltaic Power Generation" has become an urgent problem to be solved. During low-voltage ride-through, in the voltage recovery phase after fault clearance, grid-connected photovoltaic arrays often absorb reactive power from the grid, leading to unstable DC-side voltage recovery of the photovoltaic array's DC / AC inverter.

[0003] Currently, the design of low-voltage ride-through control strategies for grid-connected photovoltaic (PV) arrays focuses on adjusting and replacing maximum power point tracking (MPPT) strategies, without considering the voltage recovery phase after a fault during low-voltage ride-through. Instead, it merely injects reactive current into the grid according to the voltage drop magnitude as per the "Technical Specification for Grid-Connected Photovoltaic Inverters." This results in the PID control of the grid-connected PV array inverter remaining in saturation during the voltage recovery phase after the fault is cleared, leading to slow, unstable, and unbalanced voltage recovery, deviating from the target value. Summary of the Invention

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

[0005] Therefore, this invention provides a control method and system for grid-connected distributed photovoltaic low-voltage ride-through inverters based on proxy sliding mode control, which solves the problem that during the low-voltage ride-through period, after the fault is cleared and the voltage recovery phase is in the saturation state of the grid-connected photovoltaic array inverter's own PID control, the voltage recovery is slow and unstable, deviating from the target value.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

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

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

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

[0010] The control law of the sliding mode control is combined with the control law of the controller to obtain the control law based on the proxy sliding mode control. According to the control law based on the proxy sliding mode control, the controller outputs the current reference value of the controlled object.

[0011] The reactive current is obtained, and the voltage reference value of the inverter output is obtained by using the reactive current and the current reference value according to the inverter current inner loop control. The voltage reference value is subjected to Parker inverse transformation to obtain the three-phase voltage reference value. The three-phase voltage reference value is used to generate control signals to control the controlled object through a pulse generator.

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

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

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

[0015] The sliding surface is the weighting coefficient of sliding control multiplied by the derivative of the difference between the desired position and the surrogate position, plus the difference between the desired position and the surrogate position.

[0016] When the agent's position reaches the sliding surface, the sliding surface becomes zero, and the agent's position and velocity errors will decrease exponentially to zero. The agent will then converge to the desired trajectory and reach the expected value.

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

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

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

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

[0021] The auxiliary variable is defined as follows:

[0022]

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

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

[0025]

[0026] Where ρ and σ are auxiliary variables, x p x is the proxy location, and x is the location of the target object. d For the desired position, K is the weighting coefficient of sliding mode control, and f SMC f is the control force for sliding mode control. PID Let m be the control force of the controller, and m be the agent mass.

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

[0028] Let m = 0, which can be represented as:

[0029]

[0030] The functional relationship is defined as follows:

[0031]

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

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

[0034] The sliding mode control law based on the proxy is expressed as follows:

[0035]

[0036] Where ρ and σ are auxiliary variables, F is the control gain of sliding mode control, and k d Let K be the derivative gain of the controller, and K be the weighting coefficient of the sliding mode control. k is the time derivative. i k is the integral gain of the controller. p This is the proportional gain of the controller.

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

[0038] The first control law setting module is used to obtain the controlled object, set the control law of the controller, and connect the controlled object to the proxy object through the controller.

[0039] The second controller setting module is used to control the proxy object using sliding mode control, and to set the control law of the sliding mode control. The control law of the sliding mode control includes that when the sliding surface is reached, the error signal of the sliding mode control converges to zero.

[0040] The module is used to combine the control law of the sliding mode control with the control law of the controller to obtain the control law based on the proxy sliding mode control. According to the control law based on the proxy sliding mode control, the controller outputs the current reference value of the controlled object.

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

[0042] Thirdly, 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, they implement the steps of the grid-connected distributed photovoltaic low-voltage ride-through inverter control method based on proxy sliding mode control.

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

[0046] Compared with the prior art, the beneficial effects of the present invention are as follows: By introducing feedforward compensation, the present invention can quickly compensate for the mutual coupling between the d-axis and q-axis currents of the inverter output, and achieve rapid dynamic decoupling, thereby improving the inverter's response speed and control accuracy. After a grid fault occurs, especially during low-voltage ride-through, the control strategy of this application can support the smooth recovery of voltage, avoiding the problems of slow and unstable voltage recovery that may be caused by traditional PID control. After the fault is cleared during low-voltage ride-through, it supports the smooth recovery of the inverter's DC-side voltage, and there will be no situation where the voltage surges due to controller saturation. The inverter's DC-side voltage stably recovers to normal operating conditions. Attached Figure Description

[0047] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0048] Figure 1 This is a schematic diagram of the overall process logic of the 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 This refers to the DC chain voltage controlled by PI in the grid-connected distributed photovoltaic low-voltage ride-through inverter control method based on proxy sliding mode control described in one embodiment of the present invention.

[0050] Figure 3 This refers to the DC chain voltage based on proxy sliding mode control in the grid-connected distributed photovoltaic low-voltage ride-through inverter control method based on proxy sliding mode control, as described in one embodiment of the present invention. Detailed Implementation

[0051] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the protection scope of the present invention.

[0052] Example 1

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

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

[0055] S200: Use sliding mode control to control the proxy object, set the control law of sliding mode control, the control law of sliding mode control includes that when the sliding surface is reached, the error signal of sliding mode control converges to zero;

[0056] S300: The control law of sliding mode control is combined with the control law of the controller to obtain the control law based on proxy sliding mode control. According to the control law based on proxy sliding mode control, the controller outputs the current reference value of the controlled object.

[0057] S400: Obtain reactive current, use the reactive current and current reference value to obtain the inverter output voltage reference value according to the inverter current inner loop control, perform Parker inverse transformation on the voltage reference value to obtain the three-phase voltage reference value, and use the three-phase voltage reference value to generate control signals to control the controlled object through a pulse generator;

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

[0059]

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

[0061]

[0062] in, This is the ratio of the actual voltage to the rated voltage. I is the reference value for reactive current. N This is the inverter's rated current. V represents the reference values ​​for the d-axis and q-axis voltages output by the inverter. d v q i represents the actual d-axis and q-axis voltages of the inverter. d * i q * i represents the reference values ​​for the d-axis and q-axis currents output by the inverter. d i q K represents the actual d-axis and q-axis currents of the inverter. iP K iI This refers to the proportional gain and integral gain of the inner current loop.

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

[0064] It should be noted that the strategy based on proxy sliding mode control has the fast tracking characteristics of PID control under normal operating conditions, and at the same time can provide smooth and overdamped response under large disturbances, enabling the controller to 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 grid, 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 this embodiment of the application, step S100 includes the following sub-step A1;

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

[0067] Specifically, feedforward compensation is introduced to quickly compensate for the d-axis and q-axis currents i of the inverter output. d i q The mutually coupled parts implement i d i q Rapid dynamic decoupling between them;

[0068] Measure the three-phase voltage value of grid connection V abc The voltage vector rotation angle θ is obtained through a phase-locked loop (MAF-PLL), and the rotation angle θ is used to adjust the three-phase voltage v. abc and three-phase current i abc Performing the Park transformation, we obtain the DC component v in the synchronously rotating dq-axis coordinate system. d and v q and DC current component i d and i q ;

[0069] Sliding mode control based on a proxy can be viewed as an extension of the PID controller and an approximation of sliding mode control (SMC). The controlled object is the DC-DC link capacitor voltage of the DC / AC inverter, which is connected to a virtual mass (proxy) via a PID controller. The PID controller generates a force f. PID To maintain the positional error of the controlled object relative to the agent equal to zero, the force f generated by sliding mode control is also used. SMCIt will affect the position of the agent; sliding mode control keeps the positional error between the agent's position and the desired position of the controlled object equal to zero.

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

[0071]

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

[0073]

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

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

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

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

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

[0079] Specifically, the proxy object uses sliding mode control to track the desired position and achieves smooth and overdamped response under large disturbances by selecting the gain of the sliding mode control.

[0080] The goal of sliding mode control is to position the agent to the desired position, which is achieved by defining a sliding surface, represented as follows:

[0081]

[0082] Where K is the weighting coefficient of sliding mode control, and the trajectory recovered from a large input error is adjusted by changing the value of K. d For the desired position, x p The location of the agent.

[0083] When agent x p Upon reaching the sliding surface, s=0, and the position and velocity errors of the agent will decrease exponentially to zero, causing the agent to gradually converge to the required trajectory and achieve the desired control target.

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

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

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

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

[0088]

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

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

[0091] It should be noted that by defining a sliding surface and utilizing the weighting coefficients of sliding mode control, the trajectory recovered by the system from large input errors can be adjusted, enabling the surrogate position to quickly and smoothly track the desired position, thereby enhancing the system's dynamic response capability. When the surrogate position reaches the sliding surface S... PBSMC When the value is 0, the position and velocity errors of the agent will decay exponentially to zero, meaning that the system can quickly and stably reach the desired value, improving the accuracy of control. The sliding mode control strategy can provide a smooth and overdamped response when facing large disturbances, which enhances the system's resistance to external disturbances and improves the system's robustness.

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

[0093] In C1: Auxiliary variables are defined as follows:

[0094]

[0095]

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

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

[0098]

[0099] Where ρ and σ are auxiliary variables, x p x is the proxy location, and x is the location of the target object. d For the desired position, K is the weighting coefficient of sliding mode control, and f SMC f is the control force for sliding mode control. PID Let m be the control force of the controller, and m be the agent mass.

[0100] In C4: Let m = 0, which is represented as:

[0101]

[0102] The functional relationship is defined as follows:

[0103]

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

[0105] In C5: the proxy sliding mode control law is expressed as:

[0106]

[0107] Where ρ and σ are auxiliary variables, F is the control gain of sliding mode control, and k d Let K be the derivative gain of the controller, and K be the weighting coefficient of the sliding mode control. k is the time derivative. i k is the integral gain of the controller. p This is the proportional gain of the controller.

[0108] Specifically, the control laws for modifying the controller and sliding mode control are expressed as follows:

[0109]

[0110] It should be noted that by defining variables and modifying the control law forms of the controller and sliding mode control, the control force can be accurately synthesized, ensuring 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. Combining the control force of sliding mode control and the control force of the controller provides stronger robustness, enabling the system to remain stable when facing large disturbances.

[0111] The above is an illustrative scheme of a grid-connected distributed photovoltaic (PV) low-voltage ride-through inverter control method based on proxy sliding mode control, according to this embodiment. It should be noted that the technical solution of this grid-connected distributed PV low-voltage ride-through inverter control system based on proxy sliding mode control belongs to the same concept as the aforementioned grid-connected distributed PV low-voltage ride-through inverter control method based on proxy sliding mode control. Details not described in detail in the technical solution of the grid-connected distributed PV low-voltage ride-through inverter control system based on proxy sliding mode control in this embodiment can be found in the description of the aforementioned grid-connected distributed PV low-voltage ride-through inverter control method based on proxy sliding mode control.

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

[0113] The first control law setting module is used to obtain the controlled object, set the control law of the controller, and connect the controlled object to the proxy object through the controller.

[0114] The second controller setting module is used to control the proxy object using sliding mode control, and to set the control law of the sliding mode control. The control law of the sliding mode control includes that when the sliding surface is reached, the error signal of the sliding mode control converges to zero.

[0115] The module is used to combine the control law of the sliding mode control with the control law of the controller to obtain the control law based on the proxy sliding mode control. According to the control law based on the proxy sliding mode control, the controller outputs the current reference value of the controlled object.

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

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

[0118] The system includes a memory and a processor. The memory stores computer-executable instructions, and the processor executes these instructions to implement the control method for grid-connected distributed photovoltaic low-voltage ride-through inverters based on proxy sliding mode control, as proposed in the above embodiments.

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

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

[0121] Based on the above description of the implementation methods, those skilled in the art will clearly understand that the present invention can be implemented using software and necessary general-purpose hardware, and of course, it can also be implemented using hardware. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as a computer floppy disk, read-only memory (ROM), random access memory (RAM), flash memory, hard disk, or optical disk, etc., including several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods of the various embodiments of the present invention.

[0122] Example 2

[0123] Reference Figures 2-3 This embodiment differs 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 explain the technical effects used in this method.

[0124] A Simulink simulation is performed using a two-stage three-phase grid-connected distributed photovoltaic array system as an example.

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

[0126] DC / DC converter parameters: DC chain voltage rating, maximum and minimum values ​​are 500V, 700V and 300V respectively, and DC chain capacitor is 36mF.

[0127] DC / AC inverter parameters: Inverter rated at 125kVA, maximum output current of 563A, maximum output voltage of 320V; current inner loop proportional gain and integral gain K. iP and K iI The values ​​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, number of series modules 5, and maximum output power 100.72KW. It operates under external conditions of 25℃ and 1000W / ㎡ irradiance, and employs a maximum power point tracking (MPPT) strategy, similar to typical photovoltaic arrays.

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

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

[0131] The control law is set as follows:

[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 was:

[0135] PI control, parameter K p0 K i0 The values ​​are 700 and 800 respectively, with a control rate of:

[0136]

[0137] Comparing the two schemes, the DC chain voltage during low-voltage ride-through is measured as follows: Figure 2 and Figure 3 As shown;

[0138] contrast Figure 2 and Figure 3 It was found that during the 1.0-1.15s fault occurrence, the DC chain voltage suddenly increased due to the low voltage on the grid side. After the 1.15s fault ended, the DC chain voltage under the PI control strategy still suddenly increased and was unstable under the subsequent normal grid voltage. In contrast, the DC chain voltage based on the proxy sliding mode control strategy remained stable, achieving a smooth recovery of DC voltage after the fault was cleared during the low voltage ride-through.

[0139] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within 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: Obtain the controlled object, set the control law of the controller, and connect the controlled object to the proxy object through the controller; The proxy object is controlled using sliding mode control, and the control law of the sliding mode control is set. The control law of the sliding mode control includes that when the sliding surface is reached, the error signal of the sliding mode control converges to zero. The control law of the sliding mode control is combined with the control law of the controller to obtain the control law based on the proxy sliding mode control. According to the control law based on the proxy sliding mode control, the controller outputs the current reference value of the controlled object. The reactive current is obtained, and the voltage reference value of the inverter output is obtained by using the reactive current and the current reference value according to the inverter current inner loop control. The voltage reference value is subjected to Parker inverse transformation to obtain the three-phase voltage reference value. The three-phase voltage reference value is used to generate control signals to control the controlled object through a pulse generator. The controller's control law is a PID control law, expressed as follows: Where x is the position of the controlled object, x p For proxy location, k p k is the proportional gain of the PID controller. i k is the integral gain of the PID controller. d For the derivative gain of the PID controller, v dc This is the DC link voltage. This is a reference value for the DC link voltage. The control law for sliding mode control is implemented by defining a sliding surface, expressed as follows: Where K is the weighting coefficient of sliding mode control, and the trajectory recovered from a large input error is adjusted by changing the value of K. d For the desired position, x p For the location of the agent; The control law for the proxy sliding mode control is expressed as follows: Where ρ and σ are auxiliary variables, F is the control gain of sliding mode control, and k d Let K be the derivative gain of the controller, and K be the weighting coefficient of the sliding mode control. k is the time derivative. i k is the integral gain of the controller. p This is the proportional gain of the controller.

2. The control method for grid-connected distributed photovoltaic low-voltage ride-through inverters based on proxy sliding mode control as described in claim 1, characterized in that, The control laws for the controller include: The control force of the controller is the difference between the agent position and the controlled object position multiplied by the proportional gain of the controller, plus the integral of the difference between the agent position and the controlled object position multiplied by the integral gain of the controller, plus the derivative of the difference between the agent position and the controlled object position multiplied by the derivative gain of the controller.

3. The control method for grid-connected distributed photovoltaic low-voltage ride-through inverters based on proxy sliding mode control as described in claim 2, characterized in that, Slip mode control includes: The sliding surface is the weighting coefficient of sliding control multiplied by the derivative of the difference between the desired position and the surrogate position, plus the difference between the desired position and the surrogate position. When the agent's position reaches the sliding surface, the sliding surface becomes zero, and the agent's position and velocity errors will decrease exponentially to zero. The agent will then converge to the desired trajectory and reach the expected value.

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

5. The control method for grid-connected distributed photovoltaic low-voltage ride-through inverters based on proxy sliding mode control as described in claim 4, characterized in that, The control laws based on proxy sliding mode control include: The auxiliary variable is defined as follows: Modify the form of the control law for the controller and sliding mode control; Applying the control forces of the controller and sliding mode control to the agent, the agent's motion equation is expressed as: Where ρ and σ are auxiliary variables, x p Let x be the location of the proxy, and x be the location of the controlled object. d For the desired position, K is the weighting coefficient of sliding mode control, and f SMC f is the control force for sliding mode control. PID Let m be the control force of the controller, and m be the agent mass.

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

7. A system applying the grid-connected distributed photovoltaic low-voltage ride-through inverter control method based on proxy sliding mode control as described in any one of claims 1-6, characterized in that, include: The first control law setting module is used to obtain the controlled object, set the control law of the controller, and connect the controlled object to the proxy object through the controller. The second controller setting module is used to control the proxy object using sliding mode control, and to set the control law of the sliding mode control. The control law of the sliding mode control includes that when the sliding surface is reached, the error signal of the sliding mode control converges to zero. The module is used to combine the control law of the sliding mode control with the control law of the controller to obtain the control law based on the proxy sliding mode control. According to the control law based on the proxy sliding mode control, the controller outputs the current reference value of the controlled object. The control module is used to acquire reactive current, obtain the voltage reference value of the inverter output by the reactive current and the current reference value according to the inverter current inner loop control, perform Parker inverse transformation on the voltage reference value to obtain three-phase voltage reference value, and generate control signals from the three-phase voltage reference value through a pulse generator to control the controlled object. The controller's control law is a PID control law, expressed as follows: Where x is the position of the controlled object, x p For proxy location, k p k is the proportional gain of the PID controller. i k is the integral gain of the PID controller. d For the derivative gain of the PID controller, v dc This is the DC link voltage. This is a reference value for the DC link voltage. The control law for sliding mode control is implemented by defining a sliding surface, expressed as follows: Where K is the weighting coefficient of sliding mode control, and the trajectory recovered from a large input error is adjusted by changing the value of K. d For the desired position, x p For the location of the agent; The control law for the proxy sliding mode control is expressed as follows: Where ρ and σ are auxiliary variables, F is the control gain of sliding mode control, and k d Let K be the derivative gain of the controller, and K be the weighting coefficient of the sliding mode control. k is the time derivative. i k is the integral gain of the controller. p This is the proportional gain of the controller.

8. 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, they implement the steps of the grid-connected distributed photovoltaic low-voltage ride-through inverter control method based on proxy sliding mode control as described in any one of claims 1 to 6.

9. A computer-readable storage medium storing computer-executable instructions that, when executed by a processor, implement the steps of the grid-connected distributed photovoltaic low-voltage ride-through inverter control method based on proxy sliding mode control as described in any one of claims 1 to 6.

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