Grid-connected inverter fault ride-through method and system considering symmetric and asymmetric faults

Abstract

The invention discloses a grid-connected inverter fault ride-through method and system considering symmetric and asymmetric faults, and relates to the technical field of electric power, and the method comprises the steps: obtaining power grid voltage measurement data and power grid current measurement data, and carrying out the fault ride-through of a grid-connected inverter based on the power grid voltage measurement data and the power grid current measurement data; generating reference voltage data and reference phase data through droop control; based on the power grid voltage measurement data and the reference voltage data, outputting through a finite control set model prediction control strategy to obtain a switching signal for driving an inverter switch; when the power grid current measurement data exceed a preset current rated value, judging that the current is in a fault state, calculating to obtain a virtual impedance value based on the fault state, and generating a voltage correction value based on the virtual impedance value and the power grid current measurement data to adjust the reference voltage data; and according to the adjusted reference voltage data, a switching signal for driving an inverter switch is updated, and accurate current constraint under symmetric and asymmetric faults is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electric power, in particular to a grid-connected inverter fault ride-through method and system considering symmetric and asymmetric faults. BACKGROUND

[0002] The traditional GFM inverter adopts a three-stage cascaded architecture of "outer ring power control-inner ring voltage / current control-end modulation": the outer ring power controller generates a voltage reference instruction according to the grid demand, the inner ring voltage controller and the current controller track the reference in turn, and finally the control signal is converted into a power device driving signal through a traditional pulse width modulator (such as SPWM). If the current inner ring is omitted for the sake of simplifying the architecture and only relying on the voltage controller to operate independently, two problems will be caused: one is that it is difficult to maintain the rated current output of the inverter under normal working conditions, and the running stability is poor; the second is that the output current waveform is severely distorted during grid fault, which cannot meet the power quality requirements. In addition, the current reference value in this traditional cascaded architecture lacks direct closed-loop constraints, and it cannot quickly limit the current amplitude when a fault occurs, which is easy to break through the transient withstand limit of 1.0-1.2 p.u. of semiconductor devices.

[0003] The prior art grid-connected inverter fault ride-through strategy includes the following methods: (1) The traditional GFL inverter fault ride-through strategy only injects a specific proportion of active / reactive power according to the grid voltage drop depth, but its topology depends on the phase-locked loop (PLL) to synchronize with the grid, which cannot provide sustained voltage support like the GFM inverter, and often needs to trigger off-grid protection during faults rather than maintaining grid operation, which is difficult to meet the future grid's demand for fault support of distributed power sources (DG); (2) The fixed parameter-based virtual impedance control scheme uses a pre-set fixed value of virtual resistance and virtual reactance to alleviate the overcurrent problem, but the parameters need to be manually adjusted, which cannot adapt to the working conditions when the grid parameters change dynamically (such as line impedance fluctuations) or the fault type switches (symmetric / asymmetric faults), which may lead to a decrease in current control accuracy or system oscillation, and it is difficult to balance the steady-state and transient performance; (3) The conventional voltage-current double-loop cascaded control scheme has limited bandwidth, which cannot quickly respond to grid voltage mutations in the initial stage of fault, and is easy to produce transient overcurrent; and during the fault recovery process, due to the lag of voltage regulation, there may be a risk of overvoltage, and the traditional pulse width modulator needs to be additionally configured, which not only increases the system complexity, but also further reduces the dynamic response speed, and cannot meet the high-bandwidth control demand. SUMMARY

[0004] To solve the problems mentioned in the background, the purpose of the present application is to provide a grid-connected inverter fault ride-through method and system considering symmetric and asymmetric faults.

[0005] In the first aspect, the purpose of the present application can be achieved by the following technical solution: a grid-connected inverter fault ride-through method considering symmetric and asymmetric faults, the method comprising the following steps: Obtaining grid voltage measurement data and grid current measurement data, and generating reference voltage data and reference phase data through droop control based on the grid voltage measurement data and the grid current measurement data; Generating current reference instructions through proportional integral control based on the grid voltage measurement data and the reference voltage data; and outputting switch signals for driving the inverter switch through a finite control set model predictive control strategy based on the current reference instructions, the grid voltage measurement data and the grid current measurement data; When the grid current measurement data exceeds a preset current rating, it is determined that this is a fault state, and a virtual impedance value is calculated based on the grid current measurement data and the preset current rating based on the fault state, and a voltage correction amount is generated based on the virtual impedance value and the grid current measurement data; Adjusting the reference voltage data based on the voltage correction amount, and updating the switch signals for driving the inverter switch according to the adjusted reference voltage data, the proportional integral control and the finite control set model predictive control strategy to limit the fault current.

[0006] In combination with the first aspect, in some implementations of the first aspect, the method further comprises: the droop control comprises active droop control and reactive droop control.

[0007] In combination with the first aspect, in some implementations of the first aspect, the method further comprises: the active droop control process comprises: Establishing a linear droop relationship between the output angular frequency and the active power to achieve autonomous distribution of active power and system frequency stability in a multi-source parallel system, and the calculation formula is as follows: (1) In the formula, is the actual output angular frequency of the power supply unit, is the rated angular frequency, is the active droop coefficient, is the actual output active power of the power supply unit, is the rated active power; The process of the reactive droop control comprises: based on the coupling relationship between the voltage amplitude and the reactive power, the excitation regulation characteristics of a synchronous generator are simulated to achieve distributed autonomous distribution of reactive power and node voltage stability control, and the calculation formula is as follows: (2) In the formula, This represents the actual output voltage amplitude of the power supply unit. This is the rated voltage amplitude. The reactive power droop factor represents the actual reactive power output of the power supply unit. This is the rated reactive power.

[0008] In conjunction with the first aspect, in some implementations of the first aspect, the method further includes: the proportional-integral control performs steady-state error-free tracking of grid voltage measurement data and reference voltage data by optimizing the design of the proportional coefficient and integral time constant, and finally derives the current reference command; The finite control set model predictive control strategy is based on a pre-established mathematical model of the power conversion unit. By traversing all feasible power device switching state sets, it predicts the future operating state of the system under each switching state and outputs the switching signal that drives the inverter switch. It includes several constraints and multi-dimensional performance indicators. The constraints include peak fault current limit, voltage amplitude boundary, power device switching frequency constraint, and current harmonic content threshold. The multi-dimensional performance indicators include minimizing current tracking error, reducing voltage distortion rate, optimizing switching loss, and improving dynamic response speed.

[0009] In conjunction with the first aspect, in some implementations of the first aspect, the method further includes: the adaptive adjustment process of the virtual impedance value is as follows: The nominal impedance parameter is preset, and the status identifier is initially set to 0. When the status identifier is 0, it indicates that the peak value of the grid current measurement data has not yet reached the preset current rating during the transient stage. The impedance value is adjusted by an amplitude ten times that of the incremental parameter. When the peak value of the grid current measurement data reaches the preset current rating, the status identifier switches to 1, and the impedance value is adjusted with incremental parameters to achieve adaptive adjustment of the virtual impedance value.

[0010] In conjunction with the first aspect, in some implementations of the first aspect, the method further includes: the process of updating the switching signal driving the inverter switch, comprising: The switching signals driving the inverter are updated by modifying the cost function of the predictive control strategy using a finite control set model. The cost function is modified as follows: by introducing a preset parameter penalty term, the finite control set model predictive control strategy prioritizes suppressing the current peak at the initial stage of the fault when updating the switching signal that selects the drive inverter switch. The preset parameter penalty term is generated based on the difference between the predicted current value and the preset short-term current rating.

[0011] In conjunction with the first aspect, in some implementations of the first aspect, the method further includes: the steps for handling asymmetric faults under the fault state are as follows: By separating the positive and negative sequences of the grid voltage measurement data through a second-order generalized integrator SOGI, the negative sequence voltage component data is obtained. Negative-sequence current control commands are generated based on negative-sequence voltage component data and preset adjustable coefficients. Based on the negative-sequence current control commands and a finite control set model predictive control strategy, asymmetric fault handling is achieved.

[0012] Secondly, in order to achieve the above objectives, the present invention discloses a grid-connected inverter fault ride-through system considering both symmetrical and asymmetrical faults, comprising: The data processing module is used to acquire grid voltage measurement data and grid current measurement data, and based on the grid voltage measurement data and grid current measurement data, generate reference voltage data and reference phase data through droop control; The switching signal output module is used to generate a current reference command based on grid voltage measurement data and reference voltage data through proportional-integral control; and to output the switching signal that drives the inverter switch through a predictive control strategy based on the current reference command, grid voltage measurement data and grid current measurement data using a finite control set model. The fault determination module is used to determine that when the grid current measurement data exceeds the preset current rating, the current is in a fault state. Based on the fault state, the virtual impedance value is calculated by the grid current measurement data and the preset current rating. Based on the virtual impedance value and the grid current measurement data, a voltage correction amount is generated. The switching signal update module is used to adjust the reference voltage data based on the voltage correction amount. Based on the adjusted reference voltage data and the proportional-integral control and finite control set model predictive control strategies, the switching signal driving the inverter switch is updated to limit the fault current.

[0013] In another aspect of the present invention, in order to achieve the above-mentioned objective, a terminal device is disclosed, including a memory, a processor, and a computer program stored in the memory and capable of running on the processor. The memory stores the computer program capable of running on the processor. When the processor loads and executes the computer program, it employs the grid-connected inverter fault ride-through method considering symmetrical and asymmetrical faults as described above.

[0014] In another aspect of the present invention, in order to achieve the above-mentioned objective, a computer-readable storage medium is disclosed, wherein a computer program is stored in the computer program, and when the computer program is loaded and executed by a processor, the grid-connected inverter fault ride-through method considering symmetrical and asymmetrical faults as described above is employed.

[0015] The beneficial effects of this invention are: This invention proposes an integrated scheme that combines cascaded PI-MPC composite control, adaptive fault current limiting virtual impedance, and second-order generalized integrator negative sequence extraction. This strategy is based on a cascaded PI-MPC architecture using finite control set model predictive control. Through outer-loop droop control and inner-loop FCS-MPC direct modulation, high-bandwidth control can be achieved without a traditional pulse width modulator. The adaptive FCL VI scheme employs a single-parameter iterative algorithm to dynamically match different fault levels to maintain the current rating. FCS-MPC direct modulation combined with a cost function penalty mechanism accurately suppresses the initial fault current peak. SOGI negative sequence extraction, combined with an adjustment factor k, ensures that the voltage of non-faulty phases remains stable within the allowable range. This invention combines excellent steady-state and transient fault current limiting capabilities with robustness to changes in grid parameters, and fault recovery without overcurrent or overvoltage risks. It also optimizes the power distribution of parallel distributed generators under normal operating conditions, effectively reducing the controller's dependence on the accuracy of the system model. It achieves precise current constraint under symmetrical and asymmetrical faults, suppression of fault transient peak values, and rapid recovery after a fault, thereby improving the operational safety and reliability of GFM inverters under grid disturbance scenarios. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Figure 1 This is a schematic diagram of the method flow of the present invention; Figure 2 This is a schematic diagram of the PI-MPC proposed in this invention; Figure 3 This is a schematic diagram of active power drop control; Figure 4 This is a schematic diagram of reactive power droop control; Figure 5 This is a schematic diagram of the simulation results; Figure 6 This is a schematic diagram of the system structure of the present invention. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] Example 1: likeFigure 1 As shown, a fault ride-through method for grid-connected inverters considering symmetrical and asymmetrical faults is presented. The method includes the following steps: S101: Acquire grid voltage measurement data and grid current measurement data, and based on the grid voltage measurement data and grid current measurement data, generate reference voltage data and reference phase data through droop control; like Figure 3 , 4 As shown, droop control includes active droop control and reactive droop control.

[0019] Specifically, the active power droop control strategy originates from the speed regulation characteristics of synchronous generators. Its core is to establish a linear droop relationship between the output angular frequency and active power, thereby achieving autonomous allocation of active power and system frequency stability in multi-source parallel systems. This strategy does not rely on external communication links; it adjusts the output angular frequency based on locally measured active power feedback, possessing a "plug-and-play" flexibility. It is suitable for active power control in microgrid islanded or grid-connected modes. Its mathematical expression is: (1) In the formula, This refers to the actual output angular frequency of the power supply unit. The rated angular frequency, This is the active power droop coefficient. This refers to the actual active power output of the power supply unit. This refers to the rated active power.

[0020] When the system load increases, leading to a rise in active power demand, the power supply unit outputs active power. Increase, according to the above formula, the output angular frequency Reduce proportionally; conversely, when the load decreases, Decrease The corresponding increase. Through this self-regulating mechanism, multiple power supply units operating in parallel can share the active load according to the set proportion of their respective droop coefficients. The value of must be inversely proportional to the rated capacity of the power supply unit to ensure the accuracy of power allocation for capacity matching, while also meeting the system's small-signal stability criterion to ensure stability during dynamic response.

[0021] The reactive power droop control strategy is based on the coupling relationship between voltage amplitude and reactive power. By simulating the excitation regulation characteristics of a synchronous generator, it achieves distributed autonomous allocation of reactive power and stable node voltage control. This strategy addresses the strong correlation between reactive power and voltage amplitude in power systems by adjusting the output voltage amplitude using locally measured reactive power signals, effectively suppressing reactive circulating currents between parallel power supply units and improving system power quality. Its mathematical expression is: (2) In the formula, This represents the actual output voltage amplitude of the power supply unit. This is the rated voltage amplitude. The reactive power droop factor represents the actual reactive power output of the power supply unit. This is the rated reactive power.

[0022] When the reactive load of the system increases, the power supply unit outputs reactive power. Increase, output voltage amplitude The droop factor is reduced proportionally; when reactive load decreases... Decrease A corresponding rebound is expected. In scenarios such as low-voltage microgrids where the lines are resistive, virtual impedance technology is typically used to make the equivalent line impedance inductive, thereby decoupling active and reactive power and improving the power distribution accuracy of reactive droop control. Reactive droop coefficient. The design needs to take into account both the allowable range of voltage deviation and the sensitivity of reactive power distribution.

[0023] S102: Based on grid voltage measurement data and reference voltage data, a current reference command is generated through proportional-integral control; based on the current reference command, grid voltage measurement data, and grid current measurement data, a switching signal to drive the inverter switch is obtained by predictive control strategy output through a finite control set model. Among them, proportional-integral (PI) control optimizes the design of the proportional coefficient and integral time constant, enabling the PI controller to have excellent steady-state tracking accuracy and dynamic adjustment performance. It can track the voltage reference command output by the droop control layer without steady-state error, effectively suppressing voltage deviations caused by grid disturbances, load fluctuations and nonlinear characteristics of power devices, and improving the steady-state quality and anti-interference capability of the system voltage.

[0024] The Finite Control Set Model Predictive Control (FCS-MPC) strategy is based on a mathematical model of the power conversion unit. It predicts the future operating state of the system under each feasible power device switching state by traversing all possible switching states. The FCS-MPC strategy integrates core system constraints, including peak fault current limits, voltage amplitude boundaries, power device switching frequency constraints, and current harmonic content thresholds, as well as multi-dimensional performance indicators such as minimizing current tracking error, reducing voltage distortion rate, optimizing switching losses, and improving dynamic response speed, into a unified cost function. By solving for the minimum value of this cost function, it achieves coordinated scheduling and globally optimal decision-making for multiple control objectives, effectively resolving the performance conflicts caused by single-objective optimization in traditional control.

[0025] The PI controller and the FCS-MPC strategy are organically integrated to form a PI-MPC composite control architecture. This architecture fully leverages the advantages of the PI controller in steady-state zero-steady-state tracking and the technical characteristics of the FCS-MPC strategy in dynamic response speed, constraint handling capability, and multi-objective optimization, achieving a synergistic improvement in steady-state accuracy and dynamic performance, while meeting the core requirements of GFM system network construction and fault current limiting.

[0026] Based on the FCS-MPC strategy, the direct decision-making mechanism for switching states eliminates the need for additional traditional pulse width modulation (PWM) circuitry in the control system. By predicting and evaluating each candidate switching state and optimizing the cost function, the system can directly output the switching drive signal for the power devices. This not only simplifies the hardware configuration and software complexity of the control architecture but also significantly reduces the transmission delay of control commands, improves the switching response speed of the power devices, and enables rapid response to current surges under fault conditions. This allows for accurate and rapid suppression of fault currents, ensuring the safe and stable operation of the power conversion unit and the entire GFM system.

[0027] S103: When the grid current measurement data exceeds the preset current rating, it is determined that the current is a fault state. Based on the fault state, the virtual impedance value is calculated by the grid current measurement data and the preset current rating. The voltage correction amount is generated based on the virtual impedance value and the grid current measurement data. The adaptive adjustment process of the virtual impedance value is as follows: The nominal impedance parameter is preset, and the status identifier is initially set to 0. When the status identifier is 0, it indicates that the peak value of the grid current measurement data has not yet reached the preset current rating during the transient stage. The impedance value is adjusted by an amplitude ten times that of the incremental parameter. When the peak value of the grid current measurement data reaches the preset current rating, the status identifier switches to 1, and the impedance value is adjusted using incremental parameters to achieve adaptive adjustment of the virtual impedance value. The threshold is the rated value, which is 1 p.u.

[0028] Specifically, during the low-voltage fault traversal process, due to the sudden drop in grid-side voltage at the moment of the fault, the voltage output by the GFM, due to its simulated inertia and damping, is expressed by the formula: This application proposes a fault current limiting strategy applicable to virtual synchronous generator systems. During the entire operating cycle of a low-voltage fault, the grid-side voltage suddenly drops at the moment of the fault. The virtual synchronous generator, through a control algorithm simulating the rotational inertia and damping characteristics of a synchronous generator, prevents the inverter's output voltage from decreasing in a short period of time. Its core characteristic can be characterized by the following formula: (3) In the formula: D is the moment of inertia of the virtual synchronous motor; D is the damping coefficient. , These are the actual output angular velocity of the VSG and the grid synchronization angular velocity, respectively. These are the active power reference values; This is the active power droop coefficient.

[0029] Because the voltage on the grid side suddenly drops, while the voltage output by the inverter does not, a very large current will be generated between the inverter and the grid. The formula for this is: (4) In the formula: This is the inverter's own output voltage; The voltage at the grid connection point; This is the connection impedance between the inverter and the power grid; This is the fault current.

[0030] Therefore, to ensure that the output current of the grid-connected converter is strictly constrained within the safe operating range of the semiconductor power devices when subjected to transient electrical stress caused by a sudden drop in grid voltage, thus preventing thermal accumulation failure or structural damage due to transient overcurrent, and to ensure that the current remains controllable, it is necessary to fulfill the reactive power support obligations stipulated by grid connection standards during fault periods. This is achieved by precisely controlling the injection of inductive reactive current to help raise the grid voltage, rather than causing protective disconnection due to current runaway, thereby ensuring that the converter remains connected to the grid during fault ride-through and providing the necessary dynamic voltage support for system recovery.

[0031] This application proposes a control method for an FCL VI control scheme during a fault. The detailed steps of this method are as follows: by setting a virtual impedance... The current amplitude is limited within the inverter's rated range, and an adaptive iterative calculation method based on a single parameter Z is used to ensure stable operation of the inverter under rated conditions; whereby... and The core idea of ​​this determination method is to allow the inverter to simulate an impedance characteristic similar to a synchronous generator when it detects overcurrent, thereby autonomously limiting the fault current. The output current reaches the set maximum limit value. At that time, the voltage reference value of the inverter's internal controller It will be limited so that its amplitude does not exceed a voltage drop determined by a virtual impedance.

[0032] It should be limited so that its amplitude does not exceed a voltage drop determined by the virtual impedance. Specifically, this constraint can be expressed as: (5) (6) (7) The constraint is that the magnitude of the voltage drop is equal to the rated voltage. (8) Substitute the current and impedance: (9) This application order: (10) Substituting equation (10) into equation (9) yields: (11) According to equation (10), we can solve for... for: (12) Then, according to equation (10), it can be resolved. for: (13) In the formula: Virtual impedance The ratio; This is the rated output voltage of the inverter; This refers to the maximum allowable output current of the inverter; It is the magnitude of the voltage drop; The angle between voltage and current; The virtual impedance described in this application has adaptive characteristics, used to maintain a constant current amplitude under different fault levels; after fault detection is triggered, the value of Z is initialized to the nominal load impedance, that is, the ratio of the nominal output voltage amplitude to the nominal output current amplitude, and the status identifier is initially set to zero; during the virtual impedance control activation process, the system continuously monitors the peak current of each phase. When the status identifier is zero, it indicates that the current has not yet reached the rated value in the transient stage, and the impedance value is adjusted with an amplitude ten times that of the incremental parameter h; when the current reaches the rated value 1p.u., the status identifier switches to 1, and the impedance value is adjusted in steps of h to achieve accurate tracking of the rated current; the incremental parameter h is optimized to achieve rapid adjustment of the transient current while ensuring the steady-state performance of the system; the control method selects the inductor current ( () is used as a control variable to achieve direct control of the power switch current.

[0033] The steps for handling asymmetric faults under fault conditions are as follows: By separating the positive and negative sequences of the grid voltage measurement data through a second-order generalized integrator SOGI, the negative sequence voltage component data is obtained. Negative-sequence current control commands are generated based on negative-sequence voltage component data and preset adjustable coefficients. Based on the negative-sequence current control commands and a finite control set model predictive control strategy, asymmetric fault handling is achieved.

[0034] The method for extracting the negative sequence component is as follows: a second-order generalized integrator (SOGI) is used to separate the fault voltage into positive and negative sequences. The negative sequence component of the terminal voltage can determine the injection of the negative sequence current. After separation, it is multiplied by a factor k, where k is the gain coefficient and is a constant. The factor k can ensure that the voltage of the non-faulty phase is maintained within the allowable normal voltage range (0.9 per unit to 1.1 per unit).

[0035] (17) S104: Adjust the reference voltage data based on the voltage correction amount, and update the switching signal driving the inverter switch according to the adjusted reference voltage data, as well as the proportional-integral control and finite control set model predictive control strategies, in order to limit the fault current.

[0036] The process of updating the switching signal of the inverter drive switch includes: The switching signals driving the inverter are updated by modifying the cost function of the predictive control strategy using a finite control set model. The cost function is modified as follows: by introducing a preset parameter penalty term, the finite control set model predictive control strategy prioritizes suppressing the current peak at the initial stage of the fault when updating the switching signal that selects the drive inverter switch. The preset parameter penalty term is generated based on the difference between the predicted current value and the preset short-term current rating.

[0037] Upon fault triggering, a finite control set model is used to predict the direct modulation control strategy. The method includes predicting the filter inductor current for the next sampling period based on all possible switching states. Substitute the predicted current values ​​for each switching state into the cost function for calculation; to limit the current peak value in the first few cycles after a fault occurs, when the predicted current value exceeds the short-term switching rating t, the cost function is used to calculate... Introducing parameters The calculation process of this parameter is detailed in Equation (16) to suppress the first peak value of the inductor current; the optimal switching decision is determined by evaluating the switching state that minimizes the cost function; this optimization process is executed in real time in each sampling period, and active current limiting control is achieved by directly selecting the switching state.

[0038] (14) (15) (16) in: For filtering resistors, The sampling period is For filtering inductors, For the first The measured value of the inductor current at each sampling time. For the first The inverter output voltage in the switching state. For the first The measured value of the grid voltage at each sampling time. for Shaft current reference value, for Shaft current reference value, For the first Predicted AC side current at each sampling time. for The first axis current The predicted value of the AC side inductor current at each sampling time. for The first axis current The predicted value of the AC side inductor current at each sampling time. This is the rated value for short-term switching current.

[0039] Specifically, the present invention will be further illustrated below through embodiments: During the simulation, the grid voltage dropped to 0.2 pu at 4 seconds and then recovered at 4.5 seconds. The simulation results are as follows. Figure 5 As shown. From top to bottom, the values ​​are: mains voltage, output current. and inverter output current The simulation results show that the grid-type converter remains stable during the three stages of grid fault instant, fault process, and fault recovery. The output current harmonics are very small and are limited to the rated value of 1pu. No overcurrent phenomenon occurs, which verifies the effectiveness of the control proposed in this patent.

[0040] Example 2: To achieve the above objective, such as Figure 6 As shown, based on Embodiment 1, this invention discloses a grid-connected inverter fault ride-through system considering both symmetrical and asymmetrical faults, comprising: Data processing module 11 is used to acquire grid voltage measurement data and grid current measurement data, and generate reference voltage data and reference phase data based on grid voltage measurement data and grid current measurement data through droop control; The switching signal output module 12 is used to generate a current reference command based on grid voltage measurement data and reference voltage data through proportional-integral control; and to output a switching signal to drive the inverter switch through a finite control set model predictive control strategy based on the current reference command, grid voltage measurement data and grid current measurement data. The fault determination module 13 is used to determine that the grid current measurement data exceeds the preset current rated value when the grid current measurement data exceeds the preset current rated value. Based on the fault state, the virtual impedance value is calculated by the grid current measurement data and the preset current rated value. Based on the virtual impedance value and the grid current measurement data, a voltage correction amount is generated. The switching signal update module 14 is used to adjust the reference voltage data based on the voltage correction amount, and update the switching signal driving the inverter switch according to the adjusted reference voltage data and the proportional-integral control and finite control set model predictive control strategies to limit the fault current.

[0041] Based on the same inventive concept, this invention also provides a computer device, comprising: one or more processors, and a memory for storing one or more computer programs; the programs include program instructions, and the processor executes the program instructions stored in the memory. The processor may be a Central Processing Unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. It is the computing and control core of the terminal, used to implement one or more instructions, specifically for loading and executing one or more instructions stored in a computer storage medium to implement the above-described method.

[0042] It should be further explained that, based on the same inventive concept, the present invention also provides a computer storage medium storing a computer program, which, when executed by a processor, performs the above-described method. This storage medium can be any combination of one or more computer-readable media. A computer-readable medium can be a computer-readable signal medium or a computer-readable storage medium. A computer-readable storage medium can be, for example, but not limited to, an electrical, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any combination thereof. More specific examples of computer-readable storage media (a non-exhaustive list) include: an electrical connection having one or more wires, a portable computer disk, a hard disk, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fiber, portable compact disk read-only memory (CD-ROM), optical storage device, magnetic storage device, or any suitable combination thereof. In the present invention, a computer-readable storage medium can be any tangible medium containing or storing a program that can be used by or in conjunction with an instruction execution system, apparatus, or device.

[0043] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this disclosure. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0044] The foregoing has shown and described the basic principles, main features, and advantages of this disclosure. Those skilled in the art should understand that this disclosure is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of this disclosure. Various changes and modifications can be made to this disclosure without departing from its spirit and scope, and all such changes and modifications fall within the scope of this disclosure as claimed.

Claims

1. A method of grid-connected inverter fault ride-through considering symmetric and asymmetric faults, characterized in that, The method comprises the following steps: The method comprises the following steps: The method comprises the following steps: The method comprises the following steps: The method comprises the following steps:

2. The method for grid connected inverter fault ride through considering symmetric and asymmetric faults according to claim 1, characterized in that, The droop control comprises active power droop control and reactive power droop control.

3. The grid-connected inverter fault ride-through method considering symmetric and asymmetric faults according to claim 2, characterized in that: The active power droop control process comprises the following steps: The active power droop control process comprises the following steps: （1） wherein is the actual output angular frequency of the power supply unit, is the rated angular frequency, is the active droop coefficient, is the actual output active power of the power supply unit, is the rated active power; The reactive power droop control process comprises the following steps: The reactive power droop control process comprises the following steps: （2） In the formula, is the actual output voltage amplitude of the power supply unit, is the rated voltage amplitude, is the reactive droop coefficient, and is the actual output reactive power of the power supply unit, and is the rated reactive power.

4. The method for grid connected inverter fault ride through considering symmetric and asymmetric faults according to claim 1, characterized in that, The proportional integral control performs zero-error tracking on the grid voltage measurement data and the reference voltage data by optimizing the proportional coefficient and the integral time constant, and finally obtains the current reference instruction; The finite control set model predictive control strategy is based on the mathematical model of the power conversion unit established in advance, and the switching signals of the driving inverter switches are output by predicting the future operating state of the system under each switching state by traversing all feasible power device switching state sets; the finite control set model predictive control strategy comprises a plurality of constraints and multi-dimensional performance indicators; the plurality of constraints comprise fault current peak value limitation, voltage amplitude boundary, power device switching frequency constraint and current harmonic content threshold; the multi-dimensional performance indicators comprise current tracking error minimization, voltage distortion rate reduction, switching loss optimization and dynamic response speed improvement.

5. The method for grid connected inverter fault ride through considering symmetric and asymmetric faults according to claim 1, characterized in that, The adaptive adjustment process of the virtual impedance value is as follows: preset nominal impedance parameters, and initially set a state identifier to 0; when the state identifier is 0, it indicates that the peak value of the grid current measurement data has not reached the transient stage of the preset current rating; the impedance value is adjusted at an amplitude of ten times the increment parameter; When the peak value of the grid current measurement data reaches the preset current rating, the state identifier is switched to 1, and the impedance value is adjusted by the increment parameter to realize adaptive adjustment of the virtual impedance value.

6. The method for grid-tied inverter fault ride through considering symmetric and asymmetric faults according to claim 1, wherein, The process of updating the switching signals of the driving inverter switches comprises the following steps: The updating of the switching signal of the driving inverter switch is driven by modifying a cost function of a limited control set model predictive control strategy; The modification of the cost function is as follows: by introducing a preset parameter penalty term, the limited control set model predictive control strategy is caused to preferentially suppress the current peak value in the initial stage of the fault occurrence when updating the selection of the switching signal of the driving inverter switch based on the preset parameter penalty term; wherein the preset parameter penalty term is generated based on the difference between the predicted current value and the preset short-term current rating value.

7. The method for grid connected inverter fault ride through considering symmetric and asymmetric faults according to claim 1, characterized in that, The step of processing the asymmetric fault in the fault state is as follows: The positive and negative sequence separation of the grid voltage measurement data is performed through a second-order generalized integrator SOGI to obtain negative sequence voltage component data; The negative sequence current control instruction is generated based on the negative sequence voltage component data and a preset adjustable coefficient, and the processing of the asymmetric fault is realized based on the negative sequence current control instruction in combination with the limited control set model predictive control strategy.

8. A grid-connected inverter fault ride-through system considering symmetric and asymmetric faults, employing the grid-connected inverter fault ride-through method considering symmetric and asymmetric faults according to any one of claims 1 to 7, characterized in that, It comprises: The data processing module is configured to obtain grid voltage measurement data and grid current measurement data, and generate reference voltage data and reference phase data through droop control based on the grid voltage measurement data and the grid current measurement data; The switching signal output module is configured to generate a current reference instruction through proportional integral control based on the grid voltage measurement data and the reference voltage data, and output the switching signal of the driving inverter switch through the limited control set model predictive control strategy based on the current reference instruction, the grid voltage measurement data and the grid current measurement data; The fault determination module is configured to determine that the fault state occurs when the grid current measurement data exceeds the preset current rating value, calculate a virtual impedance value based on the fault state, the grid current measurement data and the preset current rating value, and generate a voltage correction amount based on the virtual impedance value and the grid current measurement data; The switching signal updating module is configured to adjust the reference voltage data based on the voltage correction amount, and update the switching signal of the driving inverter switch according to the adjusted reference voltage data, the proportional integral control and the limited control set model predictive control strategy, so as to limit the fault current.

9. A terminal device comprising a memory, a processor, and a computer program stored in the memory and capable of running on the processor, characterized in that, The memory stores a computer program capable of running on the processor, and the processor loads and executes the computer program, which adopts the grid-connected inverter fault ride-through method considering symmetric and asymmetric faults according to any one of claims 1 to 7.

10. A computer-readable storage medium having stored therein a computer program, characterized in that, The computer program is loaded and executed by the processor, which adopts the grid-connected inverter fault ride-through method considering symmetric and asymmetric faults according to any one of claims 1 to 7.

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