239 results about "Low voltage ride through" patented technology

The invention discloses an online prediction method for a transient frequency track of a power grid under coexistence of wind power low voltage ride through and off-grid, and belongs to the technical field of operation and control of a power system. A multi-source heterogeneous data fusion monitoring system is constructed, power grid and wind turbine generator data are collected, faults are recognized through an improved algorithm, and feature vectors are output; building an energy flow model based on a fault result, calculating a trajectory divergence index by using technologies such as phase-space reconstruction, estimating power vacancy, and obtaining a power unbalance sequence; designing a prediction algorithm by using the sequence, predicting a frequency trajectory in combination with an improved K-nearest neighbor algorithm and a trajectory feature library, and introducing a confidence coefficient to evaluate a correction error; and finally, establishing a three-level control response system, and implementing multi-time scale cooperative control according to a prediction result. The method can accurately predict the frequency trajectory, effectively deal with the wind power fault, improve the stability of the power grid and the wind power consumption capability, and provide powerful guarantee for the safe and stable operation of the power grid.

The invention discloses a low-voltage ride-through control method of a flywheel energy storage system, which is based on a low-voltage ride-through control strategy of model predictive current control (MPCC) so as to improve the low-voltage ride-through capability of the flywheel energy storage system when a power grid fails. A future current value is predicted through system modeling and a prediction algorithm, so that effective control is realized. The MPCC-based machine side-power grid side coordination control strategy can quickly respond to the voltage sag of the power grid, provide reactive power support, stabilize the voltage of the direct current bus, and ensure the safe and reliable operation of the flywheel energy storage system during the voltage sag period of the power grid. A traditional pulse width modulation (PWM) technology is abandoned, the optimal switching state is directly selected through a limited control set, and hardware implementation of a power grid side converter is simplified. A differential control strategy aiming at a power grid symmetric fault (three-phase voltage sudden drop) and an asymmetric fault (single-phase grounding) is provided, the method is suitable for a complex power grid fault scene, and the system universality is improved.

A low voltage ride through control method for a grid-forming inverter based on dynamic internal potential adjustment comprises the following steps: detecting a voltage per unit value of a grid-connected point in real time, and comparing the voltage per unit value with a threshold value to judge a voltage drop event and trigger low voltage ride through control; dynamically calculating active and reactive power reference values through a reactive compensation equation and an active current limiting equation according to the voltage amplitude and the power reference value before falling during the ride-through period; inputting the active reference value into a virtual rotor motion equation to generate a reference phase, and outputting a phase reference signal in combination with a dual-mode phase compensation controller; superposing the reactive reference value with the reference voltage through a reactive voltage regulating ring to generate a voltage amplitude reference signal; synthesizing an internal potential according to the phase and the amplitude reference signal, and obtaining an inductive current reference value through virtual impedance control and current amplitude limiting; and finally, a driving signal is generated through the current inner loop controller and the modulation module. According to the invention, overcurrent can be effectively inhibited, rapid reactive power support is provided, and synchronous stability and smooth transition in a fault period and a recovery process are ensured.

The invention discloses a tracking-network construction combined low-voltage ride-through control method based on transient support. The method comprises the following steps: S1, analyzing transient voltage characteristics and requirements of a network construction-tracking network converter; s2, analyzing a transient voltage support target of the network construction-network following type hybrid multi-machine system; s3, constructing a network construction-network following type hybrid multi-machine system control strategy; and S4, on the basis of the network construction-network following type hybrid multi-machine system control strategy constructed in the S3, optimizing the low voltage ride-through control of the network following type converter and the transient voltage control of the network construction type converter. According to the control method disclosed by the invention, the advantages of the network-building / network-following converter are complemented, the control between the network-building / network-following converter and the network-building / network-following converter is coordinated, and the transient voltage of the power grid is actively supported by using the multi-machine converter system.

The invention discloses a direct-current voltage self-balancing method in the high-low voltage ride-through process of a high-voltage frequency converter, and the method comprises the steps: obtaining an electric signal of the high-voltage frequency converter, calculating the Lyapunov index of a system in real time based on the electric signal, so as to quantify the chaotic state of the system, and generating a real-time Lyapunov index sequence; according to the real-time Lyapunov index sequence, the gradient of the real-time Lyapunov index sequence relative to a preset system state variable is determined, and a Lyapunov gradient field is constructed; using the Lyapunov gradient field to generate a basic control quantity through nonlinear mapping; and converting the basic control quantity into a pulse width modulation parameter to form a PWM control signal set to be applied to the high-voltage frequency converter. According to the method, the Lyapunov gradient field is constructed to provide prospective direction guidance for control, so that the chaotic oscillation is quickly suppressed, and the dynamic stability of the system under power grid disturbance is remarkably improved.

The invention is suitable for the technical field of power electronics and power transmission, and provides a low voltage ride-through control method and system for a network construction type converter, and the method comprises the steps: carrying out the conventional VSG control according to a VSG control strategy, and continuously monitoring the difference between the voltage of a power grid and a set reference value, so as to judge whether a fault occurs or not; when it is detected that the power grid breaks down, homodyne control is carried out on an active power control ring and a reactive power control ring of the grid-forming type converter so as to fix the phase and the amplitude of the output voltage of the converter; calculating and injecting a positive sequence compensation voltage and a negative sequence compensation voltage according to the drop degree of the power grid voltage; and according to the predicted impact current value, dynamically calculating and inputting adaptive virtual impedance. The power angle and the voltage in the fault period can be ensured to be stable, transient overcurrent is effectively restrained, and large power fluctuation is not caused.

The invention discloses an enhanced SVG low voltage ride through method, and belongs to the technical field of electrical automation equipment, and the method comprises the steps: carrying out the three-phase voltage synthesis of a self-built voltage amplitude and a self-built voltage phase, and obtaining a current reference value through an electromagnetic square; according to the self-built voltage phase and the current reference value, a bridge arm differential mode voltage modulation wave is obtained through inner loop current control; obtaining a main circuit commutation actual value of the enhanced SVG, and obtaining a bridge arm common-mode voltage modulation wave through circulating current suppression control in combination with the self-built voltage phase; actual energy and rated energy of the enhanced SVG are obtained, and an energy modulation signal is obtained through an energy control ring; and after modulation is carried out according to the bridge arm differential mode voltage modulation wave, the bridge arm common mode voltage modulation wave and an energy modulation signal, a switching signal is generated to control the enhanced SVG, and low voltage ride through is realized. According to the invention, the problem that the enhanced SVG fails or is off-network under the condition of low voltage can be solved.

The invention relates to the technical field of photovoltaic energy storage converters, and particularly discloses an energy storage converter control method and system under low voltage ride through, and the method comprises the steps: obtaining a grid-connected point voltage value of a photovoltaic power station, determining a voltage state value according to the grid-connected point voltage value of the photovoltaic power station, and judging a low voltage ride through state of a power grid according to the voltage state value; if it is judged that the power grid is in the low-voltage ride-through state, an energy storage converter control strategy is determined according to energy storage converter operation parameters in the power grid low-voltage ride-through process; obtaining performance data of the energy storage converter, and determining an initial control strategy adjustment parameter according to the performance data of the energy storage converter; and correcting the initial control strategy adjustment parameter according to the voltage state value to obtain a corrected control strategy adjustment parameter, and adjusting the energy storage converter control strategy according to the corrected control strategy adjustment parameter to obtain a final control strategy. The control effect of low-voltage ride-through can be effectively improved, and the reliability and stability of power grid operation are ensured.

The invention discloses a VSG-based low-voltage ride-through hybrid control method for a network-building converter. The method comprises the following steps: acquiring grid-connected point voltage and output current of a grid-forming converter in real time, and judging whether to enter a low-voltage ride-through state according to a grid voltage drop degree; in the initial stage of a fault, a current reference saturation mode is adopted to quickly limit the output current of the converter so as to prevent a power device from being damaged by overcurrent; in the fault duration stage, a dynamic self-adaptive virtual impedance and reactive power reference coordinated regulation mechanism is introduced, so that the converter gradually recovers the reactive power injection capability while limiting the fault current, thereby realizing effective support for the grid-connected point voltage; when the voltage of the power grid drops seriously, the capacity of the inverter can be reserved for the reactive power support by temporarily reducing the output of the active power. According to the method, the current protection and voltage support requirements during the fault period are considered, and the operation stability and the power grid adaptive capacity of the grid-forming converter in the low voltage ride-through process are improved.

The embodiment of the invention discloses a junction temperature control method and device for an inverter switching device, and the method comprises the steps: determining a target reactive current for supporting the operation of a power grid according to a measured power grid impedance parameter under the condition of low voltage ride through, and determining the minimum bus voltage of an inverter under the target reactive current, and then the output reactive current of the inverter is controlled to be the target reactive current, so that stable operation of the power grid can be supported under the condition of low voltage ride through of the power grid. The bus voltage of the inverter is adjusted between the preset maximum bus voltage and the preset minimum bus voltage, the target bus voltage meeting the condition that the junction temperature of the switching device does not exceed the preset junction temperature upper limit is determined, and the junction temperature of the switching device in the inverter does not exceed the safety range by controlling the inverter to operate at the target bus voltage subsequently. And the operation safety of the system is improved.

The invention provides a grid-connected converter fault transient process control parameter security domain determination method and device, and relates to the technical field of power systems. The grid-connected converter fault transient process control parameter safety domain determination method comprises the following steps: solving a power system equation of a target phase-locked loop by using structural parameters of a target power grid, and obtaining a first analytical expression of an output phase of the target phase-locked loop in a low-voltage ride-through stage after a short-circuit fault occurs in the target power grid; according to the first analytical expression, determining a low-pass phase-locked stability constraint; wherein the low-voltage ride-through phase-locked stable constraint is used for constraining that the output phase of the target phase-locked loop is not out of step in the low-voltage ride-through stage; determining a first parameter domain of a control parameter of the target grid-connected converter according to the low-pass phase-locked stability constraint; and determining a control parameter security domain of the target grid-connected converter based on the first parameter domain. According to the method, the safety domain of the control parameters of the grid-connected converter can be efficiently and accurately determined, so that the short-circuit fault ride-through capability of the grid-connected converter is effectively improved.

The invention discloses a double-fed fan low voltage ride through cooperative control method based on power prediction, and belongs to the technical field of wind power generation. The method comprises the following steps: inputting data; performing power prediction based on a CNN-LSTM (Convolution and Long Short Term Memory Neural Network); converter capacity dynamic distribution calculation; the invention relates to an improved direct power control strategy design. According to the method, the CNN-LSTM power prediction model is introduced, so that the problems that traditional direct power control depends on real-time power feedback, a control instruction lags, and consequently, the voltage of a direct-current bus is unstable and reactive power support is delayed during low-voltage ride-through are solved. Through the predicted active power curve, the capacity distribution strategy of the converter is adjusted in advance, so that the reactive power support response is accelerated. Through the adaptive hysteresis control technology, the switching frequency is reduced in the low-voltage ride-through period to protect the device, so that the low-voltage ride-through operation capability of the doubly-fed fan is improved.

The invention discloses a photovoltaic power grid fault transient control method, device and equipment, and relates to the technical field of photovoltaic auxiliary equipment, and the method comprises the following steps: obtaining the operation data of a photovoltaic grid-connected point, constructing a three-phase coupling characteristic matrix, and generating a disturbance discrimination result according to the dynamic evolution of the three-phase coupling characteristic matrix; based on a disturbance judgment result, collecting three-phase output current of the photovoltaic inverter, calculating disturbance increment of each phase of current, extracting a stable current component during a fault period based on low-voltage ride-through control logic, and calculating equivalent support power of the stable current component at a fault point; the equivalent support power is compared with a preset arc extinguishing threshold value, and the dissociation condition of the fault point is dynamically evaluated; when the fault point is not free, the photovoltaic inverter is controlled to perform state conversion, so that the equivalent support power is lower than an arc extinguishing threshold value; and after detecting that the voltage of the fault point is recovered and the arc light is extinguished, dynamically adjusting the reclosing time sequence based on the voltage recovery rate. The problems that arc light is difficult to extinguish and the reclosing failure rate is high are solved.

The invention provides a low-voltage ride-through control method and system for power electronic equipment. The method comprises the steps that the control mode of the power electronic equipment is set to be double-closed-loop control; in the double-closed-loop control mode, according to outer-loop control parameters of the power electronic equipment, instruction values of positive and negative sequence currents of outer-loop control are calculated; carrying out amplitude limiting on the instruction values of the positive and negative sequence current, and carrying out vector fusion on the instruction values of the positive and negative sequence current after amplitude limiting to obtain the instruction values of the positive and negative sequence current after the maximum value is limited; performing positive and negative sequence current control according to the positive and negative sequence current instruction value after the maximum value is limited, and completing low-voltage ride-through; vector fusion is carried out on the instruction values of the positive sequence current and the negative sequence current after amplitude limiting, fault current suppression based on the low voltage ride through process can be achieved, the large overcurrent phenomenon is avoided, tripping conditions are reduced, and it is guaranteed that low voltage ride through can be achieved with high probability on the premise that normal control strategy logic is not affected.

The invention discloses a DFIG and SVG collaborative reactive power support strategy adopting active-disturbance-rejection control. A first-order linear active-disturbance-rejection controller is designed to replace traditional PI control of a voltage outer ring of a doubly-fed wind generating set grid side converter; if the voltage drop occurs at the grid-connected point of the wind power plant, designing a q-axis current instruction value of the grid-side converter during the fault period as q-axis input of current inner loop control of the grid-side converter of the doubly-fed wind generating set, so that the doubly-fed wind generating set emits reactive power; after compensation, if the power factor of the doubly-fed wind generating set is smaller than a preset threshold value, the SVG device is made to send out reactive power according to the designed q-axis current instruction value of the SVG during the fault period. And after the fault is cleared, the q-axis current instruction value of the SVG is redesigned, so that the SVG device absorbs reactive power, and the overvoltage risk of the grid-connected point is reduced. According to the invention, a DFIG and SVG cooperative reactive power support strategy of active disturbance rejection control is adopted to meet the reactive power demand in the low voltage ride through period, and the operation stability of the wind power plant is effectively improved.

The invention provides a distributed photovoltaic grid-connected converter low-voltage ride-through control method based on sum-difference coordinate transformation, and solves the problems of insufficient synchronism, poor stability, insufficient reactive power support potential excavation and the like existing in collaborative response under power grid voltage drop during distributed photovoltaic grid connection. According to the method, impedance modeling and equivalent symmetry transformation are carried out on the distributed photovoltaic inverter, and a coupling multi-dimensional matrix equation is established; an original coupling system is decoupled into a sum current channel and a plurality of difference current channels, the control complexity is simplified, and an open-loop output impedance expression and a closed-loop output impedance expression are deduced; secondly, formulating a refined active / reactive current collaborative distribution strategy for different voltage drop depths, dynamically calculating the minimum reactive current during voltage drop, preferentially meeting the national standard, and maximizing active output or balancing loss under the limit of rated current; and finally, through sum-difference coordinate transformation, the total current demand and distribution are efficiently decoupled and issued to a current loop controller of each inverter, so that rapid, synchronous and stable cooperative operation of multiple inverters is realized.

The invention discloses a dynamic reactive current control method and a dynamic reactive current control system for a grid-forming type grid-connected converter, and the method comprises the steps: adding compensation control in a voltage amplitude control link of the grid-forming type grid-connected converter on the basis of the control of the grid-forming type grid-connected converter, and superposing a voltage compensation signal on a voltage reference value so as to realize the dynamic reactive current control of the grid-forming type grid-connected converter. The control method comprises the steps of signal acquisition and calculation, low voltage ride through state judgment, reactive power limitation calculation in a normal state, reactive power limitation calculation in a low voltage ride through state, voltage compensation control and voltage set value control. According to the method, the voltage compensation item calculated based on the reactive current limitation is superposed on voltage control, the voltage reference value is limited during low-voltage ride through, and the compensation item is calculated based on the reactive current limitation, so that the limitation on the reactive current is more direct, and the accuracy of the low-voltage ride through is improved. The converter is protected, and meanwhile the converter has higher reliability in the transient process.

The invention discloses an improved control method for low voltage ride through of a distributed direct-driven wind turbine generator, and belongs to the technical field of grid-connected control of wind turbine generators. And when the voltage of the power grid drops, the distributed direct-driven fan enters a low-voltage ride-through state. The method comprises the following steps: firstly, establishing a dq-axis grid-connected system model of the distributed direct-driven fan; and then, by taking'reduction of active loss and improvement of terminal voltage 'as double control objectives, under the constraint of a grid-connected guide rule, a machine-side / grid-side current limit and a power limit, an improved multi-objective particle swarm optimization algorithm is adopted to solve optimal set values of active and reactive current online in real time, and the optimal set values directly act on a grid-side converter. Compared with an existing proportional reactive power injection method, on the premise that the grid-connected guide rule requirement is met during the fault period, the method can simultaneously provide reactive power support and raise the terminal voltage; active loss is reduced, and the power grid frequency is supported; according to the method, the low-voltage ride-through capability and the power generation economy of the wind power plant are remarkably improved.

Systems, devices, and methods for controlling grid-tied inverters with instantaneous synchronization and low-voltage-ride-through (LVRT) capabilities under a wide range of grid cable impedance without using a phase-locked loop.

The invention discloses a doubly-fed wind turbine generator control parameter optimization method based on the lowest point of the frequency of a power system under low voltage ride through, and the method comprises the steps: 1, considering the influence of a wind speed, a pitch angle and a rotating speed on a capture coefficient, and solving the capture power; 2, providing a virtual synchronous machine control strategy for active compensation of the wind turbine generator, solving a transfer function between the rotating speed of the wind turbine generator and the system frequency, and deducing a power frequency response transfer function of the wind turbine generator; 3, solving the equivalent inertia time constant of the wind turbine generator based on the transfer function, considering the influence of different working conditions of the wind turbine generator in low voltage ride through, performing weighted calculation on the equivalent inertia time constant of the system, and quantifying the power frequency response characteristics of the wind turbine generator in different working conditions; 4, solving a frequency variation based on a system equivalent inertia time constant and a power frequency response characteristic; and 5, solving system trajectory sensitivity, constructing a Hessian matrix based on the sensitivity, solving a parameter optimal value by an interior point method, and raising a frequency lowest point. The calculation accuracy of the frequency variation of the power system is improved.

The invention discloses a converter feedforward decoupling control method and system for improving low voltage ride through capability, and the method comprises the steps: firstly carrying out the dynamic lead compensation of a measurement voltage after d-q conversion, so as to actively offset the amplitude attenuation and phase delay introduced by hardware links, such as a low-pass filter, in a measurement link, and restore a real power grid voltage dynamic state; and based on the accurately compensated and corrected voltage signal, positive and negative sequence separation and feed-forward quantity calculation are carried out, and finally a reference voltage instruction is generated. In this way, it can be ensured that the input signal of feedforward control accurately reflects the instantaneous change of the power grid voltage, the dynamic response speed and precision of a control system are greatly improved, current overshoot and oscillation in the voltage drop period are effectively restrained, the low-voltage ride-through capacity of a converter is remarkably enhanced, and the stability of new energy grid connection is guaranteed.

The invention relates to the field of low voltage ride-through control, and particularly discloses a wind power converter low voltage ride-through cooperative control method and system, which starts conventional LVRT response through a fault detection module, provides basic reactive power support and inhibits active power, and evaluates a power grid recovery state through a power grid recovery state evaluation module. Key indexes such as grid-connected point voltage recovery slope, frequency deviation and system short-circuit capacity are comprehensively analyzed, and a power grid recovery health degree index is quantitatively generated. Then, based on the index, a self-adaptive active power recovery slope is decided by combining local states such as a direct current bus voltage of the fan itself and the like. And finally, the active power recovery module smoothly recovers power output according to the adaptive slope. Through the mode, the power recovery behavior of the fan is tightly coupled with the real-time bearing capacity of the power grid, cooperative recovery control of low voltage ride through is realized, the stability of the power grid is ensured, and the efficiency and safety of power recovery are improved.

The invention discloses a network construction type converter low voltage ride through control method and system based on voltage sag depth dynamic adjustment, and a storage medium. The method comprises the following steps: dividing voltage sag depth grades; collecting a grid-connected point voltage signal for preprocessing, calculating the voltage drop depth according to the preprocessed voltage, and judging the level of the voltage drop depth; if the voltage sag depth is in a normal state, traditional VSG control is executed to complete low voltage ride through, otherwise, the reactive-voltage sag coefficient, the output reactive power and the virtual impedance are updated according to the voltage sag depth; when the voltage drop is not recovered to a normal state or is recovered to be normal but does not last for a set time, continuously carrying out the process after dividing the depth grade of the voltage drop, otherwise, adjusting the droop coefficient according to discretization exponential attenuation, and recovering the active power according to a discretization active slope recovery strategy; according to the invention, the power grid support efficiency and safety in the low voltage ride through process can be improved, and secondary oscillation in the recovery period can be avoided.

The invention discloses a self-adaptive control method and system for a wind generating set in a low voltage ride through process, and the method comprises the steps: S1, collecting the operation data of the wind generating set in real time, the operation data comprising the rotating speed of a generator and a low voltage ride through process flag bit; s2, judging whether the flag bit in the low-voltage ride-through process is true or not; if so, switching the unit control system from a conventional power generation control mode to a low voltage ride through control mode; otherwise, maintaining the unit in the conventional power generation control mode; in the low-voltage ride-through control mode, transmission chain resistance-increasing self-adaptive control, variable-pitch response self-adaptive control and advanced variable-pitch self-adaptive control are executed in parallel; and S3, according to the final resistance increasing torque, the superposed variable pitch rate and the self-adaptive advanced variable pitch value, comprehensive control over the unit is executed. On the premise that blade clearance and load safety are ensured, unit power fluctuation in the low-voltage ride-through process can be reduced, and unit operation stability and safety are improved.

The invention discloses a frequency lowest point evaluation method considering a low-voltage ride-through process of a new energy unit, and belongs to the technical field of power systems. The method comprises the following steps: establishing a whole-system quasi-steady-state model, respectively constructing models for a synchronous machine, a new energy unit and a load, and replacing a differential equation of power electronic equipment such as the new energy unit with a nonlinear algebraic equation; based on the model, node voltage and injection current are updated through an alternate iteration method, key quasi-steady-state points when the new energy unit enters a low-voltage ride-through state and is in an off-network state are identified, and overall unbalanced power of the system is output; inputting the unbalanced power of each key quasi-steady-state point into the ASF model, and fitting a system frequency curve to obtain the lowest point of the frequency by considering the power vacancy of the low-voltage ride-through and off-network stages. The method does not need to depend on time domain simulation, can quickly and accurately evaluate the lowest point of the frequency, and is suitable for online stability evaluation of the power system.

The invention discloses a power distribution network voltage sag monitoring point multi-target selection method considering a distributed power supply low voltage ride through characteristic. The method comprises the following steps: providing a distributed power supply low voltage ride through strategy; deriving a voltage sag amplitude analytical expression under various short circuit fault types considering the low voltage ride through characteristic of the distributed power supply; introducing a position variable to construct a function relation between a voltage sag amplitude and a fault position; solving a voltage sag domain critical point by using a differential evolution algorithm; based on the sag domain critical point, establishing a monitoring point multi-target selection model taking economical efficiency, redundancy and construction urgency minimization as a target function; solving the established monitoring point multi-target selection model by adopting a multi-target particle swarm algorithm to obtain a Pareto optimal solution set; and according to the obtained Pareto optimal solution set, adopting an ideal point method to screen out an optimal point distribution scheme. According to the method, the voltage sag domain can be accurately divided, and multi-objective optimization of economical efficiency, low redundancy and low construction urgency of monitoring point layout is realized on the premise of satisfying panoramic observability.

The invention discloses a full-power type wind turbine generator fault occurrence moment current analysis method and related equipment, and the method comprises the steps: obtaining control parameters and operation parameters of a full-power type wind turbine generator, and when low-voltage fault ride-through is detected, substituting the control parameters and the operation parameters into a fault ride-through controller model, fault current partition logic is combined to obtain fault current analytic expressions corresponding to different fault state intervals, and then the current instruction data are substituted into the fault current analytic expressions under the corresponding fault state intervals, so that current analysis is carried out through the fault current analytic expressions and a closed-loop transfer function, and fault current analysis is carried out through the fault current analytic expressions and the closed-loop transfer function. And obtaining the fault current at the fault occurrence moment of the full-power wind turbine generator. According to the scheme, the control strategy of the active and reactive current during low voltage ride through is analyzed, and the current analysis formula of the fault occurrence moment corresponding to each fault current partition is obtained by combining different fault current partitions, so that the fault current of the unit fault occurrence moment is obtained based on the current analysis formula.

The invention discloses a relay protection short-circuit current calculation method and device of a photovoltaic-energy storage combined system. The method comprises the steps that an inverter equivalent mathematical model of the photovoltaic-energy storage combined power generation system is established, and the inverter equivalent mathematical model enables an inverter in a fault state to be equivalent to a positive sequence current source; based on the inverter equivalent mathematical model, in combination with a low voltage ride-through control strategy, determining a function relationship between the output of the positive sequence current source and the positive sequence voltage of the grid-connected point, and forming a fault current calculation expression; and obtaining positive sequence voltage information of the grid-connected point when the power grid fails, substituting the positive sequence voltage information into the fault current calculation expression, and calculating to obtain the short-circuit current provided by the photovoltaic-energy storage combined system.

The invention discloses a photovoltaic inverter low voltage ride through capability improvement method based on staged control parameter optimization, and belongs to the technical field of photovoltaic power generation control optimization, and the method comprises the following steps: S1, dividing a transient process into three stages, considering different dynamic characteristics of unit operation corresponding to each stage, and constructing evaluation indexes of each stage; s2, performing correlation analysis on each control parameter and the evaluation index of the photovoltaic grid-connected inverter by adopting a Spearman correlation coefficient analysis method, and determining the control parameter having strong correlation with the evaluation index of each stage; and S3, according to a correlation analysis result, performing staged optimization on the control parameters of the inverter by using a particle swarm algorithm. By the adoption of the method, physical characteristics of the whole low-voltage ride-through process are considered, a low-voltage ride-through process multi-target evaluation system is established, and the relation between the control parameters and the performance of all stages of the transient state is revealed through correlation analysis.

The invention provides a cooperative low-voltage ride-through control method and related device based on a network construction type and network following type three-terminal interconnection system, and the method comprises the steps: triggering a cooperative low-voltage ride-through control mechanism in response to a voltage drop fault generated at an AC side connected with a network construction type converter; performing cooperative control on each converter based on the mechanism; wherein the control network construction type converter only undertakes AC side voltage establishment and current safety survival functions, realizes current limiting control through adaptive virtual impedance, and does not participate in DC side energy adjustment of a common DC bus; the DC voltage control type grid-following converter is controlled to suppress DC voltage double-frequency fluctuation of the common DC bus, and actively absorb and compensate double-frequency power disturbance introduced by the grid-forming converter; and controlling the active power control type grid-following converter to avoid active power adjustment during the voltage drop fault period. A collaborative low-voltage ride through control mechanism is provided, the direct-current voltage fluctuation is reduced, and the overall low-voltage ride through capacity of the system is improved.