176 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.

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 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 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 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 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 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 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 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 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.

A low voltage ride through detection method and device are provided. The low voltage ride through detection method comprises: determining an adjustment value of a preset parameter of a power grid based on a grid voltage, wherein the preset parameter comprises at least one of current, current frequency and power factor angle; adjusting the preset parameter of the power grid based on the adjustment value; and detecting whether the power grid satisfies a low voltage ride through condition based on the grid voltage after the preset parameter of the power grid is adjusted, thereby enabling a wind power generator to accurately identify a power grid fault under a weak power grid to enter low ride through, while avoiding instability of a power grid fault ride through system under a weak power grid.

The invention discloses a fault component compensation type low-voltage ride-through control method and system of a distributed power generation system and a storage medium, and the method comprises the steps: introducing a difference value between a d-axis voltage instantaneous component of a common coupling point and a system rated voltage into a quadrature-axis voltage compensation branch during the voltage drop period of a power grid, and obtaining a quadrature-axis voltage compensation amount through compensation coefficient calculation, the calculation result is added to the phase-locked loop control link, the q-axis voltage of the common coupling point tracked by the phase-locked loop is adjusted in real time, and the problem that the phase angle of the distributed power generation system is prone to loss stability during the transient state is effectively solved without any additional control information. And the low-voltage ride-through capability of the distributed power generation system under the extreme working condition is obviously enhanced.

The utility model provides a power supply circuit for preventing low voltage ride through and a wind power converter, in the power supply circuit, a first change-over switch comprises a first switch body and a first normally open contact, and a second change-over switch comprises a second switch body, a second normally open contact and a normally closed contact; the first switch body and the normally closed contact are connected in series and then are connected between the first control end and the second control end of the controller; a first power supply input end of the uninterruptible power supply is connected with a first power supply end of the alternating current power supply, one end of the first normally open contact is connected with a second power supply end of the alternating current power supply, the other end of the first normally open contact is connected with a second power supply input end of the uninterruptible power supply, and the second normally open contact is connected with the first normally open contact in parallel; the second switch body is connected between the first power supply output end and the second power supply output end of the uninterruptible power supply. When the high voltage of the primary side of the auxiliary power supply drops too much and the time is too long, the coil of the pre-stage contactor is prevented from being damaged.

The invention discloses a current differential protection adaptability analysis method for an alternating current line of a new energy network flexible direct output system, and belongs to the technical field of power system relay protection. Establishing a system fault equivalent model based on a low-voltage ride-through control strategy of power electronic equipment at two sides of the outgoing line; according to different asymmetric fault types and a fault point boundary condition equation, deriving mathematical models of positive-sequence, negative-sequence and zero-sequence currents on the two sides of a fault phase line; calculating a differential current and a braking current, and establishing a function relationship between the differential current and the braking current and the VSG internal potential reference value, the transition resistance and the current sequence component ratio; and the action sensitivity of protection under different working conditions is judged by comparing the current differential protection ratio braking coefficient setting value with the current differential protection ratio braking coefficient setting value. The association rule of the current differential protection refusal risk and the low-pass control parameters under the high transition resistance fault is disclosed, a basis is provided for protection setting and control strategy optimization of a network construction flexible direct output system, and the problems that a protection adaptability analysis method is weak and the influence rule of the control parameters is not clear yet are solved.

The application discloses a kind of wind turbine group low voltage ride through model construction method and device, comprising: obtaining the operating variable dataset of wind turbine group;According to the operating variable dataset, the initial wind turbine group low voltage ride through model constructed is trained, to obtain wind turbine group low voltage ride through model.The application does not need to construct wind turbine group equivalent model and other mechanism model through the physical principle of wind turbine group, avoids the state of each wind turbine in wind turbine group is different to need to model each wind turbine respectively, and directly realizes the construction of wind turbine group low voltage ride through model through the operating data of wind turbine group, and then does not need to determine the parameter information of each wind turbine in wind turbine group, so that the application has high accuracy and high reliability.

Embodiments of the application disclose a direct-drive wind turbine low-voltage ride-through control method and related equipment. The method comprises: generating a ride-through high-level signal to activate a low-voltage ride-through mode when a low-voltage ride-through trigger module detects that a current voltage value of a target power grid where a target direct-drive wind turbine is located is lower than a preset reference value; calculating a voltage drop depth according to the current voltage value and the preset reference value; a low-voltage period reactive power control module of a grid-side control system controls the target direct-drive wind turbine to output reactive power to the target power grid to support the power grid according to the voltage drop depth; and an active power control module of a machine-side control system controls output power of the target direct-drive wind turbine according to the voltage drop depth. The direct-drive wind turbine low-voltage ride-through control method overcomes the direct-current voltage overvoltage oscillation defect of the prior art and limits the machine-side electromagnetic power during the wind turbine low-voltage ride-through period from the source.

This invention discloses a method and system for evaluating segmented voltage regulation intensity during the low-voltage ride-through process of a new energy power plant, comprising: acquiring key operating parameters of the new energy power plant; calculating voltage constraints at different stages based on the key operating parameters, determining the voltage constraint range corresponding to each stage, thereby dividing the low-voltage ride-through process into three stages; determining the reactive current corresponding to each stage, determining the reactive power based on the reactive current, and establishing a voltage regulation characteristic analysis model corresponding to each stage based on the reactive power; acquiring the grid connection point voltage amplitude at different sampling times during the low-voltage ride-through process of the new energy power plant, determining the target stage corresponding to each grid connection point voltage amplitude based on the grid connection point voltage amplitude and the voltage constraint range, and determining the voltage regulation intensity of the new energy power plant at different sampling times during the low-voltage ride-through process based on the voltage regulation characteristic analysis model corresponding to the target stage.

The embodiment of the invention provides a low-voltage ride-through protection threshold value setting method and device. The method comprises the steps that the power grid strength and equivalent impedance of an alternating current power grid connected with a grid-connected point in a power system are determined; obtaining grid-connected impedance and equivalent transmission power of an energy system connected to a new energy side in the power system; determining the new energy permeability in the power system; constructing a voltage stability analysis model according to the actual power grid parameters of the power system and a preset interface equation; and processing the power grid strength, the equivalent impedance, the grid-connected impedance, the equivalent transmission power and the new energy permeability by using the voltage stability analysis model to obtain a low voltage ride through protection threshold setting value. The method provided by the invention comprehensively considers the power grid strength and the new energy permeability, and is suitable for most new energy grid-connected scenes.

A network type power supply fault current suppression method based on additional virtual impedance and power angle control, comprising: if it is judged that the network type power supply with virtual synchronous generator (VSG) as the main structure is below the threshold after the fault occurs, the reactive power reference value is calculated and adjusted according to the drop degree to meet the low voltage ride through condition; the difference between the VSG output voltage and the grid voltage and the maximum bearing current of the inverter are used to quantitatively calculate the virtual impedance required for current limiting; the active power reference value is modified by using the reactive loop reference voltage before and after the fault to maintain the VSG power angle stability; the mathematical model of the inverter in the VSG is constructed, the virtual impedance is added to the control loop by using the coordinate transformation and the grid side current transformation, and the output drive signal is controlled by inputting the voltage modulation into the SVPWM, so that the inverter completes the overcurrent limiting. The application solves the problem that the output current of the network type new power system increases too fast to cause system instability when the fault occurs.

This invention patent application provides a low-voltage ride-through control method and system for power electronic equipment based on negative-sequence current, comprising: performing primary and secondary limiting on the command values ​​of positive and negative sequence currents in the outer loop according to a predetermined positive and negative sequence current command threshold range; obtaining positive and negative sequence voltage reference values ​​through the transfer function of the inner loop controller based on the command value of the positive sequence current obtained after primary limiting, the command value of the negative sequence current obtained after secondary limiting, and the corresponding measured values ​​of the positive and negative sequence currents; generating positive and negative sequence command values ​​based on the positive and negative sequence voltage reference values ​​using coordinate system transformation; and controlling the power electronic equipment to complete low-voltage ride-through according to the positive and negative sequence command values. The negative sequence current command protection range of this invention is a reasonable limitation of the negative sequence current command value during a fault, achieving the effect of reducing the negative sequence component of the system, enabling rapid recovery to the pre-fault state, and not conflicting with new energy control.

The present application relates to the technical field of smart grid, and discloses a virtual synchronous machine low-voltage ride-through control method, system and medium, the method first determines the operating state of the virtual synchronous machine based on the electrical quantity of the virtual synchronous machine, and on the basis of taking into account the transient stability and the maximum output power capacity of the virtual synchronous machine, adjusts the active reference value during the fault to ensure that the operating point exists, which can maximize the current capacity of the virtual synchronous machine converter, improve the dynamic reactive voltage support capability of the virtual synchronous machine and the transient synchronization stability of the system. At the same time, during the fault recovery stage, based on the virtual internal electromotive force steady-state amplitude compensation control, the active power impact caused by the excessive internal electromotive force amplitude of the virtual synchronous machine reactive voltage integral control at the fault recovery time is avoided; the reactive power is quickly restored to the normal value, the over-release of the reactive power caused by the integral control is reduced, the voltage peak value at the end of the voltage fault is reduced, and the transient voltage stability of the system is improved.

The application relates to a low-voltage ride-through control method of a virtual synchronous generator considering power angle stability and overcurrent suppression, which comprises the following steps: obtaining a virtual synchronous generator control model, monitoring transient stability and voltage drop of the virtual synchronous generator control model, and obtaining a monitoring result; when transient synchronous instability appears in the monitoring result, adjusting an active power reference instruction during a transient period according to actual output active power by using an adaptive active power instruction strategy; and when voltage drop or voltage drop recovery appears in the monitoring result, suppressing transient impact overcurrent based on an adaptive virtual synchronous impedance control strategy. The application not only realizes non-divergence and non-fluctuation of a power angle during any voltage drop depth, but also realizes fast and smooth recovery to a normal influence mode without overcurrent.

The application discloses a kind of wind-fire bundling system transient stability boundary construction method and device, method includes: based on the structure characteristics and operating characteristics of wind-fire bundling system, the equivalent model of wind-fire bundling system is established;Based on the operation of wind-fire bundling system in different fault stages, and in combination with the equivalent model, and the wind power generator set output and grid point residual voltage of wind-fire bundling system during fault low voltage ride through, determine the power and phase angle curve of wind-fire bundling system in different fault stages;Based on the power and phase angle curve of wind-fire bundling system in different fault stages, determine the stability margin of wind-fire bundling system about wind power generator set output and grid point residual voltage;Based on the stability margin about wind power generator set output and grid point residual voltage during fault, construct the transient stability boundary based on wind power generator set output and grid point residual voltage.The application can be according to wind power generator set output and grid point residual voltage, quickly and accurately judge whether wind-fire bundling system is located in stable region.

The application provides a repeated low voltage ride through risk assessment method and system based on a sliding mode theory analysis, and belongs to the technical field of low voltage ride through risk assessment. The application comprises the following steps: based on a grid-connected system model of a grid-following type converter with low voltage ride through control, eight-order unified state space expression is constructed in combination with a current inner loop, a phase-locked loop and a dynamic of an alternating current main circuit; a sliding mode surface function is constructed by using a difference between a grid-connected point voltage and a LVRT switching threshold value, and a direction derivative of a sub-state space vector field about the sliding mode surface function in a normal operation mode and a LVRT mode is used as a chatter criterion; and the evolution trend of the grid-connected point voltage near the low voltage ride through threshold value is judged according to the sign characteristic of the chatter criterion, so as to assess the risk of repeated low voltage ride through. The application can quantitatively reflect the influence of device side and grid side parameters on the repeated low voltage ride through of the system, and provides a novel and practical method for stability assessment and parameter optimization of a new energy grid-connected system.