2654 results about "Grid voltage" patented technology

The invention discloses a charging chip real-time power scheduling control method, and relates to the technical field of new energy automobile charging pile power scheduling, and the method comprises the following steps: S1, obtaining the operation parameters of charging equipment in real time, including the voltage fluctuation value of an input power grid, the output current of a charging interface, and the temperature of a charging chip; according to the method, the power grid voltage fluctuation, battery SOC / temperature and chip working condition multi-source data are collected in real time, a multi-target optimization model of dynamic weight distribution is combined, the service life loss of the battery is minimized, the charging efficiency and the power grid load are balanced at the same time, the user charging mode and the battery state difference are taken into consideration by adopting a priority scheduling strategy, and the charging efficiency is improved. Millisecond-level power fine control is achieved through cooperative adjustment of the PWM duty ratio and the switching frequency, personalized charging requirements are met, the overall energy efficiency is improved, a dual safety defense line is constructed through a graded load reduction protection mechanism and a fuzzy control algorithm, and a power distribution scheme is intelligently reconstructed when a power grid is abnormal or a battery is overheated.

The invention discloses an energy storage control and adjustment method and system for distributed photovoltaic consumption, and relates to the technical field of renewable energy sources, and the method comprises the steps: obtaining illumination intensity, temperature data and historical load data, and predicting the future photovoltaic power generation amount and load demand changes; analyzing the voltage fluctuation of the power grid and the charging demand of the energy storage system based on the prediction results of the photovoltaic generating capacity and the load demand; according to the health state of the energy storage battery, optimizing the charging and discharging depth, and outputting an energy storage adjustment plan; dynamically optimizing the charging and discharging plan and reactive power regulation of the energy storage system by using a multi-objective optimization algorithm, and generating an optimal reactive power regulation instruction; according to the reactive power adjustment instruction, performing transformer area self-adaptive cooperative control to obtain a cooperative control result; according to the invention, through an area adaptive cooperative control mechanism, the reactive power regulation capability of the adjacent areas can be automatically coordinated when the regulation capability of the local energy storage system is insufficient, and the stability of the power grid and the utilization efficiency of the energy storage system are further enhanced.

The invention relates to a V2G-based alternating current charging power adjusting method and device. The method comprises the following steps: carrying out multi-scale data acquisition and preprocessing on a V2G alternating current charging system to obtain a standardized system state data set; constructing a system dynamic model comprising a power grid voltage characteristic and a charging power characteristic; carrying out decomposition to obtain a power output mapping relation calculation, and obtaining a power modulation control parameter; establishing a fast and slow time scale coordination control framework, and designing a power regulation agent and a voltage regulation agent to obtain a coordination control strategy; checking a charging power limit value constraint, a voltage limit value constraint and a power factor constraint to obtain a constraint violation judgment result, and executing constraint projection calculation to obtain a target control instruction; and controlling a power conversion circuit of the charging pile to execute power regulation operation. According to the invention, a hierarchical control structure is adopted, the control complexity of the system is reduced, and the robustness and the adaptive ability of the control strategy are improved.

The invention discloses a fault ride-through hierarchical control method for a network-constructed converter, and the method comprises the steps: introducing a virtual resistor formed by fault current negative feedback into the voltage and current inner loop control of the network-constructed converter based on VSG control through a current inner loop dynamic amplitude limiting control layer after the converter enters a fault ride-through state, the size of the virtual resistor is adjusted in real time along with the amplitude of the fault current so as to carry out dynamic current limiting control on the virtual resistor; and the power outer loop dynamic compensation control layer dynamically adjusts an active power instruction value and a reactive power instruction value of the network construction type converter based on VSG control during the fault ride-through period according to the voltage drop degree of the power grid after the converter enters the fault ride-through state. And respectively performing active-frequency control and reactive-voltage control based on the active power instruction value and the reactive power instruction value. In addition, the method also comprises a state coupling and parameter self-adaption module. According to the method, the GFM converter can have better dynamic performance in the fault recovery stage.

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.

The invention discloses a power distribution network voltage control method based on distributed photovoltaic active-reactive cooperation, and the method comprises the steps: analyzing the influence of reactive / active injection on voltage stability through building a sensitivity matrix, deducing a critical control gain constraint condition, and guaranteeing the static stability of the voltage of a power distribution network; a photovoltaic inverter active / reactive cooperative control general model suitable for different scenes is constructed based on an intra-day scheduling and real-time control two-stage framework, and control curve parameters of each node photovoltaic inverter are optimized by taking minimization of network loss cost, active reduction cost, inverter voltage regulation cost and voltage deviation as targets in the intra-day scheduling stage; in the real-time control stage, active power reduction and reactive power regulation are dynamically coordinated based on an optimal control curve, reactive power margin is preferentially utilized to suppress voltage rise, and power flow distribution is directly regulated through active power reduction when reactive power capacity is saturated. According to the method, the safety and economy of the power grid are considered, and theoretical support and a practical solution are provided for voltage control of the high-permeability photovoltaic power distribution network.

According to the new energy grid-connected electric energy metering method and device, broadband harmonic characteristic information and inter-harmonic characteristic information are respectively obtained according to preprocessed power grid voltage and power grid current; after the broadband harmonic characteristic information and the inter-harmonic characteristic information are input into the influence analysis topology network, a first error compensation parameter is calculated by using an electric energy metering error output by the influence analysis topology network; based on a non-sinusoidal signal simulation model, combining the preprocessed power grid voltage and power grid current with the step wave signal to obtain a non-sinusoidal wave signal; performing error compensation calculation on the non-sine wave signal to obtain a second error compensation parameter; obtaining time-varying error data of the electric energy meter by using historical operation data of the electric energy meter; a target error compensation parameter is calculated based on the first error compensation parameter, the second error compensation parameter and the time-varying error data of the electric energy meter, the electric energy meter performs electric energy metering based on the target error compensation parameter, an electric energy metering result is obtained, and the accuracy of new energy grid-connected electric energy metering is improved.

The invention provides a wind power control system based on wind speed prediction, and relates to the field of intelligent scheduling control, and the system obtains a time sequence of real-time wind speed values and historical data of the wind speed values in a preset time period, encodes the real-time wind speed time sequence and historical subsequences respectively, extracts global long-term dependence and local disturbance characteristics, and carries out the prediction of the wind speed values according to the global long-term dependence and local disturbance characteristics. Semantic association of real-time features and historical similar scenes is dynamically fused through decision anchor points, a high-precision wind speed prediction value is generated based on fusion, real-time deviation analysis of the prediction value and cut-out wind speed is carried out, and a hierarchical power limiting strategy is triggered by combining a dynamic threshold adjustment mechanism. According to the scheme, the nonlinear time sequence rule of the wind speed is automatically captured through deep learning, the actual working condition change is dynamically responded, the prediction precision is effectively improved, the control delay is shortened, the power generation efficiency is optimized, and the power grid voltage stability is guaranteed.

The invention provides a GFM converter fault ride-through control method and system. According to the method, when the voltage drop of a power grid is detected, the power angle stability and the voltage supporting capability during a fault period are enhanced by adaptively adjusting active and reactive power reference values; meanwhile, when the output current exceeds a set threshold value, the virtual resistor and the reactance are dynamically injected, the transient impact current is rapidly suppressed, and dual limitation on the fault current is achieved. The control system comprises a voltage and current acquisition unit, a fault detection module, a self-adaptive power instruction control module, a dynamic virtual impedance control module and an instruction generation module, and all the modules operate cooperatively to form a complete closed-loop control structure. According to the method, the operation stability and the power grid supporting capacity of the GFM converter in weak power grid and fault scenes can be improved, and the requirements of power grid specifications such as GC0137 and the like are met.

The invention relates to the technical field of new energy power generation, in particular to an adaptive distributed new energy power generation equipment cooperative control method and system, and the method comprises the steps: extracting the state feature representation of each new energy power generation equipment from the operation parameters of the new energy power generation equipment; based on the state feature representation, determining an action boundary estimated value of each new energy power generation device by using a deep reinforcement learning algorithm; extracting an equipment state-action data pair according to the action boundary estimation value, and generating an empirical extended data set by simulating different disturbance amplitudes; based on the empirical extended data set, obtaining equipment operation reward parameters of the new energy power generation equipment by using a weighting method; obtaining a sharing experience correction set based on the equipment operation reward parameters; and iteratively determining a multi-device cooperative control optimization strategy by using a gradient optimization algorithm based on the shared experience correction set and the state feature representation. According to the invention, cooperative control of the new energy power generation equipment under abnormal fluctuation of the power grid voltage is realized, and the stability and safety of the power grid are improved.

A passivity-based dual-mode integrated control method for a grid-connected inverter (GCI) is provided. In view of the insufficient robustness of the conventional single-mode GCI in a high-impedance and low-inertia weak grid, and the problem of wideband oscillation of the grid voltage and grid current or even system instability in nonlinear application scenarios such as grid structure / parameter variation, and plug-and-play of the inverter, the dual-mode integrated control method performs modeling on the GCI based on a port-controlled Hamiltonian (PCH) model, thereby obtaining integrated control with a weighted passivity-based feedback control law for the GCI based on a grid-following (GFL) mode and a grid-forming (GFM) mode. Based on the dual-mode integrated control method, the stable operation of the GCI in severe grid conditions with large fluctuation of the impedance, and desirable robustness of the GCI in nonlinear working scenarios can be ensured.

The invention provides a split type direct current charging multi-split group charging and group control control system, and belongs to the technical field of split type direct current charging piles. The split type direct current charging system comprising a main control cabinet, a power distribution unit, a charging pile terminal and other hardware architectures is constructed; a voltage monitoring unit, a current sensor module, a harmonic filter and other multi-dimensional sensor networks are integrated to acquire power grid state data in real time, and a sliding time window method is used to carry out segmented analysis on the data to extract power grid characteristic parameters; establishing a multi-objective optimization model comprising a power balance equation and a power grid stability equation to calculate an optimal power distribution matrix, adopting a neural network to realize intelligent distribution and dynamic balance adjustment of the power of each charging pile terminal, and starting an emergency power redistribution mechanism to ensure stable operation of the system when the power grid is detected to be abnormal. The technical problem of unbalanced power distribution of the multi-pile charging system caused by power grid voltage fluctuation and harmonic pollution is solved.

The invention relates to a dynamic power regulation and control method and system for an electric vehicle charging pile, and the method comprises the following steps: S1, based on the real-time operation data of a charging pile cluster, employing a multi-source information fusion technology, collecting a power grid voltage fluctuation signal through a Hall sensor disposed at a charging pile end, and combining with the battery charge state data transmitted by a vehicle-mounted BMS, and eliminating noise interference by using an improved Kalman filtering algorithm, and realizing multi-dimensional data fusion by using a D-S evidence theory to generate a multi-source working condition feature set. The method has the advantages that the power grid voltage fluctuation signal and the battery charge state data are integrated through the multi-source information fusion technology, the improved Kalman filtering algorithm is adopted to eliminate noise interference, multi-dimensional data fusion is achieved in combination with the D-S evidence theory, the integrity and reliability of working condition feature extraction are remarkably improved, and the working condition feature extraction efficiency is improved. And the LSTM-ARIMA hybrid prediction model is utilized to synchronously process the nonlinear features and the periodic rules.

The invention relates to a load matching optimization method of a multi-channel gate driver and related equipment thereof. The method comprises the following steps of: acquiring grid current, grid voltage and switching frequency of the multi-channel parallel grid driver to obtain driver load operation data; performing region division processing on the operation space to obtain a safe operation region and a transition region; inputting a first adaptive prediction model for feature extraction to obtain a load balancing prediction result; parallel optimization calculation is carried out on the control strategy to obtain each driving channel control parameter, and each driving channel control parameter comprises a grid driving voltage regulating variable and a driving time sequence regulating variable; performing real-time adjustment on each driving channel control parameter to obtain a load balance adjustment instruction; and performing performance index evaluation calculation to obtain a performance optimization parameter, and updating the first adaptive prediction model to obtain a second adaptive prediction model. According to the invention, through cooperative control of voltage regulation and time sequence compensation, dynamic balance of each channel load is realized.

The invention provides a wide-voltage self-adaptive closed-loop vector swimming pool pump anti-interference method, and relates to the technical field of motor control and power electronics, and the method comprises the steps: collecting three-phase power supply voltage fluctuation characteristic parameters and motor operation state parameters in real time; performing amplitude compensation and phase synchronization correction on the voltage parameter based on the dynamic voltage compensation factor; a closed-loop vector anti-interference control model is constructed, and model parameters are adjusted in real time through a vector immunity coefficient; dynamically correcting control output by adopting a multivariable feedback regulation mechanism; executing an anti-interference instruction and synchronously updating PWM modulation parameters, and verifying a control effect in combination with hardware-in-the-loop simulation; and parameter self-learning optimization is realized through a genetic algorithm. The dynamic anti-interference capability under power grid voltage fluctuation and harmonic interference is improved, intelligent thermal management is realized through a temperature-voltage-current multi-dimensional coupling model, full-life-cycle self-adaptive optimization of the system is guaranteed, and the problems of compensation lag, insufficient harmonic suppression and poor long-term stability are effectively solved.

The invention relates to the technical field of distributed energy storage and intelligent power grid control, in particular to an intelligent distributed energy storage cluster collaborative management system. Comprising a state acquisition module used for acquiring local power grid state parameters of an edge computing node in real time; the power grid state parameters comprise power grid frequency, power grid voltage and a heartbeat communication state with the cloud management platform; the risk calculation module is used for calculating quantified island risk indexes; the mode judgment module is used for determining a current operation mode decision; the mode switching module is used for switching the system from a vertical cooperative mode to a horizontal autonomous mode when the island risk index is greater than an island switching threshold value; and when the island risk index is smaller than or equal to the island switching threshold value, the system is maintained to operate in the vertical cooperation mode. According to the system, misjudgment and missed judgment of a traditional single threshold value mode are overcome, it is ensured that the mode switching module can be switched to the horizontal autonomous mode from the vertical cooperative mode in time under the real risk, and decision making is accurate and reliable.

The invention provides a method and system for achieving elevator energy feedback data communication. The method comprises the steps that multi-modal data are collected, and fault features are extracted, encrypted and packaged; and after decryption, phase deviation of elevator operation and power grid voltage is calculated by utilizing an algorithm, a current phase is synchronously fed back, and a feedback instruction is generated. Uploading the harmonic suppression parameter to an energy center, calculating a demand, generating a region-level feedback strategy, dynamically distributing a feedback power upper limit, synchronizing the harmonic suppression parameter, and obtaining region-level feedback data. And aggregating feedback data, and setting a global optimization target, including cost minimization, feedback maximization and carbon emission reduction. And calculating feedback energy and carbon integral according to a target adjustment algorithm, automatically settling to an operator account, and adjusting the target of the next period. Through an algorithm and an optimization mechanism, the problem of energy waste of a brake resistor in a traditional feedback technology is solved, the feedback efficiency is improved, and energy waste is reduced.

The invention discloses an offshore wind power low-frequency networking system based on hybrid topology and a control method, in N onshore receiving end nodes of the offshore wind power low-frequency networking system, one node adopts an M3C current converter, N-1 nodes adopt DRU and MMC current converters, an offshore low-frequency power grid voltage is established through the M3C current converter, and the M3C current converter is connected with the M3C current converter; the power flow control of other power control nodes is realized through the DRU and the MMC, and by adopting the technical scheme of the invention, the engineering construction cost can be obviously reduced under the condition of ensuring the reliable operation of the system, and the method has a good application prospect.

The invention relates to the technical field of generator control, and particularly discloses an SVG static var generator control method and system, and the method comprises the steps: constructing a reactive-voltage sensitivity matrix containing a node sensitivity weight based on the real-time measurement data of a power grid, and obtaining a node sensitivity matrix; a dynamic sorting strategy of device priority grading is generated, a distributed compensation priority queue of all devices is obtained, and the devices comprise an SVG cluster and a photovoltaic inverter cluster; executing reactive power distribution under a capacity constraint condition based on the distributed compensation priority queue, and generating a target reactive power compensation amount with the capacity constraint condition; generating a hierarchical coordination control instruction of the SVG and the inverter according to the target reactive compensation amount, and obtaining a hierarchical control instruction set; executing the distributed cooperative compensation driven by the hierarchical control instruction set, and completing the dynamic regulation of the power grid voltage; the reactive power regulation capability of different devices in a power grid can be fully utilized, the accuracy and response speed of reactive power distribution are improved, and resource waste and excessive compensation are avoided.

The invention provides an electric energy quality compensation method and system based on power electronics, and relates to the technical field of power grid dispatching, and the method comprises the steps: collecting the voltage, current, harmonic content, reactive power, three-phase unbalance degree and other real-time multi-mode data of a power grid, and extracting key frequency spectrum features through wavelet transform denoising and windowing interpolation Fourier transform; and constructing a power quality feature vector. A self-adaptive fuzzy logic algorithm and power grid operation parameters are combined, a threshold value of a power quality index is dynamically adjusted, a multi-stage optimization strategy is divided based on the number of standard-exceeding indexes and importance analysis, and a dynamic compensation priority and a compensation strategy are generated. An improved particle swarm optimization algorithm is introduced, an inertia weight is dynamically adjusted, a constraint penalty function is introduced, output parameters of a power electronic compensation device are optimized, and effective compensation of power quality is realized by taking minimization of total active loss as a target.

The invention discloses an accurate zero crossing point control method for a built-in relay of a large-current electric energy meter, which relates to the technical field of power electronics and intelligent metering and comprises the following steps of: receiving a power grid voltage digital signal, determining a voltage zero crossing point by comparing symbol changes of adjacent sampling values, establishing a phase corresponding relation between voltage and current, and calculating a current phase corresponding relation; generating current zero crossing point prediction data; when a relay switching instruction is received, the specific moment of the next current zero crossing point is calculated, and the control signal sending moment is determined; a relay driving control signal is sent, the actual action completion moment of the relay is collected, the deviation from the expected zero crossing moment is calculated, and the mechanical action delay time parameter of the relay is corrected. By predicting the current zero-crossing time and considering the mechanical action delay characteristic of the relay, accurate switching of the built-in relay at the actual current zero-crossing point is achieved, meanwhile, the self-adaptive adjusting capacity is achieved, the arc energy during large-current switching is reduced, the service life of the relay is prolonged, and the reliability of the electric energy meter is improved.

The invention aims to solve the problem that a control coordinate system and a power grid reference coordinate system are out of synchronization due to the fact that the power transmission capability of a system cannot meet the requirement of a power instruction after a low-voltage fault occurs. The invention provides a virtual power compensation (VPC) synchronous control strategy with power compensation capability, the strategy keeps synchronous with a power grid during a low-voltage fault period and still has the capability of supporting the amplitude and frequency of the voltage of the power grid, and the recovery after the fault is realized through an improved current limiting strategy. The provided VPC and current amplitude limiting strategy solves the transient instability problem of a virtual synchronous generator (VSG) under large disturbance, fault removal and recovery are achieved, and fault detection, on-line control switching and power reference value self-adaption are completely not needed any more in the process. Simulation and experiment results verify the effectiveness of the method.

The invention provides a magnetic suspension motor control method and device and a magnetic suspension motor, and relates to the technical field of magnetic suspension motor control, and the technical scheme is characterized in that the method comprises the steps: detecting the voltage change rate of a power grid, and judging a voltage fluctuation mode based on a preset threshold value; environment RFID tag information is read through a scene code analysis unit, and a current scene code is obtained; retrieving a maximum compensation current value, a current change rate threshold value and a PID integral time constant from a preset parameter matrix based on the voltage fluctuation mode and the scene code; and limiting the current change rate of the motor winding according to the current change rate threshold, and executing motor control through the maximum compensation current value and the PID integral time constant. The magnetic suspension motor control method and device and the magnetic suspension motor provided by the invention have the advantages of improving the operation stability of the motor in voltage fluctuation and multi-noise scenes, suppressing electromagnetic noise and adapting to different scenes.

The invention relates to an optical storage and charging alternating current and direct current hybrid micro-grid construction control method and device and a medium. According to the method, level-to-level management is carried out on an energy storage converter according to an SOC value of an energy storage device. And the converter with the high priority is switched to a VSG mode, and whether the voltage and frequency fluctuation of the micro-grid exceeds an adjustment dead zone or not is detected. When the frequency fluctuation is exceeded, active power output is adjusted through a VSG mode; when the voltage fluctuation is exceeded, the reactive power output is adjusted. And the energy storage equipment is switched to the VSG mode step by step, and when the requirements cannot be met, the photovoltaic equipment and the electric automobile support power grid are put into use in sequence. Before the photovoltaic equipment is connected, the voltage of the photovoltaic equipment is synchronized to be consistent with that of the connected energy storage equipment, and the VSG mode is converted. And if further support is still needed, the electric vehicle is used for feeding by adjusting a charging pile control algorithm. And the voltage and the phase need to be synchronized before the electric vehicle is connected so as to cooperatively support the micro-grid. According to the method, the voltage and frequency stability of the micro-grid system is remarkably improved.

The invention relates to the technical field of photovoltaic voltage regulation, and discloses a distributed photovoltaic power distribution network voltage control system and method. According to the system and the method, voltage and power information of each measurement point is acquired through a data acquisition module, related data of the photovoltaic inverter is collected, and a communication module receives the data and transmits the data to a control module and a monitoring management module; the control module calculates voltage-power sensitivity, a power factor, voltage deviation, power loss and reactive power compensation requirements according to the data, evaluates the running state of the current power grid and judges whether reactive voltage regulation is needed or not, and the monitoring and management module calculates system response time and fault occurrence probability and controls the system response time and the fault occurrence probability. And judging whether the control effect reaches the expectation or not, analyzing faults and abnormities, providing an adjustment strategy for the voltage stability and the photovoltaic power generation efficiency by the optimization scheduling module, acting on the control module again, optimizing system operation by issuing a new control signal, generating a system optimization report and sending the system optimization report to a display end.

The invention relates to the technical field of MOS (metal oxide semiconductor), and discloses a VDMOSFET (vertical double-diffused metal oxide semiconductor field effect transistor) device with low threshold voltage, which comprises a drain electrode, a semiconductor epitaxial layer, a source electrode, a grid electrode and a grid oxide layer covering the surface of the grid electrode, and is characterized in that an N substrate layer, an N drift layer, an N well layer, a P well layer and a heavily doped P layer are formed in the semiconductor epitaxial layer through ion implantation, the grid electrode comprises a triangular grid electrode and a rectangular grid electrode, the grid oxide layer covering the surface of the triangular grid electrode is in contact with the N substrate layer, and the N drift layer is divided into a left part and a right part by the grid oxide layer. According to the invention, the grid electrode is designed to further comprise the triangular grid electrode, the electric field effect of the grid electrode between the tip part of the triangular grid electrode and the drain electrode is better, but the grid oxide layer wrapped by the triangular grid electrode at the tip part is thicker, so that charges flowing out of the drain electrode gather towards the inside of the heavily doped N layer more quickly along the grid oxide layer; at the moment, more charge flow can be provided in a smaller grid voltage environment.

The invention discloses a GaN totem-pole bridgeless PFC converter harmonic suppression method based on adaptive virtual admittance, and belongs to the technical field of converter control. The invention aims to solve the problem that LC resonance in a GaN totem-pole bridgeless PFC converter in a wide load range causes power grid voltage distortion to be converted into grid-side current harmonics. Comprising the following steps: decoupling a virtual admittance vector in a polar coordinate system, and optimizing under different load working conditions to obtain an optimal virtual admittance set; the system delay influence is compensated to ensure the robustness of the proposed method under different operation conditions; and a load power adaptive virtual admittance mechanism is constructed based on a segmented cubic Hermite interpolation method, so that suppression of network-side specific current harmonics in a wide load range is realized. The self-adaptive suppression method is used for self-adaptive suppression of the grid-side current harmonics of the GaN totem-pole bridgeless PFC converter.

The invention relates to the technical field of photovoltaic grid connection, and particularly provides an active support control method and an active support control device for transient voltage of a transmitting end power grid of an LCC-HVDC (line commutated converter high voltage direct current power transmission) system, and the active support control method and the active support control device for the transient voltage of the transmitting end power grid of the LCC-HVDC system. Comprising the following steps: correcting an output voltage phase of a synchronization link in a virtual synchronous generator control strategy based on active power and frequency output by a network construction type photovoltaic converter, and correcting an output voltage amplitude of a voltage amplitude link in the virtual synchronous generator control strategy based on a measured value of a sending end power grid voltage; and using the virtual synchronous generator control strategy to control the network construction type photovoltaic current converter in the LCC-HVDC system containing the network construction type photovoltaic current converter. According to the technical scheme provided by the invention, the stability of photovoltaic access to the weak power grid can be improved, and the reactive power output by the converter can be automatically adjusted after the transient voltage of the sending-end power grid occurs due to the commutation failure of the LCC-HVDC system, so that the transient voltage is effectively supported, and the phenomenon of reverse adjustment of the reactive power is prevented.

The invention discloses a low-cost high reactive overload energy storage converter topology and a modulation strategy thereof, is used for improving the reactive overload capacity of an energy storage converter, and belongs to the technical field of alternating current-direct current converters. According to the invention, the auxiliary diode is additionally arranged on the traditional ANPC bridge arm, so that the reverse current of the IGBT module is shared during high-proportion reactive output of the converter, and the reactive overload capacity of the converter can be efficiently improved with low cost on the basis of fully utilizing the existing equipment. Besides, a reactive overload capacity enhancement modulation strategy based on third harmonic injection is provided for the topology, and third harmonics are injected into modulation waves, so that the utilization rate of an auxiliary diode is improved, and the output capacity of reactive current is further enhanced. According to the method, a 100kVA prototype is tested and verified in Simulink / Plecs, the device cost of the proposed topology is only increased by 5.45% on the basis of a traditional ANPC, the reactive overload capacity is increased by 22%, and the power grid voltage supporting capacity of the energy storage converter can be effectively enhanced.

The invention provides a grid-connected and off-grid switching method of a multi-machine parallel energy storage system, a controller and the energy storage system, and belongs to the field of energy storage. The energy storage system comprises a plurality of energy storage converters connected in parallel, and the method comprises the steps that when the energy storage system works in an off-grid mode, if it is detected that a power grid recovers to be normal, all the energy storage converters are controlled to track the voltage of the power grid, and the off-grid voltage of all the energy storage converters and the voltage of the power grid are kept synchronous; when it is detected that the off-grid voltage of each energy storage converter and the grid voltage are kept synchronous, a grid-connected switch is controlled to be closed; after being connected in parallel, the energy storage converters are connected with a power grid through a grid-connected switch; and controlling the working loop of each energy storage converter to be switched from an off-grid loop to a grid-connected loop. According to the invention, automatic switching from the off-grid state to the grid-connected state during parallel operation of a plurality of energy storage converters can be realized, and power-failure-free switching from the off-grid state to the grid-connected state can be realized.