249 results about "Negative sequence current" patented technology

The invention provides a fault ride-through control method and a fault ride-through control system for a grid-forming converter, which are characterized in that the current of the grid-forming converter under an asymmetric fault is controlled by adopting a negative-sequence current reference generation strategy aiming at an inner ring of a controller, and negative-sequence reactive current is injected into a power grid; adopting a partial sequence current amplitude limiting strategy to control the maximum phase current amplitude of the injected asymmetric current not to exceed an amplitude limiting value; controlling the boundary of an active reference value by adopting an active reference value amplitude limiting strategy for an active synchronization ring; a synchronous damping link is adopted to enhance damping in power angle swing; for a reactive voltage loop, a reactive voltage variable coefficient control strategy is adopted to control the output of the maximum reactive current; and an internal potential locking strategy is adopted to suppress overvoltage. According to the invention, negative-sequence reactive power is provided, and overcurrent of each phase is avoided; the power angle characteristic is improved, and the transient stability is improved; stable transient voltage support is provided in a current output capability range; and after the fault is recovered, the voltage of the converter grid-connected point is smoothly recovered.

The invention discloses a three-phase imbalance compensation method and system based on negative sequence current and a medium, and relates to the technical field related to power imbalance compensation, and the method comprises the steps: executing the three-phase current, voltage and reactive power data collection of a power distribution network, and carrying out the three-phase imbalance recognition through negative sequence current analysis; carrying out additional acquisition of a load mode and environment data on the power distribution network; taking the data acquisition result and the additional data set as input data to execute negative-sequence current change trend prediction; a double-layer compensation device is configured for cooperative control optimization; power distribution network balance compensation is executed through a time sequence compensation strategy, and time sequence window feedback is established; and carrying out adaptive strategy correction. The technical problems that in the prior art, a three-phase imbalance compensation strategy lacks perspectiveness and self-adaptive capacity and cannot cope with a dynamically-changing power grid scene, and consequently compensation precision and stability are poor are solved, and the technical effects that perspectiveness and predictive compensation is achieved, and three-phase imbalance compensation precision and stability are improved are achieved.

The invention provides a platform area power grid tail end voltage flexible regulation and control method and system. The method comprises the steps that a sampling module measures common coupling point voltage at the tail end of a platform area power grid; the impedance calculation unit obtains load end impedance; the current calculation unit calculates the current of the common coupling point through the voltage of the common coupling point and the impedance of the load end; the current resolving unit is used for resolving the common coupling point current into negative-sequence current and zero-sequence current; the compensation current unit calculates a compensation current component required for maintaining the stability of the voltage at the tail end of the transformer area power grid through the negative-sequence current and the zero-sequence current; the PWM unit generates a compensation current control signal; and the IGBT module outputs compensation current to the common coupling point. When three phases are unbalanced, the first disturbance generation circuit accurately injects a disturbance signal to effectively regulate and control the voltage at the tail end of a power grid in a transformer area; and the second disturbance generation circuit analyzes the stability of the tail end of the station area power grid by using coordinate transformation and a PI controller.

The invention belongs to the technical field of new energy, and particularly relates to a fault voltage ride-through optimization method and system for a network construction type energy storage converter. Carrying out positive and negative sequence separation and Clark-Park coordinate transformation on the three-phase power grid voltage and the inversion current, calculating active power and reactive power of the network-forming type energy storage converter, and carrying out power loop control to obtain three-phase reference voltage and angular velocity; performing voltage loop control, and dynamically adjusting a positive sequence active current and a positive sequence reactive current according to whether a low-voltage-crossing indication signal exists or not; performing positive-sequence current loop control and negative-sequence current loop control, and then performing inverse Clark-park conversion to obtain positive-sequence three-phase reference voltage and negative-sequence three-phase reference voltage; and superposing the positive-sequence three-phase reference voltage and the negative-sequence three-phase reference voltage for PWM (Pulse Width Modulation). According to the invention, when the power grid voltage is unbalanced due to a fault, the oscillation of the direct current side voltage and power caused by the negative sequence component is eliminated, and the power angle stability is improved and the fault current is suppressed by dynamically adjusting the related reference value during the fault voltage ride-through period.

The invention discloses a three-phase unbalanced power flow line loss analysis method, which comprises the following steps of: establishing a power flow model of a three-phase unbalanced system based on a sequence component method; the power flow model comprises admittance matrixes respectively corresponding to a positive sequence, a negative sequence and a zero sequence, and equivalent admittance corresponding to any two of the positive sequence, the negative sequence and the zero sequence; converting the power flow model, and determining a first relational expression among the coupled positive sequence current, the equivalent admittance and the uncoupled positive sequence current, and a second relational expression among the coupled negative sequence current, the equivalent admittance and the uncoupled negative sequence current; determining a positive sequence electrical component according to the first relational expression, and determining a negative sequence electrical component according to the second relational expression; and determining the line loss of the three-phase unbalanced system according to the positive sequence electrical component and the negative sequence electrical component. According to the method provided by the invention, the accuracy of line loss analysis can be improved.

The invention discloses an improved flexible direct current fault control method for improving current differential protection adaptability, and belongs to the technical field of power system relay protection and new energy power generation system grid-connected control. The method comprises the following steps: detecting a voltage drop abrupt change signal and a negative sequence voltage signal of a flexible DC output end, and starting a control strategy when the signals are satisfied; detecting a terminal voltage signal and active power of a new energy sending-out terminal, and calculating a new energy side current phase angle and a power angle; calculating a flexible DC side current phase angle control value and a negative sequence dq axis current reference value based on the parameters; and controlling the flexible DC side to output a negative-sequence current corresponding to the negative-sequence dq-axis current reference value, so as to actively adjust the current phase of the flexible DC side, reduce the phase angle difference between the fault current of the flexible DC side and the fault current of the new energy side, and discriminate the internal and external faults of the region through traditional current differential protection. According to the invention, the degree of freedom is controlled and the current phase is adjusted by using the flexible direct-current side negative-sequence current to reduce the phase angle difference of the two sides, so that the problem that the current differential protection adaptability in the double-end weak feedback system is reduced is solved, additional hardware is not needed, and the power grid safety and the new energy stable grid connection are ensured.

The invention discloses an active and reactive comprehensive oscillation quantity minimization cooperative control method under a current constraint condition, and the method comprises the steps: analyzing an inverter side current converter in a power grid voltage imbalance state, and quantifying the frequency doubling fluctuation quantity of active power and reactive power caused by a negative sequence component; a third harmonic voltage compensation method is adopted to suppress negative sequence current, the third harmonic voltage compensation amount of the converter is dynamically adjusted, and three-phase current balance is regulated and controlled; on the basis of active and reactive power fluctuation suppression of a negative-sequence current compensation method, an optimization function with the purpose of minimizing the comprehensive fluctuation quantity of active power and reactive power is constructed by utilizing controllable negative-sequence current compensation quantity and eliminating frequency doubling fluctuation quantity of active power and reactive power, and an optimal negative-sequence current compensation scheme is solved in real time by adopting a particle swarm optimization algorithm. Cooperative suppression of three-phase current balance and power oscillation is achieved, and the operation stability and the power transmission capacity of the inverter side converter under an asymmetric fault are remarkably improved under the current amplitude limiting condition.

The invention provides a negative sequence voltage control method and a negative sequence voltage control system for a network-constructed converter, and relates to the technical field of network-constructed converter control. Calculating negative-sequence reactive power absorbed by the converter and the maximum negative-sequence reactive power which can be absorbed by the converter under the specified fault working condition, and comparing the negative-sequence reactive power and the maximum negative-sequence reactive power to obtain a negative-sequence active power instruction and a negative-sequence reactive power instruction; performing droop control by using the negative sequence active power instruction; pI control is carried out by using a negative sequence reactive power instruction; when a fault occurs, performing three-phase voltage and current sequence decomposition to obtain a negative sequence voltage amplitude and phase and a negative sequence current amplitude and phase of the converter; and performing power measurement according to the amplitude and phase of the negative-sequence voltage output by the converter and the amplitude and phase of the negative-sequence current to obtain negative-sequence active power and reactive power transmitted between the converter and the power grid.

The invention relates to an asymmetric fault ride-through cooperative control method and system for a virtual synchronous generator, and belongs to the technical field of power electronics and new energy power generation. Aiming at the problems of three-phase current asymmetry, overcurrent, transient instability and the like faced by a virtual synchronous generator when a power grid has an asymmetric fault, the method comprises the following steps: firstly, setting a negative sequence current reference to be zero through positive and negative sequence separation control so as to keep output current symmetry, and freezing a reactive power ring; secondly, comprehensively considering current amplitude limiting, voltage supporting capacity and system capacity, and dynamically calculating optimal solutions of positive sequence excitation reference amplitudes under different fault depths; finally, positive and negative sequence power components and excitation dynamic changes are considered, an active reference instruction real-time dynamic adjustment method is provided, and a power angle is controlled to be stabilized at a target value by adjusting a power reference value in real time. The method can effectively improve the transient stability during the fault ride-through period, maximally supports the power grid voltage while ensuring that the current is not out of limit, and improves the system capacity utilization rate.

The invention relates to an overvoltage risk assessment method, device and equipment for non-full-phase operation of a new energy access weak power grid system. The method comprises the following steps: acquiring electrical quantity data of the new energy access weak power grid system, and a voltage source, grid-connected equivalent impedance, series equivalent impedance and non-full-phase operation line impedance of a power transmission line of the new energy access weak power grid system with a single-phase fault; calculating n positive sequence current vectors and negative sequence current vectors according to each piece of electrical quantity data; calculating n positive sequence port voltage vectors and negative sequence port voltage vectors according to the fault data, each positive sequence current vector and each negative sequence current vector; according to the positive sequence voltage component rated value, each positive sequence port voltage vector and each negative sequence port voltage vector, actual positive sequence voltage and actual negative sequence voltage are obtained through calculation; and according to the actual positive sequence voltage, the actual negative sequence voltage and the positive sequence voltage component rated value, calculating to obtain a single-phase voltage maximum value, and according to the single-phase voltage maximum value, judging whether the system has an overvoltage risk in a non-full-phase operation state.

The invention discloses an AC / DC power distribution network protection method and device based on a negative sequence voltage ratio. The method comprises the following steps: constructing a fault identification criterion of a two-phase interphase short-circuit fault of the AC / DC power distribution network according to negative sequence voltage fault characteristics of internal and external faults of the AC / DC power distribution network; determining the fault type of the protection line according to the negative sequence current at the head end measuring point of the AC / DC power distribution network protection line and a pre-constructed fault type identification criterion; when the fault type is a three-phase fault, an overcurrent protection method is adopted to protect the protection line; and when the fault type is a two-phase interphase short-circuit fault, determining an internal and external fault identification result of the protection line according to the negative sequence voltage of the measuring points at the two ends of the protection line, the negative sequence comparison voltage and a fault identification criterion.

The invention belongs to the technical field of power grids, and particularly relates to a hydrogen fuel cell grid-connected inverter fault test and ride-through method. Comprising the following steps: S1, simulating three-phase symmetrical voltage drop, inter-phase voltage drop and single-phase voltage drop of a power grid through a low-voltage fault generation device; s2, collecting the voltage of a power grid through a high-precision voltage sensor, and when the voltage of the power grid drops, judging whether the system needs to carry out low-voltage ride through at the moment according to a distributed energy low-voltage ride through curve; and S3, when the system needs to carry out low-voltage ride-through, a dual-second-order generalized integrator pre-filtering phase-locked loop (DSOGI-PLL) is combined with grid-connected point voltage full-feedback compensation, negative-sequence components generated by symmetric and asymmetric drop of the power grid voltage are eliminated, and current impact suppression and negative-sequence current elimination are realized. The problem of power grid synchronization under the condition of power grid voltage drop is finally solved.

The invention discloses an impedance-adjustable series hybrid cascade static synchronous compensator and a control method thereof. The method comprises the following steps: acquiring grid-connected point voltage and load current information, and performing positive and negative sequence component analysis on the grid-connected point voltage and load current information; calculating a compensation line current component with the same size and opposite phase as the positive and negative sequence components of the load current so as to compensate the reactive power and the negative sequence current of the grid-connected point load; zero-sequence injection current used for in-phase active power balance is calculated, and reference operation current of each cascade branch is obtained; calculating the output reactive power of each phase based on the cascade branch voltage of each phase and the reference operation current, calculating the corresponding trigger angle of each phase thyristor under the condition that the adjustable impedance bears all phase voltages and generates all reactive power, and generating a pulse control signal to realize the control of the adjustable impedance; and each phase cascade converter adopts quasi-proportional resonance control to track the reference operation current, and generates a corresponding PWM signal to respectively control each phase cascade converter.

The invention discloses a permanent magnet synchronous motor turn-to-turn short circuit fault diagnosis method based on a high-frequency negative-sequence component, and the method comprises the steps: obtaining a high-frequency voltage injection signal according to the three-phase current of a motor, obtaining a high-frequency current signal through space vector pulse width modulation, injecting the high-frequency current signal into the motor, obtaining the three-phase voltage and three-phase current of the current motor, and extracting a high-frequency component in the three-phase voltage and three-phase current; high-frequency negative-sequence voltage and high-frequency negative-sequence current are obtained according to the extracted high-frequency components, and fault features are constructed; comparing the fault feature with a fault threshold value, judging that the permanent magnet synchronous motor is healthy if the fault feature is smaller than the fault threshold value, and judging that the permanent magnet synchronous motor is faulty if the fault feature is larger than or equal to the fault threshold value. According to the method, extra detection hardware is not needed, real-time detection and positioning of the turn-to-turn short circuit fault can be realized by using the negative sequence component of the motor in the high-frequency domain in the servo operation state of the permanent magnet synchronous motor, and the method has relatively high applicability and robustness.

The invention discloses an autonomous power ripple suppression method based on a grid-connected multi-port converter, and the method comprises the steps: carrying out the negative-sequence current elimination at an AC port, carrying out the power ripple suppression at a DC port, automatically transferring a differential power ripple to a ripple port, and eliminating the dependence on the prior knowledge of the ripple; in addition, even under the unbalanced power grid working condition, balanced three-phase power grid current and ripple-free direct current output voltage can be obtained at the same time, and an additional power ripple controller does not need to be designed.

The invention relates to the technical field of power electronic application, in particular to a negative-sequence voltage compensation control method of a network-forming STATCOM (Static Synchronous Compensator). Comprising the steps of bridge arm current reference instruction unit phasor calculation, reactive voltage control, bridge arm positive sequence and negative sequence reactive current instruction calculation, bridge arm current reference instruction amplitude limiting logic, zero sequence voltage injection control and modulation wave instruction calculation. According to the method, the negative-sequence current output by the networking STATCOM in the asymmetric transient fault is always inductive, the proportion coefficient of the amplitude of the negative-sequence current instruction can be adjusted according to the requirements of an engineering project, and the cost is reduced; by dynamically solving a quadratic equation of unary of a reactive current amplitude limiting coefficient, an active current instruction is not limited by amplitude, balance control of direct current voltage is preferentially ensured, the reactive current is reasonably limited in amplitude, a total current reference instruction value is always in a maximum design value range of short-time overcurrent, and the stability and the safety of the device are improved.

The invention discloses an unbalance compensation method and system for an energy storage converter, and belongs to the field of power electronics and electric energy quality treatment. The system comprises a power instruction analysis module, a current reference generation module, a negative sequence current control loop module, a zero sequence control loop module, a positive sequence control loop module, a pulse width modulation module, a first conversion module and a second conversion module, the current reference generation module is respectively connected with the negative sequence current control loop module and the positive sequence control loop module; the third end and the fourth end of the negative sequence current control loop module are connected with the pulse width modulation module through the second conversion module; the third end and the fourth end of the zero sequence control loop module and the third end and the fourth end of the positive sequence control loop module are connected with the pulse width modulation module through the first conversion module. According to the method, the energy storage and compensation functions of the PCS can be seamlessly integrated under a unified control framework, so that the control system is greatly simplified, and the performance is remarkably improved.

The present disclosure provides a method, a device and a system for detecting a single-phase broken conductor. The method includes: collecting a three-phase current at a measurement point; obtaining a positive sequence current and a negative sequence current from the collected three-phase current; calculating a change of the positive sequence current and a change of the negative sequence current within a first time interval; and when an amplitude of the positive sequence current decreases, an amplitude of the negative sequence current increases, a decrease of the amplitude of the positive sequence current is greater than a first predetermined value, and a ratio of a magnitude of change of the negative sequence current to a magnitude of change of the positive sequence current is greater than a second predetermined value, determining that a first set of faults occur, the first set of faults including a single-phase broken conductor.

The invention discloses a time domain distance protection method and system combined with a control strategy and distributed capacitance current, and the method comprises the steps: employing negative sequence current to suppress the adaptability of a control strategy based on converters at two ends of a line in a double-end weak feed AC system, and recognizing the problems that negative sequence networks at two sides in a composite sequence network are open-circuited and a non-fault phase generates overvoltage; aiming at the identification problem, an MMC negative-sequence current suppression control strategy is improved into a negative-sequence voltage suppression and voltage reduction V / F cooperative control strategy; based on a cooperative control strategy, a transition resistance item in the distance protection equation is split into an equivalent transition resistance and equivalent transition inductance complex model, and a line pi-type equivalent model is adopted to deduce a fault differential equation; and solving a differential equation containing a fault distance through a least square method to realize high-precision fault positioning.

The present application provides a power distribution system and a method for controlling its power distribution switches, which determines the load fluctuation entropy of the target power distribution system during the power distribution process through the load information when voltage jitter occurs during the power distribution process and the rated load of the distribution switch; determines the voltage disorder degree during the negative-sequence voltage jitter through the negative-sequence voltage record in the negative-sequence power data, and then determines the current symmetry of the negative-sequence current through the negative-sequence current record in the negative-sequence power data; determines the negative-sequence balance deviation of the three-phase power in the negative-sequence state based on the voltage disorder degree and the current symmetry; determines the critical threshold for the safe operation of the distribution switch when the distribution load changes through the load fluctuation entropy and the negative-sequence balance deviation, and then intelligently switches the opening and closing states of the distribution switches in the target power distribution system based on the critical threshold. By adopting the solution of the present application, adaptive switching of the distribution switch state during intermittent load jitter of the distribution system can be achieved, thereby improving the anti-interference performance of the distribution system during the power distribution process.

The invention relates to the technical field of modular multilevel converter control, in particular to an active-disturbance-rejection direct-current side fluctuation suppression method based on an MMC alternating-current side fault working condition. The method mainly aims at solving the problems that an existing suppression scheme based on a PI controller is insufficient in performance and difficult in parameter adjustment, and a control scheme based on an active disturbance rejection controller is complicated in parameter debugging and difficult in obtaining optimal parameters although the performance is better. The method comprises the following steps: step 1, suppressing a negative sequence current generated by an MMC system when an alternating current side has a fault; step 2, constructing a second-order LADRC model; and step 3, current inner loop control is carried out by using a second-order LADRC controller set by a particle swarm optimization algorithm. According to the method, a traditional PI controller is replaced by the second-order LADRC controller, parameters are set in combination with the particle swarm optimization algorithm, the ride-through capacity of the MMC system under the alternating current side fault is remarkably improved, and better dynamic response and interference immunity are achieved.

The invention discloses a dual-channel electric drive multiplexing type vehicle-mounted charging system unbalanced current suppression method, which comprises the following steps of: firstly, popularizing and applying a positive and negative sequence separation method for decoupling a dual-synchronous coordinate system to a dual-channel six-phase motor, and calculating positive and negative sequence components of a dq axis of a dual-channel system under a current unbalanced working condition; utilizing Park and VSD transformation to map the data to an alpha beta xy0102 sub-plane; secondly, setting a positive-sequence current given value and a negative-sequence current given value to be 0 by using a six-phase current distribution method for minimizing electromagnetic torque; then, independent PI control is carried out on each sub-plane; and finally, correspondingly adding the output quantities of the positive sequence current and the negative sequence current of each sub-plane, returning to a natural coordinate system through TVSD-1, and then outputting SPWM, thereby realizing a three-phase charging working condition. According to the method, the suppression of the negative-sequence current can be realized, the sine degree of the power grid current is improved, the torque ripple is suppressed, and the system safety is guaranteed.

The invention relates to an active support method and device for a grid-connected system under a power grid fault and a storage medium, and belongs to the technical field of smart power grids. According to the invention, when the power grid generates the symmetric fault, the optimal short-circuit current control point is utilized to re-assign the d-axis current reference value and the q-axis current reference value, the short-circuit current response characteristic of the receiving-end converter station to the power grid fault is changed, and the problems that the sea wind-flexible direct current grid-connected system cannot provide voltage support for the power grid and cannot provide voltage support for the power grid are effectively solved. Active power can be continuously output to the power grid, and the problems of frequency stability and synchronous stability are caused; when the power grid generates an asymmetric fault, the converter station actively absorbs negative sequence current to provide active support for the power grid, the unbalance degree of a fault point is reduced, and meanwhile, the positive sequence voltage support capability of the power grid is reserved; the short-circuit current bearing capacity of the flexible DC converter station is improved, and the power grid supporting capacity of the sea wind-flexible DC grid-connected system is improved on the premise that the fault ride-through performance is guaranteed.

The invention relates to the technical field of motor control in the intelligent power grid industry, and discloses a space vector control method for a twelve-phase permanent magnet synchronous motor flywheel energy storage system, a control circuit of the flywheel energy storage system relates to power electronic components such as various semiconductor field-effect tubes, and the space vector control method is used for high-precision control of a motor. Comprising the steps of S1, twelve-phase space vector decoupling fault-tolerant control, S2, high-order harmonic energy recovery closed loop, S3, quantum annealing parameter optimization layer, S4, flux linkage adaptive observer network construction and S5, 18-dimensional switching vector table construction. According to the scheme, through multi-reference coordinate system transformation and a redundant phase reconstruction algorithm, rapid fault-tolerant response of the twelve-phase motor during a single-phase or two-phase fault is realized, a current path is dynamically recombined during the fault, a negative-sequence current compensation ring is combined, torque ripple is effectively suppressed, and the reliability of the motor is improved under a high-speed charging and discharging working condition. The harmonic distortion rate is detected in real time through the sliding window FFT, the bandwidth of the controller is adjusted, and the problem that the dynamic response of a traditional fault-tolerant strategy is insufficient is solved.

The invention provides a multi-target control method for a permanent magnet direct drive fan under an asymmetric fault of a power grid, and solves the technical problems of power fluctuation suppression and current unbalance degree reduction control target coordination optimization in fault ride-through. Comprising the following steps: S1, establishing a positive and negative sequence coordinate system model of a permanent magnet direct-driven wind turbine generator grid-side converter, and carrying out positive and negative sequence separation on voltage and current of the grid-side converter; s2, grid-side converter reference current instructions of the three control targets are calculated; s3, constructing a uniform expression form of the reference current of the grid-side converter; s4, active power fluctuation suppression and negative sequence current suppression are selected as coordinated optimization control targets for control; and S5, constructing a multi-objective optimization function, solving to obtain a current reference value of the converter, and performing current closed-loop control on the grid-side converter. The method has the advantages that multi-target coordination optimization control over the permanent magnet direct-driven wind turbine generator set under the power grid voltage fault is achieved, and the low-voltage ride-through capacity and the grid connection performance of the permanent magnet direct-driven wind turbine generator set are enhanced.

The invention discloses a phasor differential protection method and system based on regulation and control characteristics of a low-frequency converter, and belongs to the technical field of relay protection. The method comprises the following steps: calculating negative-sequence current and positive-sequence voltage at two sides of a protected line based on three-phase voltage and current phasors; judging whether the drop depth of the positive sequence voltage meets a three-phase fault criterion, if so, not adjusting a braking coefficient, and if not, adjusting the braking coefficient through the amplitude ratio of the negative sequence current, and calculating a self-adaptive braking coefficient based on the regulation and control characteristics of the low-frequency converter based on the adjusted braking coefficient; and constructing a phasor differential protection criterion based on the adaptive braking coefficient, obtaining fault current vectors at two sides of the protected line, and starting phasor differential protection for the protected line when the fault current vectors meet the differential protection criterion. According to the method, protection sensitivity and reliability can be considered, and the sensitivity of main protection of the flexible low-frequency power transmission line is improved.

The embodiment of the invention relates to the technical field of wind turbine generator control, and provides a dynamic compensation control method and system for a rotor voltage of a wind turbine generator, and the method comprises the steps: decomposing a power grid voltage and a rotor current into a positive-sequence component and a negative-sequence component in real time through constructing a self-adaptive decoupling control architecture based on a dual-synchronous coordinate system; a positive-sequence channel is responsible for accurately tracking active and reactive power instructions and guaranteeing a power generation task, and a negative-sequence channel is responsible for accurately tracking a positive-sequence channel and a negative-sequence channel; the negative sequence channel aims at eliminating negative sequence current and suppresses second harmonic pulsation; a dynamic compensation gain mechanism is further introduced, the fault severity is evaluated by quantifying the unbalance degree of a power grid in real time, and the intensity of negative sequence compensation is adaptively adjusted, so that the control strategy can maximally suppress pulsation when a slight fault occurs, and the safety of the converter is preferentially guaranteed and the overcurrent risk is avoided when a serious fault occurs.

The invention provides a power frequency overvoltage analysis method and device considering negative sequence current control, and relates to the technical field of electronic power, and the method comprises the steps: constructing a sequence voltage balance model at a non-full-phase fault based on obtained circuit information; combining the sequence voltage balance model with a three-phase boundary condition of a non-full-phase fault to construct a sequence current model at the fault; solving positive and negative sequence components of the terminal voltage by using the sequence current model and adopting a sequence-dividing loop iteration algorithm; and generating the power frequency overvoltage at the fault according to the positive and negative sequence components of the generator terminal voltage and the obtained positive and negative sequence components of the generator terminal output current. According to the power frequency overvoltage analysis method and device considering negative sequence current control provided by the invention, the influence rule of positive and negative sequence output of a new energy unit on the power frequency overvoltage level of a fault point is accurately evaluated during the non-full-phase operation period of a new energy collection system, and a theoretical basis is provided for making a control strategy.

The present invention proposes a low voltage ride-through control method and system for a grid-type distributed photovoltaic inverter, which relates to the field of power electronics technology. Based on the electrical quantity parameters of the grid-type distributed photovoltaic inverter, the virtual voltage, active power, and reactive power reference values are adaptively adjusted; a virtual current value is calculated based on the virtual voltage, active power, and reactive power reference values through a voltage source virtual synchronous machine; Euler-Lagrangian modeling is performed on the voltage source virtual synchronous machine, and an improved passive controller is constructed to track the virtual current value and a given negative sequence current value to obtain a modulation wave; a drive signal is generated according to the modulation wave to control the operation of the grid-type distributed photovoltaic inverter; the present invention proposes a control method for a grid-type distributed photovoltaic inverter with high anti-interference and fast response, which takes the advantages of virtual synchronous machine control and passive control while avoiding their disadvantages, so that the grid-type inverter has a certain inertia damping characteristic while also having a fast low voltage ride-through capability.

The present application relates to the technical field of power system relay protection, and particularly relates to a kind of offshore wind power through flexible low-frequency transmission system sending out line protection method, offshore wind farm is connected with modular multi-level matrix converter after being sent out by low-frequency through booster transformer, and is incorporated into large power grid after being frequency converted by M3C. When M3C of offshore wind farm fails, negative sequence current suppression and positive sequence current limiting strategy are adopted for fault ride-through, and relay protection devices are installed at both ends of low-frequency sending out line and communicate. The current sampling values before and after the fault on both sides of the line are reconstructed in phase space, and the difference between the permutation entropies is used to construct a protection scheme, which overcomes the problem of sensitivity reduction of traditional current differential protection for sending out line, reduces the amount of data interaction, and reduces the pressure of protection communication and the requirement of data synchronization. It is not affected by the control strategy of wind turbine and modular multi-level matrix converter at both ends of the line, fault ride-through mode, transition resistance and fault location, and has high reliability and good speed.