191 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 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 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 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 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 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 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 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 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.

The invention belongs to the technical field of relay protection of a power distribution network of a power system, and provides a single-phase broken line grounding fault detection method for an ungrounded neutral system, which comprises the following steps of: 1, acquiring three-phase current signals of each feeder line; step 2, performing morphological filtering processing on the acquired negative sequence current signal; step 3, mapping the filtered negative sequence current signal to a time-frequency space with u as a variable; 4, searching an optimal twiddle factor according to the energy focusing characteristic of the time-frequency current signal; according to the method, the symmetric component method, the morphological filtering and the coordinate transformation technology are combined, so that the accuracy and the stability of single-phase broken line grounding fault feature extraction of the neutral ungrounded system are remarkably enhanced, and the precision and the reliability of fault detection are greatly improved; and meanwhile, the optimal twiddle factor is adaptively determined based on the feeder energy concentration ratio, so that the detection strategy can flexibly adapt to different fault conditions, and the fault detection efficiency and success rate under a complex power grid structure and variable operation conditions are effectively improved.

The application provides an asymmetric short-circuit current calculation method and system for large-scale new energy stations, and the method comprises the following steps: judging a fault type and a fault phase; constructing a fault composite sequence network; calculating negative sequence impedance of each new energy station, and calculating positive sequence initial voltage of each new energy station; calculating output short-circuit current of each new energy station; obtaining a simplified equivalent circuit through circuit simplification according to the fault composite sequence network; calculating positive sequence voltage of each new energy station; comparing the positive sequence voltage of each new energy station with the positive sequence initial voltage, judging whether a voltage difference meets convergence accuracy, solving output negative sequence current and zero sequence current of each new energy station according to a circuit equation; and outputting output phase current of each new energy station. The application overcomes the influence of a converter control on a phase selection element, can effectively shorten the iteration number, avoids the process of solving matrix inverse operation by using a node voltage method, has good engineering practicability and precision, and can be applied to large-scale new energy stations.

The application discloses a kind of non-full-phase operation wind power system sequence network equivalence and voltage calculation method and device, the method includes: when the single-phase fault of wind power system occurs and wind power machine terminal voltage is lower than entering low-voltage ride-through threshold, the positive sequence current, negative sequence current and zero sequence current of wind turbine in fault steady-state stage are determined, to construct wind power side controlled current source model;Positive sequence network, negative sequence network and zero sequence network of wind power system in non-full-phase operation stage are constructed, and system side is equivalent to voltage source in each sequence network, to establish three sequence Thevenin equivalence model at fault break;Three sequence currents and three sequence voltages at fault break are determined based on wind power side controlled current source model and three sequence Thevenin equivalence model, and further determine three sequence voltages and three-phase voltages at wind turbine grid connection point.The application enables voltage analysis in non-full-phase operation stage to reflect wind power side controlled current source characteristics, to provide basis for new energy grid connection point voltage variation analysis.

The invention discloses an intelligent traction power supply system power adjusting method and system. Comprising the following steps: calculating real-time transfer power, and calculating compensation current in real time by combining a power transfer error and negative sequence current; calculating a current tracking value based on the current inner loop instruction value and the voltage synchronization signal; designing a feedforward-feedback composite controller, and respectively calculating a feedforward compensation quantity and a feedback control quantity; based on the feedback control quantity and the feedforward compensation quantity, the total duty ratio of the PWM modulation signal is calculated, and a railway power regulator is driven to output an actual current value; the control method and system provided by the invention are low in engineering implementation cost, adaptive to the RPC application scene of the traction substation, and easy to popularize.

This application proposes a method and apparatus for detecting phase loss in a power plant starting transformer, relating to the field of power fault detection technology. The method includes: acquiring the signal energy distribution of the starting transformer; constructing an energy feature vector reflecting the relative energy relationship between the three-phase current signals and inputting it into a phase loss identification model to obtain the initial probability of phase loss faults in each phase; performing state inversion calculations by combining real-time calculated zero-sequence and negative-sequence current amplitudes to infer the changes in the equivalent circuit parameters of the transformer's internal windings and leads before and after the fault, thereby correcting the initial probability to obtain a confidence level, and finally generating a phase loss detection report including the fault phase and fault severity. This application comprehensively characterizes the energy correlation characteristics of the three-phase currents through energy feature vectors and corrects the initial probability of the model using changes in equivalent circuit parameters, eliminating random biases in the output of a single model, achieving accurate matching between the fault determination result and the actual fault state of the transformer, and improving the accuracy of fault phase identification.

The invention discloses an electric energy quality regulation and control method and device for a network construction type V2G charging pile parallel system, and the method comprises the steps: randomly determining one charging pile in the charging pile parallel system as a voltage source charging pile, and enabling the other charging piles to serve as current source charging piles; acquiring a first negative-sequence current based on the first instantaneous active power of the voltage source charging pile, and constructing a sharing control model based on the first instantaneous active power and the second instantaneous active power corresponding to each current source charging pile by taking the first negative-sequence current as a reference, so that the sum of harmonic power of all charging piles is 0; and determining an electric energy quality regulation coefficient corresponding to each current source charging pile based on a sharing control model, and regulating the corresponding current source charging pile based on the electric energy quality regulation coefficient. According to the regulation and control method provided by the invention, multi-objective optimization of ripple suppression of the output voltage and current of the parallel system of the charging pile and the direct-current side voltage can be realized, and the regulation and control reliability is improved while the economical efficiency is considered.

The application discloses a method and system for off-grid sequence separation droop control of a converter adapted to unbalanced load, which comprises the following steps: performing positive sequence droop control on active power and reactive power under a positive sequence fundamental frequency to obtain a positive sequence voltage vector and a positive sequence fundamental angle; performing negative sequence droop control on active power and reactive power under a negative sequence fundamental frequency to obtain a negative sequence voltage vector and a negative sequence fundamental angle; obtaining a negative sequence voltage dq-axis component reference value according to the positive sequence fundamental angle and the negative sequence fundamental angle; simultaneously, taking the positive sequence voltage vector and 0 as a positive sequence voltage dq-axis component reference value; and obtaining a modulation voltage of a power unit of the converter according to the positive sequence voltage dq-axis component reference value and the negative sequence voltage dq-axis component reference value, the positive sequence dq-axis component and the negative sequence dq-axis component of the converter serving as feedback values, and voltage and current double-loop regulation control being based. The application realizes active power and reactive power sequence separation extraction control, improves load voltage unbalance degree, realizes load negative sequence current sharing, enhances system stability, and has stronger unbalanced load capacity.

The invention discloses a high-resistance grounding fault detection method and device for an inverter grid-connected system, and belongs to the technical field of power system control. The high-resistance grounding fault detection method comprises the steps that in the first regulation and control stage, the maximum current constraint of a converter and the reactive power support requirement of a power grid are met; enabling first positive and negative sequence current amplitudes currently output by the inverter to be equal, and enabling the phase difference to be 180 degrees; in the second regulation and control stage, positive-sequence reactive current is injected for supporting voltage recovery, the amplitudes of first positive and negative sequence current currently output by the inverter are made to be equal to the positive-sequence reactive current, and the phase difference is 180 degrees; according to the invention, through controllable injection of inverter sequence components in different stages, an electrical quantity increment fault loop equation is constructed to realize protection discrimination, the influence of transition resistance and system parameter uncertainty on impedance distance measurement is reduced, the quickness and reliability of a line high-resistance grounding fault are improved, and the method is suitable for line protection of an inverter grid-connected scene.

The invention discloses a negative voltage suppression method and device for a network-forming inverter and a storage medium. The method comprises the following steps: executing signal splitting according to a three-phase electric signal at a grid connection point, and determining a positive sequence component and a negative sequence component; executing droop control according to the positive sequence component, and determining a positive sequence voltage modulation instruction; according to the negative-sequence component, coordinate transformation and negative-sequence current closed-loop control are executed, and a negative-sequence voltage modulation instruction is determined; and determining a comprehensive modulation signal according to the positive sequence voltage modulation instruction and the negative sequence voltage modulation instruction. According to the invention, positive and negative sequence separation is carried out on the three-phase electric signal, the suppression strategy taking the negative-sequence current as an object is constructed, and the power grid angle and the transmission line impedance angle are combined to realize negative-sequence current control, so that the negative-sequence component is weakened. Meanwhile, the positive sequence signal is independently used for droop control, voltage and frequency support of the inverter is guaranteed, correction for frequency reference value oscillation is introduced into droop control, and the transient performance of the grid-forming inverter under the unbalanced power grid is improved.

A power converter 10 contains a separation computer (a first transformation unit 122 and a separator 124), a PLL circuit 142, a PLL circuit 162, a negative-sequence current amplitude command generator 168, a negative-sequence current command generator 169, and a signal generator (a current control unit 180 and a pulse generator 190). The separation computer calculates positive-sequence voltages (Vpα and Vpβ) and negative-sequence voltages (Vnα and Vnβ) from three-phase AC voltages of a power grid. The PLL circuit 142 calculates a positive-sequence phase (θp) from the positive-sequence voltages (Vpα and Vp(3)). The PLL circuit 162 calculates a negative-sequence phase (θn) and a negative-sequence voltage amplitude (Vn) from the negative-sequence voltages (Vnα and Vnβ). The negative-sequence current amplitude command generator 168 calculates a negative-sequence current amplitude command value (In) based on the negative-sequence voltage amplitude (Vn).The opposite-system current command generator 169 calculates opposite-system current command values ​​(Ina, Inb, and Inc) based on the opposite-system current amplitude command value (In) and the opposite-system phase (θn). The signal generator generates the control signal (PLS) based on a result obtained by adding (i) positive-system current command values ​​based on the positive-system phase (θp) and (ii) the opposite-system current command values ​​(Ina, Inb, and Inc).