548 results about "Virtual synchronous generator" patented technology

The invention discloses an optimal virtual inertia control method based on a virtual synchronous generator in the distributed power generation control field. According to the method, a control strategy of a virtual synchronous generator is employed for a micro-grid inverter to organically combine three control degrees of freedom including a droop coefficient m, a virtual inertia J and a virtual damping D, and thus optimization of key parameters of the virtual synchronous generator is achieved. Through adoption of the method, the inertia advantage of a conventional synchronous generator is fully exhibited, and the stability and the inherent dynamic performance of an inverter are also taken into consideration. Moreover, the output power and frequency oscillation problems brought by virtual inertia are solved while the power and the capacity configuration of an energy storage apparatus are considered.

The invention provides a microgrid and microsource control method based on a virtual synchronous electric generator. The method comprises the following steps of building a mechanical equation and an electromagnetic equation of the virtual synchronous electric generator, carrying out microsource active control through active adjustment of the virtual synchronous electric generator, carrying out microsource reactive control through reactive adjustment of the virtual synchronous electric generator and achieving seamless switching between different operating modes of a microgrid. The microgrid and microsource control method based on the virtual synchronous electric generator has the active and reactive adjustment capacity similar to that of the synchronous electric generator, can simulate the inertia and the damping characteristic of the synchronous electric generator, can overcome the impact on a power grid from inertialessness of a traditional grid-connected inverter, and can effectively improve the capacity of the power grid to accept the renewable energy sources.

The invention relates to a virtual synchronous generator control method based on self-adapting moment inertia. The output of a grid-connected inverter in distributed generation is connected with an AC bus of a filter capacitor Cf which is in parallel connection with the grid-connected inverter through a filter inductor Lf; sampling is performed to obtain the output power, the voltage and the current of an output interface of an inverter; the output power, the voltage and the current are transmitted to a VSG (virtual synchronous generator) algorithm; the calculated terminal voltage of a VSG stator is sent to be controlled by a voltage external loop; the voltage external loop adopts a PI controller to stably load the voltage; the current of the filter capacitor is sent to be controlled by a voltage internal loop; the voltage internal loop adopts a PI controller to increase the response speed; a control signal is outputted by a voltage-current dual-closed loop to the grid-connected inverter; the moment inertia in the virtual synchronous generator in the control method can be changed in a self-adapted manner according to the change capacity of the system frequency. Through the adoption of the virtual synchronous generator control method disclosed by the invention, the transient state process of the system is reduced; a great deal of harmonic waves in the system is offset; the stability of frequency and the stability of voltage can be improved; the adaptability and the power supply quality of a micro-electrical network are improved; the problem that in a conventional method, the output frequency is reduced, is solved.

The present invention discloses a microgrid inverter and a grid-connected and off-grid control method thereof. The method includes: a dispatchable microgrid inverter supporting a microgrid voltage frequency works in different control modes under grid-connected and off-grid conditions; when the microgrid works under grid-connected or off-grid conditions, a central control unit controls the dispatchable microgrid inverter to work in a PQ control mode, a droop control mode or a virtual synchronous generator control mode, and to transmit electricity to a large power grid or absorb electricity from the large power grid according to requirements of the microgrid central control unit; when the microgrid is in an isolated island operation mode, the dispatchable microgrid inverter is required to show voltage source characteristics to the external, and can support the voltage frequency of the power grid; in a microgrid with a master-slave control structure, the dispatchable microgrid inverter works in a VF control mode; and in a microgrid with peer-to-peer control, droop control or virtual synchronous generator control is adopted. The method can control the inverter to work in different control modes according to actual operation conditions of the microgrid, thereby increasing security and reliability of the operation of the microgrid.

The invention provides a virtual synchronous generator virtual inertia and virtual damping coefficient adaptive control method, which relates to the technical field of smart grid and intelligent algorithms. Firstly, the inverter based on the virtual synchronous generator is modeled, and the correlation between the output frequency of the inverter and the virtual inertia J and the virtual damping coefficient D is obtained. Then the fitness function of the adaptive control method of virtual inertia J and virtual damping coefficient D based on the improved particle swarm optimization algorithm isdetermined. Finally, the improved particle swarm optimization algorithm is applied to the active power. In the frequency control part, the real-time adaptive control of virtual inertia J and virtualdamping coefficient D is realized in order to minimize the frequency deviation and stabilize the system. The invention provides a virtual synchronous generator virtual inertia and virtual damping coefficient real-time adaptive control method, which fully utilizes the characteristics of the virtual inertia and introduces the virtual damping coefficient, so that the inverter is more stable and the frequency offset is smaller.

This invention discloses a system and method to operate a doubly-fed induction generator (DFIG) as a grid-friendly virtual synchronous generator (VSG). It comprises a DFIG modeled as a virtual differential gear that links a rotor shaft driven by a prime mover, a virtual stator shaft coupled with a virtual synchronous generator G and a virtual slip shaft coupled with a virtual synchronous motor M, and a variable frequency drive that behaves as a virtual synchronous motor-generator set to regulate the speed of the virtual synchronous motor M so that the speed of the virtual stator shaft, i.e., the speed of the virtual synchronous generator G, is within a narrow band around the grid frequency even when the rotor shah: speed changes. As a result, a grid-connected DFIG can be controlled to behave like a virtual synchronous generator without using a PLL.

The invention discloses a virtual synchronous generator-based photovoltaic power control strategy, which comprises a photovoltaic power generation system, an energy storage device and an inversion device, wherein a power supply output end of the photovoltaic power generation system is respectively connected with an energy storage end of the energy storage device and an inversion end of the inversion device; the output end of the inversion device is connected with a power grid; the inversion device carries out a power control through a virtual synchronous generator method; the output power of the inversion device is adjusted through the virtual synchronous generator method to reach a stable state; the output power is adjusted according to load fluctuation; stable frequency and voltage of the photovoltaic system can be maintained; and the grid-connected generation performance of a photovoltaic power station is effectively improved.

The invention relates to a presynchronization control method based on a virtual synchronous generator. The method comprises the steps that a three-phase network voltage amplitude value Vg, a three-phase network voltage frequency omega g and a three-phase network voltage phase angle theta g are obtained; a voltage amplitude value Vo output by an inverter, voltage frequency omega o output by the inverter and a voltage phase angle theta o output by the inverter are obtained; a frequency feedback integration element is cut in; a voltage feedback integration element is cut in; a proportional integral adjuster III is cut in; and a grid connection switch is closed, so that the synchronous generator is connected into a power grid. According to the technical scheme, the fact that before virtual synchronous generator grid connection, the frequency, the amplitude, the phase and the grid voltage output by the virtual synchronous generator are the same can be guaranteed, accordingly small grid connection instant impact current is achieve, and inverter smooth friendly grid connection is guaranteed.

The invention discloses a method for controlling energy storage type wind power station control with a synchronization property, belonging to the technical field of wind power generation control. The method is characterized in that an energy storage battery system is configured at the alternating current side of the wind power station, a control strategy based on a synchronous generator model is adopted for the inverter of the energy storage battery system, and the wind power station and the energy storage battery system are equivalent to a virtual synchronous generator, thus the wind power station has a synchronization interface property. By utilizing the method disclosed by the invention, the output power of the wind power station is smooth, and the influence of the output power fluctuation of the wind power station on the power network frequency is reduced effectively; and the property of a synchronous generator is embodied to a power network, the system power balance can be maintained automatically according to the system loading fluctuation, thus the system voltage frequency is stable.

The invention discloses an inverter secondary-frequency-regulation control circuit based on a virtual synchronous generator. The inverter secondary-frequency-regulation control circuit comprises an inverter, an LC filter and a power measurement module, and also comprises a voltage loop and a VSG controller. The input end of the VSG controller is connected with the output end of the power measurement module, the output end of the VSG controller is connected with the input end of the voltage loop, and the output end of the voltage loop is connected with the inverter; the VSG controller comprises a power frequency controller and an excitation controller, the power frequency controller is used for simulating a rotor motion equation of the synchronous generator, the excitation controller is used for reactive-voltage droop control, the amplitude information of command voltage generated by the excitation controller and the phase information of command voltage generated by the power frequency controller are synthesized, and an input command signal em of the voltage loop cam be obtained. According to the inverter secondary-frequency-regulation control circuit, the VSG control strategy can automatically track load fluctuation and change output force of inverter secondary-frequency-regulation control circuit under the island model, and frequency support is provided for a micro grid.

The invention discloses an overrunning virtual synchronous generator (VSG+) method with rotary inertia and damping self-optimization-trending. The method comprises the following steps: step one, a mechanical equation and an electromagnetic equation of a virtual synchronous generator (VSG) are established; step two, the rotary inertia J and damping D in a VSG model are increased as |delta f| is increased, wherein delta f is an absolute value of a difference between a power network rated frequency and the actual frequency of the VSG; and step three, according to self-adjustment of the rotary inertia J and the damping D, closed-loop control is performed on the |delta f|, and finally, grid connection of a distributed photovoltaic power generation system is realized. According to the VSG+ method with the rotary inertia and damping self-optimization-trending, provided by the invention, the rotary inertia J and the damping D in the VSG are adaptively adjusted as the |delta f| changes, the rotary inertia J and the damping D after adjustment then perform feedback regulation on the |delta f|, and finally, zero impact during grid connection of photovoltaic inverters is realized, such that the acceptance capability of a power network for the distributed photovoltaic power generation system is improved.

The invention discloses a microgrid inverter multi-loop control method based on a virtual synchronous generator, and the method comprises power control of an outer loop and voltage current control of an inner loop. The power control of the outer loop comprises the following steps: measuring the three-phase voltage and current of an output side of an inverter, calculating active power and reactive power according to the instantaneous power theory, carrying out calculation and regulation through an active power-frequency equation, a reactive frequency equation, a torque inertia equation and an electromagnetic transient equation of a synchronous motor, obtaining the amplitude of an output voltage and a phase angle given value, and then carrying out modulation through voltage and current double loops. The method can achieve the non-corresponding control of voltage size and frequency well, outputs active and reactive power, can achieve precise manual control, and has the characteristics of V / F and PQ control. When a fault happens to a power grid, the method can simulate the primary modulation, primary voltage regulation and inertia characteristics of the synchronous generator, participates in the power grid adjustment, provides frequency and voltage support, and facilitates the stabilization of the power grid.

The present invention discloses an adaptive control method of a moment of inertia suitable for a virtual synchronous generator, and belongs to the field of photovoltaic grid-connected inverters. The method comprises the steps of: determining a moment-of-inertia initial value J0 by employing system parameters, and according to power angle features of a virtual synchronous generator, regulating themoment of inertia in real time in the frequency change process. The method provided by the invention develops the control flexibility of the grid-connected inverter to the maximum extent, can inhibitoscillation when dynamic response of the frequency and the active power is performed, reduces the dynamic response time, considers the system stability and improves the consumption of the new energy power integration.

The invention discloses a virtual synchronous generator-based dynamic power compensation method of a diesel storage hybrid independent micro-grid. The method comprises a virtual synchronous generator control method for fixing virtual inertia and a damping parameter under the condition of steady-state operation of a system, a virtual synchronous generator control method for self-correcting the virtual inertia and the damping parameter under the condition of load disturbance on the system, and a virtual synchronous generator control method for negative inertia in a dynamic recovery process of a frequency of the system. By the virtual synchronous generator-based dynamic power compensation method, the frequency stability of a diesel storage hybrid independent micro-grid system comprising a micro-grid energy storage inverter under a steady-state condition is considered; reduction of frequency amplitude deviation of the system by the independent micro-grid system under the condition of the load disturbance is ensured; and fast recovery of the frequency of the system can also be ensured, so that the power supply quality of the system is effectively improved; and the virtual synchronous generator-based dynamic power compensation method can be widely applied to the independent micro-grid system for networking operation for the micro-grid energy storage inverter and a diesel generator set.

The invention discloses an inverter grid-connected control method based on the virtual synchronous generator technology and belongs to the field of distributed power generation system grid-connected researches. According to the technical scheme, the method includes the steps that a grid-connected inverter phase voltage phase value is obtained through calculation by simulating a conventional synchronous generator unit active power control method; a grid-connected inverter phase voltage amplitude value is obtained through calculation by simulating a conventional synchronous generator unit reactive power control method; a three-phase voltage reference value is worked out according to the inverter phase voltage phase value and the inverter phase voltage amplitude value, a three-phase modulated wave is figured out according to direct current side voltage obtained through detection, and the three-phase modulated wave is compared with a carrier wave to obtain six switching signals to control turn-off and turn-on of switching devices in a main circuit. System damping and active power-frequency droop control are achieved by means of control link signals, and power grid frequency does not need to be detected. The method simplifies a control structure and avoids the problems caused by a frequency detection link. Effectiveness of the method is verified through simulation and experiment results.

The invention discloses a master-slave control method for an energy storage inverter based on a virtual synchronous generator. The energy storage inverter comprises a master control inverter and a slave control inverter, wherein the master control inverter adopts a voltage source output mode based on the virtual synchronous generator to provide amplitude and frequency of network voltage, provide virtual inertia and a virtual damping ratio according to the capacity of the master control inverter, and meanwhile provide static active and passive current quotas to each inverter; the slave control inverter adopts a current source output mode based on the virtual synchronous generator to receive static active and passive current quotas issued by the master control inverter, and meanwhile provide the virtual inertia according to the capacity of the slave control inverter. According to the method, in island parallel operation, a load is non-uniform and fluidity is relatively low under various load conditions, and relatively high output voltage power quality is provided; compared with traditional master-slave control, a controller structure does not need to be changed when switching between grid connection and disconnection is performed, and the master control inverter and the slave control inverter independently provide the virtual inertia without depending on communication, so that improvement on system stability under dynamic condition is facilitated, and the reliability is relatively high.

The invention relates to a detecting system and method for virtual synchronous generator grid connection based on hardware-in-the-loop simulation. The detecting system comprises the following sequentially connected parts: an upper computer, a lower computer simulator, an I / O module, a controller for a virtual synchronous generator to be tested and a digital waveform recorder. The detecting system for virtual synchronous generator grid connection based on hardware-in-the-loop simulation can provide system modeling and simulation for various types of virtual synchronous generators and different types of energy storage units, photovoltaic power generation units and wind turbines of the generators. As a new detecting method for grid connection performance of a power generation unit of a virtual synchronous generator, the detecting method can perform system-level hardware-in-the-loop simulation detection on the basis of completing the mathematical modeling for the virtual synchronous generator to be tested, the integration level is high, and the detecting requirement for grid connection performance of virtual synchronous generators of different voltage levels in the market can be met.

The invention discloses a method and a device for controlling three-phase unbalanced current of a virtual synchronous generator. The method comprises the following steps: establishing a rotor movement equation of the virtual synchronous generator (VSG) and a virtual excitation equation of the VSG; decomposing unbalanced voltage of a power grid into positive sequence voltage, negative sequence voltage, zero sequence voltage and corresponding phase-sequence current, and decomposing active power and reactive power output by the VSG to analyze an encountered imbalance problem; calculating a reference instruction of dq axis current according to the output three-phase voltage signal; and converting the reference instruction of the current into a pulse-width modulation (PWM) voltage modulation signal through a self-designed current inner ring, and controlling the virtual synchronous generator to run through the PWM voltage modulation signal, so as to enable the output three-phase current of the virtual synchronous generator to reach the balance. According to the control method disclosed by the embodiment of the invention, the VSG can still output three-phase balanced current when the three-phase voltage of the power grid is unbalanced, so that the operation safety of the power grid can be relatively well ensured; and the method and the device are safe, reliable, simple and convenient.

The invention discloses an inverter system based on the improved power distribution policy of a virtual synchronous generator. The inverter system comprises a grid-connected inverter system which is controlled by a virtual synchronous generator and is composed of a direct current voltage source, a three-phase bridge inverter circuit, an LCL filter, a public power grid, a load and a control drive circuit. The inverter system consists of an active regulator, an excitation regulator, a VSG algorithm module, and a voltage and current double closed-loop control module. The introduction of the control of the synchronous generator overcomes the problems of fast response and low inertia of a traditional grid-connected inverter. The permeability of renewable energy in a micro grid can be effectively improved. The dynamic characteristic of a synchronous generator rotor is introduced into a second-order transient model, which eliminates the influence of a traditional constant damping coefficienton droop control. In addition, by improving the reactive-voltage droop control, the influence of the inverter output filter impedance and the line impedance on reactive power distribution is reduced,and reasonable distribution of the inverter output power is ensured.

The invention relates to a multi-target optimization control method based on a virtual synchronous generator during power grid voltage imbalance. According to the method, a balance current VSG method is firstly utilized to acquire a reference current instruction value in a dq coordinate system; a current instruction value in the grid connected inverter dq coordinate system is acquired through the reference current instruction value in combination with an imbalance power grid voltage parameter when three targets including current three-phase balance, and active or reactive power no fluctuation are realized; a correction value of the three targets is acquired according to relationships between the current instruction value and the reference current instruction value; an optimization coefficient is introduced, and unification of an output current instruction correction value parameter of each target is carried out to acquire an output current instruction correction value of multi-target optimization; the current instruction value is corrected according to the correction value; the current after correction in the dp coordinate system is tracked, through adjusting the optimization coefficient, output current three-phase balance is realized, multi-target control on constant output active or reactive power is realized, and optimum grid connected inverter output performance is realized.

The invention discloses a control method for a virtual synchronous generator capable of being adapted to imbalanced power grid and load conditions. The control method comprises the following steps that 1) an active ring simulates the mechanical characteristics of a speed controller and a rotor to obtain an output positive sequence voltage frequency and a phase position instruction; 2) a reactive ring simulates a n excitation controller to obtain an output positive sequence voltage amplitude value instruction; 3) a voltage-control and virtual synchronous impedance ring simulates the electrical characteristics of a stator; 4) positive and negative sequence current rings carry out accurate tracking on the positive and negative sequence current instructions respectively, and eliminates the negative sequence current output; and 5) a modulation signal is obtained by the combination of the positive and negative sequence current rings, and then the modulation signal is subjected to PWM to obtain a switching signal. Compared with the prior art, the output active power fluctuation and frequency fluctuation caused by imbalance of the power grid can be eliminated; and in addition, it is ensured that the output current of the virtual synchronous generator is balanced constantly, so that overhigh electrical stress of a certain bridge arm of the inverter can be avoided.

The invention discloses a virtual synchronous generator control method and device for an energy storage converter, which can achieve a purpose that the damping power only acts in the dynamic process of frequency fluctuation, the damping power after a steady state is constant to be zero, the deviation of the steady-state active power cannot be affected due to change of the damping coefficient, and it is guaranteed that the active power tracks the instruction value according to the set droop proportion while power oscillation is restrained. Besides, while the energy storage converter can provide inertia support and grid-connected and off-grid seamless switching, the device has the capability of quickly controlling a voltage and current loop, quickly controls an output current through the current loop, facilitates reduction of current distortion, and improves the electric energy quality of the energy storage converter during grid-connected and island mode operation.

The invention relates to a virtual synchronous generator fault current suppression method based on adaptive virtual impedance. When a power grid fails, the voltage of a power grid drops, a VSG can generate large fault current, particularly at the moment when a fault occurs and is removed, the VSG can generate large impact current; when the output current of the VSG exceeds the maximum value of thecurrent capable of being borne by an inverter, irreversible damage to the VSG system can be caused, and meanwhile, the stability of the power grid is further reduced. The VSG does not have a fault ride-through capability, so that the VSG can only have the fault ride-through capability through a reasonable control scheme. According to the method of the invention, VSG fault current is suppressed bythe self-adapting of virtual impedance and the modification of a VSG reference voltage during the fault, so that the VSG has the fault ride-through capability on the premise of not changing a controlstructure. The method has high control precision. With the method adopted, fault current and impact current can be effectively suppressed; and the control structure is not changed.

The invention discloses a VSG(Virtual Synchronous Generator)-based control structure for active supporting of the grid frequency and voltage of a PMSG (Direct Drive Permanent Magnet Synchronous Generator). The control structure is composed of a wind turbine generator and a back-to-back four-quadrant converter. The back-to-back four-quadrant converter consists of a machine-side converter and a grid-side converter; the machine-side converter is used for maintaining the voltage of a direct-current side capacitor; and the grid-side converter is used for controlling normal operation of the rotatingspeed of a draught fan and power balancing based on an MPPT algorithm and carrying out active supporting on the grid frequency and voltage based on a control strategy of the VSG, wherein dynamic support is realized by releasing the energy of the direct-current side capacitor and the kinetic energy of the rotor during supporting. According to the control structure, a defect that grid connection can not be realized until the PPL phase locking is used by the wind turbine generator is overcome. The wind turbine generator is equivalent to a voltage source type VSG to support fluctuation of the grid voltage and frequency.

A micro power grid frequency control method and a system are provided, wherein the method comprises the steps of obtaining d-axis and q-axis components of an output voltage, an output current and a filtering inductance current of an LC filter at the grid side of an inversion power supply; obtaining the output reactive power, the output active power and an output voltage amplitude of the LC filter in combination with the d-axis and the q-axis components of the output voltage and the output current; obtaining a virtual excitation electromotive force by taking the output reactive power and the output voltage amplitude as the input of a virtual excitation controller; obtaining an active power increment by inputting an output angular frequency of a virtual synchronous generator controller into a frequency controller; and obtaining a d-axis and a q-axis reference instruction value and an output angular frequency of the inverter output voltage by taking the output active power, the virtual excitation electromotive force, the active power increment and the d-axis component and the q-axis component of the filtering inductance current as the input of the virtual synchronous generator controller. According to the invention, the micro power grid frequency change caused by load disturbance can be effectively inhibited; and the island micro power grid can be operated stably.

The invention discloses a unified damping ratio-based damping coefficient adaptive control method of a virtual synchronous generator. The method comprises the following steps of (1) simulating primary frequency modulation and the mechanical characteristic of a rotor and obtaining a frequency and a phase of output voltage; (2) detecting real-time power angle information and calculating a damping coefficient according to a designed adaptive damping function to obtain damping power; (3) superposing the damping power to output active power for feedback and calculating an output voltage frequency and a phase instruction of the virtual synchronous generator according to the step (1); and (4) generating a voltage reference value by a voltage amplitude instruction and the phase instruction, and obtaining a control signal of a converter through a voltage closed loop. Compared with an existing method, the virtual synchronous generator can ensure an oscillation suppression effect at different steady state operation points and has relatively good dynamic characteristics; and the anti-interference capability of the frequency is strengthened.

The invention discloses a current compensation based power decoupling method of a virtual synchronous power generator. The power decoupling method comprises the following steps of 1) acquiring a dq component of an output current of a virtual synchronous motor through sampling, acquiring power angle information by a mechanical property simulation part, and further calculating reactive power-power angle decoupling current compensation instruction; 2) acquiring transient state variable quantity of a virtual excitation electromotive force, and calculating active power-voltage decoupling current compensation instruction by combining the dq component, obtained in the step 1), of the output current; and 3) correcting the reactive power-power angle decoupling current compensation instruction obtained in the step 1) and the active power-voltage decoupling current compensation instruction obtained in the step 2) to obtain a new current instruction, and obtaining a switching signal through a current ring to drive a switching network. The invention proposes the power decoupling method applicable to the virtual synchronous motor, and the influence of a power angle on droop control can be eliminated; and compared with the prior art, the power decoupling method has the advantages that dynamic power oscillation and a steady-state error brought by power coupling can be eliminated.

A distributed virtual synchronous-generator low voltage crossing control method is disclosed. The method comprises the following steps of using an improved virtual synchronous generator reactive powerring to accelerate a response speed of the reactive power ring and increase a reactive power support capability to a grid connection point; when a grid connection point voltage is detected to drop and an instantaneous overcurrent is detected, introducing virtual impedance control, correcting a voltage reference value and restraining the instantaneous overcurrent; using a balance current virtual synchronization control method to control positive and negative sequence currents, and when a grid connection voltage is imbalance, realizing balance control of an output current and restraining a stable state overcurrent; and according to a low voltage crossing requirement, resetting a power instruction value so that a system satisfies a reactive current injection requirement, and after a fault isremoved, setting the power instruction value to an original value. Through the above steps, low voltage crossing requirements of instantaneous and stable state overcurrent restraining, reactive current injection according to the requirement and the like are satisfied.

The invention relates to a photovoltaic-energy storage combined operation power generation system based on a virtual synchronous generator control strategy and a control method thereof. The system istechnically characterized by comprising a photovoltaic-energy storage power generation system, a measuring component, a three-phase load and an alternating current power grid, wherein the photovoltaic-energy storage power generation system comprises a photovoltaic array, an energy storage battery, a photovoltaic direct current converter, a photovoltaic inverter and an energy storage inverter; andoutput ends of the photovoltaic inverter and the energy storage inverter are connected to a power grid alternating current bus. In the invention, the virtual synchronous generator control strategy isadopted by the energy storage inverter; and the operating characteristics of a synchronous machine with inertia and damping are adjusted by adjusting the energy storage device, so that the overall external characteristics of the photovoltaic and energy storage device are similar to the operating characteristics of the conventional synchronous machine. The own output power of the system can be adjusted for the photovoltaic output fluctuation and the load fluctuation, the frequency and voltage fluctuation of the photovoltaic system are stabilized, and the dynamic performance of a photovoltaic grid-connected plant is effectively improved.

The invention discloses a low-voltage ride-through control method for a grid-connected inverter based on control mode switching. The method comprises the following steps: during normal operation of the grid, a grid-connected inverter adopts a VSG control mode, the d-axis and q-axis positive and negative sequence components of the grid voltage are acquired and the phase angle of three-phase modulated wave is output in a PR current control mode, and the phase angle is used to follow the grid-connected inverter in order to output a voltage phase angle; when the grid fails, the given values of the d-axis and q-axis positive and negative sequence components of the current are calculated, the given value of current under a static coordinate system is obtained through inverse rotation transformation, a PR current controller generates a voltage signal, and the grid-connected inverter is quickly switched from the VSG control mode to a PR current control mode; and at the end of failure, the grid-connected inverter is switched back to the VSG control mode from the PR current control mode at an appropriate time. A grid-connected inverter can be smoothly switched between control modes. The grid-connection impact current can be limited, and reactive power can be provided for the grid. Thus, low-voltage ride-through of a virtual synchronous generator under grid failure is realized.