116 results about "Lcl filter" patented technology

The invention relates to the technical field of hybrid inverters, and discloses a hybrid inverter supporting reactive compensation and a control method thereof, and the hybrid inverter comprises a DC input unit, a three-phase full-bridge inversion unit, a grid-connected switching unit, a signal acquisition unit and a digital control unit. The direct current input unit comprises a photovoltaic interface, a battery interface and a direct current bus and is used for converging photovoltaic and energy storage electric energy; the three-phase full-bridge inversion unit is composed of a power device and an LCL filter and converts direct current into alternating current. The grid-connected switching unit comprises a static switch and an isolation transformer and is used for controlling power grid connection; the signal acquisition unit detects voltage and current signals; and the digital control unit judges a grid-connected mode or an off-grid mode according to the signal, calculates a reactive current reference value and generates a PWM (Pulse Width Modulation) control signal so as to realize reactive compensation control in the grid-connected mode and the off-grid mode. According to the invention, reactive power compensation capability is provided in both grid-connected and off-grid operation modes, and stable operation of the inverter in various working conditions is ensured.

The invention relates to the technical field of voltage source type grid-connected inverter control, and particularly discloses a voltage source type inverter active damping control strategy based on power grid voltage feed-forward, which comprises an LCL filter module, an inductance voltage differential feedback active damping loop, a power grid voltage feed-forward compensation loop and a proportion-resonance controller. By introducing a grid-side inductive voltage first-order differential feedback link, the damping characteristic of the system is enhanced, and LCL resonance is suppressed; and meanwhile, a power grid voltage feed-forward loop is designed, so that the interference of power grid disturbance on grid-connected current is eliminated. According to the virtual resistance parameter design method based on the optimal damping ratio and the feed-forward loop transfer function optimization strategy, the dynamic response capability, the resonance suppression effect and the weak power grid adaptability of the voltage source type inverter can be effectively improved, and the system stability and the electric energy quality are remarkably improved.

The invention belongs to the technical field of electronic power, and particularly relates to an LCL grid-connected inverter model-free predictive current control system and method based on sampling noise compensation, and the system comprises an inverter main circuit, an LCL filter and a controller. The controller is configured to firstly calculate a current gradient and a voltage gradient according to a collected system operation signal; then, a second-order generalized integrator is used for conducting accurate compensation on sampling noise contained in the gradient; and finally, executing a model-free predictive control algorithm based on the compensated gradient, and preferably selecting an optimal voltage vector through a multi-objective value function integrating inverter side current, capacitor voltage and network side current. According to the method, sampling noise interference is effectively suppressed, the control precision and the anti-interference capability of the system are improved, and stable and efficient operation of the LCL grid-connected inverter can be realized without additional damping.

The invention relates to the technical field of microgrids, in particular to an integrated light storage and charging grid-connected direct-current microgrid system and a control strategy thereof, and the system comprises a plurality of groups of photovoltaic arrays, a direct-current bus, an energy storage battery pack, a supercapacitor bank, a large power grid, a charging pile, a bidirectional DC-AC converter, a DC-DC converter and a power distribution unit, the photovoltaic array is connected with the direct current bus through a Boost circuit; the direct current bus is connected with the energy storage battery pack and the super capacitor bank through a DC-DC converter; the DC bus is connected with the large power grid through a bidirectional DC-AC converter and an LCL filter. The DC bus is electrically connected with the plurality of charging piles, and the outputs of the plurality of charging piles are connected in parallel through a controllable high-voltage DC contactor; and the power distribution unit is used for dynamically controlling the number of parallel output paths of the charging piles according to load requirements.

The invention relates to the technical field of data center energy storage, and discloses a data center flywheel energy storage system and method based on an LCL filter, and the method comprises the steps: collecting a power grid side current signal, decomposing a harmonic component, and dynamically adjusting the parameters of the LCL filter to suppress harmonic waves; determining and executing a charging and discharging control strategy according to the direct-current bus voltage and the flywheel rotating speed; flywheel vibration and acceleration are monitored in real time, operation stability is evaluated, and a control strategy is corrected; and the harmonic suppression effect is optimized by combining rotating speed feedback and voltage data compensation filter parameters. The system comprises a harmonic suppression module, a charge and discharge control module, a stability evaluation module and a filtering parameter optimization module. Through multi-parameter dynamic adjustment and multi-module cooperative control, composite suppression of power grid harmonics and accurate adjustment of the flywheel energy storage state are achieved, the system operation stability and the filtering effect are improved, and the method is suitable for a data center energy storage scene.

The application discloses a kind of LCL grid-connected current feedback active damping control method and system, belong to power filter control technical field, including the grid-connected current i2 of the acquisition inverter net side;Grid-connected current i2 flows through negative low-pass-high-pass filter and is handled, obtains feedback current;Feedback current and the output of inverter current controller are superposed, as the control signal of LCL filter.The application will not amplify high-frequency harmonic current, and the control system still has good robustness when LCL filter parameter changes.

The invention discloses a large-capacity energy storage converter based on a DAB-ANPC cascade architecture, which comprises a pre-stage DC-DC converter and a post-stage DC-AC inverter which are cascaded, the pre-stage DC-DC converter adopts a dual active bridge (DAB) circuit and comprises a primary and secondary full bridge, a high-frequency isolation transformer, a series inductor and a blocking capacitor, and electrical isolation and wide voltage input are realized; the back-stage DC-AC inverter is a three-phase three-level active neutral point clamp (ANPC) topology, each phase of bridge arm comprises six full-control switches, loss is balanced through the clamp switches, and the output end of the back-stage DC-AC inverter is connected with the LCL filter. According to the invention, DAB power transmission is controlled and adjusted through single phase shift, and an ANPC switch tube conduction time sequence is dynamically allocated by adopting stacked carrier SPWM modulation, so that the problems of electrical isolation and wide voltage can be solved, and a new energy fluctuation scene is compatible; the device loss is balanced, local overheating is avoided, and the system efficiency and reliability are improved; soft switching and LCL filtering are cooperated, so that the switching loss and harmonic interference are reduced, and the cost is reduced; bidirectional energy flow is supported, and the charging and discharging requirements of an energy storage power station are met.

The invention relates to an equivalent modeling method and device for a lithium battery energy storage power station, computer equipment, a readable storage medium and a program product, and relates to the technical field of simulation modeling. The accuracy of the equivalent model obtained through simulation can be improved. The method comprises the following steps: determining a plurality of lithium battery energy storage power stations needing equivalence in a power system, constructing single body models of lithium batteries, and carrying out equivalence modeling by adopting an arrangement mode of connecting in series and then connecting in parallel on the basis of the single body models to obtain an equivalence model of a lithium battery pack; performing parameter aggregation on the LCL filter according to the equivalent circuit diagram of the LCL filter in the lithium battery energy storage power station to obtain equivalent reactance values respectively corresponding to two inductors and one capacitor in the LCL filter; simulating a rotor motion equation of the virtual synchronous generator by adopting a VSG control strategy, and performing controller parameter aggregation based on the rotor motion equation to obtain a parameter aggregation result; and performing equivalent modeling on the plurality of lithium battery energy storage power stations based on the equivalent model, the equivalent reactance value and the parameter aggregation result.

The invention discloses a multipath parallel current-sharing high-frequency auxiliary power supply system based on ADRC-PI double closed loops, which comprises an LCL filter and a power supply system, and is characterized in that the LCL filter is connected with the power supply system, and the power supply system comprises a plurality of devices arranged in parallel; wherein each device comprises a boost chopping module, an inversion module, a diode uncontrolled rectification module and a Buck module, and the system adopts double-loop control of voltage outer loop-current inner loop combination for the boost chopping module of each device. An ADRC is designed as a voltage outer ring and a PI is designed as a current inner ring, and an automatic current sharing strategy is added to control the output voltage of the boost module and the current sharing condition between multiple paths of equipment; and the inverter module and the Buck module adopt a fixed duty ratio to control the output power of the power supply to be matched with the power required by the load. According to the invention, the output power quality and transient performance of the multi-path parallel current-sharing high-frequency auxiliary system are improved.

A common mode choke device is provided with a first common mode choke and a second common mode choke, the first common mode choke and the second common mode choke are arranged in parallel such that annular iron cores are coaxial, and a pair of opposing metal rings formed as annular metal plates are attached to opposing annular surfaces of the first common mode choke and the second common mode choke. A pair of opposed metal rings is connected to a reference potential. The pair of opposing metal rings function as a capacitance of a parasitic capacitance corresponding to the area of the opposing surfaces and the distance between the opposing surfaces, and thus the common mode choke device functions as an LCL filter.

The application discloses a control method of an LCL type grid-connected inverter based on capacitor voltage feedforward compensation and composite active damping, which comprises the following steps: collecting a coupling point voltage from a common coupling point of an LCL type grid-connected inverter, processing the coupling point voltage to obtain phase angle information; collecting a grid current, calculating a first damping signal based on the grid current, and calculating an original reference current based on the grid current and the phase angle information; calculating an error signal based on the grid current and the original reference current, generating an original reference voltage based on the error signal; collecting a capacitor voltage of an LCL filter circuit in the LCL type grid-connected inverter, calculating a second damping signal based on the capacitor voltage; calculating an optimized reference voltage based on the original reference voltage, the first damping signal and the second damping signal; generating a PWM driving signal based on the optimized reference voltage, and controlling the LCL type grid-connected inverter by using the PWM driving signal. The application not only has good economic efficiency and resonance peak suppression effect, but also can suppress background harmonics while maintaining stable operation of the grid-connected inverter under a weak grid.

To address the problem that conventional grid-connected renewable energy sources, when connected to the grid at a high rate, effectively reduce grid inertia and are prone to abnormal interactions with the grid, leading to problems such as low-frequency oscillations, subsynchronous oscillations, and harmonic oscillations, the present invention proposes a grid-connected control system for wind power and photovoltaic power generation, comprising: a wind turbine, a synchronous generator, a wind turbine-side converter, a capacitor, a grid-side converter, an LCL filter, a grid, a photovoltaic power generation unit, a photovoltaic converter, a control loop for the wind turbine-side converter, a control loop for the grid-side converter, and a control loop for the photovoltaic converter. This invention enables wind power and photovoltaic power generation to be connected to the grid through the same grid-side converter, reducing costs. It also presents a voltage source-like characteristic to the grid, similar to that of a synchronous generator, providing inertia and frequency support to the grid, while enhancing the stability of their interaction with the grid and suppressing oscillations.

The invention discloses a self-adaptive control architecture method for improving the stability of a weak power grid photovoltaic grid-connected system, and belongs to the technical field of inverter control. In order to solve the stability problem of a following grid type inverter caused by power grid impedance change under an existing current double-closed-loop control strategy, the method realizes robustness improvement of a system through an additional controller, and comprises the following steps: firstly, establishing a main circuit comprising a two-level inverter and an LCL filter and a stable traditional current double-closed-loop control system under a strong power grid; and then voltage and current in the circuit are measured to construct an oscillation suppressor adaptive to the impedance change of the power grid. Starting from a photovoltaic grid-connected system based on a grid-following inverter and a traditional current double-closed-loop strategy, damping compensation for the impedance change of the power grid is realized by introducing an additional controller, and a reliable scheme is provided for a new energy grid-connected system to cope with the impedance change of the power grid.

The invention relates to the technical field of grid-connected inverters, in particular to a method for correcting positive virtual impedance of an LCL type inverter in a Nyquist frequency, which comprises the following steps of: accurately determining parameters of capacitor voltage feedback branches in an LCL filter, establishing an equivalent formula of virtual impedance, and adjusting parameters in primary differential feedback so as to correct the positive virtual impedance of the LCL type inverter in the Nyquist frequency. The method successfully widens the positive damping frequency range, optimizes the impedance characteristics of the inverter through the virtual impedance of the parallel proportional term, the primary differential term and the secondary differential term and the calculation of the total parallel impedance formula, and obtains the impedance characteristics of the inverter by drawing various impedance-frequency curves. Comprising a virtual impedance-frequency curve, a parallel impedance-frequency curve and a primary differential impedance-frequency curve, and an intuitive impedance characteristic analysis tool is provided for a system designer and an engineer; and finally, by drawing a total impedance-frequency curve and verifying whether the system maintains the positive resistance characteristic in the Nyquist frequency range, the stability of the system is ensured.

The goal is to miniaturize and lighten common mode choke coil devices. [Solution] A first common mode choke coil and a second common mode choke coil are arranged parallel to each other so that their annular cores are coaxial. A pair of opposing metal rings, formed as annular metal plates, are attached to the opposing annular surfaces of the first and second common mode choke coils, and the pair of opposing metal rings are connected to a reference potential. Since the pair of opposing metal rings function as capacitances with parasitic capacitances corresponding to the area of ​​the opposing surfaces and the distance between the opposing surfaces, the common mode choke coil device functions as an LCL filter.

The embodiment of the utility model provides a magnetic integrated inductor assembly for an LCL filter and the LCL filter. The magnetic integrated inductor assembly comprises: a magnetic core having at least one magnetic circuit; the first winding and the second winding are wound at different magnetic circuit positions of the magnetic core respectively and are magnetically coupled and superposed through at least one magnetic circuit of the magnetic core, and the first winding and the second winding are arranged to enable the first winding to form machine-side inductance and enable the second winding to form resonant inductance. Therefore, the inductance value and the filtering performance can be improved, the ripple current and the magnetic core loss are reduced, and the copper wire consumption and the magnetic core size are reduced.

The utility model discloses a novel nine-level H-type inverter device, which comprises a direct-current power supply, a load, five resistors, six capacitors, twelve diodes, nine switch tubes and two inductors, four diodes and one switch tube form a secondary loop, and two inductors and one capacitor form an LCL filter circuit. The four switch tubes form an H-type inverter bridge connection mode, compared with other nine-level inverters, the novel nine-level H-type inverter is simpler in structure, and a secondary loop and a tertiary loop do not influence each other, that is, two levels emitted by the secondary loop and four levels emitted by the tertiary loop do not influence each other. A current and voltage loop is provided through a secondary loop, and the distortion rate of output voltage and current is reduced through an LCL filter circuit. The circuit provided by the utility model guarantees the normal operation of the inverter in an AC power supply system, and reduces the failure rate of electrical equipment and unnecessary loss.

This invention relates to a Kalman filter active damping iterative learning model predictive control method for grid-connected inverters. First, by using only measured signals of inverter-side current and grid-side voltage through a Kalman filter, the state variables of the LCL filter are estimated in real time, replacing physical sensors and reducing hardware costs. Second, based on the estimated capacitor voltage, the active damping current is calculated, and a composite current reference value for the inverter side is generated to actively suppress resonance. Then, an iterative learning control outer loop is introduced to compensate for periodic disturbances such as dead-zone effects, generating a compensation current using historical error data to improve current quality. Finally, finite set model predictive control is used to optimize the switching state, achieving high-precision tracking. This invention reduces the number of sensors, enhances anti-interference capability and robustness, and significantly reduces the total harmonic distortion of the output current. It is suitable for distributed renewable energy generation systems, ensuring the stable and efficient operation of grid-connected inverters.

The invention relates to the technical field of electronic circuits, in particular to a method and device for calculating active damping in a wind power generation system, and the method comprises the steps: constructing an active damping transfer function suitable for a single-ring network construction type permanent magnet synchronous wind power generation system based on a control strategy of a single-ring network construction type inverter and a control strategy of the permanent magnet synchronous wind power generation system; calculating a proportionality coefficient and a time constant based on a system parameter meeting a first preset condition, a system characteristic quantity meeting a second preset condition and a stability index meeting a third preset condition in the single-ring network construction type permanent magnet synchronous wind power generation system; and quantifying the active damping transfer function according to the proportionality coefficient and the time constant to obtain an active damping compensation transfer function. Therefore, the problems that in the prior art, due to the fact that the resonance dynamic and non-minimum phase characteristics of the LCL filter and the influence of RAP control on the LCL resonance mode are not considered, the high-frequency resonance dominant instability phenomenon is likely to occur, and in addition, necessary theoretical support is lacked are solved.

This invention discloses a one-stop intelligent megawatt box system based on TE-SVM modulation and its intelligent controller and control method, including an MPPT controller for tracking the maximum power of a DC / DC converter, a positive and negative sequence voltage decomposition module, a phase-locked loop, and a C-type control for the LCL filter. f With R f A current correction module that corrects the three-phase average current output from the component; a positive-sequence theoretical active power reference current conversion module; a positive-sequence theoretical reactive power reference current conversion module; and an output voltage U. α +、U β + Two-phase positive sequence static voltage converter module, output voltage U α -, U β A two-phase negative-sequence static voltage converter module, a TE-SVM waveform generation module based on the TLS-ESPRIT algorithm for estimating smart grid frequencies, and the TE-SVM waveform generation module utilizing voltage U α +、U β + and U α -, U β - Synthesize a reference voltage and generate a waveform based on the estimated smart grid frequency to control the inverter to perform inversion.

The invention discloses a virtual impedance adjusting system for a three-phase four-wire converter, and the system comprises a T-type three-level three-bridge arm main circuit which is used for controlling the state of a bridge arm power switch tube of a current conversion part, and achieving the energy exchange of a DC side and an AC side; the LCL filter is used for suppressing harmonic components in the output current of the inverter; and the control unit is used for independently controlling each bridge arm or each phase so as to adjust the virtual impedance. The invention further discloses a virtual impedance adjusting method of the three-phase four-wire converter. According to the invention, through mathematical model derivation and control strategy design, wide-range accurate control of virtual impedance is realized.

Aiming at the problems that the inertia of a power grid is equivalently reduced and abnormal interaction with the power grid is easy to cause low-frequency oscillation, subsynchronous oscillation, harmonic oscillation and the like during high-proportion grid connection of the conventional grid-following type new energy, the invention provides a wind power and photovoltaic multiplexing grid-constructing type control system, and aims to solve the problems that the inertia of the power grid is equivalently reduced and low-frequency oscillation, subsynchronous oscillation, harmonic oscillation and the like are caused. Comprising a wind wheel, a synchronous generator, a fan side converter, a capacitor, a power grid side converter, an LCL type filter, a power grid, a photovoltaic power generation unit, a photovoltaic converter, a control loop of the fan side converter, a control loop of the power grid side converter and a control loop of the photovoltaic converter. Wind power and photovoltaic power are connected to the power grid through the same grid-side converter, cost is reduced, voltage source external characteristics similar to those of a synchronous generator can be presented for the power grid, inertia and frequency support can be provided for the power grid, interaction stability between the system and the power grid is enhanced, oscillation is suppressed, and the like.

An embodiment of the present invention discloses a parameter estimation method and related devices for an LCL grid-connected converter. The method includes: constructing a mathematical model of the LCL grid-connected converter based on Kirchhoff's theorem and the Pade approximation transformation method, and obtaining the voltage and current models of the LCL grid-connected converter; constructing an auxiliary matrix based on the voltage and current signals, and obtaining parameter estimation error information based on the auxiliary matrix; constructing a parameter estimation error leakage term with a sliding mode form based on the parameter estimation error information, and determining a finite-time convergence adaptive rate according to the parameter estimation error leakage term to obtain the parameter estimation result of the LCL grid-connected converter. Aiming at the uncertainty problems of the parameters of the LCL filter of the grid-connected converter and the control delay, the resonance peak and the corresponding phase information of the LCL filter can be accurately estimated, and better effects are achieved in terms of the parameter convergence rate and the parameter convergence accuracy.

The application provides a three-phase LCL grid-connected NPC inverter system based on fast model predictive control, which comprises a fast model predictive controller, which carries out fast control on the NPC inverter by selecting a calculation sector composed of a current output voltage vector of the NPC inverter and several voltage vectors near the current output voltage vector; and the synchronization of the LCL filter grid-connected current and the power grid is realized by changing the prediction control reference current angle; the calculation sector is a sub-sector composed of output voltage vectors participating in the prediction control calculation on the complex plane of the voltage vectors. The scheme provided by the application realizes the balance of the DC side midpoint voltage by selecting a suitable short vector in the redundant short vector, reduces the calculation amount and avoids the design of the weight coefficient; the calculation amount is further reduced by reducing the calculation sector, so that the fast calculation of the optimal output voltage vector and the fast control purpose are achieved.

The utility model relates to active power electronic filter and power electronic technical field discloses a kind of active power filter based on high-power IGBT single tube parallel driving, including multisignal fusion detection module, DSP control module, drive control module, IGBT power bridge arm module, auxiliary power module, support module and LCL filter module, the DSP control module is electrically connected with drive control module and support module respectively, the drive control module is electrically connected with IGBT power bridge arm module, the output end of switching power supply is electrically connected with the input end of multisignal fusion detection module, the IGBT power bridge arm module is electrically connected with LCL filter module.The utility model in, by adopting the design of IGBT single tube parallel, unnecessary intermediate connecting piece is reduced, equipment volume is effectively reduced, the problem such as the space occupancy big and installation inconvenience caused by complex structure is solved.

The application relates to a bidirectional controllable direct current source and a control method thereof, which comprises a main power circuit, a first control board, a second control board, a third control board, a communication board and an auxiliary power supply; the main power circuit is used for converting marine three-phase 380V alternating current power supply into controllable direct current with controllable size and direction through an EMI filter, a soft start circuit, an LCL filter circuit, an APFC circuit, an LLC circuit and a high-frequency H-bridge commutation circuit, and providing the direct current to a load winding. When the output current of the bidirectional controllable direct current source is commutated, a reverse voltage is applied to the load winding, the load inductance current is rapidly reduced, the zero-crossing point out-of-control problem under a large inductance load is solved, and the current output requirement of the bidirectional controllable direct current source in a wide load range is met.

The present invention discloses a rail transit power supply energy control method and system based on LCL and RPC, which can effectively solve the problem in the existing technology that harmonic control is difficult to effectively compensate for harmonics under the complex and changeable working conditions of high-speed trains. The specific technical solution is: analyze and obtain the harmonic change law and power compensation state of harmonics changing with the EMU and traction network; construct an LCL filter in a multiple RPC structure according to the law and obtain the resonant frequency; receive the user's production data according to the operating state of the traction power supply system model, and design the operating state into six types of locomotive working conditions; simulate the locomotive harmonic source model under different working conditions through the LCL filter to obtain simulation results; according to the simulation results, conduct experiments on the parameter algorithm of the LCL filter to obtain the target parameters and then embed them into the locomotive harmonic source model; analyze the harmonics and compensation power of the traction power supply system model according to the target parameters, obtain the results and build a visualization system.

The invention relates to a predictive control method and system for a weak connection type micro-grid converter. The method comprises the following steps of collecting operation data and parameters of an LCL filtering type converter; constructing a discrete data model based on a difference relationship, and updating coefficients of the discrete data model by using a forgetting factor method; on the basis of the candidate switch states and the parameter-dependence-free prediction model, taking prediction value error minimization as a target, constructing a multi-target value function to evaluate all candidate switch states of the weak connection type micro-grid, and solving the multi-target value function to obtain an optimal switch state; based on the candidate switch state and a reference model of the prediction model without parameter dependence, taking prediction value error minimization as a target, constructing and solving a multi-target value function to evaluate the switch state of the weak connection type micro-grid, and obtaining an optimal switch state; and controlling the weak connection type micro-grid based on the optimal on-off state.

The present application relates to the field of power electronics, in particular to a common-mode voltage suppression three-phase four-wire converter LCL filter parameter determination method, wherein the method comprises: using double Fourier decomposition, analyzing the entire frequency spectrum of the common-mode voltage suppression PWM of the two-level four-bridge arm converter, obtaining the frequency domain distribution of the PWM modulation voltage; based on the frequency domain distribution of the PWM modulation voltage, according to the differential mode transfer function and the common mode transfer function of the equivalent circuit of the three-phase four-wire system, establishing the functional relationship of the filter parameters to the circuit characteristic output parameters; based on the preset constraint condition, solving the functional relationship to obtain the filter parameter feasible region, and determining the final LCL filter parameter according to the filter parameter feasible region. Therefore, the problems of parameter design depending on artificial experience, circuit simulation, and time-consuming and laborious design process are solved, and the efficiency and reliability of parameter design are improved.

The present invention discloses a two-degree-of-freedom predictive control method for an LCL filter-type three-phase grid-connected inverter system, belonging to the field of power electronic converter control. A predictive control reference instruction is obtained by sampling the parameters of the inverter-side current, capacitor voltage, grid-side current, and grid voltage at time k, and a continuous and discrete model of the LCL filter-type three-phase grid-connected inverter system is established. A control function based on the grid-side current reference tracking error and its gradient is designed, and a predictive model is established. A predictive cost function based on the control function is constructed, and the predictive control reference instruction is obtained using the minimum value of the predictive cost function. The optimal voltage vector and action duty cycle are then determined based on the predictive control reference instruction, and a control pulse signal is generated according to a symmetrical five-segment pulse mode. The control pulse signal acts on each switch tube in the inverter to achieve predictive control of the LCL filter-type three-phase grid-connected inverter system. The method has simple steps, is easy to use, has a constant switching frequency, and has good stability.