443 results about "Lcl filter" patented technology

A new current loop control system method is proposed for a single-phase grid-tie power conditioning system that can be used under a standalone or a grid-tie mode. This type of inverter utilizes an inductor-capacitor-inductor (LCL) filter as the interface in between inverter and the utility grid. The first set of inductor-capacitor (LC) can be used in the standalone mode, and the complete LCL can be used for the grid-tie mode. A new admittance compensation technique is proposed for the controller design to avoid low stability margin while maintaining sufficient gain at the fundamental frequency. The proposed current loop controller system and admittance compensation technique have been simulated and tested. Simulation results indicate that without the admittance path compensation, the current loop controller output duty cycle is largely offset by an undesired admittance path. At the initial simulation cycle, the power flow may be erratically fed back to the inverter causing catastrophic failure. With admittance path compensation, the output power shows a steady-state offset that matches the design value. Experimental results show that the inverter is capable of both a standalone and a grid-tie connection mode using the LCL filter configuration.

The utility model relates to a voltage type source rectifier stable control system and method based on LCL filter wave, belonging to the source rectifying technical range of electronic technology. The system comprises a DC voltage control cell, a current control cell, an active damp control cell and a voltage space vector generating cell. the utility model produces six PWM signals to gain the current signal of the filter wave capacitor branch directly or indirectly, outputs the reference value of the damp voltage and achieves the stable control on the system. The method provides an adjustable sine control on the DC voltage output and input current through the active damp vector control of the voltage type source rectifier stable control system, the damp voltage reference value outputted by the active damp vector control cell, and the network voltage to execute summation operation. The utility model has the advantages of controllable DC voltage, low aberrance rate of the network input current, high power factor, satisfying the requirement of energy double-redirection flowing, and achieving the stability of the system without increasing the quantity of hardware damp resistance.

An exemplary method and an apparatus implementing the method for an arrangement having a three-phase, multi-level inverter, an output LCL-filter connecting the inverter to a grid, and a virtual-ground connection between the LCL-filter and the neutral point of the DC-link. The method includes determining a zero-sequence component of an LCL-filter inverter-side current, calculating a zero-sequence damping and balancing voltage term based on the LCL-filter inverter-side current zero-sequence component and voltages over the two halves of the DC-link, and adding the zero-sequence damping and voltage balancing term to the output voltage reference.

The invention relates to a capacitance current feedforward control method for a grid-connected inverter with an LCL filter and belongs to the field of electric energy conversion. The capacitance current feedforward control method for the grid-connected inverter with the LCL filter solves the problem of low stability of the grid-connected inverter with the LCL filter in the prior art and the problem of reduced efficiency of a system due to phase difference between grid side voltage and current. The method comprises the following steps of: 1, acquiring three-phase power grid voltage and acquiring a vector angle theta of the power grid voltage; 2, acquiring three-phase output current of the inverter and acquiring direct current components ild and ilq of the inverter side current; 3, acquiring three-phase filter capacitance current and acquiring direct current components icd and icq of the filter capacitance current; 4, setting set values of the inverter output current to perform proportional integral (PI) adjustment on a processed signal, outputting uq, performing PI adjustment on the processed signal, and output ud; and 5, inversely converting the ud and the uq into u(alpha) and u(beta) and performing pulse width modulation on the u(alpha) and the u(beta) to acquire six paths of switching signals which are used for controlling six switching tubes of the three-phase inverter so as to perform capacitance current feedforward control on the grid-connected inverter.

The invention relates to an active damping method of an LCL grid-connected inverter system. The active damping method is realized through the following steps of: setting conjugated zero points or independent zero points to set off conjugated resonance limit points generated by an LCL filter in the grid-connected inverter system or to draw the conjugated resonance limit points to a stable area, and adopting grid-side inductive current to feed back and introduce a state variable in the LCL filter to conduct feedback compensation. By conducting feedback compensation on grid-side inductive voltage, the resonance damping of the LCL filter is controlled, the waveform and the amplitude of grid current of the grid-connected inverter system are controlled and the influence of grid voltage harmonic wave on the grid current can be effectively suppressed. The active damping method is a simple and effective realization method. A realization circuit comprises parallel and series active damping circuits.

A method of controlling the grid-side current of a single-phase grid-connected converter having an LCL filter connected between the output of the converter and the grid. The method includes measuring a grid voltage (vS) and at least one signal in a group of signals consisting of a grid-side current (i0), a converter-side current (i1) and a capacitor voltage (vC0). The method includes estimating the fundamental component (vS,1) of the grid voltage (vS), forming a grid-side current reference (i0*), a converter-side current reference (i1*) and a capacitor voltage reference (vC0*) for the grid-side current of the LCL filter using the fundamental component of the grid voltage (vS,1), forming estimates for the non-measured signals in said group of signals, forming a grid-side current difference term (ĩ0), a converter-side current difference term (ĩ1) and a capacitor voltage difference term ({tilde over (v)}C0) from the differences between the references and measured / estimated values of said signals, forming an injection term for damping the resonance of the LCL filter by using an active damping injection mechanism (ADI), in which the grid-side current difference term (ĩ0), the converter-side current difference term (ĩ1) and the capacitor voltage difference term ({tilde over (v)}C0) are used, forming an estimate of harmonic distortion term ({circumflex over (φ)}) using the grid-side current difference term (ĩ0), and controlling the output voltage (e) of the converter on the basis of the grid voltage, formed injection term and formed estimate of the harmonic distortion term ({circumflex over (φ)}) to produce a grid side (i0) current corresponding to the current reference.

A power regenerative converter includes: a power conversion unit configured to convert AC power supplied from an AC power supply into DC power and convert DC power into AC power to be supplied as regenerative electric power to the AC power supply supply; an LCL filter including a reactor unit having a plurality of reactors connected in series between the power conversion unit and the AC power supply, and capacitors each having one end connected to a series connection point of the reactors in the reactor unit; a drive control unit for controlling the power conversion unit based on an AC voltage command; and a voltage command compensation unit for calculating a compensation value in accordance with a capacitor voltage being a voltage at the series connection point of the reactors and adding the compensation value to the AC voltage command input to the drive control unit.

The invention relates to a LCL (Lower Control Unit) filtering controlled rectifying active damping control method of electric currents on a feedback variable current side, belonging to an active rectifying method of power electronics. The method comprises the following steps: a direct current voltage control unit is used for finishing the control on a direct current voltage and producing d-shaft active currents of an electric current control unit; a q-shaft current given is used for controlling reactive components of a rectifier; a soft phase locking unit is used for locking a power grid voltage phase position and realizing the synchronous rotational transformation of the power-grid voltage and sampling currents on the variable current side; the current given and a sampling actual value are fed into the electric current control unit; the output quantity of the electric current control unit is accumulated with the electric current on the variable current side which is fed back by usinga first-order high-pass filter to generate the given quantity of a voltage space vector unit; and finally, the voltage space vector unit generates six PWM (Pulse-Width Modulation) signals to finish the control on the rectifier. The method solves the stability problem of a LCL (Low Control Unit) filtering voltage type controlled rectifier and realizes the control of the rectifier on direct-currentvoltages and currents on line side under the condition that the electric current or voltage detection of a capacitor branch is not needed.

A three-phase rectification module, the system thereof and harmonic suppression method are provided. The module includes a LCL filter unit, a three-phase uni-directional rectification unit coupled to the LCL filter unit, and a rectifier control unit for controlling power factor of three-phase AC power source and DC output voltage of the three-phase uni-directional rectification unit. A commutation diode is serially connected on the bridge-arm of each set of uni-directional rectification branch which is included in the three-phase uni-directional rectification unit, making it function as current uni-direction. Herein, the power factor of the three-phase AC power source is matched with the parameters of the LCL filter unit, such that the absolute value of the phase difference between AC input voltage and current of the three-phase uni-directional rectification unit is close or equal to a preset threshold.

The invention discloses a flywheel energy storage system grid-connected control method and an energy storage system thereof. A grid side converter control method of the flywheel energy storage system grid-connected control method comprises the following steps: converting grid side currents ia1, ib1 and ic1 and converter side currents ia2, ib2 and ic2 under a static coordinate system into direct current components id1 and iq1, and id2 and iq2 under a two-phase rotating coordinate system respectively; and taking the direct current components under the two-phase rotating coordinate system as feedback signals of grid side converter control under the rotating coordinate system to control the sizes and the flow directions of flywheel energy storage system grid-connected active power and passive power. A motor side converter control method of the flywheel energy storage system grid-connected control method comprises the following steps: converting motor stator currents ia3, ib3 and ic3 under the static coordinate system into direct current components id3, iq3 under the two-phase rotating coordinate system; and taking the id3, iq3 and direct current bus voltage Udc as feedback signals of motor side converter control under the rotating coordinate system to maintain constant direct current bus voltage Udc. An LCL filter (102) of the energy storage system applying the control method consists of a grid side inductor (201), a converter side inductor (203) and a filter capacitor (202).

The invention discloses an active damping control device for an LCL (Lower Control Limit) filtering PWM (Pulse-Width Modulation) current converter, which is improved to solve the problem that an additional sensor is required to be introduced for active damping control, and a current control structure is innovated. The invention designs a novel AC-side current feedback compensation damping control mode based on a double proportional control module and a band-pass filter. Through current on the AC side, the controlled quantity of the active damping control device is compensated. Firstly, the method is taken as active damping control without additionally arranging a damping resistor and then directly compensates through the current on the AC side, so that the additional sensor is not required to be arranged. The active damping control device has the benefits that on the basis of resonance problem that an LCL filter is restrained to be introduced, the practical damping resistor and the additional sensor are not required to be additionally arranged, so that both the efficiency and the cost of systems can be improved to a certain degree.

The invention discloses an LCL-type single-phase grid-connected inverter power control and active damping optimization method. An equivalent synchronous coordinate PI controller is adopted, a two-phase virtual orthogonal system is constructed by adopting an all-pass filter, the problem that data used in previous construction methods have asynchrony or noise interference is introduced is solved, regulation of grid-connected currents at fundamental frequency in a zero steady state error is achieved, and the stability of the system is improved. According to the LCL-type single-phase grid-connected inverter power control and active damping optimization method, the primary differential and the high-frequency components of the grid-connected currents are fed back in real time, the damping of the system is increased, the resonance peak of the LCL filter is restrained, an optimized parameter selection method is given, single-current feedback factors are reduced to a variable, the defect that parameters are difficult to select in single current high-frequency component feedback is overcome, and the reliability and the dynamic nature of the system are improved.

A solar energy grid-connected inverter control system based on LCL filtration comprises a photovoltaic array, an electromagnetic interference filter, namely an EMI filter, a power module, an LCL filter, an isolation transformator TB1, a sample circuit, a filter circuit and a controller which includes a maximum capacity tracking MPPT unit. MPPT adopts an intelligent algorithm based on a hybrid algorithm of a simulated annealing method and a genetic algorithm. The hybrid optimization algorithm takes the operation process of the genetic algorithm as the main process and also combines a simulated annealing mechanism that is used for further adjusting optimized instruction data. The control system has the advantages of good stability, strong performance and high efficiency and reliability.

The invention discloses a grid-connected inverter for low-frequency current ripple output restraining of a fuel cell and a control device. The grid-connected inverter comprises the fuel cell FC, a boosting converter, a full bridge inverter and an LCL filter. The control device comprises a voltage sensor, a current sensor and a DSP digital controller. The boosting converter comprises an inverse-current-preventing diode, an input filtering capacitor Cin, a filtering inductor LB, an electric MOSFET and an output capacitor CDC. The full bridge inverter comprises four electric MOSFETs. The LCL filter comprises a capacitor C1 and two inductors L1 and L2. The DSP digital controller comprises a proportioner, a phase-locked loop, a subtracter, a PI adjuster, a multiplying unit, a summator, a signal generator, a comparer and a phase inverter. By establishing the boosting converter, energy decoupling on an input side and an output side is achieved, the fact that currents on the input side do not contain low-frequency ripples is guaranteed, the manufacturing cost of the grid-connected inverter is lowered, power conversion efficiency is improved, and an electric energy converting device suitable for fuel battery power generation is achieved.

The invention discloses a three-phase inverter parallel-connection control method without an output isolation transformer. The method comprises the following steps: an output end of each three-phase inverter is connected with an LCL filter, and a filtering capacitor of each LCL filter is connected with a dumping resistor in series, so that the stability is improved, the harmonic wave of a harmonic point is limited, and stability range of control parameters is increased. By means of pre-synchronization before parallel connection and carrier synchronization in the process of parallel connection operation, the phases among the three-phase inverters and parallel-connected communication buses are synchronized, carriers among the three-phase inverters connected in parallel are synchronized, and stability of parallel connection is guaranteed. By means of the algorithms combining pole assignment capacitor voltage control and virtual resistance matching control, the response speed of the inverters is improved, the control performance is improved, and the influence on parallel-connection current sharing by circuit resistance is lowered. By means of seamless mode switching and alternative current over-current and short-circuit failure protection base on three-ring control, under the condition of absence of the output isolation transformer, the three-phase inverter parallel-connection control method is used for independently resolving short-circuit failures of a parallel-connection micro power grid.

The invention discloses an active power filter device based on a coupled inductance, which is composed of a signal acquisition module, a main control module, a drive module, a power conversion module and an LCL filter module based on a coupled inductance. The steps of extracting command current are as follows: first, extract sinωt and cosωt which are synchronized with grid A-phase voltage ua through digital phase-locked loop; secondly, transform the three-phase grid current into dqo coordinates to obtain current id, iq in dqo coordinate system , io; the third is to perform digital low-pass filtering on id and iq to extract their DC components; the fourth is to inversely transform io, sinωt and cosωt to dqo coordinates; the fifth is to perform subtraction to obtain the three-phase grid current The fundamental reactive and harmonic currents in . After hysteresis comparison control, PWM gating signals and trigger pulses are generated to control the orderly on-off of each IGBT in the power conversion module to generate PWM voltage, which is filtered by the filter module and then injected into the grid for compensation.

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 provides a parameter design method for a high-voltage high-capacity VSC (voltage source converter). The VSC is connected with an electric grid through an LCL (lower control limit) filter, the LCL filter comprises an electric grid side electric reactor, a valve side reactor and a filter capacitor, and the filter capacitor is connected in parallel between the valve side reactor and the electric grid side electric reactor. The problems for filtering out harmonic waves filled into the electric grid by the VSC and inhibiting the converter main loop resonance led in by the LCL filter are solved through setting the parameters of the LCL filter and a controller of the VSC. Compared with the simple experience algorithm and the complicated calculating method of the existing LCL filter, the method has the advantages that the parameter of the filter is designed according to the operation characteristics of the VSC and the frequency-domain characteristics of the LCL filter, simplicity is realized, the implementation is easy, the engineering construction can be realized, the theoretical basis is full, the harmonic pollution to the electric grid is low, and the grid-connected electric energy quality requirement of the national standard on the VSC can be met.

The invention discloses a single-current feedback control method of a three-phase LCL filtering type PWM rectifier. Aiming at a conventional double-current feedback control active damping method, all that is required is to detect a current value on one side of a PWM rectification net, and a capacitance current is not required to be sampled, so that additional sensors are reduced, the reliability of a system is improved, and the hardware cost is reduced; a feedback coefficient of the current on one side of the net is adjusted in real time, so that the system damping is increased, and a resonance peak of an LCL filter is restrained; and a feedforward network voltage is introduced, and an input current on one side of the net is subjected to power decoupling control, so that the dynamic property of the system is further improved. The three-phase PWM rectifier has the advantages of high power factor, high response speed, high reliability, relatively simple design and the like.

The invention discloses a low voltage ride through control method for a high-power photovoltaic inverter. The method comprises the following steps: firstly, considering a low voltage ride through situation under the condition of grid voltage sag, particularly unbalanced sag on the basis of a high-power photovoltaic inverter structure of an LCL filter, calculating reference given values of positive sequence current and negative sequence current specific to the control aim of restraining the negative sequence current, and compensating idle work of filter capacitor absorption via a control algorithm to ensure high-power-factor grid connection while running at different power levels; secondly, designing to add a filter capacitor current feed-forward signal into a modulation signal on the basis of positive and negative sequence double current loop control, and adjusting a feed-forward coefficient to realize active damping control under unbalanced control; and lastly, designing a disturbance quantity feed-forward coefficient to restrain transient current impact. Due to the adoption of the method, current impact at the moment of grid voltage sag can be restrained effectively, three-phase balanced output of current before and after grid voltage sag is ensured, and the control effect meets the electric energy quality requirement of a power grid on the grid connection of the photovoltaic inverter.

The invention discloses a method for designing a hybrid damping parameter of an LCL filter in a photovoltaic grid-connected inverter, and belongs to the technical fields of new energy sources and distributed grid-connected generation. The method is characterized in that: the resonance of the LCL filter is suppressed by adopting an active damping / passive damping cooperative working method, whereina filter capacitive current feedback control method is adopted for an active damping part and the method of connecting filtering capacitance in series with damping resistance is adopted for a passivedamping part. For the LCL filter, the damping resistance required by passive damping and a feedback coefficient of active damping are computed under the condition of ensuring a sufficient damping coefficient, and a designed cooperative damping control scheme is checked to make the loss of the damping resistance as low as possible, avoid the influence of system control delay on damping running; and the damping is adapted to strong power grid access and the weak power grid access of remote areas. The method is applied to photovoltaic grid-connected generation systems adopting the LCL filter, fuel cells and grid-connected wind power generation systems.

The invention discloses a novel photovoltaic inverter control method based on BP neural network and dual-mode structure repetitive control. According to the invention the output of the photovoltaic grid-connected inverter is connected to a power network after LCL filtering to carry out a sampling link. The phase theta extracted by the improved PLL is fed into the dqalpha beta transform. The difference between the reference voltage of the DC side and the actual voltage of the DC side is inputted into the PI controller; Obtaining the actual current signal ig through abcalpha beta transformationfrom the sampled current of the power network side. The difference between the reference grid-connected current ig and the actual current signal ig in the alpha beta coordinate system after the dqalpha beta transformation is subjected to the alpha beta abc transformation, and then is fed into the composite controller together with the actual current signal ig and the reference grid-connected current ig. The signal processed by the composite controller is sent to the notch filter for processing, and then the processed signal is sent to the SVPWM module, so as to generate periodic switching signals for controlling the grid-connected photovoltaic inverter, thereby suppressing the harmonics of the grid-connected photovoltaic inverter into the power grid. The compensation effect of the invention is superior to the traditional photovoltaic grid-connected inverter.

The invention discloses a novel control method of an LCL type three-phase shunt active power filter, which constructs a system of an active power filter with LCL filter based on an active damping optimization control method of a single-network-side inductance current feedback and a current tracking control method of a novel generalized integrator. A high-pass filter is added to the feedback loop to optimize the parameters, which overcomes the disadvantageous influence of the existing active damping method on the stability of the system in the fundamental domain. At that same resonant frequency, first-order generalized integrator with opposite phase order, As such, that novel generalize integrator realizes infinite gain only at the positive sequence resonant frequency or only at the negative sequence resonant frequency, The novel generalized integrator has the characteristics of selective compensation for positive and negative sequence signals with the same frequency, and can distributedifferent gains, reduce the complexity of control algorithm, improve the computational efficiency, solve the problem of harmonic compensation under the condition of unbalanced power network and load,and improve the compensation performance and flexibility of application.

The invention discloses an LCL filter utilizing integrated inductors. The LCL filter can be applied to a single-phase inverter or a three-phase grid-connected inverter, the size of magnetic cores can be effectively reduced, and the power density of grid-connected inverters is improved. The LCL filter comprises an inverter side inductor L1, a filter capacitor C, and a grid side inductor L2, wherein the input end of the inductor L1 is connected with the middle point of a leg of the inverter, the output end of the inductor L1 is connected with the input ends of the inductor L2 and the capacitor C, and the output end of the inductor L2 is connected with a power grid. Windings of the inductor L1 and the inductor L2 are wound on two independent magnetic cores respectively, a public magnetic post without air gap is arranged between the two magnetic cores, and magnetic flux of linkages of windings of the inductor L1 and the inductor L2 are counteracted on the public magnetic post, and the magnetic flux of the public magnetic post is reduced, so that the size of the public magnetic can be reduced. Simultaneously, coupling does not exist between the inductor L1 and the inductor L2, so that the integrated LCL filter has the same characteristic with that in discrete conditions.

The invention discloses a rotational coordinate transformation based current decoupling control method for a three-phase grid-connected inverter. With regard to a grid-connected inverter with an LCL (Inductor Capacitor Inductor) filter, an inversion three-phase output current signal and a grid-side three-phase current signal are transformed into two groups of orthogonal current signals in a synchronous rotation coordinate system through adopting coordinate transformation, the two groups of orthogonal current signals are subjected to the calculation of weighted average to be used as an inverter current controlled feedback signal and an inverter current controlled decoupling signal under a rotational coordinate system, the feedback signal is compared with a control given signal to obtain anerror signal, and the obtained error signal is subjected to proportional-integral regulation and then is subjected to a combined operation with the decoupling signal to obtain a pulse duty-ratio signal for controlling a three-phase inverter switch to operate under the rotational coordinate system, so that output current waveform and amplitude control of the grid-connected inverter can be realized. Through adopting the method disclosed by the invention, the signal coupling problem existing in three-phase current control of the LCL filter three-phase grid-connected inverter can be effectively solved, the capacity of independently controlling each phase of output current is enhanced, and the favorable output current waveform of a grid-connected system can be achieved.

The invention relates to a method for controlling a three-phase photovoltaic grid-connected inverter when a power grid voltage is unbalanced. The method comprises the steps of establishing a three-phase photovoltaic grid-connected system main circuit and an inverter control system, collecting signals, carrying out clark transform, synchronizing power grids, extracting the phase sequence, calculating a reference current, controlling a current loop, carrying out inverse clark transform, controlling PWM and driving an inverter. The method has the advantages that a photovoltaic power source is efficiently connected to the power grids under the situation that the power grids are normal; the grid-connected current harmonics are effectively eliminated through an LCL filter, and high-power factor grid connection is achieved through a PR current controller; when the power grids break down, the faults can be omitted, and three control targets of voltage supporting, voltage balancing and power vibration eliminating are achieved.

A method for operation of a converter circuit is specified, wherein the converter circuit has a converter unit with a multiplicity of drivable power semiconductor switches and an LCL filter which is connected to each phase connection of the converter unit, in which method the drivable power semiconductor switches are driven by means of a drive signal which is formed from reference voltages. The reference voltages are formed by subtraction of damping voltages from reference-phase connection voltages, with the damping voltages being formed from filter capacitance currents, weighted with a variable damping factor of the LCL filter. An apparatus for carrying out the method is also specified.

The invention relates to an energy storage converter and a battery energy storage system of the energy storage converter. The energy storage converter comprises an AC / DC module, an LCL filter, a main contactor, an alternating current EMI filter, an alternating current side pre-charging circuit, a main circuit breaker, a CL filter, a direct current EMI filter, a direct current side pre-charging circuit and a direct current side circuit breaker, wherein the alternating current side of the AC / DC module is sequentially connected with the LCL filter, the main contactor, the alternating current EMI filter and the main circuit breaker, the alternating current side pre-charging circuit is connected to the two ends of the main contactor in parallel, the direct current side of the AC / DC module is sequentially connected with the CL filter, the direct current EMI filter and the direct current side circuit breaker, and the direct current side pre-charging circuit is connected to the two ends of the direct current side circuit breaker in parallel. According to the energy storage converter and the battery energy storage system, the problem of power fluctuation in a micro-grid is solved, and the running reliability of the micro-grid is improved.

The invention provides a parameter design method of a grid-connected inverter LLCL filter. The method mainly aims to decompose complex LLCL filter parameter design into corresponding traditional LCL filter parameter design and parameter design of a series resonance branch circuit. The method comprises the following steps that firstly, parameters of the LLCL filter according to the parameter design method of a traditional LCL filter are initialized, wherein the parameters include bridge arm side inductance L1, power grid side inductance L2 and total capacitance Ct; secondly, parallel-connection filtering capacitance C of the LLCL filter, resonance capacitance Cf of the LC resonance branch circuit and resonance capacitance Lf of the LC resonance branch circuit are calculated according to the parameters of the LLCL filter obtained in the step one; thirdly, parameter values selected in the step one and the step two are verified. If the verification passes, the parameter design is completed; if the verification does not pass, a user returns to the step one, and new round of parameter selection is performed.

The invention provides an LCL (Less Container Load) filter with serially-connected splitting capacitor and damping resistor and a design method of the LCL filter which are applied to the technical field of wind power, wherein a grid side electric reactor and a grid-connected inverter side electric reactor are sequentially connected in series, and a first three-phase filter capacitor and a damping resistor are connected in series to a serial-connection node of the two electric reactors; a second three-phase filter capacitor is directly connected to the serial-connection node of the two electric reactors; a three-phase network source is connected to a Lg terminal of the grid side electric reactor; and a three-phase alternating current side of a wholly-controlled rectifier bridge of a grid-connected inverter is connected to terminals of the electric reactors. By using the LCL filter, the stability problem of a voltage type controllable inverter of the LCL filter is solved, the power consumption on the damping resistor can be effectively reduced, the overall efficiency of a grid-connected inverter system can be increased, and thus, the system heat radiation design pressure is relieved.