CN104868774A - Grid-connected inverter of combination of LCL and multiple LC branches and current control method - Google Patents

Abstract

The invention discloses a grid-connected inverter of combination of LCL and multiple LC branches. The inverter comprises a PWM inverter, a LCL-LC filter, two current transformers used for monitoring a grid-connected current, a current control loop and a PWM driving circuit, wherein the current control loop is used for grid-connected control and contains current weight calculation, current error calculation and proportional-integral control. The PWM inverter is connected to the LCL-LC filter. The LCL-LC filter is connected to the current control loop. The current control loop is connected to the PWM driving circuit. The PWM driving circuit is connected to the PWM inverter. The two current transformers measure an intermediate current which flows through a C branch and a LC series resonance branch and a current flowing through network side series inductors respectively. The intermediate current is added to the current according to a certain weight coefficient and the sum is served as a feedback control signal of an inverter output current. The feedback control signal is compared to a current instruction signal so as to acquire an error value. An output signal after the obtained error value passes through a PI regulator is served as an inverter PWM modulating signal so as to control an output current waveform and an amplitude of a LCL-LC grid-connected inverter.

Description

The combining inverter that LCL combines with many LC branch road and current control method

Technical field

The present invention relates to grid converter control technology field, particularly relate to combining inverter and current control method that a kind of LCL combines with many LC branch road.

Background technology

Common LCL-LC combining inverter, its circuit as depicted in figs. 1 and 2, generally include PWM inverter, for grid-connected connect run LCL-LC filter, for grid-connected current measure current transformer, for cutting-in control containing electric current weighting calculate and current error calculate and proportional integral regulate current regulator, PWM drive circuit.

Described PWM inverter adopts four insulated gate bipolar transistors, in parallel again after series connection between two, such as, shown in Fig. 1 and Fig. 2, the first insulated gate bipolar transistor S ₁with the second insulated gate bipolar transistor S ₂composition first via series circuit, the 3rd insulated gate bipolar transistor S ₃with the 4th insulated gate bipolar transistor S ₄form No. second series circuit, first via series circuit and No. second series circuit in parallel again, and with DC power supply V _dcparallel connection, the first insulated gate bipolar transistor S ₁with the second insulated gate bipolar transistor S ₂between wire as the first output of PWM inverter, the 3rd insulated gate bipolar transistor S ₃with the 4th insulated gate bipolar transistor S ₄between wire as the second output of PWM inverter, the first output and the second output form PWM inverter output voltage u _i.

The described LC series resonance branch road comprising a road LCL circuit and two-way parallel connection for the grid-connected LCL-LC filter connecting operation, LCL circuit comprises the first inductance L of series connection ₁with the second inductance L ₂and electric capacity C, every road LC series resonance branch road comprises filter capacitor and the filter inductance of series connection, the first inductance L ₁first end connect the first output of PWM inverter, the first inductance L ₁the second end connect the second inductance L ₂first end, the second inductance L ₂second end connect electrical network, PWM inverter second output connect electrical network; Series resonance branch road first filter inductance with the second filter inductance first end be all connected to the first inductance L ₁with the second inductance L ₂between, series resonance branch road first filter capacitor with the second filter capacitor the second end all connect electrical network; Electric capacity C positive pole connects the first inductance L ₁the second end, negative pole connects the first filter inductance with the first filter capacitor between.

As shown in Figure 1, the collection terminal for the current transformer of grid-connected current measurement connects the first inductance L ₁first end, collection be that (collection terminal of the current transformer of net current measurement connects the first inductance L for the electric current of PWM inverter side ₁first end or the second end gather electric current unaffected), by the current i of PWM inverter side ₁as feedback current send to adder, adder is by feedback current with instruction current i ^*carry out add operation, then send to PWM drive circuit by current regulator, thus control the output of PWM inverter.

As shown in Figure 2, the collection terminal for the current transformer of grid-connected current measurement connects the second inductance L ₁the second end, collection be the electric current of grid side, by the current i of grid side ₂as feedback current send to adder, adder is by feedback current with instruction current i ^*carry out add operation, then send to PWM drive circuit by current regulator, thus control the output of PWM inverter.

Inverter is that output current controls when being incorporated into the power networks, to ensure that output current is sine wave that is strict, that have high power factor, but traditional LCL-LC parallel inverter current control method is mostly to flow through electric current (the i.e. inverter output current i of inverter side inductance ₁) or flow through electric current (the power network current i of grid side inductance ₂) be feedback current, the methods such as recycling PI adjustment regulate the output current controlling combining inverter to error signal.But the filter due to LCL-LC structure is high order system, make filter near corner frequency, there is very large gain spike, for stablizing of Guarantee control system, the gain of pi regulator is restricted, value is less, thus make system less in the open-loop gain of low-frequency range, reduce the resistivity of combining inverter to the harmonious wave interference of output current steady-state error, also easily by the impact of electrical network voltage distortion.

Summary of the invention

The object of this invention is to provide combining inverter and current control method that a kind of LCL combines with many LC branch road, under the prerequisite meeting control stability, enhancing system distorts to electrical network the LCL-LC parallel inverter current control method of the resistivity of harmonious wave interference, restriction power network current wave distortion and harmonic content.

The technical solution used in the present invention is:

The combining inverter that a kind of LCL combines with many LC branch road, comprise PWM inverter, the LCL-LC filter for grid-connected connection operation, the current regulator for cutting-in control and PWM drive circuit, PWM inverter connects LCL-LC filter, LCL-LC filter connects current regulator, current regulator connects PWM drive circuit, and PWM drive circuit connects PWM inverter; It is characterized in that: also comprise two current transformers for monitoring grid-connected current and the current regulator containing electric current weighting calculating and current error calculating and proportional integral adjustment for cutting-in control; The sampling end of the first current transformer connects the second end of the first inductance, and for measuring the electric current of PWM inverter side first inductance, the sampling end of the second current transformer connects the second end of the second inductance, for measuring the electric current of grid side second inductance; The described current regulator containing electric current weighting calculating and current error calculating and proportional integral adjustment for cutting-in control comprises the first amplifier and the second amplifier, first adder and second adder, pi regulator and PWM circuit for generating; First adder, second adder, pi regulator and PWM circuit for generating are connected successively, and the output of the first current transformer and the second current transformer is connected to first input end and second input of first adder respectively by the first amplifier and the second amplifier, the input of the output of first adder and instruction current access second adder, PWM circuit for generating connects PWM drive circuit; Described being used for the signal of the first current transformer collection according to weight coefficient k containing the current regulator that electric current weighting calculates and current error calculates and proportional integral regulates for cutting-in control ₁the signal that amplification, the second current transformer gather is according to weight coefficient k ₂amplify, and make k ₁with k ₂ratio value meet feedback current and reduce to function of first order relative to the signal gain of inverter output voltage.

The parallel inverter current control method that LCL according to claim 1 combines with many LC branch road, is characterized in that: comprise the following steps:

Steps A: install two current transformers for monitoring grid-connected current; The sampling end of the first current transformer connects the second end of the first inductance, and the sampling end of the second current transformer connects the second end of the second inductance; The output of the first current transformer and the second current transformer is connected to first input end and second input of first adder respectively by the first amplifier and the second amplifier;

Step B: calculate PWM inverter side current i ₁relative to inverter output voltage u _isignal gain, i.e. the transfer function of output filter and judge this transfer function class's number;

If PWM inverter side current i ₁as elementary feedback current i.e. i ₁be equivalent to then PWM inverter side current i ₁relative to inverter output voltage u _itransfer function for:

$\begin{array}{c}{G}_{u_i-i_1}\left(s\right)=\frac{i_1\left(s\right)}{u_i\left(s\right)}\\ =\frac{{\mathrm{sL}}_2+Z_f}{s^2{L}_1{L}_2+{\mathrm{sLZ}}_f}\\ =\frac{s(1-\mathrm{\α})L+Z_f}{sL\left(s\right(\mathrm{\α}(1-\mathrm{\α})L+Z_f)}\end{array}$ Formula (1)

Wherein, Z _ffor the total resistance of LCL branch road and two LC branch circuit parallel connections; u _ifor PWM inverter output voltage; i ₁for flowing through the electric current of combining inverter side; L ₁for combining inverter side first inductance; L ₂for grid side second inductance; Wherein: L=L ₁+ L ₂, L ₁=α L, α are proportionality coefficients;

As can be seen from formula (1), PWM inverter side current i ₁relative to inverter output voltage u _itransfer function be function of third order;

Step C:

Calculate grid side current i ₂relative to inverter output voltage u _isignal gain, i.e. the transfer function of output filter and judge this transfer function class's number;

If the grid side current i that the second current transformer gathers ₂as elementary feedback current i.e. i ₁be equivalent to then grid side current i ₁relative to inverter output voltage u _itransfer function for:

$\begin{array}{c}{G}_{u_i-i2}\left(s\right)=\frac{i_2\left(s\right)}{u_i\left(s\right)}\\ =\frac{Z_f}{s^2{L}_1{L}_2+{\mathrm{sLZ}}_f}\\ =\frac{Z_f}{sL\left(s\right(\mathrm{\α}(1-\mathrm{\α})L+Z_f)}\end{array}$ Formula (2)

Wherein, i ₂for flowing through the electric current of grid side;

As can be seen from formula (2), grid side current i ₂relative to inverter output voltage u _itransfer function be function of third order;

Step D: the grid side current signal of the current signal of the inverter side of collection and the second current transformer collection is carried out amplification and weighted calculation process by the first current transformer, obtains new feedback current i _f, and calculate new feedback current i _frelative to inverter output voltage u _isignal gain;

Step D1: by the current i of the second inductance that the first current transformer gathers ₁send to the first amplifier, if the weight coefficient of the first amplifier is k ₁, the current signal of the second current transformer collection sends to the second amplifier, if the weight coefficient of the second amplifier is k ₂-k ₁;

Signal after amplification is sent to first adder by the step D2: the first amplifier and the second amplifier, and after the weighted calculation of first adder, the signal of output is as new feedback current i _f;

I _f=k ₁i ₁+ (k ₂-k ₁) i ₂formula (3)

Step D3: new feedback current i _frelative to inverter output voltage u _itransfer function be:

$\begin{array}{c}{G}_{u_i\→i_f}\left(s\right)=\frac{i_f\left(s\right)}{u_i\left(s\right)}\\ =\frac{k_2\[s\frac{k_1}{k_2}(1-\mathrm{\α})L+Z_f\]}{sL\left(s\right(\mathrm{\α}(1-\mathrm{\α})L+Z_f)}\end{array}$ Formula (4)

As can be seen from formula (4), new feedback current i _frelative to inverter output voltage u _itransfer function be function of third order;

Step e: utilize the active depression of order, (4) formula is reduced to function of first order;

If formula (4) in weight coefficient meet abbreviation can obtain:

$G_{u_i\→i_f}\left(s\right)=\frac{i_f\left(s\right)}{u_i\left(s\right)}=\frac{k_2}{sL}$ Formula (5)

As can be seen from formula (5), new feedback current i _frelative to inverter output voltage u _itransfer function

Reduce to first-order system;

Step F: the new feedback current i that step e is obtained _frelative to inverter output voltage u _ifirst-order transfer function send to second adder, and compare with corresponding control command electric current, the signal of the error amount obtained after pi regulator is successively through PWM circuit for generating and PWM drive circuit, the signal that PWM drive circuit exports as the modulation signal of PWM inverter, the output current wave of control LLCL combining inverter and amplitude.

The present invention utilizes two current transformers to measure the intermediate current flowing through C branch road and LC series resonance branch road and the electric current netting side series inductance respectively, and be added the feedback control signal of gained as inverter output current using these two electric currents according to certain weight coefficient, compare with corresponding current command signal, the output signal of the error amount obtained after pi regulator is as inverter PWM modulation signal, the output current wave of control LCL-LC combining inverter and amplitude, by selecting suitable weight coefficient, realize the depression of order of controlled device transfer function, control performance is improved, achieve the stable output of combining inverter, and effectively enhance the resistivity of harmonious wave interference that electrical network distorted.

Accompanying drawing explanation

Fig. 1 is for utilizing inverter output current i ₁for the LCL-LC combining inverter circuit diagram of feedback signal;

Fig. 2 is for utilizing power network current i ₂for the LCL-LC combining inverter circuit diagram of feedback signal;

Fig. 3 is combining inverter circuit diagram of the present invention;

Fig. 4 is combining inverter control block diagram of the present invention.

Embodiment

As shown in Figure 3 and Figure 4, the present invention includes PWM inverter 1, the LCL-LC filter 2 for grid-connected connection operation, the current regulator 4 for cutting-in control and PWM drive circuit 5, PWM inverter 1 connects LCL-LC filter 2, LCL-LC filter 2 connects current regulator 4, current regulator 4 connects PWM drive circuit 5, and PWM drive circuit 5 connects PWM inverter 1; Article two, series resonance branch road LC is respectively used to eliminate switching frequency subharmonic and multiplied frequency harmonic thereof.

Also comprise two current transformers for monitoring grid-connected current and the current regulator 4 containing electric current weighting calculating and current error calculating and proportional integral adjustment for cutting-in control; The sampling end of the first current transformer 3-1 connects the first inductance L ₁the second end, for measuring PWM inverter side first inductance L ₁electric current, the sampling end of the second current transformer 3-2 connects the second inductance L ₂the second end, for measuring grid side second inductance L ₂electric current; The described current regulator 4 containing electric current weighting calculating and current error calculating and proportional integral adjustment for cutting-in control comprises the first amplifier K11 and the second amplifier K21, first adder V1 and second adder V2, pi regulator and PWM circuit for generating; First adder V1, second adder V2, pi regulator and PWM circuit for generating are connected successively, and the output of the first current transformer 3-1 and the second current transformer 3-2 is connected to first input end and second input of first adder V1 respectively by the first amplifier K11 and the second amplifier K21, the input of the output of first adder V1 and instruction current access second adder V2, PWM circuit for generating connects PWM drive circuit; Described being used for the signal of the first current transformer 3-1 collection according to weight coefficient k containing the current regulator that electric current weighting calculates and current error calculates and proportional integral regulates for cutting-in control ₁the signal that amplification, the second current transformer 3-2 gather is according to weight coefficient k ₂amplify, and make k ₁with k ₂ratio value meet feedback current and reduce to function of first order relative to the signal gain of inverter output voltage.

The parallel inverter current control method that LCL combines with many LC branch road, is characterized in that: comprise the following steps:

Steps A: install two current transformers for monitoring grid-connected current; The sampling end of the first current transformer 3-1 connects the first inductance L ₁the second end, the sampling end of the second current transformer 3-2 connects the second inductance L ₂the second end; The output of the first current transformer 3-1 and the second current transformer 3-2 is connected to first input end and second input of first adder V1 respectively by the first amplifier K11 and the second amplifier K21;

Step B: calculate PWM inverter side current i ₁relative to inverter output voltage u _isignal gain, i.e. the transfer function of output filter and judge this transfer function class's number;

If PWM inverter side current i ₁as elementary feedback current i.e. i ₁be equivalent to then PWM inverter side current i ₁relative to inverter output voltage u _itransfer function for:

$\begin{array}{c}{G}_{u_i-i_1}\left(s\right)=\frac{i_1\left(s\right)}{u_i\left(s\right)}\\ =\frac{{\mathrm{sL}}_2+Z_f}{s^2{L}_1{L}_2+{\mathrm{sLZ}}_f}\\ =\frac{s(1-\mathrm{\α})L+Z_f}{sL\left(s\right(\mathrm{\α}(1-\mathrm{\α})L+Z_f)}\end{array}$ Formula (1)

Wherein, Z _ffor the total resistance of LCL branch road and two LC branch circuit parallel connections; u _ifor PWM inverter output voltage, u _iin i be the English initial of inverter, only use as distinguishing; i ₁for flowing through the electric current of combining inverter side; L ₁for combining inverter side first inductance; L ₂for grid side second inductance; Wherein: L=L ₁+ L ₂, L ₁=α L, α are proportionality coefficients; in fp for distinguish subscript, without special implication;

As can be seen from formula (1), PWM inverter side current i ₁relative to inverter output voltage u _itransfer function be function of third order;

Step C:

Calculate grid side current i ₂relative to inverter output voltage u _isignal gain, i.e. the transfer function of output filter and judge this transfer function class's number;

If the grid side current i that the second current transformer 3-2 gathers ₂as elementary feedback current i.e. i ₁be equivalent to then grid side current i ₁relative to inverter output voltage u _itransfer function for:

$\begin{array}{c}{G}_{u_i-i2}\left(s\right)=\frac{i_2\left(s\right)}{u_i\left(s\right)}\\ =\frac{Z_f}{s^2{L}_1{L}_2+{\mathrm{sLZ}}_f}\\ =\frac{Z_f}{sL\left(s\right(\mathrm{\α}(1-\mathrm{\α})L+Z_f)}\end{array}$ Formula (2)

Wherein, i ₂for flowing through the electric current of grid side; in fd for distinguish subscript, without special implication;

As can be seen from formula (2), grid side current i ₂relative to inverter output voltage u _itransfer function be function of third order;

Step D: the grid side current signal that the current signal of the inverter side of collection and the second current transformer 3-2 gather is carried out amplification and weighted calculation process by the first current transformer 3-1, obtains new feedback current i _f, and calculate new feedback current i _frelative to inverter output voltage u _isignal gain;

Step D1: the second inductance L that the first current transformer 3-1 is gathered ₂current i ₁send to the first amplifier K11, if the weight coefficient of the first amplifier K11 is k ₁, the current signal that the second current transformer 3-2 gathers sends to the second amplifier K21, if the weight coefficient of the second amplifier K21 is k ₂-k ₁;

Signal after amplification is sent to first adder V1 by the step D2: the first amplifier K11 and the second amplifier K21, and after the weighted calculation of first adder V1, the signal of output is as new feedback current i _f;

I _f=k ₁i ₁+ (k ₂-k ₁) i ₂formula (3)

Step D3: new feedback current i _frelative to inverter output voltage u _itransfer function be:

$\begin{array}{c}{G}_{u_i\→i_f}\left(s\right)=\frac{i_f\left(s\right)}{u_i\left(s\right)}\\ =\frac{k_2\[s\frac{k_1}{k_2}(1-\mathrm{\α})L+Z_f\]}{sL\left(s\right(\mathrm{\α}(1-\mathrm{\α})L+Z_f)}\end{array}$ Formula (4)

As can be seen from formula (4), new feedback current i _frelative to inverter output voltage u _itransfer function be function of third order;

Step e: utilize the active depression of order, (4) formula is reduced to function of first order;

If formula (4) in weight coefficient meet abbreviation can obtain:

$G_{u_i\→i_f}\left(s\right)=\frac{i_f\left(s\right)}{u_i\left(s\right)}=\frac{k_2}{sL}$ Formula (5)

As can be seen from formula (5), new feedback current i _frelative to inverter output voltage u _itransfer function

Reduce to first-order system;

Step F: the new feedback current i that step e is obtained _frelative to inverter output voltage u _ifirst-order transfer function send to second adder V2, and compare with corresponding control command electric current, the signal of the error amount obtained after pi regulator is successively through PWM circuit for generating and PWM drive circuit, the signal that PWM drive circuit exports as the modulation signal of PWM inverter, the output current wave of control LLCL combining inverter and amplitude.

Claims (2)

1. the combining inverter that combines with many LC branch road of a LCL, comprise PWM inverter, the LCL-LC filter for grid-connected connection operation, the current regulator for cutting-in control and PWM drive circuit, PWM inverter connects LCL-LC filter, LCL-LC filter connects current regulator, current regulator connects PWM drive circuit, and PWM drive circuit connects PWM inverter; It is characterized in that: also comprise two current transformers for monitoring grid-connected current and the current regulator containing electric current weighting calculating and current error calculating and proportional integral adjustment for cutting-in control; The sampling end of the first current transformer connects the second end of the first inductance, and for measuring the electric current of PWM inverter side first inductance, the sampling end of the second current transformer connects the second end of the second inductance, for measuring the electric current of grid side second inductance; The described current regulator containing electric current weighting calculating and current error calculating and proportional integral adjustment for cutting-in control comprises the first amplifier and the second amplifier, first adder and second adder, pi regulator and PWM circuit for generating; First adder, second adder, pi regulator and PWM circuit for generating are connected successively, and the output of the first current transformer and the second current transformer is connected to first input end and second input of first adder respectively by the first amplifier and the second amplifier, the input of the output of first adder and instruction current access second adder, PWM circuit for generating connects PWM drive circuit; Described being used for the signal of the first current transformer collection according to weight coefficient k containing the current regulator that electric current weighting calculates and current error calculates and proportional integral regulates for cutting-in control ₁the signal that amplification, the second current transformer gather is according to weight coefficient k ₂amplify, and make k ₁with k ₂ratio value meet feedback current and reduce to function of first order relative to the signal gain of inverter output voltage.

2. the parallel inverter current control method that combines with many LC branch road of LCL according to claim 1, is characterized in that: comprise the following steps:

Steps A: install two current transformers for monitoring grid-connected current; The sampling end of the first current transformer connects the second end of the first inductance, and the sampling end of the second current transformer connects the second end of the second inductance; The output of the first current transformer and the second current transformer is connected to first input end and second input of first adder respectively by the first amplifier and the second amplifier;

Step B: calculate PWM inverter side current i ₁relative to inverter output voltage u _isignal gain, i.e. the transfer function of output filter and judge this transfer function class's number;

If PWM inverter side current i ₁as elementary feedback current i _fp, i.e. i ₁be equivalent to i _fp, then PWM inverter side current i ₁relative to inverter output voltage u _itransfer function for:

$\begin{array}{c}{G}_{u_i-i_1}\left(s\right)=\frac{i_1\left(s\right)}{u_i\left(s\right)}\\ =\frac{{\mathrm{sL}}_2+Z_f}{s^2{L}_1{L}_2+{\mathrm{sLZ}}_f}\\ =\frac{s(1-\mathrm{\α})L+Z_f}{\mathrm{sL}\left(s(\mathrm{\α}(1-\mathrm{\α})L+Z_f\right)}\end{array}$ Formula (1)

Wherein, Z _ffor the total resistance of LCL branch road and two LC branch circuit parallel connections; u _ifor PWM inverter output voltage; i ₁for flowing through the electric current of combining inverter side; L ₁for combining inverter side first inductance; L ₂for grid side second inductance; Wherein: L=L ₁+ L ₂, L ₁=α L, α are proportionality coefficients;

As can be seen from formula (1), PWM inverter side current i ₁relative to inverter output voltage u _itransfer function be function of third order;

Step C:

Calculate grid side current i ₂relative to inverter output voltage u _isignal gain, i.e. the transfer function of output filter and judge this transfer function class's number;

If the grid side current i that the second current transformer gathers ₂as elementary feedback current i _fd, i.e. i ₁be equivalent to i _fd, then grid side current i ₁relative to inverter output voltage u _itransfer function for:

$\begin{array}{c}{G}_{u_i-i_2}\left(s\right)=\frac{i_2\left(s\right)}{u_i\left(s\right)}\\ =\frac{Z_f}{s^2{L}_1{L}_2+{\mathrm{sLZ}}_f}\\ =\frac{Z_f}{\mathrm{sL}\left(s(\mathrm{\α}(1-\mathrm{\α})L+Z_f\right)}\end{array}$ Formula (2)

Wherein, i ₂for flowing through the electric current of grid side;

As can be seen from formula (2), grid side current i ₂relative to inverter output voltage u _itransfer function be function of third order;

Step D: the grid side current signal of the current signal of the inverter side of collection and the second current transformer collection is carried out amplification and weighted calculation process by the first current transformer, obtains new feedback current i _f, and calculate new feedback current i _frelative to inverter output voltage u _isignal gain;

Step D1: by the current i of the second inductance that the first current transformer gathers ₁send to the first amplifier, if the weight coefficient of the first amplifier is k ₁, the current signal of the second current transformer collection sends to the second amplifier, if the weight coefficient of the second amplifier is k ₂-k ₁;

Signal after amplification is sent to first adder by the step D2: the first amplifier and the second amplifier, and after the weighted calculation of first adder, the signal of output is as new feedback current i _f;

I _f=k ₁i ₁+ (k ₂-k ₁) i ₂formula (3)

Step D3: new feedback current i _frelative to inverter output voltage u _itransfer function be:

$\begin{array}{c}{G}_{u_i\→i_f}\left(s\right)=\frac{i_f\left(s\right)}{u_i\left(s\right)}\\ =\frac{k_2[s+\frac{k_1}{k_2}(1-\mathrm{\α})L+Z_f]}{\mathrm{sL}\left(s(\mathrm{\α}(1-\mathrm{\α})L+Z_f\right)}\end{array}$ Formula (4)

As can be seen from formula (4), new feedback current i _frelative to inverter output voltage u _itransfer function be function of third order;

Step e: utilize the active depression of order, (4) formula is reduced to function of first order;

If formula (4) in weight coefficient meet abbreviation can obtain:

$G_{u_i\→i_f}\left(s\right)=\frac{i_f\left(s\right)}{u_i\left(s\right)}=\frac{k_2}{\mathrm{sL}}$ Formula (5)

As can be seen from formula (5), new feedback current i _frelative to inverter output voltage u _itransfer function reduce to first-order system;

Step F: the new feedback current i that step e is obtained _frelative to inverter output voltage u _ifirst-order transfer function send to second adder, and compare with corresponding control command electric current, the signal of the error amount obtained after pi regulator is successively through PWM circuit for generating and PWM drive circuit, the signal that PWM drive circuit exports as the modulation signal of PWM inverter, the output current wave of control LLCL combining inverter and amplitude.