CN102545266B - Method for controlling grid-connected inverter based on feed-forward compensation - Google Patents

Abstract

The invention discloses a method for controlling a grid-connected inverter based on feed-forward compensation. The method comprises the following steps of: (1) acquiring a grid voltage, a grid side current and a capacitance current; (2) according to the grid side current, generating an instruction signal; (3) according to the grid voltage and the capacitance current, acquiring a current feed-forward signal and a voltage feed-forward signal; and (4) superposing the instruction signal, the current feed-forward signal and the voltage feed-forward signal to obtain a modulation signal, and generating a switching signal for controlling the grid-connected inverter according to the modulation signal. The method has the advantages that: a second-order differential feed-forward item of the grid voltage is compensated by a first-order differential feed-forward link of the capacitance current, so that a third-order system is reduced to a first-order system, the stability margin of the system is improved, the design process of a current regulator is simplified, and the grid side current cannot be influenced by grid voltage harmonic waves.

Description

A kind of control method of the combining inverter based on feedforward compensation

Technical field

The invention belongs to power inverter control technology field, be specifically related to a kind of control method of the combining inverter based on feedforward compensation.

Background technology

In recent years, serious day by day along with environmental pollution and energy scarcity, development and utilization regenerative resource (as solar energy, wind energy etc.) becomes pressing for of human society.And connecting the necessary interface equipment of electrical network as renewable energy system, combining inverter has become the research focus of current power electronic applications.

Be to suppress the voltage and current ripple that HF switch produces, combining inverter generally adopts L mode filter or LCL mode filter as the necessary interface parts of itself and electrical network.Because the L mode filter is limited in one's ability to the inhibition of high-frequency harmonic, generally need to adopt bigger inductance to satisfy harmonic standard.And the LCL mode filter can reduce total inductance value, and the electric current high order harmonic component is had stronger inhibition ability, therefore is widely used in high and medium power combining inverter occasion in recent years.But, adopting the grid-connection control system (comprising combining inverter, LCL mode filter, voltage-current sensor and control ring) of LCL mode filter is third-order system, there is very big amplitude gain spike in it at the resonance frequency place, it is stable to cause system's operation to be difficult for, thereby make system very responsive to the disturbance that voltage ripple of power network etc. causes, also the design of control system is had higher requirement simultaneously.

At the resonance problems of LCL mode filter, being mostly at present to adopt with capacitor current feedback is interior ring, and power network current is fed back to two closed loop controlling structures of outer shroud.Though this method can play certain inhibitory action to the resonance problems of LCL mode filter, and is helpless to the disturbance of line voltage.For suppressing the influence of line voltage disturbance, people such as Xuehua Wang are Full Feedforward of Grid Voltage for Grid-Connected Inverter With LCL Filter to Suppress Current Distortion Due to Grid Voltage Harmonics (IEEE Transactions on Power Electronics at title, 25, (12), 2010, pp.3119-3127) disclose a kind of feed forward method of line voltage in the article, its grid-connection control system as shown in Figure 1.Theoretically, this method can be eliminated the disturbing influence of line voltage fully, but the feed-forward coefficients of line voltage has comprised ratio, a subdifferential and second differential item in the article, and this obviously is difficult to realize in engineering, also is infeasible; And the control system of this method still is third-order system, so the design more complicated of current controller.

Summary of the invention

At the above-mentioned technological deficiency of existing in prior technology, the invention provides a kind of control method of the combining inverter based on feedforward compensation, when can guarantee that current on line side is not subjected to the line voltage disturbing influence, the system that makes obtains bigger stability margin.

A kind of control method of the combining inverter based on feedforward compensation comprises the steps:

(1) capacitance current of collection line voltage, current on line side and LCL mode filter;

Described LCL mode filter comprises inversion side inductance, electric capacity and grid side inductance; Described capacitance current is the electric current of electric capacity of flowing through; Described current on line side is the electric current of grid side inductance of flowing through.

(2) utilize phase-locked loop to extract the phase place of line voltage, described phase place and given power network current peak value are multiplied each other, obtain the given signal of current on line side; Make the given signal of described current on line side deduct described current on line side, obtain current error signal; Utilize current regulator that described current error signal is regulated, obtain command signal;

(3) to the described capacitance current calculation process that feedovers, obtain the current feed-forward signal; Described line voltage and feedforward proportionality coefficient are multiplied each other, obtain the electric voltage feed forward signal;

(4) with described current feed-forward signal, electric voltage feed forward signal and command signal addition, obtain modulation signal; Utilize the PWM modulator that described modulation signal and given triangular carrier signal are compared, generate switching signal, so that the switching tube in the combining inverter is controlled.

Described current regulator is PI (proportional integral) controller or PR (ratio resonance) controller.

In the described step (3), according to front feeding transfer function H _c(s)=L ₁S/k _PwmTo the capacitance current calculation process that feedovers; Wherein: k _PwmBe PWM (pulse width modulation) proportional gain, and k _Pwm=V _Dc/ V _Cm, V _DcBe DC bus-bar voltage (being the input voltage of combining inverter DC side), V _CmBe triangular carrier amplitude, L ₁Be the inductance value of inversion side inductance, s=j ω, ω are angular frequency.

Described feedforward proportionality coefficient k=1/k _PwmWherein: k _PwmBe the PWM proportional gain, and k _Pwm=V _Dc/ V _Cm, V _DcBe DC bus-bar voltage, V _CmBe the triangular carrier amplitude.

The present invention is by on the basis of power network current feedback control loop, adopted the control of capacitance current feedfoward control and voltage feed-forward control simultaneously, utilize capacitance current feedforward link to compensate line voltage second differential feedforward term, thereby not only can guarantee that current on line side is not subjected to the disturbing influence of line voltage, make whole system reduce to first-order system from third-order system simultaneously, eliminated the amplitude gain spike at LCL filter resonance frequency place, thereby make system can obtain bigger stability margin, and simplified the design of current regulator.

Description of drawings

Fig. 1 is the schematic diagram of prior art grid-connection control system.

Fig. 2 is the schematic diagram of grid-connection control system of the present invention.

Fig. 3 is the be incorporated into the power networks control flow chart of control strategy of prior art.

Fig. 4 is the be incorporated into the power networks control flow chart of control strategy of the present invention.

Fig. 5 (a) is the oscillogram of command signal among the present invention.

Fig. 5 (b) is the oscillogram of current feed-forward signal among the present invention.

Fig. 5 (c) is the oscillogram of electric voltage feed forward signal among the present invention.

Fig. 6 (a) adopts the oscillogram of current feed-forward signal compensation front and back line voltage and current on line side for the present invention.

Fig. 6 (b) is for adopting the oscillogram of the inventive method line voltage and current on line side when line voltage falls.

Embodiment

In order more specifically to describe the present invention, be elaborated below in conjunction with the control method of the drawings and the specific embodiments to combining inverter of the present invention.

As shown in Figure 3, a kind of control method of the combining inverter based on feedforward compensation comprises the steps:

(1) gathers line voltage v _g, current on line side and LCL mode filter capacitance current;

In the present embodiment, combining inverter is converted to the alternating current of 220V with the direct current of 450V, and by inputing to electrical network after the filtering of LCL mode filter.

Combining inverter is the single-phase electricity potential source type inverter VSI of 5kW, and it has 4 IGBT (Insulated Gate Bipolar Transistor, insulated gate bipolar transistor), and the switching frequency of IGBT is 8.4kHz.

The LCL mode filter comprises inversion side inductance L ₁, capacitor C and grid side inductance L ₂L ₁=1.6mH, L ₂=1.6mH, C=12 μ F.

Capacitance current is the current i of capacitor C of flowing through _CCurrent on line side is the grid side inductance L of flowing through ₂Current i _L2

(2) utilize phase-locked loop pll to extract line voltage v _gPhase place sin θ, with phase place sin θ and given power network current peak I _GmMultiply each other, obtain the given signal i of current on line side _gIn the present embodiment, the power network current peak I _Gm=25A;

Make the given signal i of current on line side _gDeduct current on line side i _L2, obtain current error signal i _u

Utilize the PI controller to current error signal i _uCarry out PI and regulate, obtain command signal v _dWherein: the transfer function of PI controller is G _c(s)=(K _pS+K _i)/s, K _pBe proportionality coefficient, K _iBe integral coefficient, s=j ω, ω are angular frequency; In the present embodiment, K _p=0.01, K _i=80.

(3) according to front feeding transfer function H _c(s)=L ₁S/k _PwmTo capacitance current i _CCarry out the single order differential and handle, obtain current feed-forward signal v _FcWith line voltage v _gK multiplies each other with the feedforward proportionality coefficient, obtains electric voltage feed forward signal v _FgWherein: L ₁Be the inductance value of inversion side inductance, s=j ω, ω are angular frequency; K=1/k _Pwm, k _PwmBe the PWM proportional gain, and k _Pwm=V _Dc/ V _Cm, V _CmBe triangular carrier amplitude, V _DcBe DC bus-bar voltage (being the input voltage of combining inverter DC side); In the present embodiment, V _Cm=1V, V _Dc=450V.

(4) with current feed-forward signal v _Fc(waveform is shown in Fig. 5 (b)), electric voltage feed forward signal v _Fg(waveform is shown in Fig. 5 (c)) and command signal v _d(waveform is shown in Fig. 5 (a)) addition obtains modulation signal v _m

Utilize the PWM modulator to make modulation signal v _mWith given triangular carrier signal v _CarrierCompare, generate 4 path switching signal S ₁～S ₄Respectively 4 IGBT in the combining inverter are controlled;

In the present embodiment, the PWM modulator adopts one pole frequency multiplication SPWM (Sinusoidal PWM) technology, and namely leading arm is operated in the power frequency pattern, only lagging leg is modulated.

In order to eliminate Voltage Harmonic to the influence of current on line side, the voltage feed-forward control control strategy that prior art adopts, as shown in Figure 3; Can the closed loop transmission expression formula from the line voltage to the current on line side be:

$I_{L2}\left(s\right)=\frac{H_g\left(s\right)k_{\mathrm{pwm}}-(L_{1}C{s}^2+1)}{L_{2}s+G_c\left(s\right)k_{\mathrm{pwm}}}{V}_g\left(s\right)$

Wherein: I _L2(s) be current on line side; V _g(s) be line voltage; H _g(s) be the voltage feed-forward control transfer function; G _c(s) be current regulator; k _PwmBe the PWM proportional gain, and k _Pwm=V _Dc/ V _Cm, V _DcBe DC bus-bar voltage, V _CmBe the triangular carrier amplitude; L ₁, L ₂, C is the inductance capacitance parameter of LCL mode filter.

For eliminating the influence of Voltage Harmonic fully, make I _L2(s)=0, can obtain the voltage feed-forward control transfer function is:

$H_g\left(s\right)=\frac{L_{1}C{s}^2+1}{k_{\mathrm{pwm}}}$

Obviously, in the prior art, for eliminating Voltage Harmonic fully to the influence of current on line side, the front feeding transfer function of line voltage has comprised second differential item and proportional, the second differential item not only is difficult to realize in engineering, and makes system introduce noise jamming easily.

In the time of can obtaining adopting prior art further according to Fig. 3, control system be from the given signal i of current on line side _g(s) the current on line side I that exports to inverter _L2(s) open-loop transfer function is:

$G_{\mathrm{ol}}\left(s\right)=G_c\left(s\right)\frac{k_{\mathrm{pwm}}}{s^3{L}_1{L}_{2}C+s({\mathrm{<figure-callout\; id="1"\; label="L"\; filenames="HDA0000134749850000021.png,HDA0000134749850000022.png"\; state="\{\{state\}\}">L</figure-callout>}}_1+L_2)}$

From following formula as can be known, when adopting prior art, control system still is third-order system, because there is very big amplitude gain spike in third-order system at the resonance frequency place, for resonance spikes is moved on to below the 0dB line fully, the cut-off frequency of open cycle system need be arranged very low, this will certainly increase the design difficulty of current regulator.

Present embodiment has not only adopted voltage feed-forward control control, but also has introduced the feedfoward control of capacitance current single order differential.Capacitance current feedfoward control link has compensated line voltage second differential feedforward term, thereby makes to have only proportional in the voltage feed-forward control transfer function, as shown in Figure 4; Can the closed loop transfer function, from the line voltage to the current on line side be:

$I_{L2}\left(s\right)=\frac{k_{\mathrm{pwm}}{H}_g\left(s\right)-1}{s({\mathrm{<figure-callout\; id="1"\; label="L"\; filenames="HDA0000134749850000021.png,HDA0000134749850000022.png"\; state="\{\{state\}\}">L</figure-callout>}}_1+L_2)+G_c\left(s\right)k_{\mathrm{pwm}}}{V}_g\left(s\right)$

Wherein: I _L2(s) be current on line side; V _g(s) be line voltage; H _g(s) be the voltage feed-forward control transfer function; G _c(s) be current regulator; k _PwmBe the PWM proportional gain, and k _Pwm=V _Dc/ V _Cm, V _DcBe DC bus-bar voltage, V _CmBe the triangular carrier amplitude; L ₁, L ₂, C is the inductance capacitance parameter of LCL filter.

For eliminating the influence of Voltage Harmonic fully, make I _L2(s)=0, can obtain the voltage feed-forward control transfer function is:

$H_g\left(s\right)=\frac{1}{k_{\mathrm{pwm}}}$

Obviously, in the present embodiment, the front feeding transfer function of line voltage has only proportional, can eliminate Voltage Harmonic fully to the influence of current on line side.

When further derivation can obtain adopting present embodiment according to Fig. 4, control system was from the given signal I of current on line side _g(s) the current on line side I that exports to inverter _L2(s) open-loop transfer function is:

$G_{\mathrm{ol}}\left(s\right)=G_c\left(s\right)\frac{k_{\mathrm{pwm}}}{s({\mathrm{<figure-callout\; id="1"\; label="L"\; filenames="HDA0000134749850000021.png,HDA0000134749850000022.png"\; state="\{\{state\}\}">L</figure-callout>}}_1+L_2)}$

Obviously, after the employing present embodiment, control system is reduced to first-order system, at this moment current regulator G _c(s) design will be just the same when adopting single inductance filter, and system stability nargin has obtained raising in essence, and system bandwidth can be got very big and not influence the stability of system, and the design of current regulator simultaneously is simplified to a great extent.

Fig. 6 (a) is for adopting the comparison diagram of capacitance current single order differential feedforward link compensation front and back, as can be seen, when adopting capacitance current single order differential feedforward compensation link, system stable operation, and export near the ideal sinusoidal current waveform the basic same-phase of power network current and line voltage.When the t=0.142s moment, remove capacitance current single order differential feedforward link, this moment, system's starting oscillation became unstable.Fig. 6 (b) is present embodiment current on line side oscillogram when line voltage falls, and as can be seen, when line voltage takes place by of short duration falling, adopt present embodiment can make current on line side have tracking effect faster, and the current distortion degree is little; This shows the validity of present embodiment.

Claims (2)

1. the control method based on the combining inverter of feedforward compensation comprises the steps:

(1) capacitance current of collection line voltage, current on line side and LCL mode filter;

(2) utilize phase-locked loop to extract the phase place of line voltage, described phase place and given power network current peak value are multiplied each other, obtain the given signal of current on line side; Make the given signal of described current on line side deduct described current on line side, obtain current error signal; Utilize current regulator that described current error signal is regulated, obtain command signal;

(3) according to front feeding transfer function H _c(s)=L ₁S/k _PwmTo the described capacitance current calculation process that feedovers, obtain the current feed-forward signal; Described line voltage is multiplied each other with feedforward proportionality coefficient k, obtain the electric voltage feed forward signal;

Wherein: described feedforward proportionality coefficient k=1/k _Pwm, k _PwmBe the PWM proportional gain, and k _Pwm=V _Dc/ V _Cm, V _DcBe DC bus-bar voltage, V _CmBe triangular carrier amplitude, L ₁Be the inductance value of inversion side inductance, s is Laplacian;

(4) with described current feed-forward signal, electric voltage feed forward signal and command signal addition, obtain modulation signal; Utilize the PWM modulator that described modulation signal and given triangular carrier signal are compared, generate switching signal, so that the switching tube in the combining inverter is controlled.

2. the control method of the combining inverter based on feedforward compensation according to claim 1, it is characterized in that: described current regulator is PI controller or PR controller.

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