CN102629837A - Method for circulating current restraining of parallel system of dual grid-connected inverters based on zero voltage vector feedforward control - Google Patents

Abstract

A method for circulating current restraining of a parallel system of dual grid-connected inverters based on zero voltage vector feedforward control belongs to the technical field of circulating current restraining of the parallel system of dual grid-connected inverters. The method solves the problem of existing system circulating current restraining methods that the dynamic response is slow when given current of two inverters changes. The dual grid-connected inverters share an alternating current bus and a direct current bus, and the method for circulating current restraining is based on the method for controlling proportional integral (PI) of parallel systems of inverters, introduces feedforward control of the difference between a non-zero vector and a duty ratio in space vector pulse width modulation (SVPWM) of two inverters, has high dynamic response speed and good control effect and is applicable to restraining the circulating current to a small range when the given current of one inverter is different from that of the other inverter. The method is applicable to parallel structures of three-phase grid-connected inverters without neutral lines.

Description

Two combining inverter parallel system circulation inhibition methods based on the control of voltage zero vector feedforward

Technical field

The present invention relates to a kind of two combining inverter parallel system circulation inhibition methods based on the control of voltage zero vector feedforward, the circulation that belongs to two combining inverter interconnected systems suppresses technical field.

Background technology

In the distributed energy electricity generation system, in order to increase power system capacity, improve system reliability, often a plurality of inverters are carried out parallel connection, this parallel-connection structure also provides path for circulation when having increased capacity.Circulation can have a negative impact to system, as waveform is distorted, and increases system loss, reduces system effectiveness, even surpasses the power grade etc. of equipment, therefore when carrying out the design of Controller of system, need suppress circulation.

The inhibition method of circulation mainly is divided into two kinds; The one, adopt the method for blocking circulation flow path; Comprise each combining inverter adopt independently DC power supply, add isolating transformer, in methods such as AC side series reactors; These methods are controlled comparatively simple, but can increase the cost and the volume of system; The 2nd, adopt software approach to suppress circulation, relatively more commonly used is that this method can not increase system cost and volume with PI control; And be easy to realize, but this method only plays regulating action to already present circulation, can't the circulation that this control cycle is about to produce be suppressed; Therefore dynamic response is slower, when the given electric current of each parallelly connected inverter equates, has and controls effect preferably; But when the given electric current of two inverters was unequal, the control effect was relatively poor.

Summary of the invention

The present invention is in the inhibition method that solves existing system circulation, and when the given electric current of two inverters changed, the problem that its dynamic response is slow provided a kind of two combining inverter parallel system circulation inhibition methods based on the control of voltage zero vector feedforward.

Two combining inverter parallel system circulation inhibition methods based on voltage zero vector feedforward control according to the invention, said pair of common ac bus of combining inverter and common dc bus, said circulation inhibition method is based on the PI control method of inverter parallel system,

Said circulation inhibition method is for to control the circulation of an inverter in two combining inverters, and it may further comprise the steps:

Step 1: to the zero-sequence current i of second inverter _Z2Sample;

Step 2: utilize the zero-sequence current i of zero-sequence current controller to second inverter _Z2Given zero-sequence current i with second inverter _{Z2_ref}Carrying out PI regulates; Simultaneously with the difference of the non-zero vector duty cycle of the space vector pulse width modulation of two inverters divided by 12; Obtain the regulated quantity of non-zero vector; After more said PI being regulated the result who obtains and does to differ from the regulated quantity of non-zero vector, the zero-sequence current controller is exported the correction value y of the second inverter zero vector ₂

Step 3: the correction value y that utilizes the second inverter zero vector ₂Real-time regulated is carried out in distribution to zero vector in the space vector pulse width modulation of second inverter, to realize the circulation inhibition to two combining inverter parallel systems.

The zero-sequence current i of said second inverter _Z2For:

i _z2＝i _a2+i _b2+i _c2，

I in the formula _A2Be a phase current of second inverter, i _B2Be the b phase current of second inverter, i _C2It is the c phase current of second inverter.

The correction value y of the second inverter zero vector of said zero-sequence current controller output ₂For:

${\mathrm{<figure-callout\; id="2"\; label="y"\; filenames="HDA0000156776790000011.png,HDA0000156776790000042.png"\; state="\{\{state\}\}">y</figure-callout>}}_2=(K_{p\_z}+\frac{K_{i\_z}}{s})\&CenterDot;(i_{z2\_\mathrm{ref}}-i_{z2})-\frac{\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="12"\; label="d"\; filenames="HDA0000156776790000011.png,HDA0000156776790000042.png"\; state="\{\{state\}\}">d</figure-callout>}}_{12}}{12},$

K in the formula _{P_z}Be the proportionality coefficient of zero-sequence current controller, K _{I_z}Be the integral coefficient of zero-sequence current controller, s is a Laplacian, Δ d ₁₂It is the difference of non-zero vector duty cycle of the space vector pulse width modulation of two inverters;

Δd ₁₂＝-d ₁₁+d ₂₁+d ₁₂-d ₂₂，

d ₁₁Be the duty ratio of first non-zero vector of first inverter, d ₂₁Be the duty ratio of second non-zero vector of first inverter, d ₁₂Be the duty ratio of first non-zero vector of second inverter, d ₂₂It is the duty ratio of second non-zero vector of second inverter.

With the sector I in the space vector pulse width modulation is example, the correction value y of the said second inverter zero vector ₂The concrete grammar that the distribution of zero vector in the space vector pulse width modulation of second inverter is carried out real-time regulated is:

The on off state of second inverter A phase in a control cycle T is controlled to be: continuing the T time from the initial time of one-period is low level; Continuing

the T time then is high level, and continuing

the T time again is low level;

The on off state of second inverter B phase in a control cycle T is controlled to be: continuing

the T time from the initial time of one-period is low level; Continuing

the T time then is high level, and continuing

the T time again is low level;

The on off state of second inverter C phase in a control cycle T is controlled to be: continuing

the T time from the initial time of one-period is low level; Continuing

time then is high level, and continuing

time again is low level;

D in the following formula ₀₂It is the duty ratio of the second inverter zero vector.

Advantage of the present invention is: the present invention is on traditional PI control basis; Introduced the feedfoward control of the difference of non-zero vector duty cycle among two inverter SVPWM; This method has higher dynamic responding speed and control effect; Also be applicable to simultaneously the given electric current different situations of two inverters, at the given electric current of two inverters not simultaneously, also can control to circulation more among a small circle in.

Description of drawings

Fig. 1 is a structure principle chart of the present invention; Reference numeral 1 is first inverter among the figure;

Fig. 2 is the topology diagram of two combining inverter parallel systems;

Fig. 3 is the averaging model of two combining inverter parallel system d shaft currents;

Fig. 4 is the averaging model of the q shaft current of two combining inverter parallel systems;

Fig. 5 is the averaging model of two combining inverter parallel system zero-axis currents;

Fig. 6 is the averaging model of two combining inverter parallel system DC bus-bar voltages;

Fig. 7 is the schematic diagram of the space vector pulse width modulation of inverter;

Fig. 8 is the distribution diagram of zero vector and non-zero vector in the second inverter space vector pulse width modulation;

Fig. 9 is the control block diagram of zero-sequence current ring;

Figure 10 is the zero-sequence current control block diagram of band feedfoward control according to the invention.

Embodiment

Embodiment one: this execution mode is described below in conjunction with Fig. 1 to Figure 10; The said two combining inverter parallel system circulation inhibition methods of this execution mode based on the control of voltage zero vector feedforward; Said pair of combining inverter is total to ac bus and common dc bus; Said circulation inhibition method is based on the PI control method of inverter parallel system

Said circulation inhibition method is for to control the circulation of an inverter in two combining inverters, and it may further comprise the steps:

Step 1: to the zero-sequence current i of second inverter 2 _Z2Sample;

Step 2: the zero-sequence current i that utilizes 3 pairs second inverters 2 of zero-sequence current controller _Z2Given zero-sequence current i with second inverter 2 _{Z2_ref}Carrying out PI regulates; Simultaneously with the difference of the non-zero vector duty cycle of the space vector pulse width modulation of two inverters divided by 12; Obtain the regulated quantity of non-zero vector; After more said PI being regulated the result who obtains and makes difference with the regulated quantity of non-zero vector, zero-sequence current controller 3 is exported the correction value y of the second inverter zero vector ₂

Step 3: the correction value y that utilizes the second inverter zero vector ₂Real-time regulated is carried out in distribution to zero vector in the space vector pulse width modulation of second inverter 2, to realize the circulation inhibition to two combining inverter parallel systems.

In this execution mode; Because the circulation equal and opposite in direction of two inverters, in the opposite direction; If the circulation to one of them inverter is controlled, then the circulation of another one inverter is also controlled naturally, therefore only need control the circulation of one of them inverter.

Embodiment two: below in conjunction with Fig. 1 this execution mode is described, this execution mode is for further specifying the zero-sequence current i of said second inverter 2 to execution mode one _Z2For:

i _z2＝i _a2+i _b2+i _c2，

I in the formula _A2Be a phase current of second inverter 2, i _B2Be the b phase current of second inverter 2, i _C2It is the c phase current of second inverter 2.

Embodiment three: below in conjunction with Fig. 1 to Figure 10 this execution mode is described, this execution mode is for to the further specifying of execution mode two, the correction value y of the second inverter zero vector of said zero-sequence current controller 3 outputs ₂For:

${\mathrm{<figure-callout\; id="2"\; label="y"\; filenames="HDA0000156776790000011.png,HDA0000156776790000042.png"\; state="\{\{state\}\}">y</figure-callout>}}_2=(K_{p\_z}+\frac{K_{i\_z}}{s})\&CenterDot;(i_{z2\_\mathrm{ref}}-i_{z2})-\frac{\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="12"\; label="d"\; filenames="HDA0000156776790000011.png,HDA0000156776790000042.png"\; state="\{\{state\}\}">d</figure-callout>}}_{12}}{12},$

K in the formula _{P_z}Be the proportionality coefficient of zero-sequence current controller 3, K _{I_z}Be the integral coefficient of zero-sequence current controller 3, s is a Laplacian, Δ d ₁₂It is the difference of non-zero vector duty cycle of the space vector pulse width modulation of two inverters;

Δd ₁₂＝-d ₁₁+d ₂₁+d ₁₂-d ₂₂，

d ₁₁Be the duty ratio of first non-zero vector of first inverter, d ₂₁Be the duty ratio of second non-zero vector of first inverter, d ₁₂Be the duty ratio of first non-zero vector of second inverter, d ₂₂It is the duty ratio of second non-zero vector of second inverter.

Embodiment four: below in conjunction with Fig. 1 to Figure 10 this execution mode is described, this execution mode is example for to the further specifying of execution mode two with the sector I in the space vector pulse width modulation, the correction value y of the said second inverter zero vector ₂The concrete grammar that the distribution of zero vector in the space vector pulse width modulation of second inverter 2 is carried out real-time regulated is:

The on off state of second inverter 2 A phase in a control cycle T is controlled to be: continuing time from the initial time of one-period is low level; Continuing

time then is high level, and continuing

time again is low level;

The on off state of second inverter 2 B phase in a control cycle T is controlled to be: continuing

time from the initial time of one-period is low level; Continuing

time then is high level, and continuing

time again is low level;

The on off state of second inverter 2 C phase in a control cycle T is controlled to be: continuing time from the initial time of one-period is low level; Continuing

time then is high level, and continuing

time again is low level;

D in the following formula ₀₂It is the duty ratio of second inverter, 2 zero vectors.

Parallelly connected three-phase grid-connected inverter adopts the ac bus and the structure of dc bus altogether altogether among the present invention, and is as shown in Figure 2.The power grade of two inverter modules equates that dc bus capacitor is 2C, and C is single three-phase grid-connected inverter dc bus capacitor.This topological structure is that circulation provides path, and more than one of circulation flow path, has illustrated wherein circulation flow path with arrow among Fig. 2, therefore when carrying out design of Controller, need suppress circulation.

When circulation is suppressed, do not control usually, but come all circulation is controlled through the control zero-sequence current to the circulation of single circulation flow path, the zero-sequence current equal and opposite in direction of obvious two inverters, in the opposite direction.If the circulation to one of them inverter is controlled, then the circulation of another one inverter is also controlled naturally, therefore only need control the circulation of one of them inverter.

The Mathematical Modeling of parallel connection three-phase grid-connected inverter under two synchronised rotating coordinate systems can be expressed as:

$\frac{d}{\mathrm{dt}}\left[\begin{array}{c}{i}_{d1}\\ i_{\mathrm{<figure-callout\; id="1"\; label="q"\; filenames="HDA0000156776790000011.png,HDA0000156776790000022.png"\; state="\{\{state\}\}">q</figure-callout>}1}\end{array}\right]=\frac{1}{L_1}\left[\begin{array}{c}{e}_d\\ e_q\end{array}\right]-\left[\begin{array}{cc}0& -\mathrm{\&omega;}\\ \mathrm{\&omega;}& 0\end{array}\right]\&CenterDot;\left[\begin{array}{c}{i}_{d1}\\ i_{q1}\end{array}\right]-\frac{1}{L_1}\left[\begin{array}{c}{d}_{d1}\\ {\mathrm{<figure-callout\; id="1"\; label="d\; q"\; filenames="HDA0000156776790000011.png,HDA0000156776790000022.png"\; state="\{\{state\}\}">d</figure-callout>}}_q\end{array}\right]\&CenterDot;v_{\mathrm{dc}}---\left(1\right)$

$\frac{d}{\mathrm{dt}}\left[\begin{array}{c}{i}_{d2}\\ i_{\mathrm{<figure-callout\; id="2"\; label="q"\; filenames="HDA0000156776790000011.png,HDA0000156776790000042.png"\; state="\{\{state\}\}">q</figure-callout>}2}\end{array}\right]=\frac{1}{L_2}\left[\begin{array}{c}{e}_d\\ e_q\end{array}\right]-\left[\begin{array}{cc}0& -\mathrm{\&omega;}\\ \mathrm{\&omega;}& 0\end{array}\right]\&CenterDot;\left[\begin{array}{c}{i}_{d2}\\ i_{q2}\end{array}\right]-\frac{1}{L_2}\left[\begin{array}{c}{d}_{d2}\\ {\mathrm{<figure-callout\; id="2"\; label="d\; q"\; filenames="HDA0000156776790000011.png,HDA0000156776790000042.png"\; state="\{\{state\}\}">d</figure-callout>}}_q\end{array}\right]\&CenterDot;v_{\mathrm{dc}}---\left(2\right)$

$\frac{{\mathrm{di}}_{\mathrm{<figure-callout\; id="2"\; label="z"\; filenames="HDA0000156776790000011.png,HDA0000156776790000042.png"\; state="\{\{state\}\}">z</figure-callout>}2}}{\mathrm{dt}}=\frac{\mathrm{\&Delta;}{d}_z\&CenterDot;v_{\mathrm{<figure-callout\; id="1"\; label="dc\; L"\; filenames="HDA0000156776790000011.png,HDA0000156776790000022.png"\; state="\{\{state\}\}">dc</figure-callout>}}}{L_{}}---\left(3\right)$

$\frac{{\mathrm{dv}}_{\mathrm{dc}}}{\mathrm{dt}}=\frac{1}{2C}\left(\begin{array}{c}\left[\begin{array}{cc}{d}_{d1}& d_{q1}\end{array}\right]\left[\begin{array}{c}{i}_{d1}\\ {\mathrm{<figure-callout\; id="1"\; label="i\; q"\; filenames="HDA0000156776790000011.png,HDA0000156776790000022.png"\; state="\{\{state\}\}">i</figure-callout>}}_q\end{array}\right]+\left[\begin{array}{cc}{d}_{d2}& d_{q2}\end{array}\right]\left[\begin{array}{c}{i}_{d2}\\ {\mathrm{<figure-callout\; id="2"\; label="i\; q"\; filenames="HDA0000156776790000011.png,HDA0000156776790000042.png"\; state="\{\{state\}\}">i</figure-callout>}}_q\end{array}\right]+\frac{\mathrm{\&Delta;}{d}_z\&CenterDot;{\mathrm{<figure-callout\; id="1"\; label="i\; z"\; filenames="HDA0000156776790000011.png,HDA0000156776790000022.png"\; state="\{\{state\}\}">i</figure-callout>}}_z}{3}+i_o\end{array}\right)---\left(4\right)$

I wherein _Zx=i _Ax+ i _Bx+ i _Cx(x=1,2), Δ d _z=d _Z1-d _Z2, d _Zx=d _Ax+ d _Bx+ d _Cx(x=1,2).

In the above-mentioned formula, i _D1Be the d axle component of first inverter three-phase current, i _Q1Be the q axle component of first inverter three-phase current, L ₁Be the inductance value of first inverter, e _dBe the d axle component of line voltage, e _qBe the q axle component of line voltage, ω is the angular frequency of electrical network, d _D1Be the d axle component of first inverter three-phase duty ratio, d _Q1Be the q axle component of first inverter three-phase duty ratio, v _DcBe DC bus-bar voltage, i _Z1Be the zero-sequence current of first inverter, L ₂Be the inductance value of second inverter, i _D2Be the d axle component of second inverter three-phase current, i _Q2Be the q axle component of second inverter three-phase current, d _D2Be the d axle component of second inverter three-phase duty ratio, d _Q2Be the q axle component of second inverter three-phase duty ratio, i _Z2Be the zero-sequence current of second inverter, Δ d _zBe the poor of two inverter zero sequence duty ratios, Δ d _z=d _Z1-d _Z2, d _Z1, d _Z2Be respectively the zero sequence duty ratio of two inverters.

Like this, the equivalent-circuit model of parallelly connected three-phase grid-connected inverter can be represented with Fig. 3 to Fig. 6.

According to the Mathematical Modeling of the zero-sequence current of parallelly connected three-phase grid-connected inverter, promptly formula (3) can be found out, the rate of change of zero-sequence current is by the difference decision of the zero sequence duty ratio of two inverters.

For single inverter,, do not consider zero-sequence component usually because circulation flow path does not exist.When two inverter parallel connections, owing to formed circulation flow path,, also can form bigger zero-sequence current even the difference of two inverter zero sequence duty ratios is less, this is because zero axle is a undamped loop of only containing inductance.Therefore when two inverter parallel connections, need to consider zero-sequence component.

In three-phase grid-connected inverter, adopt the SVPWM mode usually, this modulation system adopts two non-zero vector V usually _i(i=1,2,3,4,5,6) and zero vector V _iSynthetic control vector, vector V are come in (i=0,7) _iThe definition of (i=0～7) is as shown in Figure 7.With second inverter is example, and the duty ratio of establishing two non-zero vectors is respectively d ₁₂, d ₂₂, the zero vector duty ratio is d ₀₂, then:

d ₀₂＝1-d ₁₂-d ₂₂ (5)

Under different modulator approaches, the distribution of zero vector is different, and the dutycycle of each phase and zero sequence dutycycle all can change, but the difference of the dutycycle of two-phase can not change.And the distribution of zero vector can not influence the controlled target of system, i.e. ac-side current and DC bus-bar voltage.This shows through the distribution of control zero vector just can control zero sequence duty ratio d _zThereby, the control zero-sequence current.Sector I with shown in Figure 7 is an example, is located at a PWM in the cycle, zero vector V _zTime do

Zero vector V ₀Time do

Fig. 8 has provided the distribution diagram of zero vector and non-zero vector in the second inverter space vector pulse width modulation, wherein variable y ₂Satisfy:

$-\frac{{\mathrm{<figure-callout\; id="02"\; label="d"\; filenames="HDA0000156776790000011.png,HDA0000156776790000042.png"\; state="\{\{state\}\}">d</figure-callout>}}_{02}}{4}\&le;{\mathrm{<figure-callout\; id="2"\; label="y"\; filenames="HDA0000156776790000011.png,HDA0000156776790000042.png"\; state="\{\{state\}\}">y</figure-callout>}}_2\&le;\frac{{\mathrm{<figure-callout\; id="02"\; label="d"\; filenames="HDA0000156776790000011.png,HDA0000156776790000042.png"\; state="\{\{state\}\}">d</figure-callout>}}_{02}}{4},---\left(6\right)$

Zero vector V like this ₀, V ₇The span of duty ratio be [0, d ₀₂], and to satisfy both sums be d ₀₂At this moment,

$d_z=d_a+d_b+d_c=({\mathrm{<figure-callout\; id="12"\; label="d"\; filenames="HDA0000156776790000011.png,HDA0000156776790000042.png"\; state="\{\{state\}\}">d</figure-callout>}}_{12}+{\mathrm{<figure-callout\; id="22"\; label="d"\; filenames="HDA0000156776790000042.png"\; state="\{\{state\}\}">d</figure-callout>}}_{22}+\frac{{\mathrm{<figure-callout\; id="02"\; label="d"\; filenames="HDA0000156776790000011.png,HDA0000156776790000042.png"\; state="\{\{state\}\}">d</figure-callout>}}_{02}}{2}-2y_2)+({\mathrm{<figure-callout\; id="22"\; label="d"\; filenames="HDA0000156776790000042.png"\; state="\{\{state\}\}">d</figure-callout>}}_{22}+\frac{{\mathrm{<figure-callout\; id="02"\; label="d"\; filenames="HDA0000156776790000011.png,HDA0000156776790000042.png"\; state="\{\{state\}\}">d</figure-callout>}}_{02}}{2}-2y_2)+(\frac{{\mathrm{<figure-callout\; id="02"\; label="d"\; filenames="HDA0000156776790000011.png,HDA0000156776790000042.png"\; state="\{\{state\}\}">d</figure-callout>}}_{02}}{2}-2y_2)={\mathrm{<figure-callout\; id="12"\; label="d"\; filenames="HDA0000156776790000011.png,HDA0000156776790000042.png"\; state="\{\{state\}\}">d</figure-callout>}}_{12}+2{\mathrm{<figure-callout\; id="22"\; label="d"\; filenames="HDA0000156776790000042.png"\; state="\{\{state\}\}">d</figure-callout>}}_{22}+\frac{3}{2}{d}_{02}-6{\mathrm{<figure-callout\; id="2"\; label="y"\; filenames="HDA0000156776790000011.png,HDA0000156776790000042.png"\; state="\{\{state\}\}">y</figure-callout>}}_2,---\left(7\right)$

So: $\mathrm{\&Delta;}{d}_z=d_{z1}-{\mathrm{<figure-callout\; id="2"\; label="d\; z"\; filenames="HDA0000156776790000011.png,HDA0000156776790000042.png"\; state="\{\{state\}\}">d</figure-callout>}}_z=({\mathrm{<figure-callout\; id="11"\; label="d"\; filenames="HDA0000156776790000033.png"\; state="\{\{state\}\}">d</figure-callout>}}_{11}+2d_{21}+\frac{3}{2}{d}_{01}-6y_1)-({\mathrm{<figure-callout\; id="12"\; label="d"\; filenames="HDA0000156776790000011.png,HDA0000156776790000042.png"\; state="\{\{state\}\}">d</figure-callout>}}_{12}+2{\mathrm{<figure-callout\; id="22"\; label="d"\; filenames="HDA0000156776790000042.png"\; state="\{\{state\}\}">d</figure-callout>}}_{22}+\frac{3}{2}{d}_{02}-6y_2),---\left(8\right)$

For two converter parallel systems, because the circulation equal and opposite in direction of two inverters is in the opposite direction; If the circulation to one of them inverter is controlled; Then the circulation of another one inverter is also controlled naturally, therefore, can make the zero vector correction value y of first module ₁=0.In addition, because d _0i=1-d _1i-d _2i(i=1,2), following formula can abbreviation be:

$\mathrm{\&Delta;}{d}_z=\frac{1}{2}(-{\mathrm{<figure-callout\; id="11"\; label="d"\; filenames="HDA0000156776790000033.png"\; state="\{\{state\}\}">d</figure-callout>}}_{11}+d_{21}+d_{12}-{\mathrm{<figure-callout\; id="22"\; label="d"\; filenames="HDA0000156776790000042.png"\; state="\{\{state\}\}">d</figure-callout>}}_{22}+12y_2),---\left(9\right)$

Note Δ d ₁₂=-d ₁₁+ d ₂₁+ d ₁₂-d ₂₂, then following formula can turn to:

$\mathrm{\&Delta;}{d}_z=\frac{1}{2}(\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="12"\; label="d"\; filenames="HDA0000156776790000011.png,HDA0000156776790000042.png"\; state="\{\{state\}\}">d</figure-callout>}}_{12}+12y_2),---\left(10\right)$

When the given electric current of two inverters equated, the voltage given value of current regulator output was equal basically, so d ₁₁=d ₁₂, d ₂₁=d ₂₂, at this moment, Δ d ₁₂=0, so

Δd _z＝6y ₂ (11)

Like this, the Mathematical Modeling of zero-sequence current under synchronous rotating frame, promptly formula (3) can turn to:

$\frac{{\mathrm{<figure-callout\; id="2"\; label="di\; z"\; filenames="HDA0000156776790000011.png,HDA0000156776790000042.png"\; state="\{\{state\}\}">di</figure-callout>}}_z}{\mathrm{dt}}=\frac{6{\mathrm{<figure-callout\; id="2"\; label="y"\; filenames="HDA0000156776790000011.png,HDA0000156776790000042.png"\; state="\{\{state\}\}">y</figure-callout>}}_2\&CenterDot;{\mathrm{<figure-callout\; id="1"\; label="v\; dc\; L"\; filenames="HDA0000156776790000011.png,HDA0000156776790000022.png"\; state="\{\{state\}\}">v</figure-callout>}}_{\mathrm{dc}}}{L_{}}---\left(12\right)$

Suppose v _DcKeep constant, following formula done Laplace transform, can get:

$I_{z2}\left(s\right)=\frac{\frac{6{\mathrm{<figure-callout\; id="1"\; label="V\; dc\; L"\; filenames="HDA0000156776790000011.png,HDA0000156776790000022.png"\; state="\{\{state\}\}">V</figure-callout>}}_{\mathrm{dc}}}{L_{}}{Y}_2\left(s\right)}{s},---\left(13\right)$

Y in the following formula ₂(s), I _Z2(s) be respectively variable y ₂, i _Z2Laplace transformation.

Can find out that by following formula zero axle is full decoupled with d axle and q axle, and is a first-order system; Therefore; It is very high that the bandwidth of zero-sequence current ring can design, and adopts the controller of pi regulator as zero-sequence current here, and the set-point and the sampled value of zero-sequence current is poor; Its deviation is carried out PI regulates, can obtain the correction value of second inverter zero vector:

$y_2\left(s\right)=(K_{p\_z}+\frac{K_{i\_z}}{s})\&CenterDot;(i_{\mathrm{<figure-callout\; id="2"\; label="z"\; filenames="HDA0000156776790000011.png,HDA0000156776790000042.png"\; state="\{\{state\}\}">z</figure-callout>}2\_\mathrm{ref}}-i_{z2}),---\left(14\right)$

Like this, the control block diagram of zero-sequence current ring is as shown in Figure 9.

This method is only to existing circulation to play regulating action; Can't the circulation that this control cycle is about to produce be suppressed, therefore, dynamic response is slower; When the given electric current of each parallelly connected inverter equates; Have and control effect preferably, but when the given electric current of two inverters was unequal, the control effect was relatively poor.

When the given electric current of two inverters is unequal, according to formula (9), the Mathematical Modeling of zero-sequence current under synchronous rotating frame, promptly formula (3) can turn to:

$\frac{{\mathrm{<figure-callout\; id="2"\; label="di\; z"\; filenames="HDA0000156776790000011.png,HDA0000156776790000042.png"\; state="\{\{state\}\}">di</figure-callout>}}_z}{\mathrm{dt}}=\frac{\frac{1}{2}(\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="12"\; label="d"\; filenames="HDA0000156776790000011.png,HDA0000156776790000042.png"\; state="\{\{state\}\}">d</figure-callout>}}_{12}+12y_2)\&CenterDot;{\mathrm{<figure-callout\; id="1"\; label="v\; dc\; L"\; filenames="HDA0000156776790000011.png,HDA0000156776790000022.png"\; state="\{\{state\}\}">v</figure-callout>}}_{\mathrm{dc}}}{L_{}}---\left(15\right)$

Suppose v _DcKeep constant, following formula done Laplace transform, can get:

${\mathrm{<figure-callout\; id="2"\; label="I\; z"\; filenames="HDA0000156776790000011.png,HDA0000156776790000042.png"\; state="\{\{state\}\}">I</figure-callout>}}_z=\frac{\frac{{6\mathrm{<figure-callout\; id="1"\; label="V\; dc\; L"\; filenames="HDA0000156776790000011.png,HDA0000156776790000022.png"\; state="\{\{state\}\}">V</figure-callout>}}_{\mathrm{dc}}}{L_{}}\&CenterDot;({\mathrm{<figure-callout\; id="2"\; label="Y"\; filenames="HDA0000156776790000011.png,HDA0000156776790000042.png"\; state="\{\{state\}\}">Y</figure-callout>}}_2+\frac{\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="12"\; label="D"\; filenames="HDA0000156776790000011.png,HDA0000156776790000042.png"\; state="\{\{state\}\}">D</figure-callout>}}_{12}}{12})}{s}---\left(16\right)$

Δ D in the following formula ₁₂Be variable Δ d ₁₂Laplace transformation.

It is thus clear that circulation is except receiving zero vector correction value y ₂Control, also can receive the influence of each inverter d axle q shaft current controller output, specifically, receive the influence of the difference of two inverter non-zero vector duty cycle exactly, in order to eliminate this influence, introduce the poor of two inverter non-zero vector duty cycle, i.e. Δ d ₁₂Feedfoward control, can obtain the correction value y of zero vector like this ₂:

${\mathrm{<figure-callout\; id="2"\; label="y"\; filenames="HDA0000156776790000011.png,HDA0000156776790000042.png"\; state="\{\{state\}\}">y</figure-callout>}}_2=(K_{p\_z}+\frac{K_{i\_z}}{s})\&CenterDot;(i_{\mathrm{<figure-callout\; id="2"\; label="z"\; filenames="HDA0000156776790000011.png,HDA0000156776790000042.png"\; state="\{\{state\}\}">z</figure-callout>}2\_\mathrm{ref}}-i_{z2})-\frac{\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="12"\; label="d"\; filenames="HDA0000156776790000011.png,HDA0000156776790000042.png"\; state="\{\{state\}\}">d</figure-callout>}}_{12}}{12}---\left(17\right)$

At this moment, the control block diagram of zero-sequence current ring is shown in figure 10, and like this, interference volume is cancelled out each other with the feedforward component, and the control block diagram of zero-sequence current just can be reduced to as shown in Figure 9.

The control block diagram of whole system is as shown in Figure 1; Because the circulation equal and opposite in direction of two inverters, in the opposite direction; If the circulation to one of them inverter is controlled; Then the circulation of another one inverter is also controlled naturally, therefore only need control the circulation of one of them inverter.First inverter is only controlled d axle and q shaft current, and zero-axis current is not controlled, when carrying out the SVPWM modulation, and zero vector V ₀And V ₇Mean allocation.Second inverter also will be controlled zero-axis current except d axle and q shaft current are controlled.At first to the zero-sequence current i of second inverter _Z2Sample; Utilize the zero-sequence current controller that zero-sequence current is carried out PI then and regulate, and introduce the feedfoward control of the difference of non-zero vector duty cycle among two inverter SVPWM, the expression formula of zero-sequence current controller is shown in formula (17); Utilize zero-sequence current controller output y at last ₂Real-time regulated is carried out in distribution to zero vector among second inverter SVPWM, and the distribution of zero vector is as shown in Figure 8.

Claims (4)

1. two combining inverter parallel system circulation inhibition methods based on voltage zero vector feedforward control; Said pair of combining inverter is total to ac bus and common dc bus; Said circulation inhibition method is characterized in that based on the PI control method of inverter parallel system:

Said circulation inhibition method is for to control the circulation of an inverter in two combining inverters, and it may further comprise the steps:

Step 1: to the zero-sequence current i of second inverter (2) _Z2Sample;

Step 2: utilize the zero-sequence current i of zero-sequence current controller (3) to second inverter (2) _Z2Given zero-sequence current i with second inverter (2) _{Z2_ref}Carrying out PI regulates; Simultaneously with the difference of the non-zero vector duty cycle of the space vector pulse width modulation of two inverters divided by 12; Obtain the regulated quantity of non-zero vector; After more said PI being regulated the result who obtains and makes difference with the regulated quantity of non-zero vector, zero-sequence current controller (3) is exported the correction value y of the second inverter zero vector ₂

Step 3: the correction value y that utilizes the second inverter zero vector ₂Real-time regulated is carried out in distribution to zero vector in the space vector pulse width modulation of second inverter (2), to realize the circulation inhibition to two combining inverter parallel systems.

2. the two combining inverter parallel system circulation inhibition methods based on the control of voltage zero vector feedforward according to claim 1 is characterized in that: the zero-sequence current i of said second inverter (2) _Z2For:

i _z2＝i _a2+i _b2+i _c2，

I in the formula _A2Be a phase current of second inverter (2), i _B2Be the b phase current of second inverter (2), i _C2It is the c phase current of second inverter (2).

3. the two combining inverter parallel system circulation inhibition methods based on the control of voltage zero vector feedforward according to claim 2 is characterized in that:

The correction value y of the second inverter zero vector of said zero-sequence current controller (3) output ₂For:

$y_2=(K_{p\_z}+\frac{K_{i\_z}}{s})\&CenterDot;(i_{z2\_\mathrm{ref}}-i_{z2})-\frac{\mathrm{\&Delta;}{d}_{12}}{12},$

K in the formula _{P_z}Be the proportionality coefficient of zero-sequence current controller (3), K _{I_z}Be the integral coefficient of zero-sequence current controller (3), s is a Laplacian, Δ d ₁₂It is the difference of non-zero vector duty cycle of the space vector pulse width modulation of two inverters;

Δd ₁₂＝-d ₁₁+d ₂₁+d ₁₂-d ₂₂，

d ₁₁Be the duty ratio of first non-zero vector of first inverter, d ₂₁Be the duty ratio of second non-zero vector of first inverter, d ₁₂Be the duty ratio of first non-zero vector of second inverter, d ₂₂It is the duty ratio of second non-zero vector of second inverter.

4. the two combining inverter parallel system circulation inhibition methods based on the control of voltage zero vector feedforward according to claim 3 is characterized in that:

With the sector I in the space vector pulse width modulation is example, the correction value y of the said second inverter zero vector ₂The concrete grammar that the distribution of zero vector in the space vector pulse width modulation of second inverter (2) is carried out real-time regulated is:

The on off state of second inverter (2) A phase in a control cycle T is controlled to be: continuing

time from the initial time of one-period is low level; Continuing

time then is high level, and continuing

time again is low level;

The on off state of second inverter (2) B phase in a control cycle T is controlled to be: continuing

time from the initial time of one-period is low level; Continuing

time then is high level, and continuing

time again is low level;

The on off state of second inverter (2) C phase in a control cycle T is controlled to be: continuing

time from the initial time of one-period is low level; Continuing

time then is high level, and continuing

time again is low level;

D in the following formula ₀₂It is the duty ratio of second inverter (2) zero vector.

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