CN103346689A - Grid-connected inverter parallel system circulating current restraining method under imbalance condition of inductance - Google Patents

Abstract

The invention relates to a grid-connected inverter parallel system circulating current restraining method under an imbalance condition of inductance, relates to the technical field of the circulating current restraining of grid-connected inverter parallel systems, and aims at solving the problems in the grid-connected inverter parallel system that when the three-phase inductance of the parallel inverter is varied or imbalanced, the circulating current is still large through using the existing circulating current restraining method. Since the circulating current flowing between every two inverters is identical in value and opposite in directions, the circulating current between every two inverters can be restrained only by restraining the circulating current of one inverter, so that a purpose for restraining the system circulating current can be achieved. Under the imbalance of the three-phase inductance of the inverter, compared with a PI control method, for the method, the peak value of the circulating current can be reduced by 40 to 65 percent. The grid-connected inverter parallel system circulating current restraining method is suitable for restraining the circulating current in the grid-connected inverter parallel system.

Description

Combining inverter parallel system circulation inhibition method under the inductance unbalance condition

Technical field

The circulation that the invention belongs to the combining inverter parallel system suppresses technical field.

Background technology

To exchange side output current sine, power factor height, current distortion little because of it for three-phase PWM inverter, receives much concern in the distributed energy electricity generation system.Along with the increase of distributed energy electricity generation system capacity, the power grade of inverter is had higher requirement.In order to guarantee the reliability of system simultaneously at the power requirement that satisfies system, reduce cost and the volume of system simultaneously, often inverter is carried out direct Parallel Control, the DC side that is about to inverter with exchange side and directly be together in parallel.This parallel-connection structure also provides path for circulation when increasing power system 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, need consider to suppress circulation when therefore parallel system being controlled.Circulation inhibition method commonly used at present has:

Isolate in parallel.This method can use isolating transformer or DC side to adopt the independent direct current source to realize by exchanging side, and is simple, but can increase cost and the volume of system.

Use interphase reactor at circulation flow path, suppress circulation in order to form high impedance.This method has inhibition preferably for high frequency circulation, and for the medium and low frequency composition in the circulation, inhibition is limited.

Staggered interrupted space vector modulating method.This method can effectively reduce the THD of system, but can increase the switching loss of system, reduces system effectiveness, especially in large-power occasions.

PI controls circulation.When the given electric current of each shunt chopper equated, this method can obtain controlled effect preferably, and implements fairly simple.Yet the PI controller can only suppress the circulation that has existed in this cycle, and for the circulation that is about in following one-period produce, its control action is very limited.The given electric current of each inverter do not wait or the ac filter inductance parameters not simultaneously, dynamic response is slower, adopts this control method can make circulation peak-to-peak value 54% (relevant with concrete service conditions) that descend, and controls the circulation weak effect.

PI voltage zero vector feedforward control circulation.By introduce the zero vector feedforward can greatly improve the PI control algolithm each shunt chopper given electric current does not wait or inductance parameters not enough simultaneously, and have better dynamic and respond, can not increase volume and the cost of system.

Summary of the invention

The present invention is in order to solve in the combining inverter parallel system, when the shunt chopper three pole reactor changes or is uneven, and circulation bigger problem still during the existing method control that suppresses circulation.Combining inverter parallel system circulation inhibition method under a kind of inductance unbalance condition now is provided.

Combining inverter parallel system circulation inhibition method under the inductance unbalance condition, combining inverter in the described combining inverter parallel system is for being total to dc bus, exchanging the directly structure of parallel connection of side, described parallel system adopts the control of PI method, circulation inhibition method at above-mentioned combining inverter parallel system, this method is in two inverter parallel systems, circulation to an inverter of combining inverter is controlled, and specifically may further comprise the steps:

Step 1: to the zero-sequence current i of second inverter (2) _Z2Sample, execution in step two then;

Step 2: utilize zero-sequence current PI controller to the zero-sequence current i of second inverter (2) _Z2Zero-sequence current set-point i with second inverter (2) _{Z2_ref}It is poor to do, and with the input signal of this difference as zero-sequence current PI controller, utilizes the PI algorithm of zero-sequence current PI controller that this input signal is regulated, and obtains the PI regulated value, then while execution in step three and step 4;

Step 3: with the difference DELTA d of the non-zero vector duty cycle of the space vector pulse width modulation of first inverter (1) and second inverter (2) ₁₂Divided by 12, obtain the regulated quantity of non-zero vector, execution in step five then;

Step 4: with the difference u of the inductance residual voltage of first inverter (1) and second inverter (2) _Lz12DC bus-bar voltage u divided by 2 times _Dc, the regulated quantity of acquisition inductance residual voltage, execution in step five then;

Step 5: the regulated quantity of the regulated quantity of the non-zero vector that the PI regulated value that step 2 is obtained and step 3 obtain and the inductance residual voltage of step 4 acquisition is poor, the difference that obtains is by 3 outputs of zero sequence circulation controller, and this difference is as the correction value y of second inverter (2) zero vector ₂, execution in step six then;

Step 6: the correction value y that utilizes second inverter (2) zero vector of step 5 acquisition ₂Distribution to zero vector in the space vector pulse width modulation of second inverter (2) is regulated in real time, finishes the inhibition to circulation.

The zero-sequence current i of second inverter (2) in the above-mentioned steps one _Z2For:

$i_{\mathrm{<figure-callout\; id="2"\; label="z"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">z</figure-callout>}2}=\frac{i_{\mathrm{<figure-callout\; id="2"\; label="a"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">a</figure-callout>}2}+i_{\mathrm{<figure-callout\; id="2"\; label="b"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">b</figure-callout>}2}+i_{\mathrm{<figure-callout\; id="2"\; label="c"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">c</figure-callout>}2}}{3}---\left(1\right)$

I in the formula _K2(k=a, b c) are respectively a phase, b phase, the c phase current of second inverter (2).

Δ d described in the above-mentioned steps three ₁₂For:

Δd ₁₂=(d ₂₁-d ₁₁)-(d ₂₂-d ₁₂) （2）

D in the formula 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 (2), d ₂₂It is the duty ratio of second non-zero vector of second inverter (2).U described in the above-mentioned steps four _Lz12For:

$u_{L_{z12}}=u_{L_{z1}}-u_{L_{z2}}$

$=\frac{\mathrm{\&omega;}{i}_{d2}(L_{a2}\sin \mathrm{\&omega;t}+{\mathrm{<figure-callout\; id="2"\; label="L\; b"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">L</figure-callout>}}_b\sin (\mathrm{\&omega;t}-\frac{2}{3}\mathrm{\&pi;})+{\mathrm{<figure-callout\; id="2"\; label="L\; c"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">L</figure-callout>}}_c\sin (\mathrm{\&omega;t}+\frac{2}{3}\mathrm{\&pi;}))}{3}$

$-\frac{\mathrm{\&omega;}{i}_{d1}(L_{a1}\sin \mathrm{\&omega;t}+{\mathrm{<figure-callout\; id="1"\; label="L\; b"\; filenames="HDA00003566709800031.png,HDA00003566709800043.png"\; state="\{\{state\}\}">L</figure-callout>}}_b\sin (\mathrm{\&omega;t}-\frac{2}{3}\mathrm{\&pi;})+{\mathrm{<figure-callout\; id="1"\; label="L\; c"\; filenames="HDA00003566709800031.png,HDA00003566709800043.png"\; state="\{\{state\}\}">L</figure-callout>}}_c\sin (\mathrm{\&omega;t}+\frac{2}{3}\mathrm{\&pi;}))}{3}---\left(3\right)$

$+\frac{\mathrm{\&omega;}{i}_{q2}(L_{a2}\cos \mathrm{\&omega;t}+{\mathrm{<figure-callout\; id="2"\; label="L\; b"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">L</figure-callout>}}_b\cos (\mathrm{\&omega;t}-\frac{2}{3}\mathrm{\&pi;})+{\mathrm{<figure-callout\; id="2"\; label="L\; c"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">L</figure-callout>}}_c\cos (\mathrm{\&omega;t}+\frac{2}{3}\mathrm{\&pi;}))}{3}$

$-\frac{\mathrm{\&omega;}{i}_{q1}(L_{a1}\cos \mathrm{\&omega;t}+{\mathrm{<figure-callout\; id="1"\; label="L\; b"\; filenames="HDA00003566709800031.png,HDA00003566709800043.png"\; state="\{\{state\}\}">L</figure-callout>}}_b\cos (\mathrm{\&omega;t}-\frac{2}{3}\mathrm{\&pi;})+{\mathrm{<figure-callout\; id="1"\; label="L\; c"\; filenames="HDA00003566709800031.png,HDA00003566709800043.png"\; state="\{\{state\}\}">L</figure-callout>}}_c\cos (\mathrm{\&omega;t}+\frac{2}{3}\mathrm{\&pi;}))}{3}$

In the formula

Be the inductance residual voltage of first inverter (1),

Be the inductance residual voltage of second inverter (2), i _Dx(x=1,2) are respectively the d axle component of the three-phase current of first inverter (1) and second inverter (2), i _Qx(x=1,2) are respectively the q axle component of the three-phase current of first inverter (1) and second inverter (2), L _Kx(k=a, b, c; X=1,2) be respectively first inverter (1) and the second inverter a, b, c inductance value mutually, ω is the angular frequency of electrical network.

The correction value y of second inverter (2) zero vector in the above-mentioned steps five ₂For:

${\mathrm{<figure-callout\; id="2"\; label="y"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">y</figure-callout>}}_2=K_{p\_z}\&CenterDot;(i_{\mathrm{<figure-callout\; id="2"\; label="z"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">z</figure-callout>}2\_\mathrm{ref}}-i_{z2})+K_{i\_z}\&Integral;(i_{\mathrm{<figure-callout\; id="2"\; label="z"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">z</figure-callout>}2\_\mathrm{ref}}-i_{z2})\mathrm{dt}-\frac{\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="12"\; label="d"\; filenames="HDA00003566709800042.png,HDA00003566709800044.png"\; state="\{\{state\}\}">d</figure-callout>}}_{12}}{12}-\frac{u_{\mathrm{<figure-callout\; id="12"\; label="Lz"\; filenames="HDA00003566709800042.png,HDA00003566709800044.png"\; state="\{\{state\}\}">Lz</figure-callout>}12}}{2u_{\mathrm{dc}}}---\left(4\right)$

K in the formula _{P_z}Be the proportionality coefficient of zero-sequence current PI controller, K _{I_z}Integral coefficient for zero-sequence current PI controller.

The concrete grammar of above-mentioned steps six described real-time adjustings is:

On off state with the A phase of second inverter (2) in a control cycle T is controlled to be: from the initial time of one-period, continue low level earlier

Time, continue high level then

Time, continue low level at last

Time;

On off state with the B phase of second inverter (2) in same control cycle T is controlled to be: from the initial time of one-period, continue low level earlier

Time, continue high level then

Time, continue low level at last

Time;

On off state with the C phase of second inverter (2) in same control cycle T is controlled to be: from the initial time of one-period, continue low level earlier

Time, continue high level then Time, continue low level at last Time;

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 (2), d ₂₂Be the duty ratio of second non-zero vector of second inverter (2), d ₀₂It is the duty ratio of second inverter (2) zero vector.

Combining inverter parallel system circulation inhibition method under the inductance unbalance condition of the present invention, because the circulation equal and opposite in direction, the direction that flow through between any two inverters are opposite, only need the circulation of one of them inverter is suppressed, can realize the circulation between any two inverters is suppressed, and then reach the purpose of inhibition system circulation.When the inverter three pole reactor is uneven, compare the PI control method, the circulation peak-to-peak value can reduce 40% to 65%.

Description of drawings

Fig. 1 is the flow chart of combining inverter parallel system circulation inhibition method under the inductance unbalance condition.

Fig. 2 is when being example with two inverter parallel-connection structures, the topological structure schematic diagram of system; L wherein _Za, l _Zb, l _ZcA circulation flow path of a, b, c phase in the corresponding parallel-connection structure of difference, every circulation flow path comprises k in the inverter 1 (k=a, b, c) the last brachium pontis of phase and inverter 2k (k=a respectively, b, c) the following brachium pontis of phase, a, b, c respectively have a circulation flow path not draw mutually in addition, and these three circulation bar paths comprise k (k=a in the inverter 1 respectively, b, c) the following brachium pontis of phase and inverter 2k (k=a, b, c) the last brachium pontis of phase.

Fig. 3 is the principle schematic of combining inverter parallel system circulation inhibition method under the inductance unbalance condition.

Fig. 4 is the equivalent-circuit model schematic diagram of the zero sequence circulation flow path of combining inverter.

Fig. 5 is the schematic diagram of the space vector pulse width modulation of inverter.

Fig. 6 is that second inverter 2 is introduced zero vector correction value y ₂After the space vector distribution map.

Fig. 7 is the control block diagram of the zero-sequence current ring when adopting PI control.

Fig. 8 is the control block diagram that adopts based on the zero-sequence current ring of voltage zero vector feedforward.

Fig. 9 is the zero sequence circulation control block diagram of combining inverter parallel system circulation inhibition method under the inductance unbalance condition.

Embodiment

Embodiment one: specify present embodiment with reference to Fig. 1 and Fig. 3, combining inverter parallel system circulation inhibition method under the described inductance unbalance condition of present embodiment, combining inverter in the described combining inverter parallel system is for being total to dc bus, exchanging the directly structure of parallel connection of side, described parallel system adopts the control of PI method, circulation inhibition method at above-mentioned combining inverter parallel system, this method is in two inverter parallel systems, circulation to an inverter of combining inverter is controlled, and specifically may further comprise the steps:

Step 1: to the zero-sequence current i of second inverter 2 _Z2Sample, execution in step two then;

Step 2: utilize zero-sequence current PI controller to the zero-sequence current i of second inverter 2 _Z2Zero-sequence current set-point i with second inverter 2 _{Z2_ref}It is poor to do, and with the input signal of this difference as zero-sequence current PI controller, utilizes the PI algorithm of zero-sequence current PI controller that this input signal is regulated, and obtains the PI regulated value, then while execution in step three and step 4;

Step 3: with the difference DELTA d of the non-zero vector duty cycle of the space vector pulse width modulation of first inverter 1 and second inverter 2 ₁₂Divided by 12, obtain the regulated quantity of non-zero vector, execution in step five then;

Step 4: with the difference u of the inductance residual voltage of first inverter 1 and second inverter 2 _Lz12DC bus-bar voltage u divided by 2 times _Dc, the regulated quantity of acquisition inductance residual voltage, execution in step five then;

Step 5: the regulated quantity of the regulated quantity of the non-zero vector that the PI regulated value that step 2 is obtained and step 3 obtain and the inductance residual voltage of step 4 acquisition is poor, the difference that obtains is by 3 outputs of zero sequence circulation controller, and this difference is as the correction value y of second inverter, 2 zero vectors ₂, execution in step six then;

Step 6: the correction value y that utilizes second inverter, 2 zero vectors of step 5 acquisition ₂Distribution to zero vector in the space vector pulse width modulation of second inverter 2 is regulated in real time, finishes the inhibition to circulation.

Combining inverter parallel system circulation inhibition method under the inductance unbalance condition of the present invention, because the circulation equal and opposite in direction, the direction that flow through between any two inverters are opposite, only need the circulation of one of them inverter is suppressed, can realize the circulation between any two inverters is suppressed, and then reach the purpose of inhibition system circulation.

Embodiment two: present embodiment is that combining inverter parallel system circulation inhibition method under the embodiment one described inductance unbalance condition is described further, in the present embodiment, and the zero-sequence current i of second inverter 2 in the step 1 _Z2For:

$i_{\mathrm{<figure-callout\; id="2"\; label="z"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">z</figure-callout>}2}=\frac{i_{\mathrm{<figure-callout\; id="2"\; label="a"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">a</figure-callout>}2}+i_{\mathrm{<figure-callout\; id="2"\; label="b"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">b</figure-callout>}2}+i_{\mathrm{<figure-callout\; id="2"\; label="c"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">c</figure-callout>}2}}{3}---\left(1\right)$

I in the formula _K2(k=a, b c) are respectively a phase, b phase, the c phase current of second inverter 2.

Embodiment three: present embodiment is that combining inverter parallel system circulation inhibition method under the embodiment one described inductance unbalance condition is described further, in the present embodiment, and the d of Δ described in the step 3 ₁₂For:

Δd ₁₂=(d ₂₁-d ₁₁)-(d ₂₂-d ₁₂) （2）

D in the formula 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 2, d ₂₂It is the duty ratio of second non-zero vector of second inverter 2.

Embodiment four: present embodiment is that combining inverter parallel system circulation inhibition method under the embodiment one described inductance unbalance condition is described further, in the present embodiment, and u described in the step 4 _Lz12For:

${\mathrm{<figure-callout\; id="12"\; label="u\; L\; z"\; filenames="HDA00003566709800042.png,HDA00003566709800044.png"\; state="\{\{state\}\}">u</figure-callout>}}_{L_z}=u_{L_{z1}}-{\mathrm{<figure-callout\; id="2"\; label="u\; L\; z"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">u</figure-callout>}}_{L_z}$

$=\frac{\mathrm{\&omega;}{i}_{d2}(L_{a2}\sin \mathrm{\&omega;t}+{\mathrm{<figure-callout\; id="2"\; label="L\; b"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">L</figure-callout>}}_b\sin (\mathrm{\&omega;t}-\frac{2}{3}\mathrm{\&pi;})+{\mathrm{<figure-callout\; id="2"\; label="L\; c"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">L</figure-callout>}}_c\sin (\mathrm{\&omega;t}+\frac{2}{3}\mathrm{\&pi;}))}{3}$

$-\frac{\mathrm{\&omega;}{i}_{d1}(L_{a1}\sin \mathrm{\&omega;t}+{\mathrm{<figure-callout\; id="1"\; label="L\; b"\; filenames="HDA00003566709800031.png,HDA00003566709800043.png"\; state="\{\{state\}\}">L</figure-callout>}}_b\sin (\mathrm{\&omega;t}-\frac{2}{3}\mathrm{\&pi;})+{\mathrm{<figure-callout\; id="1"\; label="L\; c"\; filenames="HDA00003566709800031.png,HDA00003566709800043.png"\; state="\{\{state\}\}">L</figure-callout>}}_c\sin (\mathrm{\&omega;t}+\frac{2}{3}\mathrm{\&pi;}))}{3}---\left(3\right)$

$+\frac{\mathrm{\&omega;}{i}_{q2}(L_{a2}\cos \mathrm{\&omega;t}+{\mathrm{<figure-callout\; id="2"\; label="L\; b"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">L</figure-callout>}}_b\cos (\mathrm{\&omega;t}-\frac{2}{3}\mathrm{\&pi;})+{\mathrm{<figure-callout\; id="2"\; label="L\; c"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">L</figure-callout>}}_c\cos (\mathrm{\&omega;}+\frac{2}{3}\mathrm{\&pi;}))}{3}$

$-\frac{\mathrm{\&omega;}{i}_{q1}(L_{a1}\cos \mathrm{\&omega;t}+{\mathrm{<figure-callout\; id="1"\; label="L\; b"\; filenames="HDA00003566709800031.png,HDA00003566709800043.png"\; state="\{\{state\}\}">L</figure-callout>}}_b\cos (\mathrm{\&omega;t}-\frac{2}{3}\mathrm{\&pi;})+{\mathrm{<figure-callout\; id="1"\; label="L\; c"\; filenames="HDA00003566709800031.png,HDA00003566709800043.png"\; state="\{\{state\}\}">L</figure-callout>}}_c\cos (\mathrm{\&omega;t}+\frac{2}{3}\mathrm{\&pi;}))}{3}$

In the formula

Be the inductance residual voltage of first inverter 1, Be the inductance residual voltage of second inverter 2, i _Dx(x=1,2) are respectively the d axle component of the three-phase current of first inverter 1 and second inverter 2, i _Qx(x=1,2) are respectively the q axle component of the three-phase current of first inverter 1 and second inverter 2, L _Kx(k=a, b, c; X=1,2) be respectively first inverter 1 and the second inverter a, b, c inductance value mutually, ω is the angular frequency of electrical network.Embodiment five: present embodiment is that combining inverter parallel system circulation inhibition method under the embodiment one described inductance unbalance condition is described further, in the present embodiment, and the correction value y of second inverter, 2 zero vectors in the step 5 ₂For:

${\mathrm{<figure-callout\; id="2"\; label="y"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">y</figure-callout>}}_2=K_{p\_z}\&CenterDot;(i_{\mathrm{<figure-callout\; id="2"\; label="z"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">z</figure-callout>}2\_\mathrm{ref}}-i_{z2})+K_{i\_z}\&Integral;(i_{\mathrm{<figure-callout\; id="2"\; label="z"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">z</figure-callout>}2\_\mathrm{ref}}-i_{z2})\text{dt-}\frac{\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="12"\; label="d"\; filenames="HDA00003566709800042.png,HDA00003566709800044.png"\; state="\{\{state\}\}">d</figure-callout>}}_{12}}{12}-\frac{{\mathrm{<figure-callout\; id="12"\; label="u\; Lz"\; filenames="HDA00003566709800042.png,HDA00003566709800044.png"\; state="\{\{state\}\}">u</figure-callout>}}_{\mathrm{Lz}}}{2u_{\mathrm{dc}}}---\left(4\right)$

K in the formula _{P_z}Be the proportionality coefficient of zero-sequence current PI controller, K _{I_z}Integral coefficient for zero-sequence current PI controller.

Embodiment six: present embodiment is that combining inverter parallel system circulation inhibition method under the embodiment one described inductance unbalance condition is described further, and in the present embodiment, the concrete grammar of the described real-time adjusting of step 6 is:

On off state with the A phase of second inverter 2 in a control cycle T is controlled to be: from the initial time of one-period, continue low level earlier Time, continue high level then

Time, continue low level at last

Time;

On off state with the B phase of second inverter 2 in same control cycle T is controlled to be: from the initial time of one-period, continue low level earlier

Time, continue high level then

Time, continue low level at last

Time;

On off state with the C phase of second inverter 2 in same control cycle T is controlled to be: from the initial time of one-period, continue low level earlier Time, continue high level then Time, continue low level at last

Time;

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 2, d ₂₂Be the duty ratio of second non-zero vector of second inverter 2, d ₀₂It is the duty ratio of second inverter, 2 zero vectors.Three-phase grid-connected inverter in parallel adopts dc bus and the direct structure in parallel of interchange side altogether among the present invention, be example with two inverter parallel-connection structures, as shown in Figure 2, the parallel system dc bus capacitor is 2C, C is single three-phase grid-connected inverter dc bus capacitor, and two inverter module power equate.This topological structure provides path for circulation, and circulation flow path has 6, uses l among Fig. 2 _Za, l _Zb, l _ZcIllustrated wherein 3 circulation flow paths, when carrying out the controller design, need suppress circulation.

For each shunt chopper, a, b, c three-phase respectively have two circulation flow paths, and circulation be evenly distributed on each mutually in, the circulation that flows through inverter is 3 times of each phase circulation.The circulation that suppresses to suppress inverter by the mean value in each phase to the circulation of inverter.

When considering each inverter three pole reactor to the influencing of circulation, be example with two inverter parallel-connection structures, the Mathematical Modeling of parallel system under the two-phase synchronous rotating frame can be expressed as:

$\left\{\begin{array}{c}({\mathrm{<figure-callout\; id="1"\; label="L\; b"\; filenames="HDA00003566709800031.png,HDA00003566709800043.png"\; state="\{\{state\}\}">L</figure-callout>}}_b+\frac{{\mathrm{<figure-callout\; id="2"\; label="L\; cos"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">L</figure-callout>}}_{\cos }}{3}-\frac{L_{\sin 2\mathrm{<figure-callout\; id="1"\; label="p"\; filenames="HDA00003566709800031.png,HDA00003566709800043.png"\; state="\{\{state\}\}">p</figure-callout>}1}^2}{9{\mathrm{<figure-callout\; id="1"\; label="L\; b"\; filenames="HDA00003566709800031.png,HDA00003566709800043.png"\; state="\{\{state\}\}">L</figure-callout>}}_b+3L_{\sin 2n1}})\frac{{\mathrm{di}}_{\mathrm{<figure-callout\; id="1"\; label="d"\; filenames="HDA00003566709800031.png,HDA00003566709800043.png"\; state="\{\{state\}\}">d</figure-callout>}1}}{\mathrm{dt}}-\mathrm{\&omega;}({\mathrm{<figure-callout\; id="1"\; label="L\; b"\; filenames="HDA00003566709800031.png,HDA00003566709800043.png"\; state="\{\{state\}\}">L</figure-callout>}}_b+\frac{L_{\cos 2\mathrm{<figure-callout\; id="1"\; label="n"\; filenames="HDA00003566709800031.png,HDA00003566709800043.png"\; state="\{\{state\}\}">n</figure-callout>}1}}{3}-\frac{L_{\sin 2\mathrm{<figure-callout\; id="1"\; label="p"\; filenames="HDA00003566709800031.png,HDA00003566709800043.png"\; state="\{\{state\}\}">p</figure-callout>}1}^2}{9{\mathrm{<figure-callout\; id="1"\; label="L\; b"\; filenames="HDA00003566709800031.png,HDA00003566709800043.png"\; state="\{\{state\}\}">L</figure-callout>}}_b+3L_{\sin 2n1}})i_{\mathrm{<figure-callout\; id="1"\; label="q"\; filenames="HDA00003566709800031.png,HDA00003566709800043.png"\; state="\{\{state\}\}">q</figure-callout>}1}\\ =u_{d1}-e_d+\frac{L_{\sin 2\mathrm{<figure-callout\; id="1"\; label="p"\; filenames="HDA00003566709800031.png,HDA00003566709800043.png"\; state="\{\{state\}\}">p</figure-callout>}1}}{3{\mathrm{<figure-callout\; id="1"\; label="L\; b"\; filenames="HDA00003566709800031.png,HDA00003566709800043.png"\; state="\{\{state\}\}">L</figure-callout>}}_b+L_{\sin 2n1}}(u_{q1}-e_q)\\ ({\mathrm{<figure-callout\; id="1"\; label="L\; b"\; filenames="HDA00003566709800031.png,HDA00003566709800043.png"\; state="\{\{state\}\}">L</figure-callout>}}_b+\frac{L_{\sin 2\mathrm{<figure-callout\; id="1"\; label="n"\; filenames="HDA00003566709800031.png,HDA00003566709800043.png"\; state="\{\{state\}\}">n</figure-callout>}1}}{3}-\frac{L_{\sin 2\mathrm{<figure-callout\; id="1"\; label="p"\; filenames="HDA00003566709800031.png,HDA00003566709800043.png"\; state="\{\{state\}\}">p</figure-callout>}1}^2}{9{\mathrm{<figure-callout\; id="1"\; label="L\; b"\; filenames="HDA00003566709800031.png,HDA00003566709800043.png"\; state="\{\{state\}\}">L</figure-callout>}}_b+3L_{\cos 2n1}})\frac{{\mathrm{di}}_{\mathrm{<figure-callout\; id="1"\; label="q"\; filenames="HDA00003566709800031.png,HDA00003566709800043.png"\; state="\{\{state\}\}">q</figure-callout>}1}}{\mathrm{dt}}-\mathrm{\&omega;}({\mathrm{<figure-callout\; id="1"\; label="L\; b"\; filenames="HDA00003566709800031.png,HDA00003566709800043.png"\; state="\{\{state\}\}">L</figure-callout>}}_b+\frac{L_{\sin 2\mathrm{<figure-callout\; id="1"\; label="n"\; filenames="HDA00003566709800031.png,HDA00003566709800043.png"\; state="\{\{state\}\}">n</figure-callout>}1}}{3}-\frac{L_{\sin 2\mathrm{<figure-callout\; id="1"\; label="p"\; filenames="HDA00003566709800031.png,HDA00003566709800043.png"\; state="\{\{state\}\}">p</figure-callout>}1}^2}{9{\mathrm{<figure-callout\; id="1"\; label="L\; b"\; filenames="HDA00003566709800031.png,HDA00003566709800043.png"\; state="\{\{state\}\}">L</figure-callout>}}_b+3L_{\cos 2n1}})i_{\mathrm{<figure-callout\; id="1"\; label="d"\; filenames="HDA00003566709800031.png,HDA00003566709800043.png"\; state="\{\{state\}\}">d</figure-callout>}1}\\ =u_{q1}-e_q+\frac{L_{\sin 2\mathrm{<figure-callout\; id="1"\; label="p"\; filenames="HDA00003566709800031.png,HDA00003566709800043.png"\; state="\{\{state\}\}">p</figure-callout>}1}}{3{\mathrm{<figure-callout\; id="1"\; label="L\; b"\; filenames="HDA00003566709800031.png,HDA00003566709800043.png"\; state="\{\{state\}\}">L</figure-callout>}}_b+L_{\cos 2n1}}(u_{d1}-e_d)\end{array}\right.---\left(5\right)$

$\left\{\begin{array}{c}({\mathrm{<figure-callout\; id="2"\; label="L\; b"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">L</figure-callout>}}_b+\frac{L_{\cos 2\mathrm{<figure-callout\; id="2"\; label="n"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">n</figure-callout>}2}}{3}-\frac{L_{\sin 2\mathrm{<figure-callout\; id="2"\; label="p"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">p</figure-callout>}2}^2}{{9\mathrm{<figure-callout\; id="2"\; label="L\; b"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">L</figure-callout>}}_b+3{\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">L</figure-callout>}}_{2\sin 2n}})\frac{\mathrm{<figure-callout\; id="2"\; label="d\; i\; d"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">d</figure-callout>}{i}_d{2}_{}}{\mathrm{dt}}-\mathrm{\&omega;}({\mathrm{<figure-callout\; id="2"\; label="L\; b"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">L</figure-callout>}}_b+\frac{L_{\cos 2\mathrm{<figure-callout\; id="2"\; label="n"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">n</figure-callout>}2}}{3}-\frac{L_{\sin 2\mathrm{<figure-callout\; id="2"\; label="p"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">p</figure-callout>}2}^2}{9{\mathrm{<figure-callout\; id="2"\; label="L\; b"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">L</figure-callout>}}_b+3L_{\sin 2n}})i_{\mathrm{<figure-callout\; id="1"\; label="q"\; filenames="HDA00003566709800031.png,HDA00003566709800043.png"\; state="\{\{state\}\}">q</figure-callout>}1}\\ =u_{d2}-e_d+\frac{L_{\sin 2\mathrm{<figure-callout\; id="2"\; label="p"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">p</figure-callout>}2}}{3{\mathrm{<figure-callout\; id="2"\; label="L\; b"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">L</figure-callout>}}_b+L_{\sin 2n2}}(u_{q2}-e_q)\\ ({\mathrm{<figure-callout\; id="2"\; label="L\; b"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">L</figure-callout>}}_b+\frac{L_{\sin 2\mathrm{<figure-callout\; id="2"\; label="n"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">n</figure-callout>}2}}{3}-\frac{L_{\sin 2\mathrm{<figure-callout\; id="2"\; label="p"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">p</figure-callout>}2}^2}{9{\mathrm{<figure-callout\; id="2"\; label="L\; b"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">L</figure-callout>}}_b+3L_{\cos 2n2}})\frac{\mathrm{<figure-callout\; id="2"\; label="d\; i\; q"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">d</figure-callout>}{i}_q{2}_{}}{\mathrm{dt}}-\mathrm{\&omega;}({\mathrm{<figure-callout\; id="2"\; label="L\; b"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">L</figure-callout>}}_b+\frac{L_{\sin 2\mathrm{<figure-callout\; id="2"\; label="n"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">n</figure-callout>}2}}{3}-\frac{L_{\sin 2\mathrm{<figure-callout\; id="2"\; label="p"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">p</figure-callout>}2}^2}{9{\mathrm{<figure-callout\; id="2"\; label="L\; b"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">L</figure-callout>}}_b+3L_{\cos 2n2}})i_{\mathrm{<figure-callout\; id="2"\; label="d"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">d</figure-callout>}2}\\ =u_{q2}-e_q+\frac{L_{\sin 2\mathrm{<figure-callout\; id="2"\; label="p"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">p</figure-callout>}2}}{3{\mathrm{<figure-callout\; id="2"\; label="L\; b"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">L</figure-callout>}}_b+L_{\cos 2n2}}(u_{d2}-e_d)\end{array}\right.----\left(6\right)$

$\left\{\begin{array}{c}{u}_{\mathrm{dx}}=d_{\mathrm{dx}}{u}_{\mathrm{dc}}\\ u_{\mathrm{qx}}=d_{\mathrm{qx}}{u}_{\mathrm{dc}}\end{array}\right.(x=\mathrm{1,2})---\left(7\right)$

$({\mathrm{<figure-callout\; id="1"\; label="L\; m"\; filenames="HDA00003566709800031.png,HDA00003566709800043.png"\; state="\{\{state\}\}">L</figure-callout>}}_m+L_{m2})\frac{{\mathrm{<figure-callout\; id="2"\; label="d\; iz"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">d</figure-callout>}}_{\mathrm{iz}}}{\mathrm{dt}}={\mathrm{<figure-callout\; id="12"\; label="u\; Lz"\; filenames="HDA00003566709800042.png,HDA00003566709800044.png"\; state="\{\{state\}\}">u</figure-callout>}}_{\mathrm{Lz}}+\mathrm{\&Delta;}{d}_z{u}_{\mathrm{dc}}---\left(8\right)$

Wherein:

${\mathrm{<figure-callout\; id="2"\; label="L\; cos"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">L</figure-callout>}}_{\cos }=\frac{1}{2}{\mathrm{<figure-callout\; id="2"\; label="L\; ax\; cos"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">L</figure-callout>}}_{\mathrm{ax}}\cos 2\mathrm{\&omega;t}+\frac{1}{2}{L}_{\mathrm{bx}}\cos (2\mathrm{\&omega;t}+\frac{2}{3}\mathrm{\&pi;})+\frac{1}{2}{L}_{\mathrm{cx}}\cos (2\mathrm{\&omega;t}-\frac{2}{3}\mathrm{\&pi;})+\frac{L_{\mathrm{ax}}+L_{\mathrm{cx}}+2{\mathrm{<figure-callout\; id="2"\; label="L\; bx"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">L</figure-callout>}}_{\mathrm{bx}}}{2}$

${\mathrm{<figure-callout\; id="2"\; label="L\; sin"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">L</figure-callout>}}_{\sin }={\mathrm{<figure-callout\; id="2"\; label="L\; ax\; sin"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">L</figure-callout>}}_{\mathrm{ax}}\sin 2\mathrm{\&omega;t}+L_{\mathrm{cx}}\sin (2\mathrm{\&omega;t}-\frac{2\mathrm{\&pi;}}{3})+L_{\mathrm{bx}}\sin (2\mathrm{\&omega;t}+\frac{2\mathrm{\&pi;}}{3})$

${\mathrm{<figure-callout\; id="2"\; label="L\; sin"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">L</figure-callout>}}_{\sin }=-\frac{1}{2}{\mathrm{<figure-callout\; id="2"\; label="L\; ax\; cos"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">L</figure-callout>}}_{\mathrm{ax}}\cos 2\mathrm{\&omega;t}-\frac{1}{2}{L}_{\mathrm{bx}}\cos (2\mathrm{\&omega;t}+\frac{2}{3}\mathrm{\&pi;})-\frac{1}{2}{L}_{\mathrm{cx}}\cos (2\mathrm{\&omega;t}-\frac{2}{3}\mathrm{\&pi;})+\frac{L_{\mathrm{ax}}+L_{\mathrm{cx}}-2{\mathrm{<figure-callout\; id="2"\; label="L\; bx"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">L</figure-callout>}}_{\mathrm{bx}}}{2}$

$L_{\mathrm{mx}}=\frac{L_{\mathrm{ax}}+L_{\mathrm{bx}}+L_{\mathrm{cx}}}{3}$

$u_{\mathrm{Lzx}}=\frac{\mathrm{\&omega;}{i}_{\mathrm{dx}}(L_{\mathrm{ax}}\sin \mathrm{\&omega;t}+L_{\mathrm{bx}}\sin (\mathrm{\&omega;t}-\frac{2}{3}\mathrm{\&pi;})+L_{\mathrm{cx}}\sin (\mathrm{\&omega;t}+\frac{2}{3}\mathrm{\&pi;}))}{3}$

$-\frac{\mathrm{\&omega;}{i}_{\mathrm{qx}}(L_{\mathrm{ax}}\cos \mathrm{\&omega;t}+L_{\mathrm{bx}}\cos (\mathrm{\&omega;t}-\frac{2}{3}\mathrm{\&pi;})+L_{\mathrm{cx}}\cos (\mathrm{\&omega;t}+\frac{2}{3}\mathrm{\&pi;}))}{3}$

X=1,2 corresponding first inverter 1 of difference and second inverters 2, i _DxBe the d axle component of each inverter three-phase current, i _QxBe the q axle component of each inverter three-phase current, L _Kx(k=a, b, c; X=1,2) be the inductance value of each each phase of 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 _DxBe the d axle component of each inverter three-phase duty ratio, d _QxBe the q axle component of each inverter three-phase duty ratio, u _DcBe DC bus-bar voltage, i _ZxBe the zero-sequence current of each inverter, Δ d _zBe the poor of two inverter zero sequence duty ratios, Δ d _z=d _Z1-d _Z2, d _ZxBe respectively the zero sequence duty ratio of two inverters.

Like this, obtain the zero sequence circulation flow path equivalent-circuit model schematic diagram of combining inverter, as shown in Figure 4.

According to the Mathematical Modeling of the zero-sequence current of three-phase grid-connected inverter in parallel, i.e. formula (8), the rate of change that can infer the zero-sequence current between two inverters is determined jointly by the difference of the residual voltage of the difference of the zero sequence duty ratio of two inverters and ac filter inductance.Combining inverter parallel system circulation inhibition method under the inductance unbalance condition, because the circulation equal and opposite in direction, the direction that flow through between any two inverters are opposite, only need the circulation of one of them inverter is suppressed, can realize the circulation between any two inverters is suppressed, and then reach the purpose of inhibition system circulation.

For inverter parallel system because zero axle is a undamped loop of only containing inductance, in real system, below three kinds of situations more often occur:

The given electric current of two inverters is unequal;

The inductance difference of two inverters (each inverter three pole reactor balance);

The three pole reactor of each inverter changes or imbalance causes its inductance residual voltage there are differences.

Any one condition all may cause the zero sequence duty ratio of two inverters there are differences, even its difference is less, also can make the bigger zero-sequence current of formation between the inverter.Therefore, when inverter is in parallel, need consideration to the inhibition of zero-sequence component.Simultaneously as can be seen, in the circulation model of inverter parallel-connection structure, the difference of the inductance residual voltage of any two inverters can be to the interference of zero-axis current ring, and disturb general being difficult for to get rid of, but the circulation between inverter is directly related with the difference of the zero sequence duty ratio of two inverters, and the zero sequence duty ratio is a controlled variable, therefore can realize inverter by the difference of in each control cycle, regulating the zero sequence duty ratio of two inverters between the inhibition of circulation.

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 _i(i=0,7) come synthetic control vector, vector V _iThe definition of (i=0～7), as shown in Figure 5.Be example with two inverter parallel-connection structures, the duty ratio of establishing 2 two non-zero vectors of second inverter is respectively d ₁₂, d ₂₂, the zero vector duty ratio is d ₀₂, then:

d ₀₂=1-d ₁₂-d ₂₂ (9)

Different modulator approaches can obtain the allocation result of zero vector, thereby can change duty ratio and the zero sequence duty ratio of each each phase of shunt chopper, but the difference of the duty ratio of two-phase can not change arbitrarily.So the control target of system, namely ac-side current and DC bus-bar voltage can not be affected.Distribution by the control zero vector just can be controlled zero sequence duty ratio d _zThereby, the control zero-sequence current.Be example with exemplary sector shown in Figure 5, in the cycle, establish zero vector V at a PWM ₇Action time be

Zero vector V ₀Action time be As shown in Figure 6, second inverter 2 is introduced zero vector correction value y ₂After the space vector distribution map in variable y ₂Satisfy:

$-\frac{d_{02}}{4}\&le;{\mathrm{<figure-callout\; id="2"\; label="y"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">y</figure-callout>}}_2\&le;\frac{d_{02}}{4}---\left(10\right)$

So zero vector V ₀, V ₇Action time can recently regulate by its duty, the span of both duty ratios is [0, d ₀₂], and both sums are d ₀₂At this moment,

$d_{\mathrm{<figure-callout\; id="2"\; label="z"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">z</figure-callout>}2}=\frac{(d_{a2}+{\mathrm{<figure-callout\; id="2"\; label="d\; b"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">d</figure-callout>}}_b+d_{c2})}{3}$

$=\frac{({\mathrm{<figure-callout\; id="12"\; label="d"\; filenames="HDA00003566709800042.png,HDA00003566709800044.png"\; state="\{\{state\}\}">d</figure-callout>}}_{12}+d_{22}+\frac{d_{02}}{2}-2y_2)+(d_{22}+\frac{d_{02}}{2}-2y_2)+(\frac{d_{02}}{2}-2y_2)}{3}---\left(11\right)$

$=\frac{({\mathrm{<figure-callout\; id="12"\; label="d"\; filenames="HDA00003566709800042.png,HDA00003566709800044.png"\; state="\{\{state\}\}">d</figure-callout>}}_{12}+2d_{22}+\frac{3}{2}{d}_{02}-6y_2)}{3}$

To first inverter 1, formula (11) is same to be set up.So the difference of the zero sequence duty ratio of two inverters is:

$\mathrm{\&Delta;}{d}_z=d_{z1}-{\mathrm{<figure-callout\; id="2"\; label="d\; z"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">d</figure-callout>}}_z=\frac{(d_{11}+2{\mathrm{<figure-callout\; id="21"\; label="d"\; filenames="HDA00003566709800031.png"\; state="\{\{state\}\}">d</figure-callout>}}_{21}+\frac{3}{2}{d}_{01}-6y_1)}{3}-\frac{({\mathrm{<figure-callout\; id="12"\; label="d"\; filenames="HDA00003566709800042.png,HDA00003566709800044.png"\; state="\{\{state\}\}">d</figure-callout>}}_{12}+2d_{22}+\frac{3}{2}{d}_{02}-6y_2)}{3}---\left(12\right)$

Since the circulation between any two inverters, equal and opposite in direction in two inverters, and direction is opposite, controlling of one of them inverter got final product, and then circulation that can control system, therefore, for two inverter parallel-connection structures, make the zero vector correction value y of first inverter 1 ₁=0.In addition, because d _0x=1-d _1x-d _2x(x=1,2), formula (12) can abbreviation be:

$\mathrm{\&Delta;}{d}_z=\frac{1}{6}(-d_{11}+{\mathrm{<figure-callout\; id="21"\; label="d"\; filenames="HDA00003566709800031.png"\; state="\{\{state\}\}">d</figure-callout>}}_{21}+d_{12}-d_{22}+12y_2)---\left(13\right)$

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

$\mathrm{\&Delta;}{d}_z=\frac{1}{6}(\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="12"\; label="d"\; filenames="HDA00003566709800042.png,HDA00003566709800044.png"\; state="\{\{state\}\}">d</figure-callout>}}_{12}+12y_2)---\left(14\right)$

For two inverter parallel systems, ignore the difference of each inverter inductance residual voltage, when the given electric current of two inverters equated, the voltage given value of current regulator output was equal substantially, so d ₁₁=d ₁₂, d ₂₁=d ₂₂, at this moment, Δ d ₁₂=0, so

Δd _z=2y ₂ (15)

Therefore, the Mathematical Modeling of zero-sequence current under synchronous rotating frame, namely formula (8) can turn to:

$({\mathrm{<figure-callout\; id="1"\; label="L\; m"\; filenames="HDA00003566709800031.png,HDA00003566709800043.png"\; state="\{\{state\}\}">L</figure-callout>}}_m+L_{m2})\frac{\mathrm{<figure-callout\; id="2"\; label="d\; i\; z"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">d</figure-callout>}{i}_z{2}_{}}{\mathrm{dt}}=2{\mathrm{<figure-callout\; id="2"\; label="y"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">y</figure-callout>}}_2\&CenterDot;u_{\mathrm{dc}}---\left(16\right)$

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

s(L _m1+L _m2)I _z2=2U _dcY ₂ (17)

Y in the following formula ₂, I _Z2Be respectively variable y ₂, i _Z2Laplace transformation.

As can be seen from the above equation, zero axle of each inverter is full decoupled with d axle and q axle, and zero axle is a first-order system, therefore, it is very high that the bandwidth of zero-sequence current ring can design, and can adopt pi regulator as the controller of zero-sequence current, and 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, 2 zero vectors:

y ₂=K _{p_z}·(i _{z2_ref}-i _z2)+K _{i_z}∫(i _{z2_ref}-i _z2)dt (18)

The control block diagram of corresponding zero-sequence current ring as shown in Figure 7.

To there being circulation, the PI controller can play regulating action, but this control cycle is about to the circulation of generation, PI control can't in time suppress, dynamic response is slower, therefore only equate and two inverter inductance residual voltages when identical at the given electric current of each inverter in parallel, can obtain to control preferably effect, when the inductance difference (each inverter three pole reactor balance) of or each inverter unequal when the given electric current of two inverters or the inductance zero sequence that each inverter three pole reactor imbalance causes two inverters were unequal, its circulation control effect was relatively poor.

Ignore the poor of two inverter inductance residual voltages, consider that the given electric current of two inverters is unequal, the unequal situation of filter inductance can get according to formula (13):

$({\mathrm{<figure-callout\; id="1"\; label="L\; m"\; filenames="HDA00003566709800031.png,HDA00003566709800043.png"\; state="\{\{state\}\}">L</figure-callout>}}_m+L_{m2})\frac{\mathrm{<figure-callout\; id="2"\; label="d\; i\; z"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">d</figure-callout>}{i}_z{2}_{}}{\mathrm{dt}}=\frac{1}{6}(\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="12"\; label="d"\; filenames="HDA00003566709800042.png,HDA00003566709800044.png"\; state="\{\{state\}\}">d</figure-callout>}}_{12}+12y_2)\&CenterDot;u_{\mathrm{dc}}+u_{\mathrm{Lz}12}---\left(19\right)$

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

$s({\mathrm{<figure-callout\; id="1"\; label="L\; m"\; filenames="HDA00003566709800031.png,HDA00003566709800043.png"\; state="\{\{state\}\}">L</figure-callout>}}_m+L_{m2}){\mathrm{<figure-callout\; id="2"\; label="I\; z"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">I</figure-callout>}}_z=2{\mathrm{<figure-callout\; id="2"\; label="U\; dc\; Y"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">U</figure-callout>}}_{\mathrm{dc}}{Y}_{}{}_2+\frac{\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="12"\; label="D"\; filenames="HDA00003566709800042.png,HDA00003566709800044.png"\; state="\{\{state\}\}">D</figure-callout>}}_{12}}{6}{U}_{\mathrm{dc}}---\left(20\right)$

When unequal the or filter inductance of the given electric current of each inverter was unequal, all there was coupling in its zero axle with d axle and q axle, and the coupling amount can produce the control of zero axle and disturb, and for eliminating the influence of coupling amount, 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:

${\mathrm{<figure-callout\; id="2"\; label="y"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">y</figure-callout>}}_2=K_{p\_z}\&CenterDot;(i_{\mathrm{<figure-callout\; id="2"\; label="z"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">z</figure-callout>}2\_\mathrm{ref}}-i_{z2})+K_{i\_z}\&Integral;(i_{\mathrm{<figure-callout\; id="2"\; label="z"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">z</figure-callout>}2\_\mathrm{ref}}-i_{z2})\mathrm{dt}-\frac{\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="12"\; label="d"\; filenames="HDA00003566709800042.png,HDA00003566709800044.png"\; state="\{\{state\}\}">d</figure-callout>}}_{12}}{12}---\left(21\right)$

Obtain corresponding zero-sequence current ring control block diagram, as shown in Figure 8.

When the equal balance of three pole reactor of two inverters, though the given electric current of two inverters do not wait or its filter inductance not simultaneously, adopt this method also can obtain good control effect.Yet, when the three pole reactor of two inverters changes or be uneven, because can producing power frequency to zero axle, the imbalance of inductance disturbs, even adopt this method control also can't eliminate the influence that power frequency is disturbed, the control effect of circulation is relatively poor.

Consider the uneven situation of each inverter three pole reactor, according to formula (13), in conjunction with the zero sequence circulation model of the shunt chopper under the synchronous rotating frame, namely formula (4) can get:

$({\mathrm{<figure-callout\; id="1"\; label="L\; m"\; filenames="HDA00003566709800031.png,HDA00003566709800043.png"\; state="\{\{state\}\}">L</figure-callout>}}_m+L_{m2})\frac{{\mathrm{di}}_{\mathrm{<figure-callout\; id="2"\; label="z"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">z</figure-callout>}2}}{\mathrm{dt}}=\frac{1}{6}(\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="12"\; label="d"\; filenames="HDA00003566709800042.png,HDA00003566709800044.png"\; state="\{\{state\}\}">d</figure-callout>}}_{12}+12y_2)\&CenterDot;u_{\mathrm{dc}}+u_{\mathrm{Lz}12}---\left(22\right)$

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

$s({\mathrm{<figure-callout\; id="1"\; label="L\; m"\; filenames="HDA00003566709800031.png,HDA00003566709800043.png"\; state="\{\{state\}\}">L</figure-callout>}}_m+L_{m2}){\mathrm{<figure-callout\; id="2"\; label="I\; z"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">I</figure-callout>}}_z=2{\mathrm{<figure-callout\; id="2"\; label="U\; dc\; Y"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">U</figure-callout>}}_{\mathrm{dc}}{Y}_{}{}_2+\frac{\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="12"\; label="D"\; filenames="HDA00003566709800042.png,HDA00003566709800044.png"\; state="\{\{state\}\}">D</figure-callout>}}_{12}}{6}{U}_{\mathrm{dc}}+U_{\mathrm{Lz}12}---\left(23\right)$

Δ D in the following formula ₁₂, U _Lz12Be respectively variable Δ d ₁₂, u _Lz12Laplace transformation.

As seen, except zero vector correction value y ₂The influence of each inverter d axle and the output of q shaft current controller, the circulation of parallel system also is subjected to the influence of the difference of two inverter inductance residual voltages, specifically, the missionary society of two inverter inductance residual voltages produces power frequency to the zero-axis current ring and disturbs, make circulation contain certain power frequency composition, reduce the efficient of system.Disturb in order to eliminate power frequency, introduce the poor of two inverter inductance residual voltages, i.e. u at the basic following formula (21) of preceding a kind of control method _Lz12Decoupling zero control, can obtain the correction value y of zero vector like this ₂:

${\mathrm{<figure-callout\; id="2"\; label="y"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">y</figure-callout>}}_2=K_{p\_z}\&CenterDot;(i_{\mathrm{<figure-callout\; id="2"\; label="z"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">z</figure-callout>}2\_\mathrm{ref}}-i_{z2})+K_{i\_z}\&Integral;(i_{\mathrm{<figure-callout\; id="2"\; label="z"\; filenames="HDA00003566709800031.png,HDA00003566709800042.png"\; state="\{\{state\}\}">z</figure-callout>}2\_\mathrm{ref}}-i_{z2})\mathrm{dt}-\frac{\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="12"\; label="d"\; filenames="HDA00003566709800042.png,HDA00003566709800044.png"\; state="\{\{state\}\}">d</figure-callout>}}_{12}}{12}-\frac{{\mathrm{<figure-callout\; id="12"\; label="u\; Lz"\; filenames="HDA00003566709800042.png,HDA00003566709800044.png"\; state="\{\{state\}\}">u</figure-callout>}}_{\mathrm{Lz}}}{2u_{\mathrm{dc}}}---\left(24\right)$

Obtain the control block diagram of zero-sequence current ring, as shown in Figure 9, like this, interference volume is cancelled out each other with the feedforward component, and after the influence of eliminating interference volume, the control block diagram of parallel system zero-sequence current just can be simplified, as shown in Figure 7.

Obtain thus two inverter parallel-connection structures whole system the control block diagram as shown in Figure 2, for any two inverters, because the circulation equal and opposite in direction, the direction that flow through are opposite, only need the circulation of one of them inverter is controlled, and can control the circulation between two inverters.First inverter 1 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 2 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 2 _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 the difference of non-zero vector duty cycle among two inverter SVPWM and inductance residual voltage, the expression formula of zero-sequence current controller is shown in formula (24); Utilize zero-sequence current controller output y at last ₂Distribution to zero vector among the inverter 2SVPWM is regulated in real time, and the distribution of zero vector as shown in Figure 6.

This method also can be used for the individual inverter parallel-connection structure of N (N 〉=3).For the individual inverter parallel-connection structure of N (N 〉=3), wherein introduce the decoupling zero of inductance residual voltage at the circulation controller of any two inverters and control, can get rid of the inductance residual voltage to the interference of zero-axis current ring, obtain better circulation control effect.

Claims (6)

1. combining inverter parallel system circulation inhibition method under the inductance unbalance condition, combining inverter in the described combining inverter parallel system is for being total to dc bus, exchanging the directly structure of parallel connection of side, described parallel system adopts the control of PI method, circulation inhibition method at above-mentioned combining inverter parallel system, it is characterized in that, this method is controlled the circulation of an inverter of combining inverter in two inverter parallel systems, specifically may further comprise the steps:

Step 1: to the zero-sequence current i of second inverter (2) _Z2Sample, execution in step two then;

Step 2: utilize zero-sequence current PI controller to the zero-sequence current i of second inverter (2) _Z2Zero-sequence current set-point i with second inverter (2) _{Z2_ref}It is poor to do, and with the input signal of this difference as zero-sequence current PI controller, utilizes the PI algorithm of zero-sequence current PI controller that this input signal is regulated, and obtains the PI regulated value, then while execution in step three and step 4;

Step 3: with the difference DELTA d of the non-zero vector duty cycle of the space vector pulse width modulation of first inverter (1) and second inverter (2) ₁₂Divided by 12, obtain the regulated quantity of non-zero vector, execution in step five then;

Step 4: with the difference u of the inductance residual voltage of first inverter (1) and second inverter (2) _Lz12DC bus-bar voltage u divided by 2 times _Dc, the regulated quantity of acquisition inductance residual voltage, execution in step five then;

Step 5: the regulated quantity of the regulated quantity of the non-zero vector that the PI regulated value that step 2 is obtained and step 3 obtain and the inductance residual voltage of step 4 acquisition is poor, the difference that obtains is by 3 outputs of zero sequence circulation controller, and this difference is as the correction value y of second inverter (2) zero vector ₂, execution in step six then;

Step 6: the correction value y that utilizes second inverter (2) zero vector of step 5 acquisition ₂Distribution to zero vector in the space vector pulse width modulation of second inverter (2) is regulated in real time, finishes the inhibition to circulation.

2. combining inverter parallel system circulation inhibition method under the inductance unbalance condition according to claim 1 is characterized in that, the zero-sequence current i of second inverter (2) in the step 1 _Z2For:

$i_{z2}=\frac{i_{a2}+i_{b2}+i_{c2}}{3}---\left(1\right)$

I in the formula _K2(k=a, b c) are respectively a phase, b phase, the c phase current of second inverter (2).

3. combining inverter parallel system circulation inhibition method under the inductance unbalance condition according to claim 1 is characterized in that the d of Δ described in the step 3 ₁₂For:

Δd ₁₂=(d ₂₁-d ₁₁)-(d ₂₂-d ₁₂) （2）

D in the formula 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 (2), d ₂₂It is the duty ratio of second non-zero vector of second inverter (2).

4. combining inverter parallel system circulation inhibition method under the inductance unbalance condition according to claim 1 is characterized in that u described in the step 4 _Lz12For:

$u_{L_{z12}}=u_{L_{z1}}-u_{L_{z2}}$

$=\frac{\mathrm{\&omega;}{i}_{d2}(L_{a2}\sin \mathrm{\&omega;t}+L_{b2}\sin (\mathrm{\&omega;t}-\frac{2}{3}\mathrm{\&pi;})+L_{c2}\sin (\mathrm{\&omega;t}+\frac{2}{3}\mathrm{\&pi;}))}{3}$

$-\frac{\mathrm{\&omega;}{i}_{d1}(L_{a1}\sin \mathrm{\&omega;t}+L_{b1}\sin (\mathrm{\&omega;t}-\frac{2}{3}\mathrm{\&pi;})+L_{c1}\sin (\mathrm{\&omega;t}+\frac{2}{3}\mathrm{\&pi;}))}{3}---\left(3\right)$

$+\frac{\mathrm{\&omega;}{i}_{q2}(L_{a2}\cos \mathrm{\&omega;t}+L_{b2}\cos (\mathrm{\&omega;t}-\frac{2}{3}\mathrm{\&pi;})+L_{c2}\cos (\mathrm{\&omega;t}+\frac{2}{3}\mathrm{\&pi;}))}{3}$

$-\frac{\mathrm{\&omega;}{i}_{q1}(L_{a1}\cos \mathrm{\&omega;t}+L_{b1}\cos (\mathrm{\&omega;t}-\frac{2}{3}\mathrm{\&pi;})+L_{c1}\cos (\mathrm{\&omega;t}+\frac{2}{3}\mathrm{\&pi;}))}{3}$

In the formula

Be the inductance residual voltage of first inverter (1),

Be the inductance residual voltage of second inverter (2), i _Dx(x=1,2) are respectively the d axle component of the three-phase current of first inverter (1) and second inverter (2), i _Qx(x=1,2) are respectively the q axle component of the three-phase current of first inverter (1) and second inverter (2), L _Kx(k=a, b, c; X=1,2) be respectively first inverter (1) and the second inverter a, b, c inductance value mutually, ω is the angular frequency of electrical network.

5. combining inverter parallel system circulation inhibition method under the inductance unbalance condition according to claim 1 is characterized in that, the correction value y of second inverter (2) zero vector in the step 5 ₂For:

$y_2=K_{p\_z}\&CenterDot;(i_{z2\_\mathrm{ref}}-i_{z2})+K_{i\_z}\&Integral;(i_{z2\_\mathrm{ref}}-i_{z2})\mathrm{dt}-\frac{\mathrm{\&Delta;}{d}_{12}}{12}-\frac{u_{\mathrm{Lz}12}}{2u_{\mathrm{dc}}}---\left(4\right)$

K in the formula _{P_z}Be the proportionality coefficient of zero-sequence current PI controller, K _{I_z}Integral coefficient for zero-sequence current PI controller.

6. combining inverter parallel system circulation inhibition method under the inductance unbalance condition according to claim 1 is characterized in that the concrete grammar of the described real-time adjusting of step 6 is:

On off state with the A phase of second inverter (2) in a control cycle T is controlled to be: from the initial time of one-period, continue low level earlier

Time, continue high level then

Time, continue low level at last

Time;

On off state with the B phase of second inverter (2) in same control cycle T is controlled to be: from the initial time of one-period, continue low level earlier

Time, continue high level then Time, continue low level at last

Time;

On off state with the C phase of second inverter (2) in same control cycle T is controlled to be: from the initial time of one-period, continue low level earlier

Time, continue high level then

Time, continue low level at last

Time;

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 (2), d ₂₂Be the duty ratio of second non-zero vector of second inverter (2), d ₀₂It is the duty ratio of second inverter (2) zero vector.

Images