CN104467499A - Five-level inverter neutral-point balancing control method and system - Google Patents

Abstract

The invention provides a five-level inverter neutral-point balancing control method and system. The method includes the steps of detecting V2Pos and V2Neg; obtaining a two-level neutral-point voltage balancing adjusting result Vout through a difference of the V2Pos and the V2Neg according to a preset adjusting algorithm; obtaining a first total positive and negative bus charging current difference I1 by overlapping a net-side three-phase bridge arm voltage command Vx and the positive zero sequence offset; obtaining a second total positive and negative bus charging current difference I2 by overlapping the Vx and the negative zero sequence offset; obtaining the positive zero sequence offset and the negative zero sequence offset in advance, wherein the Vx is the three-phase bridge arm voltage command before amendment is carried out; determining the overlapped offset V1 according to the Vout, the I1 and the I2, wherein the amended three-phase bridge arm voltage command Vx1 is equal to a sum of V0 and the Vx, and V0=V1*|Vout|; guaranteeing that a positive bus and a negative bus keep symmetrical during working so that risks caused by over-high voltage stress caused by the neutral-point voltage offset in the switching tube motion process can be eliminated.

Description

A kind of five-electrical level inverter neutral balance control method and system

Technical field

The present invention relates to technical field of photovoltaic power generation, particularly a kind of five-electrical level inverter neutral balance control method and system.

Background technology

In photovoltaic generating system, five-electrical level inverter has lower grid-connected current ripple and lower switching loss relative to two level and three-level inverter, therefore, there is lower grid-connected current total harmonic distortion (THD, Total Harmonic Distortion) and higher efficiency under same output filter size.

But, five-electrical level inverter and three-level inverter similar, there is the problem of mid-point potential offset equally, cause the voltage stress of switching tube asymmetric, thus make some switching tube in switching process, bear too high voltage, even may cause demolition.Therefore, in order to ensure the safety of switching tube, need to control five-electrical level inverter neutral balance.

See Fig. 1, this figure is photovoltaic generating system schematic diagram of the prior art.

In photovoltaic generating system, comprise PV array 100, Boost 200, inverter 300, output filter 400 and transformer 500.

As can be seen from Figure 1, compare three-level inverter in five-electrical level inverter and add one group of DC bus more: the positive and negative inlet highway of PV array.Therefore, for five-electrical level inverter, need the busbar voltage of balance to have two groups: total positive and negative DC bus voltage to neutral V2Pos and V2Neg; The positive and negative inlet highway voltage to neutral of PV array V1Pos and V1Neg.

Net side and the on off state of Boost side and electric current alignment current potential all have impact, and the combination of five-electrical level inverter breaker in middle is than many in three level, and therefore, the neutral balance control method of three-level inverter is not also suitable in five-electrical level inverter.

Therefore, those skilled in the art need to provide a kind of five-electrical level inverter neutral balance control method and system, can balance the mid-point voltage of five-electrical level inverter, the fail safe of protection whole system.

Summary of the invention

The technical problem to be solved in the present invention is to provide a kind of five-electrical level inverter neutral balance control method and system, can balance the mid-point voltage of five-electrical level inverter, the fail safe of protection whole system.

The embodiment of the present invention provides a kind of five-electrical level inverter neutral balance control method, and be applied in five level photovoltaic inverting systems, this system comprises: PV array, the first Boost circuit, the second Boost circuit, five-electrical level inverter, first electric capacity, the second electric capacity, the 3rd electric capacity and the 4th electric capacity, the positive output end of described PV array connects+1 level input of described five-electrical level inverter, the negative output terminal of described PV array connects-1 level input of described five-electrical level inverter, the two ends of described first electric capacity connect the positive output end of described PV array and 0 level input of five-electrical level inverter respectively, and the two ends of described second electric capacity connect the negative output terminal of described PV array and 0 level input of five-electrical level inverter respectively, the input of described first Boost circuit connects the positive output end of described PV array, the output of described first Boost circuit connects+2 level input of five-electrical level inverter, the input of described second Boost circuit connects the negative output terminal of described PV array, the output of described second Boost circuit connects-2 level input of five-electrical level inverter, the two ends of described 3rd electric capacity connect the output of described first Boost circuit and described 0 level input respectively, the two ends of described 4th electric capacity connect the output of described second Boost circuit and described 0 level input respectively, the method comprises:

Detect+2 level voltage V2Pos on described 3rd electric capacity and-2 level voltage V2Neg on the 4th electric capacity;

Obtain two level neutral point voltage balances by the difference of described V2Pos and V2Neg through predetermined adjustment algorithm and regulate result Vout;

The net side three-phase brachium pontis voltage instruction Vx of described inverter is superposed respectively forward zero sequence side-play amount and obtain the first total positive and negative busbar charging current difference I1; The net side three-phase brachium pontis voltage instruction of described inverter is superposed respectively negative sense zero sequence side-play amount and obtain the second total positive and negative busbar charging current difference I2; Described forward zero sequence side-play amount and negative sense zero sequence side-play amount obtain in advance; Vx is the three-phase brachium pontis voltage instruction before revising; X is a, b and c;

It should be noted that, described forward zero sequence side-play amount and negative sense zero sequence side-play amount obtain in advance and are specially: choose forward zero sequence side-play amount and negative sense zero sequence side-play amount according to the amplitude of Vx, the amplitude maximum of such as Vx is+1, minimum value is-1, if the amplitude of current Vx is 0.8, then forward zero sequence side-play amount just gets 0.2, the difference namely between 0.8 and maximum+1.

Determine the side-play amount V1 superposed according to the size of Vout, I1 and I2, revised three-phase brachium pontis voltage instruction Vx1 is: Vx1=V0+Vx, wherein V0=V1*|Vout|;

Judge Vout>0, and during I1>I2, described V1 chooses described forward migration amount;

Judge Vout>0, and during I1<I2, described V1 chooses described negative offset amount;

Judge Vout<0, and during I1>I2, described V1 chooses described negative offset amount;

Judge Vout<0, and during I1<I2, described V1 chooses described forward migration amount.

Preferably, when described inverter is operated in five level modes, described I1=Σ I _xPos1-Σ I _xNeg1, I2=Σ I _xPos2-Σ I _xNeg2; Wherein, x is a, b and c; I _xPos1, I _xPos2for the positive bus-bar electric current of three-phase, I _xNeg2, I _xNeg1for the negative busbar electric current of three-phase;

Vx and V1Pos is compared, as Vx>V1Pos, described I _xPos1, I _xPos2and I _xNeg2, I _xNeg1obtained by formula (1);

$\left\{\begin{array}{c}{I}_{\mathrm{xPos}}=-\frac{V_x-V_{1\mathrm{Pos}}}{V_{2\mathrm{Pos}}-V_{1\mathrm{Pos}}}{I}_x\\ I_{\mathrm{xNeg}}=0\end{array}\right.---\left(1\right);$

Wherein, I _xfor net side three-phase current;

As Vx<V1Pos, Vx and-V1Neg are compared, as Vx< (-V1Neg), described I _xPos1, I _xPos2and I _xNeg2, I _xNeg1obtained by formula (2);

$\left\{\begin{array}{c}{I}_{\mathrm{xPos}}=0\\ I_{\mathrm{xNeg}}=-\frac{V_x+V_{1\mathrm{Neg}}}{V_{2\mathrm{Neg}}-V_{1\mathrm{Neg}}}{I}_x\end{array}\right.---\left(2\right);$

As Vx<V1Pos, and time Vx> (-V1Neg), described I _xPos1, I _xPos2and I _xNeg2, I _xNeg1obtained by formula (3);

$\left\{\begin{array}{c}{I}_{\mathrm{xPos}}=0\\ I_{\mathrm{xNeg}}=0\end{array}\right.---\left(3\right).$

Preferably, when described inverter is operated in three level pattern, described I1=Σ I _xPos1-Σ I _xNeg1, I2=Σ I _xPos2-Σ I _xNeg2; Wherein, x is a, b and c; I _xPos1,i _xPos2for the positive bus-bar electric current of three-phase, I _xNeg2, I _xNeg1for the negative busbar electric current of three-phase;

Vx and 0 is compared, as Vx>0, described I _xPos1, I _xPos2and I _xNeg2, I _xNeg1obtained by formula (4);

$\left\{\begin{array}{c}{I}_{\mathrm{xPos}}=-\frac{V_x}{V_{1\mathrm{Pos}}}{I}_x\\ I_{\mathrm{xNeg}}=0\end{array}\right.---\left(4\right);$

Wherein, I _xfor net side three-phase current;

As Vx<0, described I _xPos1, I _xPos2and I _xNeg2, I _xNeg1obtained by formula (5);

$\left\{\begin{array}{c}{I}_{\mathrm{xPos}}=0\\ I_{\mathrm{xNeg}}=-\frac{V_x}{V_{1\mathrm{Neg}}}{I}_x\end{array}\right.---\left(5\right).$

Preferably, also comprise: detect+1 level voltage V1Pos on described first electric capacity ,-1 level voltage V1Neg on the second electric capacity; By described V1Pos and V1Neg, all compare with the PV array output voltage instruction of 1/2nd, control positive PV busbar voltage and negative PV busbar voltage respectively according to comparative result.

Preferably, described predetermined adjustment algorithm is following any one: proportion adjustment algorithm, proportional integral regulate algorithm and proportion integration differentiation to regulate algorithm.

The embodiment of the present invention also provides a kind of five-electrical level inverter neutral balance control appliance, and be applied in five level photovoltaic inverting systems, this system comprises: PV array, the first Boost circuit, the second Boost circuit, five-electrical level inverter, first electric capacity, the second electric capacity, the 3rd electric capacity and the 4th electric capacity, the positive output end of described PV array connects+1 level input of described five-electrical level inverter, the negative output terminal of described PV array connects-1 level input of described five-electrical level inverter, the two ends of described first electric capacity connect the positive output end of described PV array and 0 level input of five-electrical level inverter respectively, and the two ends of described second electric capacity connect the negative output terminal of described PV array and 0 level input of five-electrical level inverter respectively, the input of described first Boost circuit connects the positive output end of described PV array, the output of described first Boost circuit connects+2 level input of five-electrical level inverter, the input of described second Boost circuit connects the negative output terminal of described PV array, the output of described second Boost circuit connects-2 level input of five-electrical level inverter, the two ends of described 3rd electric capacity connect the output of described first Boost circuit and described 0 level input respectively, the two ends of described 4th electric capacity connect the output of described second Boost circuit and described 0 level input respectively, this equipment comprises: positive and negative two level detection module, positive and negative two level modulation modules and positive and negative two level neutral balance modules,

Described positive and negative two level detection module, for detecting+2 level voltage V2Pos on described 3rd electric capacity and-2 level voltage V2Neg on the 4th electric capacity;

Described positive and negative two level modulation modules, for obtaining two level neutral point voltage balances adjustment result Vout by the difference of described V2Pos and V2Neg through overregulating algorithm;

Described positive and negative two level neutral balance modules, obtain the first total positive and negative busbar charging current difference I1 for the net side three-phase brachium pontis voltage instruction Vx of described inverter being superposed respectively forward zero sequence side-play amount; The net side three-phase brachium pontis voltage instruction of described inverter is superposed respectively negative sense zero sequence side-play amount and obtain the second total positive and negative busbar charging current difference I2; Described forward zero sequence side-play amount and negative sense zero sequence side-play amount obtain in advance; Vx is the three-phase brachium pontis voltage instruction before revising; X is a, b and c; Determine the side-play amount V1 superposed according to the size of Vout, I1 and I2, revised three-phase brachium pontis voltage instruction Vx1 is: Vx1=V0+Vx, wherein V0=V1*|Vout|; Judge Vout>0, and during I1>I2, described V1 chooses described forward migration amount; Judge Vout>0, and during I1<I2, described V1 chooses described negative offset amount; Judge Vout<0, and during I1>I2, described V1 chooses described negative offset amount; Judge Vout<0, and during I1<I2, described V1 chooses described forward migration amount.

Preferably, described positive and negative two level neutral balance modules comprise: the first electric current obtains submodule;

When described inverter is operated in five level modes, described I1=Σ I _xPos1-Σ I _xNeg1, I2=Σ I _xPos2-Σ I _xNeg2; Wherein, x is a, b and c; I _xPos1, I _xPos2for the positive bus-bar electric current of three-phase, I _xNeg2, I _xNeg1for the negative busbar electric current of three-phase;

Described first electric current obtains submodule, for Vx and V1Pos is compared, as Vx>V1Pos, and described I _xPos1, I _xPos2and I _xNeg2, I _xNeg1obtained by formula (1);

$\left\{\begin{array}{c}{I}_{\mathrm{xPos}}=-\frac{V_x-V_{1\mathrm{Pos}}}{V_{2\mathrm{Pos}}-V_{1\mathrm{Pos}}}{I}_x\\ I_{\mathrm{xNeg}}=0\end{array}\right.---\left(1\right);$

Wherein, I _xfor net side three-phase current;

As Vx<V1Pos, Vx and-V1Neg are compared, as Vx< (-V1Neg), described I _xPos1, I _xPos2and I _xNeg2, I _xNeg1obtained by formula (2);

$\left\{\begin{array}{c}{I}_{\mathrm{xPos}}=0\\ I_{\mathrm{xNeg}}=-\frac{V_x+V_{1\mathrm{Neg}}}{V_{2\mathrm{Neg}}-V_{1\mathrm{Neg}}}{I}_x\end{array}\right.---\left(2\right);$

As Vx<V1Pos, and time Vx> (-V1Neg), described I _xPos1, I _xPos2and I _xNeg2, I _xNeg1obtained by formula (3);

$\left\{\begin{array}{c}{I}_{\mathrm{xPos}}=0\\ I_{\mathrm{xNeg}}=0\end{array}\right.---\left(3\right).$

Preferably, described positive and negative two level neutral balance modules comprise: the second electric current obtains submodule;

When described inverter is operated in three level pattern, described I1=Σ I _xPos1-Σ I _xNeg1, I2=Σ I _xPos2-Σ I _xNeg2; Wherein, x is a, b and c; I _xPos1, I _xPos2for the positive bus-bar electric current of three-phase, I _xNeg2, I _xNeg1for the negative busbar electric current of three-phase;

Described second electric current obtains submodule, for Vx and 0 is compared, as Vx>0, and described I _xPos1, I _xPos2and I _xNeg2, I _xNeg1obtained by formula (4);

$\left\{\begin{array}{c}{I}_{\mathrm{xPos}}=-\frac{V_x}{V_{1\mathrm{Pos}}}{I}_x\\ I_{\mathrm{xNeg}}=0\end{array}\right.---\left(4\right);$

Wherein, I _xfor net side three-phase current;

As Vx<0, described I _xPos1, I _xPos2and I _xNeg2, I _xNeg1obtained by formula (5);

$\left\{\begin{array}{c}{I}_{\mathrm{xPos}}=0\\ I_{\mathrm{xNeg}}=-\frac{V_x}{V_{1\mathrm{Neg}}}{I}_x\end{array}\right.---\left(5\right).$

Preferably, also comprise: a positive and negative level detection module and a positive and negative level modulation module;

A described positive and negative level detection module, for detecting+1 level voltage V1Pos on described first electric capacity ,-1 level voltage V1Neg on the second electric capacity;

A described positive and negative level modulation module, for by described V1Pos and V1Neg, all compare with the PV array output voltage instruction of 1/2nd, controls positive PV busbar voltage and negative PV busbar voltage respectively according to comparative result.

Preferably, described predetermined adjustment algorithm is following any one: proportion adjustment algorithm, proportional integral regulate algorithm and proportion integration differentiation to regulate algorithm.

Compared with prior art, the present invention has the following advantages:

The method that the present embodiment provides, by carrying out correction to balance two level mid-point voltages to net side three-phase brachium pontis voltage instruction, first the voltage on the 3rd electric capacity and the 4th electric capacity is detected respectively, obtain revising the amplitude of side-play amount according to these two voltage differences, then by superposing forward zero sequence side-play amount and negative sense zero sequence side-play amount judges to determine finally to superpose forward or negative sense zero sequence side-play amount on the three-phase brachium pontis voltage instruction of net side.By two level neutral point voltage balances can be regulated to the correction of net side three-phase brachium pontis voltage instruction, guarantee that positive and negative busbar operationally keeps symmetrical, thus eliminate the risk that in the switching tube course of action caused because of unbalance of neutral-point voltage, voltage stress is too high.

Accompanying drawing explanation

In order to be illustrated more clearly in the embodiment of the present invention or technical scheme of the prior art, be briefly described to the accompanying drawing used required in embodiment or description of the prior art below, apparently, accompanying drawing in the following describes is only some embodiments of the present invention, for those of ordinary skill in the art, under the prerequisite not paying creative work, other accompanying drawing can also be obtained according to these accompanying drawings.

Fig. 1 is five-electrical level inverter neutral balance control method embodiment one flow chart provided by the invention;

Fig. 2 is five level photovoltaic inverting system schematic diagrames provided by the invention;

Fig. 3 is five-electrical level inverter neutral balance control method embodiment two flow chart provided by the invention;

Fig. 4 is five-electrical level inverter neutral balance control appliance embodiment one schematic diagram provided by the invention;

Fig. 5 is five-electrical level inverter neutral balance control appliance embodiment two schematic diagram provided by the invention;

Fig. 6 is five-electrical level inverter neutral balance control appliance embodiment three schematic diagram provided by the invention.

Embodiment

Below in conjunction with the accompanying drawing in the embodiment of the present invention, be clearly and completely described the technical scheme in the embodiment of the present invention, obviously, described embodiment is only the present invention's part embodiment, instead of whole embodiments.Based on the embodiment in the present invention, those of ordinary skill in the art, not making the every other embodiment obtained under creative work prerequisite, belong to the scope of protection of the invention.

For enabling above-mentioned purpose of the present invention, feature and advantage become apparent more, are described in detail the specific embodiment of the present invention below in conjunction with accompanying drawing.

Embodiment of the method one:

See Fig. 1, this figure is five-electrical level inverter neutral balance control method embodiment one flow chart provided by the invention.

The five-electrical level inverter neutral balance control method that the present embodiment provides, be applied in five level photovoltaic inverting systems, this system schematic can be shown in Figure 2, and five-electrical level inverter is wherein three-phase five-level inverter.

This system comprises: PV array, the first Boost circuit, the second Boost circuit, five-electrical level inverter, first electric capacity C1Pos, the second electric capacity C1Neg, the 3rd electric capacity C2Pos and the 4th electric capacity C2Neg, the positive output end of described PV array connects+1 level input of described five-electrical level inverter, the negative output terminal of described PV array connects-1 level input of described five-electrical level inverter, the two ends of described first electric capacity C1Pos connect the positive output end of described PV array and 0 level input of five-electrical level inverter respectively, and the two ends of described second electric capacity C1Neg connect the negative output terminal of described PV array and 0 level input of five-electrical level inverter respectively, the input of described first Boost circuit connects the positive output end of described PV array, the output of described first Boost circuit connects+2 level input of five-electrical level inverter, the input of described second Boost circuit connects the negative output terminal of described PV array, the output of described second Boost circuit connects-2 level input of five-electrical level inverter, the two ends of described 3rd electric capacity C2Pos connect the output of described first Boost circuit and described 0 level input respectively, the two ends of described 4th electric capacity C2Neg connect the output of described second Boost circuit and described 0 level input respectively, the method comprises:

S201: detect+2 level voltage V2Pos on described 3rd electric capacity C2Pos and-2 level voltage V2Neg on the 4th electric capacity C2Neg;

Be understandable that, V2Pos and V2Neg is the voltage of the positive pole anticathode of electric capacity, be therefore all on the occasion of.If the neutral-point potential balance of two level, so ideally, V2Pos and V2Neg should be equal.

S202: obtain two level neutral point voltage balances by the difference of described V2Pos and V2Neg through predetermined modulation algorithm and regulate result Vout;

The difference of V2Pos and V2Neg can reflect the neutral balance problem of two level.

It should be noted that, predetermined adjustment algorithm can be any one in ratio P adjustment algorithm, proportion integral control algorithm and proportion integration differentiation PID adjustment algorithm.

S203: the net side three-phase brachium pontis voltage instruction Vx of described inverter is superposed respectively forward zero sequence side-play amount and obtain the first total positive and negative busbar charging current difference I1; The net side three-phase brachium pontis voltage instruction of described inverter is superposed respectively negative sense zero sequence side-play amount and obtain the second total positive and negative busbar charging current difference I2; Described forward zero sequence side-play amount and negative sense zero sequence side-play amount obtain in advance; Vx is the three-phase brachium pontis voltage instruction before revising; X is a, b and c;

Determine the side-play amount V1 superposed according to the size of Vout, I1 and I2, revised three-phase brachium pontis voltage instruction Vx1 is: Vx1=V0+Vx, wherein V0=V1*|Vout|;

Judge Vout>0, and during I1>I2, described V1 chooses described forward migration amount;

Judge Vout>0, and during I1<I2, described V1 chooses described negative offset amount;

Judge Vout<0, and during I1>I2, described V1 chooses described negative offset amount;

Judge Vout<0, and during I1<I2, described V1 chooses described forward migration amount.

The method that the present embodiment provides, by carrying out correction to balance two level mid-point voltages to net side three-phase brachium pontis voltage instruction, first the voltage on the 3rd electric capacity and the 4th electric capacity is detected respectively, obtain revising the amplitude of side-play amount according to these two voltage differences, then by superposing forward zero sequence side-play amount and negative sense zero sequence side-play amount judges finally to superpose forward or negative sense zero sequence side-play amount on the three-phase brachium pontis voltage instruction of net side.By two level neutral point voltage balances can be regulated to the correction of net side three-phase brachium pontis voltage instruction, guarantee that positive and negative busbar operationally keeps symmetrical, thus eliminate the risk that in the switching tube course of action caused because of unbalance of neutral-point voltage, voltage stress is too high.

Embodiment of the method two:

See Fig. 3, this figure is five-electrical level inverter neutral balance control method embodiment two flow chart provided by the invention.

It should be noted that, be carry out balancing the method controlled to positive and negative two level in five-electrical level inverter in embodiment of the method one, also introduce in the present embodiment and carry out balancing the method controlled to a positive and negative level.

In addition, refer to when inverter works in three level in the present embodiment and be operated in 0 level and positive and negative two level.

S301: detect+1 level voltage V1Pos on described first electric capacity ,-1 level voltage V1Neg on the second electric capacity;

S302: by described V1Pos and V1Neg, all compare with the PV array output voltage instruction of 1/2nd, control positive PV busbar voltage and negative PV busbar voltage respectively according to comparative result.

S303-S305 is identical with S101-S103 respectively, does not repeat them here.

In figure, net side inverter needs to switch to three level mode of operation by five level active patterns in certain special cases, i.e. switching tube S2Pos, S2Neg and S0 work output level V2Pos ,-V2Neg and 0.Introduce the difference for two level neutral point voltage balances when inverter is operated in five level modes and three level pattern below.

When described inverter is operated in five level modes, described I1=Σ I _xPos1-Σ I _xNeg1, I2=Σ I _xPos2-Σ I _xNeg2; Wherein, x is a, b and c; I _xPos1, I _xPos2for the positive bus-bar electric current of three-phase, I _xNeg2, I _xNeg1for the negative busbar electric current of three-phase;

What IxPos1 with IxPos2 characterized is the average discharge current of one-period Intranet side x relative positive bus-bar electric capacity C2Pos.Thus Σ I _xPos1with Σ I _xPos2what characterize is that net side three-phase is to the average discharge current sum of positive bus-bar.

The discharging current of the positive bus-bar electric capacity C2Pos that such as IaPos1 is produced by A phase after representing superposition forward migration amount.When A phase voltage directive is greater than V1Pos, the state that the switching tube S2Pos that so A phase exists connection V2Pos in a switch periods opens, the average discharge current IaPos1 of the corresponding C2Pos of A just can be obtained according to S2Pos service time and A phase current size, in like manner calculate B phase and C phase to the discharging current of C2Pos in one-period, be exactly total finally superpose C2Pos in one-period by the average discharge current netted side and produce; If A phase voltage directive VaCmd is less than V1Pos, then show that switching tube S2Pos can not open within this cycle, namely A phase can not cause C2Pos to discharge, and thus the C2Pos discharging current of its correspondence is 0.

In like manner, what negative busbar electric capacity IxNeg1 with IxNeg2 characterized is the average discharge current netting the relative C2Neg of side x, thus Σ I _xNeg1with Σ I _xNeg2what characterize is that net side three-phase is to the average discharge current sum of positive bus-bar.

What I1 and I2 represented is the average discharge current difference that positive bus-bar electric capacity C2Pos and negative busbar electric capacity C2Neg is produced by net side in a switch periods; (I _bstPos-I _bstNeg) the mean charging current difference that produced by Boost circuit in a switch periods for positive bus-bar electric capacity C2Pos and negative busbar electric capacity C2Neg; I _bstPosand I _bstNegbe respectively the electric current that the first Boost circuit and the second Boost circuit are input to positive and negative busbar; Thus the corresponding relation of two level mid-point voltage deviations and I1, I2 can be obtained by (7).In formula (7), y is 1 or 2.

${\mathrm{\&Delta;V}}_2=V_{2\mathrm{Pos}}-V_{2\mathrm{Neg}}=\frac{1}{C}\&Integral;(I_{\mathrm{bstPos}}-I_{\mathrm{bstNeg}})\mathrm{dt}-\frac{1}{C}\&Integral;I_y\mathrm{dt}---\left(7\right);$

Vx and V1Pos is compared, as Vx>V1Pos, described I _xPos1, I _xPos2and I _xNeg2, I _xNeg1obtained by formula (1);

$\left\{\begin{array}{c}{I}_{\mathrm{xPos}}=-\frac{V_x-V_{1\mathrm{Pos}}}{V_{2\mathrm{Pos}}-V_{1\mathrm{Pos}}}{I}_x\\ I_{\mathrm{xNeg}}=0\end{array}\right.---\left(1\right);$

Wherein, I _xfor net side three-phase current;

As Vx<V1Pos, Vx and-V1Neg are compared, as Vx< (-V1Neg), described I _xPos1, I _xPos2and I _xNeg2, I _xNeg1obtained by formula (2);

$\left\{\begin{array}{c}{I}_{\mathrm{xPos}}=0\\ I_{\mathrm{xNeg}}=-\frac{V_x+V_{1\mathrm{Neg}}}{V_{2\mathrm{Neg}}-V_{1\mathrm{Neg}}}{I}_x\end{array}\right.---\left(2\right);$

As Vx<V1Pos, and time Vx> (-V1Neg), described I _xPos1, I _xPos2and I _xNeg2, I _xNeg1obtained by formula (3);

$\left\{\begin{array}{c}{I}_{\mathrm{xPos}}=0\\ I_{\mathrm{xNeg}}=0\end{array}\right.---\left(3\right).$

When described inverter is operated in three level pattern, described I1=Σ I _xPos1-Σ I _xNeg1, I2=Σ I _xPos2-Σ I _xNeg2; Wherein, x is a, b and c; I _xPos1, I _xPos2for the positive bus-bar electric current of three-phase, I _xNeg2, I _xNeg1for the negative busbar electric current of three-phase;

Vx and 0 is compared, as Vx>0, described I _xPos1, I _xPos2and I _xNeg2, I _xNeg1obtained by formula (4);

$\left\{\begin{array}{c}{I}_{\mathrm{xPos}}=-\frac{V_x}{V_{1\mathrm{Pos}}}{I}_x\\ I_{\mathrm{xNeg}}=0\end{array}\right.---\left(4\right);$

Wherein, I _xfor net side three-phase current;

As Vx<0, described I _xPos1, I _xPos2and I _xNeg2, I _xNeg1obtained by formula (5);

$\left\{\begin{array}{c}{I}_{\mathrm{xPos}}=0\\ I_{\mathrm{xNeg}}=-\frac{V_x}{V_{1\mathrm{Neg}}}{I}_x\end{array}\right.---\left(5\right).$

Based on a kind of five-electrical level inverter neutral balance control method that above embodiment provides, the embodiment of the present invention additionally provides a kind of five-electrical level inverter neutral balance control appliance, is explained in detail below in conjunction with accompanying drawing.

Apparatus embodiments one:

See Fig. 4, this figure is five-electrical level inverter neutral balance control appliance embodiment one schematic diagram provided by the invention.

The five-electrical level inverter neutral balance control appliance that the present embodiment provides, be applied in five level photovoltaic inverting systems, system schematic specifically can see Fig. 2.This system comprises: PV array, the first Boost circuit, the second Boost circuit, five-electrical level inverter, first electric capacity, the second electric capacity, the 3rd electric capacity and the 4th electric capacity, the positive output end of described PV array connects+1 level input of described five-electrical level inverter, the negative output terminal of described PV array connects-1 level input of described five-electrical level inverter, the two ends of described first electric capacity connect the positive output end of described PV array and 0 level input of five-electrical level inverter respectively, and the two ends of described second electric capacity connect the negative output terminal of described PV array and 0 level input of five-electrical level inverter respectively, the input of described first Boost circuit connects the positive output end of described PV array, the output of described first Boost circuit connects+2 level input of five-electrical level inverter, the input of described second Boost circuit connects the negative output terminal of described PV array, the output of described second Boost circuit connects-2 level input of five-electrical level inverter, the two ends of described 3rd electric capacity connect the output of described first Boost circuit and described 0 level input respectively, the two ends of described 4th electric capacity connect the output of described second Boost circuit and described 0 level input respectively, this equipment comprises: positive and negative two level detection module 400, positive and negative two level modulation modules 500 and positive and negative two level neutral balance modules 600,

Described positive and negative two level detection module 400, for detecting+2 level voltage V2Pos on described 3rd electric capacity and-2 level voltage V2Neg on the 4th electric capacity;

Be understandable that, V2Pos and V2Neg is the voltage of the positive pole anticathode of electric capacity, be therefore all on the occasion of.If the neutral-point potential balance of two level, so ideally, V2Pos and V2Neg should be equal.

Described positive and negative two level modulation modules 500, regulate result Vout for obtaining two level neutral point voltage balances by the difference of described V2Pos and V2Neg through predetermined adjustment algorithm;

The difference of V2Pos and V2Neg can reflect the neutral balance problem of two level.

It should be noted that, predetermined adjustment algorithm can be any one in ratio P adjustment algorithm, proportion integral control algorithm and proportion integration differentiation PID adjustment algorithm.

Described positive and negative two level neutral balance modules 600, obtain the first total positive and negative busbar charging current difference I1 for the net side three-phase brachium pontis voltage instruction Vx of described inverter being superposed respectively forward zero sequence side-play amount; The net side three-phase brachium pontis voltage instruction of described inverter is superposed respectively negative sense zero sequence side-play amount and obtain the second total positive and negative busbar charging current difference I2; Described forward zero sequence side-play amount and negative sense zero sequence side-play amount obtain in advance; Vx is the three-phase brachium pontis voltage instruction before revising; X is a, b and c; Determine the side-play amount V1 superposed according to the size of Vout, I1 and I2, revised three-phase brachium pontis voltage instruction Vx1 is: Vx1=V0+Vx, wherein V0=V1*|Vout|; Judge Vout>0, and during I1>I2, described V1 chooses described forward migration amount; Judge Vout>0, and during I1<I2, described V1 chooses described negative offset amount; Judge Vout<0, and during I1>I2, described V1 chooses described negative offset amount; Judge Vout<0, and during I1<I2, described V1 chooses described forward migration amount.

What Vout>0 characterized is that C2Pos is greater than C2Neg, thus now should select the side-play amount that in C2Pos and C2Neg discharging current difference I1 and I2, higher value is corresponding.

The method that the present embodiment provides, by carrying out correction to balance two level mid-point voltages to net side three-phase brachium pontis voltage instruction, first the voltage on the 3rd electric capacity and the 4th electric capacity is detected respectively, obtain revising the amplitude of side-play amount according to these two voltage differences, then by superposing forward zero sequence side-play amount and negative sense zero sequence side-play amount judges finally to superpose forward or negative sense zero sequence side-play amount on the three-phase brachium pontis voltage instruction of net side.By two level neutral point voltage balances can be regulated to the correction of net side three-phase brachium pontis voltage instruction, guarantee that positive and negative busbar operationally keeps symmetrical, thus eliminate the risk that in the switching tube course of action caused because of unbalance of neutral-point voltage, voltage stress is too high.

Apparatus embodiments two:

See Fig. 5, this figure is five-electrical level inverter neutral balance control appliance embodiment two schematic diagram provided by the invention.

Refer to when inverter works in three level in the present embodiment and be operated in 0 level and positive and negative two level.

The five-electrical level inverter neutral balance control appliance that the present embodiment provides, described positive and negative two level neutral balance modules comprise: the first electric current obtains submodule 601;

When described inverter is operated in five level modes, described I1=Σ I _xPos1-Σ I _xNeg1, I2=Σ I _xPos2-Σ I _xNeg2; Wherein, x is a, b and c; I _xPos1, I _xPos2for the positive bus-bar electric current of three-phase, I _xNeg2, I _xNeg1for the negative busbar electric current of three-phase;

Described first electric current obtains submodule 601, for Vx and V1Pos is compared, as Vx>V1Pos, and described I _xPos1, I _xPos2and I _xNeg2, I _xNeg1obtained by formula (1);

$\left\{\begin{array}{c}{I}_{\mathrm{xPos}}=-\frac{V_x-V_{1\mathrm{Pos}}}{V_{2\mathrm{Pos}}-V_{1\mathrm{Pos}}}{I}_x\\ I_{\mathrm{xNeg}}=0\end{array}\right.---\left(1\right);$

Wherein, I _xfor net side three-phase current;

As Vx<V1Pos, Vx and-V1Neg are compared, as Vx< (-V1Neg), described I _xPos1, I _xPos2and I _xNeg2, I _xNeg1obtained by formula (2);

$\left\{\begin{array}{c}{I}_{\mathrm{xPos}}=0\\ I_{\mathrm{xNeg}}=-\frac{V_x+V_{1\mathrm{Neg}}}{V_{2\mathrm{Neg}}-V_{1\mathrm{Neg}}}{I}_x\end{array}\right.---\left(2\right);$

As Vx<V1Pos, and time Vx> (-V1Neg), described I _xPos1, I _xPos2and I _xNeg2, I _xNeg1obtained by formula (3);

$\left\{\begin{array}{c}{I}_{\mathrm{xPos}}=0\\ I_{\mathrm{xNeg}}=0\end{array}\right.---\left(3\right).$

Described positive and negative two level neutral balance modules comprise: the second electric current obtains submodule 602;

When described inverter is operated in three level pattern, described I1=Σ I _xPos1-Σ I _xNeg1, I2=Σ I _xPos2-Σ I _xNeg2; Wherein, x is a, b and c; I _xPos1, I _xPos2for the positive bus-bar electric current of three-phase, I _xNeg2, I _xNeg1for the negative busbar electric current of three-phase;

Described second electric current obtains submodule 602, for Vx and 0 is compared, as Vx>0, and described I _xPos1, I _xPos2and I _xNeg2, I _xNeg1obtained by formula (4);

$\left\{\begin{array}{c}{I}_{\mathrm{xPos}}=-\frac{V_x}{V_{1\mathrm{Pos}}}{I}_x\\ I_{\mathrm{xNeg}}=0\end{array}\right.---\left(4\right);$

Wherein, I _xfor net side three-phase current;

As Vx<0, described I _xPos1, I _xPos2and I _xNeg2, I _xNeg1obtained by formula (5);

$\left\{\begin{array}{c}{I}_{\mathrm{xPos}}=0\\ I_{\mathrm{xNeg}}=-\frac{V_x}{V_{1\mathrm{Neg}}}{I}_x\end{array}\right.---\left(5\right).$

Apparatus embodiments three:

See Fig. 6, this figure is apparatus embodiments three schematic diagram provided by the invention.

The present embodiment is introduced, and when inverter is operated in five level, balances a positive and negative level mid-point voltage.

When inverter is operated in five level, also comprise: a positive and negative level detection module 700 and a positive and negative level modulation module 800;

A described positive and negative level detection module 700, for detecting+1 level voltage V1Pos on described first electric capacity ,-1 level voltage V1Neg on the second electric capacity;

A described positive and negative level modulation module 800, for by described V1Pos and V1Neg, all compare with the PV array output voltage instruction of 1/2nd, controls positive PV busbar voltage and negative PV busbar voltage respectively according to comparative result.

The above is only preferred embodiment of the present invention, not does any pro forma restriction to the present invention.Although the present invention discloses as above with preferred embodiment, but and be not used to limit the present invention.Any those of ordinary skill in the art, do not departing under technical solution of the present invention ambit, the Method and Technology content of above-mentioned announcement all can be utilized to make many possible variations and modification to technical solution of the present invention, or be revised as the Equivalent embodiments of equivalent variations.Therefore, every content not departing from technical solution of the present invention, according to technical spirit of the present invention to any simple modification made for any of the above embodiments, equivalent variations and modification, all still belongs in the scope of technical solution of the present invention protection.

Claims (10)

1. a five-electrical level inverter neutral balance control method, is characterized in that, be applied in five level photovoltaic inverting systems, this system comprises: PV array, the first Boost circuit, the second Boost circuit, five-electrical level inverter, first electric capacity, the second electric capacity, the 3rd electric capacity and the 4th electric capacity, the positive output end of described PV array connects+1 level input of described five-electrical level inverter, the negative output terminal of described PV array connects-1 level input of described five-electrical level inverter, the two ends of described first electric capacity connect the positive output end of described PV array and 0 level input of five-electrical level inverter respectively, and the two ends of described second electric capacity connect the negative output terminal of described PV array and 0 level input of five-electrical level inverter respectively, the input of described first Boost circuit connects the positive output end of described PV array, the output of described first Boost circuit connects+2 level input of five-electrical level inverter, the input of described second Boost circuit connects the negative output terminal of described PV array, the output of described second Boost circuit connects-2 level input of five-electrical level inverter, the two ends of described 3rd electric capacity connect the output of described first Boost circuit and described 0 level input respectively, the two ends of described 4th electric capacity connect the output of described second Boost circuit and described 0 level input respectively, the method comprises:

Detect+2 level voltage V2Pos on described 3rd electric capacity and-2 level voltage V2Neg on the 4th electric capacity;

Obtain two level neutral point voltage balances by the difference of described V2Pos and V2Neg through predetermined adjustment algorithm and regulate result Vout;

The net side three-phase brachium pontis voltage instruction Vx of described inverter is superposed respectively forward zero sequence side-play amount and obtain the first total positive and negative busbar charging current difference I1; The net side three-phase brachium pontis voltage instruction of described inverter is superposed respectively negative sense zero sequence side-play amount and obtain the second total positive and negative busbar charging current difference I2; Described forward zero sequence side-play amount and negative sense zero sequence side-play amount obtain in advance; Vx is the three-phase brachium pontis voltage instruction before revising; X is a, b and c;

Determine the side-play amount V1 superposed according to the size of Vout, I1 and I2, revised three-phase brachium pontis voltage instruction Vx1 is: Vx1=V0+Vx, wherein V0=V1*|Vout|;

Judge Vout>0, and during I1>I2, described V1 chooses described forward migration amount;

Judge Vout>0, and during I1<I2, described V1 chooses described negative offset amount;

Judge Vout<0, and during I1>I2, described V1 chooses described negative offset amount;

Judge Vout<0, and during I1<I2, described V1 chooses described forward migration amount.

2. five-electrical level inverter neutral balance control method according to claim 1, is characterized in that, when described inverter is operated in five level modes, and described I1=Σ I _xPos1-Σ I _xNeg1, I2=Σ I _xPos2-Σ I _xNeg2; Wherein, x is a, b and c; I _xPos1, I _xPos2for the positive bus-bar electric current of three-phase, I _xNeg2, I _xNeg1for the negative busbar electric current of three-phase;

Vx and V1Pos is compared, as Vx>V1Pos, described I _xPos1, I _xPos2and I _xNeg2, I _xNeg1obtained by formula (1);

$\left\{\begin{array}{c}{I}_{\mathrm{xPos}}=-\frac{V_x-V_{1\mathrm{Pos}}}{V_{2\mathrm{Pos}}-V_{1\mathrm{Pos}}}{I}_x\\ I_{\mathrm{xNeg}}=0\end{array}\right.---\left(1\right);$

Wherein, I _xfor net side three-phase current;

As Vx<V1Pos, Vx and-V1Neg are compared, as Vx< (-V1Neg), described I _xPos1, I _xPos2and I _xNeg2, I _xNeg1obtained by formula (2);

$\left\{\begin{array}{c}{I}_{\mathrm{xPos}}=0\\ I_{\mathrm{xNeg}}=-\frac{V_x+V_{1\mathrm{Neg}}}{V_{2\mathrm{Neg}}-V_{1\mathrm{Neg}}}{I}_x\end{array}\right.---\left(2\right);$

As Vx<V1Pos, and time Vx> (-V1Neg), described I _xPos1, I _xPos2and I _xNeg2, I _xNeg1obtained by formula (3);

$\left\{\begin{array}{c}{I}_{\mathrm{xPos}}=0\\ I_{\mathrm{xNeg}}=0\end{array}\right.---\left(3\right).$

3. five-electrical level inverter neutral balance control method according to claim 1, is characterized in that, when described inverter is operated in three level pattern, and described I1=Σ I _xPos1-Σ I _xNeg1, I2=Σ I _xPos2-Σ I _xNeg2; Wherein, x is a, b and c; I _xPos1, I _xPos2for the positive bus-bar electric current of three-phase, I _xNeg2, I _xNeg1for the negative busbar electric current of three-phase;

Vx and 0 is compared, as Vx>0, described I _xPos1, I _xPos2and I _xNeg2, I _xNeg1obtained by formula (4);

$\left\{\begin{array}{c}{I}_{\mathrm{xPos}}=-\frac{V_x}{V_{1\mathrm{Pos}}}{I}_x\\ I_{\mathrm{xNeg}}=0\end{array}\right.---\left(4\right);$

Wherein, I _xfor net side three-phase current;

As Vx<0, described I _xPos1, I _xPos2and I _xNeg2, I _xNeg1obtained by formula (5);

$\left\{\begin{array}{c}{I}_{\mathrm{xPos}}=0\\ I_{\mathrm{xNeg}}=-\frac{V_x}{V_{1\mathrm{Neg}}}{I}_x\end{array}\right.---\left(5\right).$

4. five-electrical level inverter neutral balance control algolithm according to claim 2, is characterized in that, also comprise: detect+1 level voltage V1Pos on described first electric capacity ,-1 level voltage V1Neg on the second electric capacity; By described V1Pos and V1Neg, all compare with the PV array output voltage instruction of 1/2nd, control positive PV busbar voltage and negative PV busbar voltage respectively according to comparative result.

5. five-electrical level inverter neutral balance control algolithm according to claim 1, is characterized in that, described predetermined adjustment algorithm is following any one: proportion adjustment algorithm, proportional integral regulate algorithm and proportion integration differentiation to regulate algorithm.

6. a five-electrical level inverter neutral balance control appliance, is characterized in that, be applied in five level photovoltaic inverting systems, this system comprises: PV array, the first Boost circuit, the second Boost circuit, five-electrical level inverter, first electric capacity, the second electric capacity, the 3rd electric capacity and the 4th electric capacity, the positive output end of described PV array connects+1 level input of described five-electrical level inverter, the negative output terminal of described PV array connects-1 level input of described five-electrical level inverter, the two ends of described first electric capacity connect the positive output end of described PV array and 0 level input of five-electrical level inverter respectively, and the two ends of described second electric capacity connect the negative output terminal of described PV array and 0 level input of five-electrical level inverter respectively, the input of described first Boost circuit connects the positive output end of described PV array, the output of described first Boost circuit connects+2 level input of five-electrical level inverter, the input of described second Boost circuit connects the negative output terminal of described PV array, the output of described second Boost circuit connects-2 level input of five-electrical level inverter, the two ends of described 3rd electric capacity connect the output of described first Boost circuit and described 0 level input respectively, the two ends of described 4th electric capacity connect the output of described second Boost circuit and described 0 level input respectively, this equipment comprises: positive and negative two level detection module, positive and negative two level modulation modules and positive and negative two level neutral balance modules,

Described positive and negative two level detection module, for detecting+2 level voltage V2Pos on described 3rd electric capacity and-2 level voltage V2Neg on the 4th electric capacity;

Described positive and negative two level modulation modules, for obtaining two level neutral point voltage balances adjustment result Vout by the difference of described V2Pos and V2Neg through overregulating algorithm;

Described positive and negative two level neutral balance modules, obtain the first total positive and negative busbar charging current difference I1 for the net side three-phase brachium pontis voltage instruction Vx of described inverter being superposed respectively forward zero sequence side-play amount; The net side three-phase brachium pontis voltage instruction of described inverter is superposed respectively negative sense zero sequence side-play amount and obtain the second total positive and negative busbar charging current difference I2; Described forward zero sequence side-play amount and negative sense zero sequence side-play amount obtain in advance; Vx is the three-phase brachium pontis voltage instruction before revising; X is a, b and c; Determine the side-play amount V1 superposed according to the size of Vout, I1 and I2, revised three-phase brachium pontis voltage instruction Vx1 is: Vx1=V0+Vx, wherein V0=V1*|Vout|; Judge Vout>0, and during I1>I2, described V1 chooses described forward migration amount; Judge Vout>0, and during I1<I2, described V1 chooses described negative offset amount; Judge Vout<0, and during I1>I2, described V1 chooses described negative offset amount; Judge Vout<0, and during I1<I2, described V1 chooses described forward migration amount.

7. five-electrical level inverter neutral balance control appliance according to claim 6, is characterized in that, described positive and negative two level neutral balance modules comprise: the first electric current obtains submodule;

When described inverter is operated in five level modes, described I1=Σ I _xPos1-Σ I _xNeg1, I2=Σ I _xPos2-Σ I _xNeg2; Wherein, x is a, b and c; I _xPos1, I _xPos2for the positive bus-bar electric current of three-phase, I _xNeg2, I _xNeg1for the negative busbar electric current of three-phase;

Described first electric current obtains submodule, for Vx and V1Pos is compared, as Vx>V1Pos, and described I _xPos1, I _xPos2and I _xNeg2, I _xNeg1obtained by formula (1);

$\left\{\begin{array}{c}{I}_{\mathrm{xPos}}=-\frac{V_x-V_{1\mathrm{Pos}}}{V_{2\mathrm{Pos}}-V_{1\mathrm{Pos}}}{I}_x\\ I_{\mathrm{xNeg}}=0\end{array}\right.---\left(1\right);$

Wherein, I _xfor net side three-phase current;

As Vx<V1Pos, Vx and-V1Neg are compared, as Vx< (-V1Neg), described I _xPos1, I _xPos2and I _xNeg2, I _xNeg1obtained by formula (2);

$\left\{\begin{array}{c}{I}_{\mathrm{xPos}}=0\\ I_{\mathrm{xNeg}}=-\frac{V_x-V_{1\mathrm{Neg}}}{V_{2\mathrm{Neg}}-V_{1\mathrm{Neg}}}{I}_x\end{array}\right.---\left(2\right);$

As Vx<V1Pos, and time Vx> (-V1Neg), described I _xPos1, I _xPos2and I _xNeg2, I _xNeg1obtained by formula (3);

$\left\{\begin{array}{c}{I}_{\mathrm{xPos}}=0\\ I_{\mathrm{xNeg}}=0\end{array}\right.---\left(3\right).$

8. five-electrical level inverter neutral balance control appliance according to claim 6, is characterized in that, described positive and negative two level neutral balance modules comprise: the second electric current obtains submodule;

When described inverter is operated in three level pattern, described I1=Σ I _xPos1-Σ I _xNeg1, I2=Σ I _xPos2-Σ I _xNeg2; Wherein, x is a, b and c; I _xPos1, I _xPos2for the positive bus-bar electric current of three-phase, I _xNeg2, I _xNeg1for the negative busbar electric current of three-phase;

Described second electric current obtains submodule, for Vx and 0 is compared, as Vx>0, and described I _xPos1, I _xPos2and I _xNeg2, I _xNeg1obtained by formula (4);

$\left\{\begin{array}{c}{I}_{\mathrm{xPos}}=-\frac{V_x}{V_{1\mathrm{Pos}}}{I}_x\\ I_{\mathrm{xNeg}}=0\end{array}\right.---\left(4\right);$

Wherein, I _xfor net side three-phase current;

As Vx<0, described I _xPos1, I _xPos2and I _xNeg2, I _xNeg1obtained by formula (5);

$\left\{\begin{array}{c}{I}_{\mathrm{xPos}}=0\\ I_{\mathrm{xNeg}}=-\frac{V_x}{V_{1\mathrm{Neg}}}{I}_x\end{array}\right.---\left(5\right).$

9. five-electrical level inverter neutral balance control appliance according to claim 7, is characterized in that, also comprise: a positive and negative level detection module and a positive and negative level modulation module;

A described positive and negative level detection module, for detecting+1 level voltage V1Pos on described first electric capacity ,-1 level voltage V1Neg on the second electric capacity;

A described positive and negative level modulation module, for by described V1Pos and V1Neg, all compare with the PV array output voltage instruction of 1/2nd, controls positive PV busbar voltage and negative PV busbar voltage respectively according to comparative result.

10. five-electrical level inverter neutral balance control appliance according to claim 9, is characterized in that, described predetermined adjustment algorithm is following any one: proportion adjustment algorithm, proportional integral regulate algorithm and proportion integration differentiation to regulate algorithm.