CN103457502A - Novel five-level inverter seven-segment type SVPWM modulation method - Google Patents

Abstract

The invention discloses a novel five-level inverter seven-segment type SVPWM modulation method. The method mainly comprises the steps of sector distinguishing, sector rotating and normalizing, small triangular area distinguishing, vector function time calculating, seven-segment vector output signal control signal generating, seven-segment three-phase voltage space-vector outputting and dead zone controlling and decoding. The novel five-level inverter seven-segment type SVPWM modulation method has the advantages that a five-level inverter SVPWM algorithm is easy to understand, calculation is simplified greatly through the sector normalizing processing, and due to the fact that no trigonometric function calculation is contained in the whole achieving process of the algorithm, digitization is convenient to achieve. The algorithm is easy to achieve regardless of whether a DSP or an FPGA is adopted, the algorithm can be expanded to the SVPWM modulation of more level inverters easily, and the novel five-level inverter seven-segment type SVPWM modulation method has important practical value to an alternating current variable frequency system.

Description

A kind of novel five-electrical level inverter seven segmentation SVPWM modulator approaches

Technical field

The present invention relates to field of power electronics, relate in particular to a kind of five-electrical level inverter seven segmentation SVPWM modulator approaches.

Background technology

Multi-electrical level inverter is compared with traditional two-level inverter, has as flexibly as control mode, and harmonic wave of output voltage content is low, and inversion efficiency is high, is suitable for the advantages such as high-power output, has been subject to social extensive concern.In recent years, the diode clamping tri-level inverter is widely used in fields such as mesohigh, high-power frequency conversion speed governing and active power filterings.If but go for higher output voltage, larger power output, just need application can export more level numbers, the more much higher electrical level inverter of electric pressure.

The PWM pulse modulation technology of multi-electrical level inverter has several, this wherein Using dSPACE of SVPWM technology (SVPWM) be easy to Digital Implementation with it, the voltage utilization advantages of higher, become one of method be most widely used in the multiple PWM modulator approach of multi-electrical level inverter.At present, the research of SVPWM algorithm and application are main or for two level and three-level inverter circuit, and to five level and more the SVPWM method research of the multi-electrical level inverter of high level number is less.Along with the increase of level number, space vector becomes geometric progression to increase, thereby makes the SVPWM algorithm of multi-electrical level inverter become very complicated.

The basic principle of the SVPWM algorithm of multi-electrical level inverter is the same with the SVPWM algorithm of two-level inverter, and key is to need one to simplify and effective Digital Realization method.For the SVPWM algorithm of five level and above multi-electrical level inverter, domestic and international effective solution is less, and the concrete Digital Realization method of SVPWM algorithm is lacked to careful research.

Summary of the invention

For the shortcoming of prior art, the object of the present invention is to provide a kind of five-electrical level inverter SVPWM modulator approach that is easy to Digital Realization.

For solving the problems of the technologies described above, the technology used in the present invention method is: a kind of five-electrical level inverter seven segmentation SVPWM modulator approaches, it is characterized in that: described method comprises the steps:

A, utilize the reference voltage original value to judge its sector of living in, when reference voltage is not, while being positioned at the 1st sector, be rotated normalized, other sector all is classified as to the 1st sector;

B, utilize after the over-rotation normalized resulting new reference voltage coordinate figure to judge its little delta-shaped region of living in and utilize the weber equation of equilibrium to calculate each vector action time that corresponding little triangle is corresponding, weber equation of equilibrium as follows:

U _refT _S=U ₁T ₁+U ₂T ₂+U ₃T ₃

T ₁+T ₂+T ₃=T _S

C, three vectors that will calculate obtain seven segmentation three-phase output region voltage vector control signal T through processing action time _n;

D, according to reference voltage place sector N, little delta-shaped region n of living in and output three-phase voltage control signal vector T _nvalue table look-up output seven segmentation three-phase voltage vectors;

E, process decoding and Dead Time are set and are obtained 24 road pwm signals.

Further, utilize the following 12 little delta-shaped regions in rule judgement reference voltage place:

Rule one: U _{ref β}>=3U _β

Rule two: 3U _β>=U _{ref β}>=2U _β

Rule three: 2U _β>=U _{ref β}>=U _β

Rule four: U _{ref β}>=U _β

Rule five: $U_{\mathrm{ref\β}}\≥\sqrt{3}(U_{\mathrm{ref\α}}-U_{\mathrm{\α}})$

Rule six: $\sqrt{3}(U_{\mathrm{ref\α}}-U_{\mathrm{\α}})>U_{\mathrm{ref\β}}\≥\sqrt{3}(U_{\mathrm{ref\α}}-2U_{\mathrm{\α}})$

Rule seven: $\sqrt{3}(U_{\mathrm{ref\α}}-2U_{\mathrm{\α}})>U_{\mathrm{ref\β}}\≥\sqrt{3}(U_{\mathrm{ref\α}}-3U_{\mathrm{\α}})$

Rule eight: $U_{\mathrm{ref\&beta;}}<\sqrt{3}(U_{\mathrm{ref\&alpha;}}-3U_{\mathrm{\&alpha;}})$

Rule nine: $U_{\mathrm{ref\&beta;}}\&GreaterEqual;\sqrt{3}(3U_{\mathrm{\&alpha;}}-U_{\mathrm{ref\&alpha;}})$

Rule ten: $\sqrt{3}(3U_{\mathrm{\&alpha;}}-U_{\mathrm{ref\&alpha;}})>U_{\mathrm{ref\&beta;}}\&GreaterEqual;\sqrt{3}(2U_{\mathrm{\&alpha;}}-U_{\mathrm{ref\&alpha;}})$

Rule 11: $\sqrt{3}(2U_{\mathrm{\&alpha;}}-U_{\mathrm{ref\&alpha;}})>U_{\mathrm{ref\&beta;}}\&GreaterEqual;\sqrt{3}(U_{\mathrm{\&alpha;}}-U_{\mathrm{ref\&alpha;}})$

Rule 12: $U_{\mathrm{ref\&beta;}}<\sqrt{3}(U_{\mathrm{\&alpha;}}-U_{\mathrm{ref\&alpha;}})$

U in formula _{ref α}, U _{ref β}be respectively reference vector U _refprojection components on α, β axle,

,

, U _dcfor DC terminal voltage; By simple arithmetical operation, can judge the true and false of above-mentioned rule, in sector 1, each little delta-shaped region meets 3 in 12 rules, and when reference voltage is positioned at other sectors, only need be by coordinate be rotated to normalized, other 5 sectors completely are classified as to the 1st sector, equally can be according to this 12 rule judgement reference voltage position.

Further, two adjacent little delta-shaped regions adopt the method for reverse circulations to export seven segmentation three-phase voltage vectors to reduce switching frequency and to avoid vector occurring when little delta-shaped region switching and the sector switch and suddenly change.

Further, table look-up and obtain seven segmentation three-phase space voltage vectors, vector table is according to reference voltage place sector N(1～6), little delta-shaped region n(1～16) and vector deferent segment control signal T _nwhich group three-phase voltage vector (1～7) determines to export jointly.

The invention has the beneficial effects as follows: this five-electrical level inverter SVPWM algorithm easy to understand, by the sector normalization, greatly simplified calculating, and do not contained trigonometric function operation in the implementation procedure of whole algorithm, be convenient to Digital Realization.Be all easily to realize this algorithm with DSP or FPGA, and can expand at an easy rate in the SVPWM modulation of multi-electrical level inverter more and go.

The accompanying drawing explanation

Below in conjunction with accompanying drawing, the invention will be further described.

Fig. 1 is neutral point clamp H bridge five-electrical level inverter main circuit topology figure;

Fig. 2 is the space voltage vector distribution map of five-electrical level inverter the 1st sector;

Fig. 3 is seven segmentation vector output maps;

Fig. 4 is five-electrical level inverter SVPWM algorithm General Implementing figure;

Fig. 5 is that other sectors are classified as the 1st sector schematic diagram;

Fig. 6 be the sector judgment rule and with the mapping table of sector;

Fig. 7 is each little leg-of-mutton relation table in judgment rule and regional I:

Fig. 8 is each voltage vector of the 1st sector relation table of action time;

Embodiment

Further illustrate the present invention below in conjunction with accompanying drawing.

The present invention has avoided complicated trigonometric function operation, has simplified calculating, is easy to Digital Realization, and its principal character is as follows:

A, utilize 12 rules to judge reference voltage particular location in space voltage vector figure, 12 rules are as follows:

Rule one: U _{ref β}>=3U _β

Rule two: 3U _β>=U _{ref β}>=2U _β

Rule three: 2U _β>=U _{ref β}>=U _β

Rule four: U _{ref β}>=U _β

Rule five: $U_{\mathrm{ref\&beta;}}\&GreaterEqual;\sqrt{3}(U_{\mathrm{ref\&alpha;}}-U_{\mathrm{\&alpha;}})$

Rule six: $\sqrt{3}(U_{\mathrm{ref\&alpha;}}-U_{\mathrm{\&alpha;}})>U_{\mathrm{ref\&beta;}}\&GreaterEqual;\sqrt{3}(U_{\mathrm{ref\&alpha;}}-2U_{\mathrm{\&alpha;}})$

Rule seven: $\sqrt{3}(U_{\mathrm{ref\&alpha;}}-2U_{\mathrm{\&alpha;}})>U_{\mathrm{ref\&beta;}}\&GreaterEqual;\sqrt{3}(U_{\mathrm{ref\&alpha;}}-3U_{\mathrm{\&alpha;}})$

Rule eight: $U_{\mathrm{ref\&beta;}}<\sqrt{3}(U_{\mathrm{ref\&alpha;}}-3U_{\mathrm{\&alpha;}})$

Rule nine: $U_{\mathrm{ref\&beta;}}\&GreaterEqual;\sqrt{3}(3U_{\mathrm{\&alpha;}}-U_{\mathrm{ref\&alpha;}})$

Rule ten: $\sqrt{3}(3U_{\mathrm{\&alpha;}}-U_{\mathrm{ref\&alpha;}})>U_{\mathrm{ref\&beta;}}\&GreaterEqual;\sqrt{3}(2U_{\mathrm{\&alpha;}}-U_{\mathrm{ref\&alpha;}})$

Rule 11: $\sqrt{3}(2U_{\mathrm{\&alpha;}}-U_{\mathrm{ref\&alpha;}})>U_{\mathrm{ref\&beta;}}\&GreaterEqual;\sqrt{3}(U_{\mathrm{\&alpha;}}-U_{\mathrm{ref\&alpha;}})$

Rule 12: $U_{\mathrm{ref\&beta;}}<\sqrt{3}(U_{\mathrm{\&alpha;}}-U_{\mathrm{ref\&alpha;}})$

U in formula _{ref α}, U _{ref β}be respectively reference vector U _refprojection components on α, β axle,

,

, U _dcfor DC terminal voltage.By simple arithmetical operation, can judge the true and false of above-mentioned rule, in sector 1, each little delta-shaped region meets 3 in 12 rules, and when reference voltage is positioned at other sectors, only need be by coordinate be rotated to normalized, other 5 sectors completely are classified as to the 1st sector, equally can be according to this 12 rule judgement reference voltage position.

Seven segmentation vector sequences of operation of B, two adjacent little triangle reverse circulations

The present invention adopts seven segmentation vector sequences of operation, in order to reduce switching frequency, start vector all adopts that vector less than normal in little triangle, the change direction of two adjacent little delta-shaped region vectors is antipodal, can avoid like this occurring the vector sudden change in the process of sector switch.10,11 two little delta-shaped regions of take in Fig. 2 describe as example.The vector sequence of operation of supposing 10 zones is: 1-2-2,2-2-2,2-1-2,2-1-1,2-1-2,2-2-2,1-2-2, the vector sequence of operation in 11 zones is: 1-2-2,1-1-2,2-1-2,2-1-1,2-1-2,1-1-2,1-2-2, the former is first counterclockwise clockwise rear, and the latter is first rear counterclockwise clockwise.If the latter is also consistent with the former vector sequence of operation, its start vector is 2-1-1, has just increased like this 3 switch motions from 1-2-2 to 2-1-1.Adopt this kind seven segmentation vector sequences of operation, if each sector sampling number reach 3 times and more than, just can guarantee that each time little delta-shaped region switches to many and can produce a switch motion, and also can not produce vector suddenly change when sector switch.

The output of C, three-phase voltage vector

The three-phase voltage output vector is that the mode by searching the phase scale obtains, and sets up in advance three-phase space voltage vector seven segmentation output phase scales, and the phase scale is exported seven segmentation three-phase voltage vectors according to three-phase voltage vector output control signal.The three-phase voltage vector output control signal triangle wave that to be three vector action times by calculating be all Ts value with amplitude and cycle produces from 1 and changes to 7 staircase waveform, and the width means respective vectors of each ladder is in the action time (as Fig. 3) of seven segmentation vectors output correspondences section.

Five-electrical level inverter SVPWM algorithm General Implementing figure as shown in Figure 4.

A, sector judgement and sector normalizing

The division of sector is normally from the α axle, by counterclockwise space voltage vector figure being divided into to 1 ~ 6 totally 6 sectors.The judgement of sector determines by three rules, this three rule and with the corresponding relation of sector as shown in Figure 6.

As seen from Figure 6, can judge very like a cork sector, reference voltage place according to the value of reference voltage.Judge reference voltage U _ref0behind the sector, place, then carry out sector rotation normalizing, obtain new reference voltage level U _ref(as shown in Figure 5), can simplify calculating aspect the little delta-shaped region judgement of back and Time Calculation like this.No matter reference voltage is positioned at several sectors as seen from Figure 5, it meets all the time

U _refα=|U _ref|cosθ U _refβ=|U _ref|sinθ

By symmetry, a demand goes out when reference voltage in 2, transformation for mula during 3 sector gets final product.When reference voltage is positioned at 2 sector, be divided into U _{ref α 0}0 and U _{ref α 0}<0 two kind of situation.

U _{ref α 0}0 o'clock:

$\cos (\frac{\mathrm{\&pi;}}{3}+\mathrm{\&theta;})=\frac{-U_{\mathrm{ref\&alpha;}0}}{\left|U_{\mathrm{ref}}\right|}$ $\sin (\frac{\mathrm{\&pi;}}{3}+\mathrm{\&theta;})=\frac{-U_{\mathrm{ref\&beta;}0}}{\left|U_{\mathrm{ref}}\right|}$

Change and can obtain by above formula:

$\frac{1}{2}\cos \mathrm{\&theta;}-\frac{\sqrt{3}}{2}\sin \mathrm{\&theta;}=\frac{-U_{\mathrm{ref\&alpha;}0}}{\left|U_{\mathrm{ref}}\right|}$ $\frac{\sqrt{3}}{2}\cos \mathrm{\&theta;}+\frac{1}{2}\sin \mathrm{\&theta;}=\frac{-U_{\mathrm{ref\&beta;}0}}{\left|U_{\mathrm{ref}}\right|}$

U _{ref α 0}<0 o'clock:

$\cos (\frac{2\mathrm{\&pi;}}{3}-\mathrm{\&theta;})=\frac{-U_{\mathrm{ref\&alpha;}0}}{\left|U_{\mathrm{ref}}\right|}$ $\sin (\frac{2\mathrm{\&pi;}}{3}-\mathrm{\&theta;})=\frac{-U_{\mathrm{ref\&beta;}0}}{\left|U_{\mathrm{ref}}\right|}$

Also can try to achieve:

$\frac{1}{2}\cos \mathrm{\&theta;}-\frac{\sqrt{3}}{2}\sin \mathrm{\&theta;}=\frac{U_{\mathrm{ref\&alpha;}0}}{\left|U_{\mathrm{ref}}\right|}$ $\frac{\sqrt{3}}{2}\cos \mathrm{\&theta;}+\frac{1}{2}\sin \mathrm{\&theta;}=\frac{U_{\mathrm{ref\&beta;}0}}{\left|U_{\mathrm{ref}}\right|}$

So when reference voltage is positioned at sector 2, coming to the same thing in two kinds of situations, transformation for mula is

$U_{\mathrm{ref\&alpha;}}=\frac{U_{\mathrm{ref\&alpha;}0}+\sqrt{3}{U}_{\mathrm{ref\&beta;}0}}{2}$ $U_{\mathrm{ref\&beta;}}=\frac{-\sqrt{3}{U}_{\mathrm{ref\&alpha;}0}+U_{\mathrm{ref\&beta;}0}}{2}$

The transformation for mula that in like manner can try to achieve when reference voltage is positioned at 3 sector is

$U_{\mathrm{ref\&alpha;}}=\frac{-U_{\mathrm{ref\&alpha;}0}+\sqrt{3}{U}_{\mathrm{ref\&beta;}0}}{2}$ $U_{\mathrm{ref\&beta;}}=\frac{-\sqrt{3}{U}_{\mathrm{ref\&alpha;}0}+U_{\mathrm{ref\&beta;}0}}{2}$

Due to sector 1 and 4,2 and 5,3 and 6 sector symmetries, so, when reference voltage is positioned at 4,5, during 6 sector, as long as calculate the corresponding coordinate transforming value of its symmetrical sector, then negate is just passable.Finally by arranging, can obtain:

$U_{\mathrm{ref\&alpha;}}=U_{\mathrm{ref\&alpha;}0}\cos \frac{(N-1)\mathrm{\&pi;}}{3}+U_{\mathrm{ref\&beta;}0}\sin \frac{(N-1)\mathrm{\&pi;}}{3}$

$U_{\mathrm{ref\&beta;}}=-U_{\mathrm{ref\&alpha;}0}\sin \frac{(N-1)\mathrm{\&pi;}}{3}+U_{\mathrm{ref\&beta;}0}\cos \frac{(N-1)\mathrm{\&pi;}}{3}$

When reference voltage is not while being positioned at the 1st sector, carry out normalized by utilizing above-mentioned formula, calculate and can be positioned at the 1st sector and processed with it is used as in ensuing little delta-shaped region judgement and time, can greatly simplify calculating like this.In addition in above-mentioned transformation for mula, although contain the such trigonometric function of sin, cos, because angle is normal value, so be in fact not contain trigonometric function in fact in computing.

B, the judgement of little delta-shaped region

For five-electrical level inverter, in its space voltage vector figure, 16 little triangles are contained in each sector, and three-level inverter only has 4, thus the judgement of little delta-shaped region will than three level complexity many.The judgement that little delta-shaped region has been mentioned in front utilizes 12 rules to carry out, and the corresponding relation of this 12 rule and little delta-shaped region as shown in Figure 7.

As shown in Figure 7, in 12 rules 3 of each little delta-shaped region are unique to be determined, only need carry out simple calculations with reference to voltage and just can judge at an easy rate reference voltage and specifically be arranged in which little delta-shaped region.

C, each vector calculate action time

The resulting reference voltage of sampling each time must drop in some little delta-shaped regions, and each little leg-of-mutton three summit correspondence three different vectors, and reference voltage just can be synthetic by these three vectors.After according to reference voltage place sector N and little delta-shaped region n, determining output vector, next also to calculate the action time of each output vector, this time is corresponding the turn-on and turn-off time of switching device also.The Fig. 2 of take carrys out the synthetic of analysis space voltage vector as example.The voltage vector of supposing expectation drops in 10 little triangles, and according to the synthetic principle of contiguous three vectors, the voltage vector of expectation will be by vector U _g, U _kand U _lsynthetic, the weber balance principle synthetic by space voltage vector has

U _refT _S=U _GT _G+U _KT _K+U _LT _L

T _G+T _K+T _L=T _S

Can calculate U according to above formula _g, U _k, U _lbe respectively the action time of vector

$T_G=4T_S-\frac{4U_{\mathrm{ref\&alpha;}}}{U}{T}_S-\frac{4\sqrt{3}}{3}\frac{U_{\mathrm{ref\&beta;}}}{U}{T}_S$

$T_K=\frac{4U_{\mathrm{ref\&alpha;}}}{U}{T}_S-3T_S-\frac{4\sqrt{3}}{3}\frac{U_{\mathrm{ref\&beta;}}}{U}{T}_S$

$T_L=\frac{8\sqrt{3}}{3}\frac{U_{\mathrm{ref\&beta;}}}{U}{T}_S$

U=3U wherein _dc/ 2, when dropping on other little delta-shaped regions, reference voltage also can calculate the action time of each vector according to the weber equation of equilibrium, specifically as shown in Figure 8, T ₁, T ₂, T ₃mean respectively in each little delta-shaped region that by lexicographical order the action time of the vector of each from arriving first, (in table, m was constant value

/ 3).No matter which sector reference voltage is positioned at, and can calculate according to table 3 action time of corresponding each vector of sampling each time.

The output of d, three-phase voltage vector

The three-phase voltage vector is by the acquisition of tabling look-up, set up in advance seven segmentation three-phase space voltage vector output tables, two adjacent triangle vector outputs sequentially adopt the method for reverse circulation, start vector adopts in little triangle that minimum vector of numbering, and vector table is according to reference voltage place sector N(1 ~ 6), little delta-shaped region n(1 ~ 16) and vector deferent segment control signal T _nwhich group three-phase voltage vector (1 ~ 7) determines to export jointly.

Vector deferent segment control signal T _nby to T ₁, T ₂, T ₃carry out that certain computing draws, specifically by by T ₁, T ₂, T ₃the sawtooth signal that is all Ts with cycle and amplitude compares and show that amplitude is changed to 7 successively from 1, and width is followed successively by T ₁/ 3-T ₂/ 2-T ₃/ 2-T ₁/ 3-T ₃/ 2-T ₂/ 2-T ₁/ 3(sector number is odd number) or T ₁/ 3-T ₃/ 2-T ₂/ 2-T ₁/ 3-T ₂/ 2-T ₃/ 2-T ₁/ 3(sector number is even number) step signal (as shown in Figure 3).

After obtaining the three-phase voltage vector, then the computing and add that dead band is controlled and just can obtain 24 road pwm signals of being decoded.

The preferred embodiment that this invention has been described at this, comprise that the inventor is for implementing known optimal mode of the present invention.The change of preferred embodiment is apparent for those of ordinary skills after reading above-mentioned explanation.The inventor wishes the change that the those of ordinary skill rational Application is such, and the inventor thinks and clearly states different application at this and also can realize the present invention.Therefore, the present invention includes all modifications and the equivalents of the purport of quoting in the claim of enclosing, this allows in applicable law.In addition, any combination of all possible change of above-mentioned key element is also comprised by the present invention, unless pointed out in addition or obvious contradiction in context at this.

Claims (4)

1. five-electrical level inverter seven segmentation SVPWM modulator approaches, it is characterized in that: described method comprises the steps:

A, utilize the reference voltage original value to judge its sector of living in, when reference voltage is not, while being positioned at the 1st sector, be rotated normalized, other sectors all are classified as to the 1st sector;

B, utilize after the over-rotation normalized resulting new reference voltage coordinate figure to judge its little delta-shaped region of living in and utilize the weber equation of equilibrium to calculate each vector action time that corresponding little triangle is corresponding, weber equation of equilibrium as follows;

U _ref T _S= U ₁ T ₁+ U ₂ T ₂+ U ₃ T ₃

T ₁+T ₂+T ₃=T _S

C, three vectors that will calculate obtain seven segmentation three-phase output region voltage vector control signal T through processing action time _n;

D, according to reference voltage place sector N, little delta-shaped region n of living in and output three-phase voltage control signal vector T _nworthly go out output seven segmentation three-phase voltage vectors;

E, process decoding and Dead Time are set and are obtained 24 road pwm signals.

2. five-electrical level inverter seven segmentation SVPWM modulator approaches according to claim 1 is characterized in that: utilize the following 12 little delta-shaped regions in rules judgement reference voltage place:

Rule one:

Rule two:

Rule three:

Rule four:

Rule five:

Rule six:

Rule seven:

Rule eight:

Rule nine:

Rule ten:

Rule 11:

Rule 12:

In formula u _{ref α} , u _{ref β} be respectively reference vector u _ref α, βprojection components on axle,

,

, U _dcfor DC terminal voltage; By simple arithmetical operation, can judge the true and false of above-mentioned rule, in sector 1, each little delta-shaped region meets 3 in 12 rules, and when reference voltage is positioned at other sectors, only need be by coordinate be rotated to normalized, other 5 sectors completely are classified as to the 1st sector, equally can be according to this 12 rule judgement reference voltage position.

3. five-electrical level inverter seven segmentation SVPWM modulator approaches according to claim 1 is characterized in that: two adjacent little delta-shaped regions adopt the method for reverse circulations to export seven segmentation three-phase voltage vectors to reduce switching frequency and to avoid vector occurring when little delta-shaped region switching and the sector switch and suddenly change.

4. five-electrical level inverter seven segmentation SVPWM modulator approaches according to claim 1, it is characterized in that: table look-up and obtain seven segmentation three-phase space voltage vectors, vector table is according to reference voltage place sector N(1～6), little delta-shaped region n(1～16) and vector deferent segment control signal T _nwhich group three-phase voltage vector (1～7) determines to export jointly.

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