CN107302318B - A kind of phase shift space vector modulating method based on H bridge cascaded multilevel inverter - Google Patents

A kind of phase shift space vector modulating method based on H bridge cascaded multilevel inverter Download PDF

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CN107302318B
CN107302318B CN201710654230.3A CN201710654230A CN107302318B CN 107302318 B CN107302318 B CN 107302318B CN 201710654230 A CN201710654230 A CN 201710654230A CN 107302318 B CN107302318 B CN 107302318B
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CN107302318A (en
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王翠
朱能飞
甘江华
崔晓斌
徐键
张兴旺
曾瑄
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Nanchang Institute of Technology
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/483—Converters with outputs that each can have more than two voltages levels
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/483—Converters with outputs that each can have more than two voltages levels
    • H02M7/4835—Converters with outputs that each can have more than two voltages levels comprising two or more cells, each including a switchable capacitor, the capacitors having a nominal charge voltage which corresponds to a given fraction of the input voltage, and the capacitors being selectively connected in series to determine the instantaneous output voltage
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/0067—Converter structures employing plural converter units, other than for parallel operation of the units on a single load
    • H02M1/007—Plural converter units in cascade

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Inverter Devices (AREA)

Abstract

The invention discloses a kind of phase shift space vector modulating methods based on H bridge cascaded multilevel inverter, for space vector modulation algorithm with the increase of concatenation unit number, basic vector greatly increases, there are a large amount of Redundanter schalter state vectors, the selection of switch state vector and its action time calculate the problems such as extremely complex, the present invention is based on α '-β ' coordinate systems, the control of H bridge cascaded multilevel inverter is realized using phase shift Space Vector Modulation Strategy, the control that cascaded multilevel inverter is realized in phase shift appropriate is carried out with the space vector modulating method of two level, each H bridge inverter unit of cascaded multilevel inverter is divided into left half bridge arm and right half bridge arm, it is modulated using two level space vectors, it obtains left half bridge arm and controls signal, signal is controlled using 180 ° of the signal phase shift as right half bridge arm, grade and grade Between corresponding bridge arm control signal phase mutual deviation π/kn.This modulator approach is simple, easy to implement, and application scalability is good.

Description

Phase-shifting space vector modulation method based on H-bridge cascaded multilevel inverter
Technical Field
The invention belongs to the field of inverter modulation, and relates to a phase-shifting space vector modulation method based on an H-bridge cascaded multilevel inverter.
Background
Because of the limitation of the voltage and the capacity of power electronic devices, the conventional two-level inverter generally adopts a high-low-high mode to obtain high-voltage high-power conversion through voltage reduction and voltage increase of a transformer, or adopts a plurality of low-capacity inversion units to realize high-voltage high-power conversion through multiple windings of the transformer, and the two high-voltage high-power converters have low system efficiency, so that people hope to improve the system efficiency by using a direct high-voltage inversion technology. Therefore, a high-voltage high-power two-level inversion technology based on direct series and parallel connection of power electronic devices is researched, however, due to the characteristics of the power electronic devices, the requirements of the series and parallel connection of the power electronic devices on dynamic and static voltage sharing and current sharing are very high, the harmonic content of the output voltage of the two-level converter is high, the design of an output filter is complex, and the two-level converter is not suitable for practical application. For the above reasons, the cascaded multilevel inverter technology is widely applied to high-voltage high-power converters.
The modulation method of the cascade multilevel inverter is mainly divided into nearest level modulation, carrier laminated modulation, carrier phase shift modulation, space vector modulation and the like. Compared with a carrier modulation method, the space vector modulation method of the cascade multilevel inverter has the advantages of good harmonic wave characteristic, high voltage utilization rate, low switching loss, convenience for digital implementation and the like.
However, the number of basic vectors of the space vector modulation method is greatly increased along with the increase of the number n of the cascade units, and a plurality of redundant switch state vectors exist in the space vector modulation method corresponding to one basic vector, the selection of the switch state vectors and the calculation of the acting time of the switch state vectors are very complicated, and the switch state vectors have various switching paths, so that the space vector modulation method is difficult to realize.
Therefore, it is necessary to design a phase-shifting space vector modulation method for an H-bridge cascaded multi-level inverter.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a phase-shifting space vector modulation method based on an H-bridge cascaded multi-level inverter, and the phase-shifting space vector modulation method based on the H-bridge cascaded multi-level inverter is simple in modulation, easy to implement and good in application expansibility.
The technical solution of the invention is as follows:
a phase-shift space vector modulation method based on an H-bridge cascade multilevel inverter carries out vector modulation based on a reference vector track model modulated by a two-level space vector, wherein the reference vector track model modulated by the two-level space vector is a reference vector track model based on α '- β' coordinates;
the coordinate system obtained by rotating the α - β coordinate system adopted by the traditional space vector modulation technology by 45 degrees anticlockwise and compressing the axial proportion is the α '- β' coordinate system, and comprises the following components:
in the α '- β' coordinate system, there are:
α 'and β' respectively represent the abscissa and ordinate of a α '- β' coordinate system, a, b and c respectively represent the three-phase output level of one stage of the cascade multi-level inverter, a, b and c can take two levels of 0 and 1, 0 represents low level, and 1 represents high level;
the α '- β' coordinate system has 7 base vectors V0(0,0) or V7(0，0)、V1(1，-1)、V2(1，0)、V3(0，1)、V4(-1，1)、V5(-1，0)、V6(0，-1)，Vj(x) represents a base vector, wherein (x) represents coordinates of the base vector; 7 basic vectors having 1 zero vector V0Or V76 non-zero vectors V1、V2、V3、V4、V5And V6α '- β' 6 non-zero basic vectors in the coordinate system form a hexagon;
two adjacent non-zero vectors and a zero vector form a sector triangle, wherein V1、V2And V0/V7("/" means "or", the same applies hereinafter) form sectors I, V2、V3And V0/V7Form sectors II, V3、V4And V0/V7Form sectors III, V4、V5And V0/V7Form sectors IV, V5、V6And V0/V7Forming sectors V, V6、V1And V0/V7Forming a sector VI;
the reference vector trajectory model based on α '- β' coordinates is represented by the following formula:
in the formula, αr' and βr' denotes the reference voltage vector V in the α ' - β ' coordinate systems, respectivelyrThe reference vector track in the formula (3) is an ellipse, when the ellipse is internally tangent to a hexagon formed by 6 non-zero basic vectors, the m is 1, the utilization rate of the power supply voltage is maximum, and the radius of the ellipse is reduced along with the reduction of the modulation coefficient m, so that the utilization rate of the power supply voltage is reduced.
The H-bridge cascaded multilevel inverter comprises 3n H-bridge units, wherein n is the serial stage number of each phase of H-bridge;
A. b, C three phases, each phase has n H bridges connected in series (the H bridge is a single-phase inverter bridge composed of 4 power tubes and has an input side and an output side, the input side and the output side are respectively a DC side and an AC side), and the series connection means that the output sides (AC sides) of the n H bridges are connected in series; one end of the serial H bridge AC ends is connected with an A end, a B end or a C end (one end of the A phase N serial H bridge AC ends is connected with the A end, one end of the B phase N serial H bridge AC ends is connected with the B end, one end of the C phase N serial H bridge AC ends is connected with the C end), and the other end is connected with an N point (a zero point of an AC power grid, or a neutral point). (the input side of each H-bridge is connected with a DC power supply, and the power switches of the H-bridge are driven by PWM pulses)
Step A: judging the reference vector VrThe sector is as follows:
sampling the reference voltage vector according to the elliptic reference voltage vector track obtained by the formula 3, wherein the sampling frequency is frTo meet the requirement of synchronous sampling, the sampling frequency f is usuallyrIs integral multiple of the frequency f of the reference voltage, and the vector of the reference voltage obtained by sampling is Vr(αr′，βr') determining the sector to which the reference voltage vector belongs by judging the value of the reference voltage vector, wherein the specific judgment is as follows:
if αr′≥0&&βr′≤0&&(αr′+βr′)＞(1+floor(αr′)+floor(βr')) to the reference vector VrLocated in sector I;
if αr′≥0&&βr' > 0 or more, the reference vector VrLocated in sector II;
if αr′＜0&&βr′＞0&&(αr′+βr′)＞(1+floor(αr′)+floor(βr')) to the reference vector VrLocated in sector III;
if αr′＜0&&βr′＞0&&(αr′+βr′)≤(1+floor(αr′)+floor(βr')) to the reference vector VrLocated in sector IV;
if αr′≤0&&βr' < 0, then the reference vector VrLocated in sector V;
if αr′≥0&&βr′≤0&&(αr′+βr′)≤(1+floor(αr′)+floor(βr')) to the reference vector VrLocated in sector VI;
wherein,&&representing an AND operation, floor (α)r′)、floor(βr') respectively represent pairs αr′、βr' round down.
Further comprising the step B: calculating the base vector action time of the synthetic reference vector:
after the position of the sector where the reference vector is located is determined, synthesizing the reference vector by adopting the basic vectors corresponding to the three vertexes of the triangle of the sector, and calculating the action time of the basic vectors of the synthesized reference vector according to the volt-second balance principle;
the base vector action time of the synthetic reference vector of each sector is as follows:
sector I: t is t0＝Ts(1-αr′)，t1＝-Tsβr′，t2＝Ts(αr′+βr′)；
Sector II: t is t0＝Ts(1-αr′-βr′)，t2＝Tsαr′，t3＝Tsβr′
Sector III: t is t0＝Ts(1-βr′)，t3＝Ts(αr′+βr′)，t4＝-Tsαr′
Sector IV: t is t0＝Ts(1+αr′)，t4＝Tsβr′，t5＝-Ts(αr′+βr′)
Sector V: t is t0＝Ts(1+αr′+βr′)，t5＝-Tsαr′，t6＝-Tsβr′
Sector VI: t is t0＝Ts(1+βr′)，t6＝-Ts(αr′+βr′)，t1＝Tsαr′；
Wherein, t0、t1、t2、t3、t4、t5、t6Respectively represent a vector V0(V7)、V1、V2、V3、V4、V5、V6Time of action of (T)sDenotes the reference voltage sampling period, TS＝1/fr。
Further comprising the step C: determining a switching path and action time of each basic vector:
and allocating the action time and sequence of the zero vector, and determining a switching path by adopting a seven-segment modulation and modulation method according to the principle of minimum switching (namely, the switching between two basic vectors can only change the switching state of a certain phase every time).
Further comprising the step of D: generating three paths of PWM signals;
based on the basic vector action time of the synthetic reference vector calculated in the step B, generating three paths of PWM signals by a seven-segment modulation method, respectively controlling the left bridge arms of the H bridge inverter units of the first stage, respectively controlling the right bridge arms of the H bridge inverter units of the first stage by shifting the three paths of signals by 180 degrees, respectively controlling the control signal phase differences pi/kn of the corresponding bridge arms between the stages, wherein k represents the frequency modulation ratio, and k is equal to frAnd/f, the value of which is the ratio of the sampling frequency of the reference voltage signal to the frequency of the reference voltage signal.
Has the advantages that:
aiming at the H-bridge cascaded multi-level inverter, the invention realizes the space vector modulation of two levels based on α '- β' coordinates, and carries out phase shift on PWM signals generated by the space vectors of the two levels to be used as switching signals of other bridge arms, thereby realizing the control of the cascaded multi-level inverter.
The invention relates to a phase-shifting space vector modulation method based on an H-bridge cascaded multilevel inverter, which aims at the problems that a space vector modulation algorithm is increased along with the increase of the number of cascaded units, basic vectors are greatly increased, a large number of redundant switch state vectors exist, the selection of the switch state vectors and the calculation of action time of the switch state vectors are extremely complicated, and the like.
Based on α '- β' coordinates, the invention aims at the H-bridge cascade multilevel inverter and utilizes a phase-shifting space vector modulation strategy to realize the control of the cascade multilevel inverter, namely, the two-level space vector modulation method is used for carrying out proper phase shifting to realize the control of the cascade multilevel inverter.
Compared with the traditional phase-shifting space vector modulation method under α - β coordinates, the method is relatively easy to determine the action time of the reference vector and the sector where the reference vector is located, is easy to realize by microprocessor programming, simplifies the calculation and improves the processing speed of a computer.
Drawings
FIG. 1 shows the distribution of two-level space vector modulation reference vector tracks and sectors under coordinates α '- β';
FIG. 2 shows the switching sequence and the allocation of action time of reference vectors in sector I (seven-segment modulation method);
FIG. 3 shows the topology of three H-bridge cascaded inverter circuits and the distribution of PWM signals;
FIG. 4 shows the topology of n H-bridge cascaded inverter circuits and the distribution of PWM signals;
fig. 5 shows phase voltage output waveforms of three H-bridge cascaded inverter circuits.
Detailed Description
The invention will be described in further detail below with reference to the following figures and specific examples:
the embodiment 1 is as shown in FIGS. 1 to 5, based on α '- β' coordinate, a phase shift space vector modulation method of an H-bridge cascaded multi-level inverter, wherein α '- β' coordinate is a coordinate system obtained by rotating a traditional α - β coordinate by 45 degrees in a counterclockwise direction and compressing an axial proportion, and the coordinate system has the advantage that all basic vectors are located at an integer coordinate point, the phase shift space vector modulation method is characterized in that each H-bridge inversion unit of the cascaded multi-level inverter is divided into a left half bridge arm and a right half bridge arm by utilizing α '- β' coordinate system, three left half bridge arms and three right half bridge arms of the H-bridge inversion unit at the same stage are respectively controlled, two-level space vector modulation is adopted to obtain a left half bridge arm control signal, the phase shift signal is 180 degrees as a right half bridge arm control signal, and modulation signals of the H-bridge inversion units between the stages are mutually different by a phase shift angle, the method simplifies the space vector modulation method of the cascaded multi-level inverter, so that the space vector modulation method is suitable for any n-stage multi-level inverter, and for realizing H-bridge cascaded multi-level space vector modulation based on 38968 '- β', the:
the preparation method comprises the following steps:
converting a traditional α - β coordinate system into a α '- β' coordinate system, wherein a basic vector expression of the traditional space vector modulation method is as follows:
s.t.|a|≤n，|b|≤n，|c|≤n
in the formula (1), α and β respectively represent coordinate values of basic vectors in a α - β coordinate system, a, b and c respectively represent output levels of three phases of the cascade multi-level inverter, n represents the number of cascade units, it can be seen from the formula (1) that the basic vectors (α) are distributed on non-integer coordinate points, and redundancy exists in the switching state vectors (a, b and c) because the formula (1) is a non-homogeneous linear equation set.
Coordinate system α '- β' obtained by rotating coordinates α - β counterclockwise by 45 ° and compressing the axial scale has:
in the α '- β' coordinate system, there are:
wherein α 'and β' respectively represent coordinate values of basic vectors in a α '- β' coordinate system, a, b and c respectively represent three-phase output levels of one stage of the cascade multi-level inverter, a, b and c can take two levels of 0 and 1, 0 represents low level, and 1 represents high level.
As can be seen from equation (3), the basis vectors (α ', β') are distributed at integer coordinate points.
The 7 basis vectors for the two-level space vector modulation can be calculated according to equation (3): v0(0,0) or V7(0，0)、V1(1，-1)、V2(1，0)、V3(0，1)、V4(-1，1)、V5(-1，0)、V6(0，-1)，Vj(x) denotes a basic vector, wherein (, x) denotes coordinates of the basic vector. 7 basic vectors having 1 zero vector V0Or V76 non-zero vectors V1、V2、V3、V4、V5And V6. Two adjacent non-zero vectors and a zero vector form a sector triangle, wherein V1、V2And V0(V7) Forming sectors I, V2、V3And V0(V7) Form sectors II, V3、V4And V0(V7) Form sectors III, V4、V5And V0(V7) Form sectors IV, V5、V6And V0(V7) Forming sectors V, V6、V1And V0(V7) Constituting sector VI.
Secondly, under α '- β' coordinates, a mathematical model of a reference vector locus of a two-level space vector modulation algorithm is established as follows:
in the formula, αr' and βr' denotes the reference voltage vector V in the α ' - β ' coordinate systems, respectivelyrM represents a modulation factor, and 0 < m < 1. The size of m reflects the utilization rate of the power supply voltage, the reference vector track in the formula (4) is an ellipse, when the ellipse is internally tangent to a hexagon formed by 6 non-zero basic vectors, m is 1, the utilization rate of the power supply voltage is the maximum, and the radius of the ellipse is reduced along with the reduction of the modulation coefficient m, so that the utilization rate of the power supply voltage is reduced.
Step A: judging the reference vector VrThe sector is as follows: sampling the reference voltage according to equation (4) to obtain a reference vector Vr(αr′，βr') determining the sector to which the reference voltage vector belongs by judging the value of the reference voltage vector, wherein the specific judgment is as follows:
if αr′≥0&&βr′≤0&&(αr′+βr′)＞(1+floor(αr′)+floor(βr')) to the reference vector VrLocated in sector I;
if αr′≥0&&βr' > 0 or more, the reference vector VrLocated in sector II;
if αr′＜0&&βr′＞0&&(αr′+βr′)＞(1+floor(αr′)+floor(βr')) to the reference vector VrLocated in sector III;
if αr′＜0&&βr′＞0&&(αr′+βr′)≤(1+floor(αr′)+floor(βr')) to the reference vector VrLocated in sector IV;
if αr′≤0&&βr' < 0, then the reference vector VrLocated in sector V;
if αr′≥0&&βr′≤0&&(αr′+βr′)≤(1+floor(αr′)+floor(βr')) to the reference vector VrLocated in sector VI;
wherein,&&representing an AND operation, floor (α)r′)、floor(βr') respectively represent pairs αr′、βr' round down.
And B: calculating the base vector action time of the synthetic reference vector:
after the position of the sector where the reference vector is located is determined, the three vertexes of the triangle of the sector corresponding to the basic vector are adopted to synthesize the reference vector, the action time of the basic vector of the synthesized reference vector is calculated according to the volt-second balance principle, taking the sector I as an example, if the reference vector is located in the sector I, the basic vector V is utilized1、V2And V0(V7) Synthetic reference vector Vr：
According to the basic vector V1、V2And V0(V7) And a reference vector VrThe vector coordinates of (a) can be found:
t0＝Ts(1-αr′)，t1＝-Tsβr′，t2＝Ts(αr′+βr′)
similarly, the action time of the basis vector of the synthesized reference vector of the other sectors can be obtained as follows:
sector II: t is t0＝Ts(1-αr′-βr′)，t2＝Tsαr′，t3＝Tsβr′
Sector III: t is t0＝Ts(1-βr′)，t3＝Ts(αr′+βr′)，t4＝-Tsαr′
Sector IV: t is t0＝Ts(1+αr′)，t4＝Tsβr′，t5＝-Ts(αr′+βr′)
Sector V: t is t0＝Ts(1+αr′+βr′)，t5＝-Tsαr′，t6＝-Tsβr′
Sector VI: t is t0＝Ts(1+βr′)，t6＝-Ts(αr′+βr′)，t1＝Tsαr′；
Wherein, t0、t1、t2、t3、t4、t5、t6Respectively represent a vector V0(V7)、V1、V2、V3、V4、V5、V6Time of action of (T)sRepresenting a reference voltage sampling period.
And C: and reasonably distributing the action time and sequence of the zero vector, and determining a switching path by adopting a seven-segment modulation and modulation method according to a minimum switching principle (namely, the switching between two basic vectors can only change the switching state of a certain phase every time).
And step D, generating three PWM signals by a seven-segment modulation method, respectively controlling the left bridge arms of the first-stage H-bridge inverter units, shifting the phases of the three PWM signals by 180 degrees, respectively controlling the right bridge arms of the first-stage H-bridge inverter units, wherein the control signal phases of the corresponding bridge arms between the stages are different from each other by pi/kn (k represents a frequency modulation ratio which is the ratio of the sampling frequency of a reference voltage signal to the frequency of the reference voltage signal), the reference vector locus and the sector distribution are modulated by two-level space vectors under α '- β' coordinates shown in figure 1, the reference vector locus is an ellipse inclined by 45 degrees, the end point of each non-zero vector is connected to obtain a hexagon inclined by 45 degrees, and the zero vector and two adjacent non-zero vectors divide the hexagon into six parts, namely six sectors.
Adopting seven-segment modulation method, when the reference vector is positioned in sector I, the basic vectors of the synthesized reference vectors are respectively V0(V7)、V1、V2The switching sequence is V0→V1→V2→V7→V2→V1→V0The corresponding action times are respectively t0/4、t1/2、t2/2、t0/2、t2/2、t1/2、t0FIG. 2 shows the switching sequence and action time of the basic vectors of the synthesized reference vector. When the reference vectors are located in sector II, the base vectors of the synthesized reference vectors are V, respectively0(V7)、V2、V3The switching sequence is V0→V3→V2→V7→V2→V3→V0The corresponding action times are respectively t0/4、t3/2、t2/2、t0/2、t2/2、t3/2、t0/4. When the reference vectors are located in sector III, the base vectors of the synthesized reference vectors are V, respectively0(V7)、V3、V4The switching sequence is V0→V3→V4→V7→V4→V3→V0The corresponding action times are respectively t0/4、t3/2、t4/2、t0/2、t4/2、t3/2、t0/4. When the reference vectors are located in sector IV, the base vectors of the synthesized reference vectors are V, respectively0(V7)、V4、V5The switching sequence is V0→V5→V4→V7→V4→V5→V0The corresponding action times are respectively t0/4、t5/2、t4/2、t0/2、t4/2、t5/2、t0/4. When the reference vectors are located in the sector V, the base vectors of the synthesized reference vectors are V, respectively0(V7)、V5、V6The switching sequence is V0→V5→V6→V7→V6→V5→V0The corresponding action times are respectively t0/4、t5/2、t6/2、t0/2、t6/2、t5/2、t0/4. When the reference vectors are located in sector VI, the base vectors of the composite reference vectors are V, respectively0(V7)、V6、V1The switching sequence is V0→V1→V6→V7→V6→V1→V0The corresponding action times are respectively t0/4、t1/2、t6/2、t0/2、t6/2、t1/2、t0/4。
In the topology structure of the three H-bridge cascaded inverter circuits shown in fig. 3, the left-arm switching tube control signal of each stage of H-bridge inverter unit is generated by a two-level space vector modulation method, and the signals of the upper and lower switching tubes of the left arm of the same H-bridge are complementary. The signal of the switching tube of the right bridge arm corresponding to the H bridge is obtained by shifting the phase of the signal of the switching tube of the left bridge arm by 180 degrees. And the control signals of the H bridge inversion units of adjacent stages are different from each other by a phase angle of pi/3 k. Specific signal allocation: three-way PWM signal (PWM) generation using two-level space vector modulation methodA11、PWMB11、PWMc11) Respectively controlling the left upper bridge arm switching tube of the first-stage H-bridge inverter unit to perform PWMA11、PWMB11、PWMC11Respectively takeInverse PWMA12、PWMB12、PWMC12Used for controlling the left lower bridge arm switching tube. The control signals of the upper and lower switch tubes of the right bridge arm of the first-stage H-bridge inverter unit are respectively obtained by phase-shifting corresponding left bridge arm signals by 180 degrees. And the control signals of the switching tubes of the second-stage three-phase H-bridge inverter unit are obtained by shifting the phase of pi/3 k phase angle by the corresponding control signals of the first stage respectively. And the control signals of the switch tubes of the third-stage three-phase H-bridge inverter unit are obtained by phase-shifting 2 pi/3 k by the corresponding control signals of the first stage respectively.
In the n H-bridge cascaded inverter circuits shown in fig. 4, the generation of the control signal of the first-stage H-bridge inverter unit is the same as the generation method of the first-stage control signal of the three H-bridge inverters shown in fig. 3, and the control signal of the switching tube of the second-stage three-phase H-bridge inverter unit is obtained by shifting the phase of pi/n by the corresponding control signal of the first stage. And the control signals of the switch tubes of the ith-stage three-phase H-bridge inverter unit are obtained by shifting the phase of the corresponding control signals of the first stage by i pi/kn respectively.
Fig. 5 is a simulated waveform diagram of output phase voltages of three H-bridge cascaded inverters. It can be seen from the figure that the output phase voltage is 7 levels, and the three phase voltages are different from each other by 120 degrees in phase, namely the output three-phase voltages are completely symmetrical.
The above is only one embodiment of the present invention, and the present invention is not limited to the topology of three H-bridge cascaded unit inverter circuits, and the present invention is suitable for the topology of n-level H-bridge cascaded unit.

Claims (4)

1. A phase-shift space vector modulation method based on an H-bridge cascade multilevel inverter is characterized in that vector modulation is carried out based on a reference vector track model modulated by a two-level space vector, wherein the reference vector track model modulated by the two-level space vector refers to a reference vector track model based on α '- β' coordinates;
the coordinate system obtained by rotating the α - β coordinate system adopted by the traditional space vector modulation technology by 45 degrees anticlockwise and compressing the axial proportion is the α '- β' coordinate system, and comprises the following components:
in the α '- β' coordinate system, there are:
α 'and β' respectively represent the abscissa and ordinate of a α '- β' coordinate system, α and β respectively represent coordinate values of basic vectors in a α - β coordinate system, a, b and c respectively represent three-phase output levels of one stage of the cascade multi-level inverter, a, b and c can take two levels of 0 and 1, 0 represents a low level, and 1 represents a high level;
the α '- β' coordinate system has 7 base vectors V0(0,0) or V7(0,0)、V1(1,-1)、V2(1,0)、V3(0,1)、V4(-1,1)、V5(-1,0)、V6(0,-1)，Vj(x) represents a base vector, wherein (x) represents coordinates of the base vector; 7 basic vectors having 1 zero vector V0Or V76 non-zero vectors V1、V2、V3、V4、V5And V6α '- β' 6 non-zero basic vectors in the coordinate system form a hexagon;
two adjacent non-zero vectors and a zero vector form a sector triangle, wherein V1、V2And V0/V7Forming sectors I, V2、V3And V0/V7Form sectors II, V3、V4And V0/V7Form sectors III, V4、V5And V0/V7Form sectors IV, V5、V6And V0/V7Forming sectors V, V6、V1And V0/V7Forming a sector VI;
the reference vector trajectory model based on α '- β' coordinates is represented by the following formula:
in the formula, αr' and βr' denotes the reference voltage vector V in the α ' - β ' coordinate systems, respectivelyrM represents a modulation coefficient, m is more than 0 and less than or equal to 1, the size of m reflects the utilization rate of the power supply voltage, the reference vector track in the formula (3) is an ellipse, when the ellipse is internally tangent to a hexagon formed by 6 non-zero basic vectors, m is 1, the utilization rate of the power supply voltage is the maximum, and the radius of the ellipse is reduced along with the reduction of the modulation coefficient m, so that the utilization rate of the power supply voltage is reduced;
the H-bridge cascaded multilevel inverter comprises 3n H-bridge units, wherein n is the serial stage number of each phase of H-bridge;
A. b, C three phases, each phase has n H-bridges connected in series, the series connection means that the output sides of the n H-bridges are connected in series; one end of the serial H bridge AC end is connected with the A or B or C end, and the other end is connected with the N point;
step A: judging the reference vector VrThe sector is as follows:
sampling the reference voltage vector according to the elliptic reference voltage vector track obtained by the formula (3), wherein the sampling frequency is frTo meet the requirement of synchronous sampling, the sampling frequency frIs integral multiple of the frequency f of the reference voltage, and the vector of the reference voltage obtained by sampling is Vr(αr',βr') determining the sector to which the reference voltage vector belongs by judging the value of the reference voltage vector, wherein the specific judgment is as follows:
if αr'≥0&&βr'≤0&&(αr'+βr')＞(1+floor(αr')+floor(βr')) to the reference vector VrLocated in sector I;
if αr'≥0&&βr' > 0 or more, the reference vector VrLocated in sector II;
if αr'＜0&&βr'＞0&&(αr'+βr')＞(1+floor(αr')+floor(βr')) to the reference vector VrLocated in sector III;
if αr'＜0&&βr'＞0&&(αr'+βr')≤(1+floor(αr')+floor(βr')) to the reference vector VrLocated in sector IV;
if αr'≤0&&βr' < 0, then the reference vector VrLocated in sector V;
if αr'≥0&&βr'≤0&&(αr'+βr')≤(1+floor(αr')+floor(βr')) to the reference vector VrLocated in sector VI;
wherein,&&representing an AND operation, floor (α)r')、floor(βr') respectively represent pairs αr'、βr' round down.
2. The phase-shifted space vector modulation method based on the H-bridge cascaded multi-level inverter according to claim 1, further comprising the step B of: calculating the base vector action time of the synthetic reference vector:
after the position of the sector where the reference vector is located is determined, synthesizing the reference vector by adopting the basic vectors corresponding to the three vertexes of the triangle of the sector, and calculating the action time of the basic vectors of the synthesized reference vector according to the volt-second balance principle;
the base vector action time of the synthetic reference vector of each sector is as follows:
sector I: t is t0＝Ts(1-αr')，t1＝-Tsβr'，t2＝Ts(αr'+βr')；
Sector II: t is t0＝Ts(1-αr'-βr')，t2＝Tsαr'，t3＝Tsβr'
Sector III: t is t0＝Ts(1-βr')，t3＝Ts(αr'+βr')，t4＝-Tsαr'
Sector IV: t is t0＝Ts(1+αr')，t4＝Tsβr'，t5＝-Ts(αr'+βr')
Sector V: t is t0＝Ts(1+αr'+βr')，t5＝-Tsαr'，t6＝-Tsβr'
Sector VI: t is t0＝Ts(1+βr')，t6＝-Ts(αr'+βr')，t1＝Tsαr'；
Wherein, t0、t1、t2、t3、t4、t5、t6Respectively represent a vector V0(V7)、V1、V2、V3、V4、V5、V6Time of action of (T)sDenotes the reference voltage sampling period, TS＝1/fr。
3. The phase-shifted space vector modulation method based on the H-bridge cascaded multi-level inverter according to claim 2, further comprising the step C of: determining a switching path and action time of each basic vector:
and distributing the action time and sequence of the zero vector, and determining a switching path by adopting a seven-segment modulation and modulation method according to the principle that the switching between two basic vectors can only change the minimum switching of the switching state of a certain phase each time.
4. The phase-shifted space vector modulation method based on the H-bridge cascaded multi-level inverter according to claim 3, further comprising the step D of: generating three paths of PWM signals;
based on the basic vector action time of the synthetic reference vector calculated in the step B, a seven-segment modulation method is used for generating three paths of PWM signals, the left bridge arms of all H-bridge inverter units of the first stage are respectively controlled, the three paths of signals are shifted by 180 degrees to respectively control the right bridge arms of all H-bridge inverter units of the first stage, and the control of corresponding bridge arms between stagesThe phase difference of the system signal is pi/kn, k represents the frequency modulation ratio, k is frAnd/f, the value of which is the ratio of the sampling frequency of the reference voltage signal to the frequency of the reference voltage signal.
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