CN106972773B - A kind of three level grid-connected inverter constant switching frequency model predictive control methods - Google Patents

A kind of three level grid-connected inverter constant switching frequency model predictive control methods Download PDF

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CN106972773B
CN106972773B CN201710244675.4A CN201710244675A CN106972773B CN 106972773 B CN106972773 B CN 106972773B CN 201710244675 A CN201710244675 A CN 201710244675A CN 106972773 B CN106972773 B CN 106972773B
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CN106972773A (en
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康龙云
冯腾
胡毕华
冯元彬
王则沣
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South China University of Technology SCUT
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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
    • H02M7/53—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 using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M7/537—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 using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
    • H02M7/5387—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 using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration
    • H02M7/53871—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 using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current
    • H02M7/53875—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 using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current with analogue control of three-phase output
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for AC mains or AC distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • 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
    • H02M7/53—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 using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M7/537—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 using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
    • H02M7/5387—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 using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration
    • H02M7/53871—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 using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current
    • H02M7/53875—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 using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current with analogue control of three-phase output
    • H02M7/53876—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 using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current with analogue control of three-phase output based on synthesising a desired voltage vector via the selection of appropriate fundamental voltage vectors, and corresponding dwelling times
    • 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
    • H02M7/53—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 using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M7/537—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 using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
    • H02M7/539—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 using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters with automatic control of output wave form or frequency
    • H02M7/5395—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 using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters with automatic control of output wave form or frequency by pulse-width modulation
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]

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

Abstract

The invention discloses a kind of three level grid-connected inverter constant switching frequency model predictive control methods, the following steps are included: the first step, three-level space vector modulation method uses three Vector modulations, determines objective function according to instantaneous power theory and Direct Power forecast Control Algorithm；Second step, the small sector position being minimized according to objective function where determining reference vector；Third step calculates the difference action time of three vectors in a switch periods；4th step determines on off sequence according to neutral point voltage balance.Method of the invention can greatly reduce the calculation amount of three level grid-connected inverter power controls, reduce gird-connected inverter active power and reactive power ripple, it with preferable dynamic and static state performance, while can realize constant switching frequency, there is better harmonic suppression effect.

Description

A kind of three level grid-connected inverter constant switching frequency model predictive control methods
Technical field
The present invention relates to three level grid-connected inverter fields, in particular to a kind of constant switch frequency of three level grid-connected inverters Rate model predictive control method.
Background technique
With the rapid development in the fields such as distributed generation resource, energy-storage system, electric car, to power quality and system effectiveness Requirement it is also higher and higher.Three-level inverter compared to traditional two-level inverter, with harmonic wave, answer by few, switch tube voltage The advantages that power is small, high pressure resistant, electromagnetic interference is small.T-type inverter compared to other three level neutral-point-clamped type inverters, there are two Main advantage: when exporting phase voltage is DC bus-bar voltage and zero, only one switch is switched on, and is reduced open-minded Loss；The electric current mean value for flowing through each switching tube is equal, and each switching tube generates identical heat.Therefore, T-type three in recent years Extensive concern of the electrical level inverter by enterprise and colleges and universities, prospect are very wide.
However, there are switching frequencies with sampling time, load parameter and system mode for traditional direct Power Control method Change and change, leads to the problem of dispersion harmonic components, also, prediction algorithm is computationally intensive, occupies a large amount of resources of chip. Therefore, it is most important to study a kind of efficient and superior performance gird-connected inverter Poewr control method.
Summary of the invention
The object of the invention is to propose a kind of three level grid-connected inverter constant switching frequencies to overcome the above problem Model predictive control method reduces the calculation amount of three level grid-connected inverter power controls, reduces gird-connected inverter wattful power Rate and reactive power ripple.
To achieve the goals above, the present invention is achieved through the following technical solutions:
A kind of three level grid-connected inverter constant switching frequency model predictive control methods, include following four step:
S1, three-level space vector modulation method use three Vector modulations, pre- according to instantaneous power theory and Direct Power It surveys control method and determines objective function；
S2, the small sector position being minimized according to objective function where determining reference vector；
S3, calculate a switch periods in three vectors difference action time；
S4, on off sequence is determined according to neutral point voltage balance.
The specific method is as follows by the three level grid-connected inverters constant switching frequency model predictive control method step S1:
The output level of the three each phases of level T-type inverter is all there are three types of state: output voltage be equal to DC bus-bar voltage, Output voltage is equal to the half of DC bus-bar voltage, output voltage is equal to 0, is set to P, O, N；Therefore 27 kinds of basis arrows are shared Amount be respectively as follows: NNN, NNO, NNP, NON, NOO, NOP, NPN, NPO, NPP, ONN, ONO, ONP, OON, OOO, OOP, OPN, OPO, OPP,PNN,PNO,PNP,PON,POO,POP,PPN,PPO,PPP；
The polar plot that 27 basis vectors are constituted is divided into six big sectors, and each big sector is divided into four small sectors, each There are six kinds of resultant vectors in big sector, selects corresponding resultant vector according to sector where reference voltage vector, specific as follows:
When reference vector is located at the first small sector, resultant vector selects zero vector v0, small vector v1, small vector v2；
When reference vector is located at the second small sector, resultant vector selects small vector v1, middle vector v4, big vector v3；
When reference vector is located at the small sector of third, resultant vector selects small vector v1, small vector v2, middle vector v4；
When reference vector is located at four small sectors, resultant vector selects small vector v2, middle vector v4, big vector v5。
Further, the influence of negligible resistance R can obtain under static α β coordinate system in conjunction with instantaneous power theory
Wherein, uα、uβ、iα、iβ、eα、eβIt is quiet in α β to respectively indicate inverter output phase voltage, phase current and network voltage The only value on coordinate system, ω, L are respectively electrical network angular frequency, current-limiting reactor value.
There are three vector v in a switch periodsi(i=1,2,3) is acted on respectively, if viWhen effect, the voltage of inverter For ui(uαi, uβi), uαi, uβiFor uiIn the value that α β static coordinate is fastened, action time ti。
And it enables
Then objective function is
Wherein, Pref、QrefThe respectively active power of gird-connected inverter and reactive power given value, Pj、Qj、TsTable respectively Show current active power value, current reactive power value, switch periods.
The specific method is as follows by the step S2 of the three level grid-connected inverters constant switching frequency model predictive control method:
The first step, by 6 combinations point of 2 adjacent long vectors in three level grid-connected inverter three dimensional vector diagrams and zero vector It Dai Ru not objective function.It is recycled by 6 times, finds out the vectorial combination when J is minimized, obtain reference vectorThe big fan at place Zone position.
All small three vectorial combinations of sector in the big sector are substituted into objective function respectively, are followed by 4 times by second step Ring finds out three vectorial combinations when J is minimized, obtains reference vectorThe locating small fan in 3 level space vector figure Zone position.
The specific method is as follows by the step S3 of the three level grid-connected inverters constant switching frequency model predictive control method:
Three vectorial combinations and changed power are substituted into following formula, the difference action time of three vectors is found out.
Wherein, eq=Pref-Pj、ep=Qref-Qj。
The specific method is as follows by the step S4 of the three level grid-connected inverters constant switching frequency model predictive control method:
There are 4 small sectors in sector big for first, there is 6 vectors, can there is 8 on off sequences；
When inverter output power is positive, Uc1> Uc2When select p-type on off sequence, increase the mid-point voltage of inverter；Uc1 < Uc2When select N-type on off sequence, reduce the mid-point voltage of inverter.
First small sector, Uc1> Uc2Corresponding on off sequence OOO-POO-PPO；Uc1< Uc2Corresponding OOO-OON-ONN；
Second small sector, Uc1> Uc2Corresponding on off sequence PNN-PON-POO；Uc1< Uc2Corresponding PON-PNN-ONN；
The small sector of third, Uc1> Uc2Corresponding on off sequence PON-POO-PPO；Uc1< Uc2Corresponding PON-OON-ONN；
4th small sector, Uc1> Uc2Corresponding on off sequence PON-PPN-PPO；Uc1< Uc2Corresponding PPN-PON-OON；
When inverter output power is negative, p-type on off sequence and N-type on off sequence alignment voltage function and effect with it is defeated On the contrary, U when power is positive outc1> Uc2When select N-type on off sequence, increase the mid-point voltage of inverter；Uc1< Uc2When select P Type on off sequence reduces the mid-point voltage of inverter.
First small sector, Uc1> Uc2Corresponding on off sequence OOO-OON-ONN；Uc1< Uc2Corresponding OOO-POO-PPO；
Second small sector, Uc1> Uc2Corresponding on off sequence PON-PNN-ONN；Uc1< Uc2Corresponding PNN-PON-POO；
The small sector of third, Uc1> Uc2Corresponding on off sequence PON-OON-ONN；Uc1< Uc2Corresponding PON-POO-PPO；
4th small sector, Uc1> Uc2Corresponding on off sequence PPN-PON-OON；Uc1< Uc2Corresponding PON-PPN-PPO；
Wherein, Uc1、Uc2Respectively direct current bus bar holds C1Capacitor C under the voltage and DC bus at both ends2The electricity at both ends Pressure.
For other five big sectors, and so on.
Compared with prior art, the invention has the advantages that and technical effect:
Method of the invention can substantially reduce the calculation amount of three level grid-connected inverter power controls, not need to increase Additional hardware circuit, it is at low cost；Inverter active power and reactive power ripple can be significantly reduced using the method for the present invention, together When can realize constant switching frequency, reduce input harmonics, there is good practicability.
Detailed description of the invention
Fig. 1 is three level grid-connected inverter structure chart of T-type.
Fig. 2 is the three dimensional vector diagram of three level grid-connected inverters.
Fig. 3 is the first big sector division and polar plot.
Fig. 4-1 is the output phase-voltage phase-current simulation waveform using the method for the present invention.
Fig. 4-2 is the active power simulation waveform using the method for the present invention.
Fig. 4-3 is the reactive power simulation waveform using the method for the present invention.
Specific embodiment
It elaborates with reference to the accompanying drawing with example to a specific embodiment of the invention.
Fig. 1 gives T-type three-level inverter structure chart, and including three bridge arms in parallel, every phase bridge arm includes two strings The IGBT switching tube of connection, the different IGBT pipe of the midpoint side series connection both direction of each phase bridge arm, the other side is connect with power grid；? Each bridge arm in parallel is terminated into same DC voltage source；The midpoint of two neutral point clamp capacitors of input voltage source parallel connection connects One end of the different IGBT pipe of the both direction of each phase bridge arm；Each IGBT pipe is driven by control circuit.
Three level grid-connected inverter constant switching frequency model predictive control methods, specific embodiment include four steps Rapid: the first step, three-level space vector modulation method uses three Vector modulations, according to instantaneous power theory and direct Power Control Method determines objective function；Second step, the small sector position being minimized according to objective function where determining reference vector；Third Step, calculates the difference action time of three vectors in a switch periods；4th step is determined according to neutral point voltage balance and is switched Sequence.
It synthesizes using three Vector Modulation of 3 level space vector in the first step and determines the implementation process of objective function Are as follows: all there are three types of states for the output level of the three each phases of level T-type inverter: output voltage is equal to DC bus-bar voltage, output Voltage is equal to the half of DC bus-bar voltage, output voltage is equal to 0, is set to P, O, N；Therefore 27 kinds of basis vectors point are shared Not are as follows: NNN, NNO, NNP, NON, NOO, NOP, NPN, NPO, NPP, ONN, ONO, ONP, OON, OOO, OOP, OPN, OPO, OPP, PNN,PNO,PNP,PON,POO,POP,PPN,PPO,PPP；
Fig. 2 is the polar plot that 27 basis vectors are constituted, and is divided into six big sectors, and each big sector can be divided into four small again There are six kinds of resultant vectors in sector, each big sector, and Fig. 3 is the polar plot of the first big sector, fan according to where reference voltage vector Area selects corresponding resultant vector, specific as follows:
When reference vector is located at the first small sector, resultant vector selects zero vector v0, small vector v1, small vector v2；
When reference vector is located at the second small sector, resultant vector selects small vector v1, middle vector v4, big vector v3；
When reference vector is located at the small sector of third, resultant vector selects small vector v1, small vector v2, middle vector v4；
When reference vector is located at four small sectors, resultant vector selects small vector v2, middle vector v4, big vector v5。
The objective function determines method, specific as follows:
The influence of negligible resistance R can obtain under static α β coordinate system in conjunction with instantaneous power theory
Wherein, uα、uβ、iα、iβ、eα、eβIt is quiet in α β to respectively indicate inverter output phase voltage, phase current and network voltage The only value on coordinate system, ω, L are respectively electrical network angular frequency, current-limiting reactor value.
There are three vector v in a switch periodsi(i=1,2,3) is acted on respectively, if viWhen effect, the voltage of inverter For ui(uαi, uβi), uαi, uβiFor uiIn the value that α β static coordinate is fastened, action time ti。
And it enables
Then after a switch periods, the transformation relation of active power and reactive power is
Then objective function is
Wherein, Pref、QrefThe respectively active power of gird-connected inverter and reactive power given value, Pj、Qj、TsTable respectively Show current active power value, current reactive power value, switch periods；Pj+1、Qj+1Respectively indicate subsequent time active power value, The reactive power value of subsequent time.
The implementation of the small sector position where determining reference vector is minimized according to objective function in the second step Journey is divided into two steps are as follows:
The first step, by 6 combinations point of 2 adjacent long vectors in three level grid-connected inverter three dimensional vector diagrams and zero vector It Dai Ru not objective function.It is recycled by 6 times, finds out the vectorial combination when J is minimized, obtain reference vectorThe big fan at place Zone position.
All small three vectorial combinations of sector in the big sector are substituted into objective function respectively, are followed by 4 times by second step Ring finds out three vectorial combinations when J is minimized, obtains reference vectorThe locating small fan in 3 level space vector figure Zone position.
The implementation process of the difference action time of three vectors in a switch periods is calculated in the third step are as follows:
Three vectorial combinations and changed power are substituted into following formula, the difference action time of three vectors is found out.
Wherein, eq=Pref-Pj、ep=Qref-Qj。
The implementation process of on off sequence is determined in 4th step according to neutral point voltage balance are as follows:
There are 4 small sectors in sector big for first, there is 6 vectors, can there is 8 on off sequences；
When inverter output power is positive, Uc1> Uc2When select p-type on off sequence, increase the mid-point voltage of inverter；Uc1 < Uc2When select N-type on off sequence, reduce the mid-point voltage of inverter.
First small sector, Uc1> Uc2Corresponding on off sequence OOO-POO-PPO；Uc1< Uc2Corresponding OOO-OON-ONN；
Second small sector, Uc1> Uc2Corresponding on off sequence PNN-PON-POO；Uc1< Uc2Corresponding PON-PNN-ONN；
The small sector of third, Uc1> Uc2Corresponding on off sequence PON-POO-PPO；Uc1< Uc2Corresponding PON-OON-ONN；
4th small sector, Uc1> Uc2Corresponding on off sequence PON-PPN-PPO；Uc1< Uc2Corresponding PPN-PON-OON；
When inverter output power is negative, p-type on off sequence and N-type on off sequence alignment voltage function and effect with it is defeated On the contrary, U when power is positive outc1> Uc2When select N-type on off sequence, increase the mid-point voltage of inverter；Uc1< Uc2When select P Type on off sequence reduces the mid-point voltage of inverter.
First small sector, Uc1> Uc2Corresponding on off sequence OOO-OON-ONN；Uc1< Uc2Corresponding OOO-POO-PPO；
Second small sector, Uc1> Uc2Corresponding on off sequence PON-PNN-ONN；Uc1< Uc2Corresponding PNN-PON-POO；
The small sector of third, Uc1> Uc2Corresponding on off sequence PON-OON-ONN；Uc1< Uc2Corresponding PON-POO-PPO；
4th small sector, Uc1> Uc2Corresponding on off sequence PPN-PON-OON；Uc1< Uc2Corresponding PON-PPN-PPO；
Wherein, Uc1、Uc2Respectively direct current bus bar holds C1Capacitor C under the voltage and DC bus at both ends2The electricity at both ends Pressure.
For other five big sectors, and so on.
Fig. 4-1,4-2,4-3 are using three level grid-connected inverter constant switching frequency Model Predictive Control sides of the invention Simulation waveform when method starts to control after 0.1 second, and wherein Fig. 4-1 is output phase voltage and phase current waveform figure, Fig. 4- 2 be active power waveform diagram, and Fig. 4-3 is reactive power waveform diagram, and simulation result: output voltage current harmonics is small, is had preferable Harmonic restraining function, gird-connected inverter active power and reactive power ripple are small, have preferable dynamic and static state performance, sufficiently demonstrate,prove Practicability of the invention is illustrated.
The above embodiment is a preferred embodiment of the present invention, but embodiments of the present invention are not by above-described embodiment Limitation, other any changes, modifications, substitutions, combinations, simplifications made without departing from the spirit and principles of the present invention, It should be equivalent substitute mode, be included within the scope of the present invention.

Claims (2)

1.一种三电平并网逆变器恒定开关频率模型预测控制方法，其特征在于，包含以下步骤：1. a three-level grid-connected inverter constant switching frequency model predictive control method, is characterized in that, comprises the following steps: S1、三电平空间矢量调制方法采用三矢量合成，根据瞬时功率理论和直接功率预测控制方法确定目标函数；S1. The three-level space vector modulation method adopts three-vector synthesis, and determines the objective function according to the instantaneous power theory and the direct power prediction control method; S2、根据目标函数取最小值确定参考矢量所在的小扇区位置；S2, taking the minimum value according to the objective function to determine the position of the small sector where the reference vector is located; S3、计算一个开关周期内的三个矢量的分别作用时间；S3. Calculate the respective action times of the three vectors in one switching cycle; S4、根据中点电压平衡确定开关序列；S4. Determine the switching sequence according to the midpoint voltage balance; 所述步骤S1具体如下：The step S1 is specifically as follows: 三电平T型逆变器每一相的输出电平都有三种状态：输出电压等于直流母线电压、输出电压等于直流母线电压的一半、输出电压等于0，分别设为P、O、N；因此共有27种基础矢量分别为：NNN、NNO、NNP、NON、NOO、NOP、NPN、NPO、NPP、ONN、ONO、ONP、OON、OOO、OOP、OPN、OPO、OPP、PNN、PNO、PNP、PON、POO、POP、PPN、PPO、PPP；The output level of each phase of the three-level T-type inverter has three states: the output voltage is equal to the DC bus voltage, the output voltage is equal to half of the DC bus voltage, and the output voltage is equal to 0, which are set to P, O, and N respectively; Therefore, there are 27 basic vectors: NNN, NNO, NNP, NON, NOO, NOP, NPN, NPO, NPP, ONN, ONO, ONP, OON, OOO, OOP, OPN, OPO, OPP, PNN, PNO, PNP , PON, POO, POP, PPN, PPO, PPP; 27个基础矢量构成的矢量图分为六个大扇区，每个大扇区分为四个小扇区，每个大扇区有六种合成矢量，根据参考电压矢量所在扇区选择相应的合成矢量，具体如下：The vector diagram composed of 27 basic vectors is divided into six large sectors, each large sector is divided into four small sectors, and each large sector has six synthetic vectors, and the corresponding synthetic vector is selected according to the sector where the reference voltage vector is located. vector, as follows: 当参考矢量位于第一小扇区时，合成矢量选择零矢量v0、小矢量v1、小矢量v2；When the reference vector is located in the first small sector, the composite vector selects zero vector v 0 , small vector v 1 , and small vector v 2 ; 当参考矢量位于第二小扇区时，合成矢量选择小矢量v1、中矢量v4、大矢量v3；When the reference vector is located in the second small sector, the composite vector selects a small vector v 1 , a medium vector v 4 , and a large vector v 3 ; 当参考矢量位于第三小扇区时，合成矢量选择小矢量v1、小矢量v2、中矢量v4；When the reference vector is located in the third small sector, the composite vector selects the small vector v 1 , the small vector v 2 , and the middle vector v 4 ; 当参考矢量位于第四小扇区时，合成矢量选择小矢量v2、中矢量v4、大矢量v5；When the reference vector is located in the fourth small sector, the composite vector selects a small vector v 2 , a medium vector v 4 , and a large vector v 5 ; 忽略电阻R的影响，在静止αβ坐标系统下，结合瞬时功率理论可得Ignoring the influence of resistance R, in the stationary αβ coordinate system, combined with the instantaneous power theory, we can get 其中，(uα，uβ)、(iα，iβ)、(eα，eβ)分别表示逆变器输出相电压、相电流、电网电压在αβ静止坐标系上的坐标；ω、L分别为电网角频率、串联电抗器值；为对有功功率P进行微分，为对有功功率Q进行微分；Among them, (u α , u β ), (i α , i β ), (e α , e β ) represent the coordinates of the inverter output phase voltage, phase current, and grid voltage on the αβ stationary coordinate system; ω, L are grid angular frequency and series reactor value respectively; To differentiate the active power P, To differentiate the active power Q; 在一个开关周期Ts内有三个矢量vi分别作用，其中i＝1，2，3；设vi作用时，逆变器的电压为ui，(uαi，uβi)为ui在αβ静止坐标系上的坐标，作用时间为ti；In a switching period T s , three vectors vi act respectively, where i =1, 2, 3; when vi acts, the voltage of the inverter is u i , (u αi , u βi ) is ui at The coordinates on the αβ stationary coordinate system, the action time is t i ; 并令and order 则目标函数J为Then the objective function J is 其中，Pref、Qref分别为并网逆变器的有功功率和无功功率给定值，Pj、Qj、Ts分别表示当前有功功率值、当前无功功率值、开关周期；Among them, P ref and Q ref are the active power and reactive power given values of the grid-connected inverter, respectively, and P j , Q j , and T s represent the current active power value, the current reactive power value, and the switching period, respectively; 所述步骤S2具体如下：The step S2 is specifically as follows: 第一步，将三电平并网逆变器空间矢量图中2个相邻长矢量和零矢量的6个组合分别代入目标函数；通过6次循环，求出当J取最小值的矢量组合，得到参考矢量所在的大扇区位置；The first step is to substitute 6 combinations of 2 adjacent long vectors and zero vectors in the space vector diagram of the three-level grid-connected inverter into the objective function respectively; through 6 cycles, find the vector combination when J takes the minimum value , get the reference vector The location of the large sector; 第二步，将该大扇区内的所有小扇区三矢量组合分别代入目标函数，通过4次循环，求出当J取最小值的三个矢量组合，得到参考矢量在三电平空间矢量图中所处的小扇区位置；The second step is to substitute all the three-vector combinations of the small sectors in the large sector into the objective function, and through 4 cycles, find the three-vector combination when J takes the minimum value, and obtain the reference vector The position of the small sector in the three-level space vector diagram; 所述步骤S3具体如下：The step S3 is specifically as follows: 把三个矢量组合以及功率变化代入下式中，求出三个矢量的分别作用时间t1、t2、t3：Substitute the combination of the three vectors and the power change into the following formula to obtain the action times t 1 , t 2 , and t 3 of the three vectors: 其中，eq＝Pref-Pj、ep＝Qref-Qj。Wherein, e q =P ref -P j , and ep =Q ref -Q j . 2.根据权利要求1所述三电平并网逆变器恒定开关频率模型预测控制方法，其特征在于，所述步骤S4具体如下：2. The constant switching frequency model predictive control method for a three-level grid-connected inverter according to claim 1, wherein the step S4 is as follows: 对于第一大扇区，有4个小扇区，有6个矢量，可以有8个开关序列；For the first large sector, there are 4 small sectors, there are 6 vectors, and there can be 8 switching sequences; 当逆变器输出功率为正，Uc1＞Uc2时选择P型开关序列，增加逆变器的中点电压；Uc1＜Uc2时选择N型开关序列，减小逆变器的中点电压；When the output power of the inverter is positive and U c1 > U c2 , select the P-type switching sequence to increase the midpoint voltage of the inverter; when U c1 <U c2 , select the N-type switching sequence to reduce the midpoint of the inverter Voltage; 第一小扇区，Uc1＞Uc2对应开关序列OOO-POO-PPO；Uc1＜Uc2对应OOO-OON-ONN；The first small sector, U c1 > U c2 corresponds to the switching sequence OOO-POO-PPO; U c1 < U c2 corresponds to OOO-OON-ONN; 第二小扇区，Uc1＞Uc2对应开关序列PNN-PON-POO；Uc1＜Uc2对应PON-PNN-ONN；The second small sector, U c1 >U c2 corresponds to the switching sequence PNN-PON-POO; U c1 <U c2 corresponds to PON-PNN-ONN; 第三小扇区，Uc1＞Uc2对应开关序列PON-POO-PPO；Uc1＜Uc2对应PON-OON-ONN；The third small sector, U c1 > U c2 corresponds to the switch sequence PON-POO-PPO; U c1 < U c2 corresponds to PON-OON-ONN; 第四小扇区，Uc1＞Uc2对应开关序列PON-PPN-PPO；Uc1＜Uc2对应PPN-PON-OON；The fourth small sector, U c1 > U c2 corresponds to the switch sequence PON-PPN-PPO; U c1 < U c2 corresponds to PPN-PON-OON; 当逆变器输出功率为负时，P型开关序列和N型开关序列对中点电压作用效果与输出功率为正时相反，Uc1＞Uc2时选择N型开关序列，增加逆变器的中点电压；Uc1＜Uc2时选择P型开关序列，减小逆变器的中点电压；When the output power of the inverter is negative, the effect of the P-type switching sequence and the N-type switching sequence on the midpoint voltage is opposite to that when the output power is positive. Mid-point voltage; when U c1 < U c2 , select the P-type switching sequence to reduce the mid-point voltage of the inverter; 第一小扇区，Uc1＞Uc2对应开关序列OOO-OON-ONN；Uc1＜Uc2对应OOO-POO-PPO；The first small sector, U c1 > U c2 corresponds to the switching sequence OOO-OON-ONN; U c1 < U c2 corresponds to OOO-POO-PPO; 第二小扇区，Uc1＞Uc2对应开关序列PON-PNN-ONN；Uc1＜Uc2对应PNN-PON-POO；The second small sector, U c1 >U c2 corresponds to the switching sequence PON-PNN-ONN; U c1 <U c2 corresponds to PNN-PON-POO; 第三小扇区，Uc1＞Uc2对应开关序列PON-OON-ONN；Uc1＜Uc2对应PON-POO-PPO；The third small sector, U c1 >U c2 corresponds to the switching sequence PON-OON-ONN; U c1 <U c2 corresponds to PON-POO-PPO; 第四小扇区，Uc1＞Uc2对应开关序列PPN-PON-OON；Uc1＜Uc2对应PON-PPN-PPO；The fourth small sector, U c1 > U c2 corresponds to the switching sequence PPN-PON-OON; U c1 < U c2 corresponds to PON-PPN-PPO; 其中，Uc1、Uc2分别为直流母线上电容C1两端的电压和直流母线下电容C2两端的电压；Wherein, U c1 and U c2 are respectively the voltage across the capacitor C 1 on the DC bus and the voltage across the capacitor C 2 under the DC bus; 对于其他五个大扇区，以此类推。And so on for the other five large sectors.
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