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 PDFInfo
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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
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. a kind of three level grid-connected inverter constant switching frequency model predictive control methods, which is characterized in that include following step
It is rapid:
S1, three-level space vector modulation method use three Vector modulations, according to instantaneous power theory and the pre- observing and controlling of Direct Power
Method processed 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 step S1 is specific 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；
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 big fan
Qu Youliu kind resultant vector 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；
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, eβ) to respectively indicate inverter output phase voltage, phase current, network voltage quiet in α β
The only coordinate on coordinate system；ω, L are respectively electrical network angular frequency, current-limiting reactor value；To carry out differential to active-power P,To carry out differential to active power Q；
In a switch periods TsIt is interior that there are three vector viIt acts on respectively, wherein i=1,2,3；If viWhen effect, the electricity of inverter
Pressure is ui, (uαi, uβi) it is uiIn the coordinate that α β static coordinate is fastened, action time ti；
And it enables
Then objective function J is
Wherein, Pref、QrefThe respectively active power of gird-connected inverter and reactive power given value, Pj、Qj、TsIt respectively indicates and works as
Preceding active power value, current reactive power value, switch periods；
The step S2 is specific as follows:
The first step combines generation respectively for 6 of 2 adjacent long vectors in three level grid-connected inverter three dimensional vector diagrams and zero vector
Enter objective function；It is recycled by 6 times, finds out the vectorial combination when J is minimized, obtain reference vectorThe big sector position at place
It sets；
All small three vectorial combinations of sector in the big sector are substituted into objective function by second step respectively, are recycled, are asked by 4 times
Out when three vectorial combinations that J is minimized, reference vector is obtainedThe locating small sector position in 3 level space vector figure
It sets；
The step S3 is specific as follows:
Three vectorial combinations and changed power are substituted into following formula, the difference action time t of three vectors is found out1、t2、t3:
Wherein, eq=Pref-Pj、ep=Qref-Qj。
2. three level grid-connected inverter constant switching frequency model predictive control methods, feature exist according to claim 1
In the step S4 is specific 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< Uc2
When 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 and output work
On the contrary, U when rate is positivec1> Uc2When select N-type on off sequence, increase the mid-point voltage of inverter；Uc1< Uc2When selection p-type open
Sequence is closed, the mid-point voltage of inverter is reduced；
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 voltage at both ends；
For other five big sectors, and so on.
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