CN106972773A - A kind of three level grid-connected inverter constant switching frequency model predictive control methods - Google Patents

Abstract

The invention discloses a kind of three level grid-connected inverters constant switching frequency model predictive control method, comprise the following steps：The first step, three-level space vector modulation method uses three Vector modulations, and object function is determined according to instantaneous power theory and Direct Power forecast Control Algorithm；Second step, according to object function take minimum value determine reference vector where small sector position；3rd step, calculates the difference action time of three vectors in a switch periods；4th step, on off sequence is determined according to neutral point voltage balance.The method of the present invention can greatly reduce the amount of calculation of three level grid-connected inverter Power Controls, reduce combining inverter active power and reactive power ripple, with preferable dynamic and static state performance, while constant switching frequency can be realized, with more preferable 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, more particularly to a kind of constant switch frequency of three level grid-connected inverters Rate model predictive control method.

Background technology

With developing rapidly for the fields such as distributed power source, energy-storage system, electric automobile, to the quality of power supply and system effectiveness Requirement also more and more higher.Three-level inverter has that harmonic wave is few compared to traditional two-level inverter, switch tube voltage should Power is small, high pressure, small electromagnetic interference the advantages of.T-shaped inverter has two compared to other three level neutral-point-clamped type inverters Main advantage：When it is DC bus-bar voltage and zero to export phase voltage, only one of which switch is switched on, and is reduced open-minded Loss；The electric current average for flowing through each switching tube is equal, and each switching tube produces identical heat.Therefore, in recent years T-shaped three Electrical level inverter is by the extensive concern of enterprise and colleges and universities, and prospect is very wide.

However, there is switching frequency with sampling time, load parameter and system mode in traditional direct Power Control method Change and change, the problem of producing scattered harmonic components, also, prediction algorithm is computationally intensive, occupies substantial amounts of resources of chip. Therefore, a kind of combining inverter Poewr control method of efficient and superior performance is studied most important.

The content of the invention

The purpose of the present invention exactly in order to overcome above mentioned problem, proposes a kind of three level grid-connected inverters constant switching frequency Model predictive control method, reduces the amount of calculation of three level grid-connected inverter Power Controls, reduces combining inverter wattful power Rate and reactive power ripple.

To achieve these goals, 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 Survey control method and determine object function；

S2, taken according to object function minimum value determine reference vector where small sector position；

S3, three vectors calculated in a switch periods difference action time；

S4, on off sequence determined according to neutral point voltage balance.

The three level grid-connected inverters constant switching frequency model predictive control method step S1 specific methods are as follows：

The output level of each phase of the T-shaped inverter of three level has three kinds of states：Output voltage be equal to DC bus-bar voltage, Output voltage is equal to the half of DC bus-bar voltage, output voltage and is equal to 0, is set to P, O, N；Therefore 27 kinds of basis arrows are had Amount is respectively：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 sector, and each big sector is divided into four small sectors, each There are six kinds of resultant vectors big sector, and the sector according to where reference voltage vector selects corresponding resultant vector, specific as follows：

When reference vector is located at the first small sector, resultant vector selection zero vector v₀, small vector v₁, small vector v₂；

When reference vector is located at the second small sector, resultant vector selection small vector v₁, middle vector v₄, big vector v₃；

When reference vector is located at three small sectors, resultant vector selection small vector v₁, small vector v₂, middle vector v₄；

When reference vector is located at four small sectors, resultant vector selection small vector v₂, middle vector v₄, big vector v₅。

Further, negligible resistance R influence, under static α β coordinate systems, can be obtained with reference to instantaneous power theory

Wherein, u_α、u_β、i_α、i_β、e_α、e_βRepresent that inverter output phase voltage, phase current and line voltage are quiet in α β respectively 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 periods_i(i=1,2,3) is acted on respectively, if v_iDuring effect, the voltage of inverter For u_i(u_αi, u_βi), u_αi, u_βiFor u_iThe value fastened in α β static coordinates, action time is t_i。

And make

Then object function is

Wherein, P_ref、Q_refThe respectively active power of combining inverter and reactive power set-point, P_j、Q_j、T_sDifference table Show current active power value, current reactive power value, switch periods.

The step S2 specific methods of the three level grid-connected inverters constant switching frequency model predictive control method are as follows：

The first step, by 6 combinations point of 2 adjacent long vectors and zero vector in three level grid-connected inverter three dimensional vector diagrams Object function is not substituted into.By 6 circulations, obtain when J takes the vectorial combination of minimum value, obtain reference vectorThe big fan at place Zone position.

All small vectorial combinations of sector three in the big sector are substituted into object function, followed by 4 times by second step respectively Ring, obtains when J takes three vectorial combinations of minimum value, obtains reference vectorThe residing small fan in 3 level space vector figure Zone position.

The step S3 specific methods of the three level grid-connected inverters constant switching frequency model predictive control method are as follows：

Three vectorial combinations and changed power are substituted into following formula, the difference action time of three vectors is obtained.

Wherein, e_q=P_ref-P_j、e_p=Q_ref-Q_j。

The step S4 specific methods of the three level grid-connected inverters constant switching frequency model predictive control method are as follows：

For the first big sector, there are 4 small sectors, there are 6 vectors, there can be 8 on off sequences；

When inverter output power is just U_c1＞ U_c2When select p-type on off sequence, increase inverter mid-point voltage；U_c1 ＜ U_c2When select N-type on off sequence, reduce inverter mid-point voltage.

First small sector, U_c1＞ U_c2Correspondence on off sequence OOO-POO-PPO；U_c1＜ U_c2Correspondence OOO-OON-ONN；

Second small sector, U_c1＞ U_c2Correspondence on off sequence PNN-PON-POO；U_c1＜ U_c2Correspondence PON-PNN-ONN；

3rd small sector, U_c1＞ U_c2Correspondence on off sequence PON-POO-PPO；U_c1＜ U_c2Correspondence PON-OON-ONN；

4th small sector, U_c1＞ U_c2Correspondence on off sequence PON-PPN-PPO；U_c1＜ U_c2Correspondence PPN-PON-OON；

When inverter output power for it is negative when, p-type on off sequence and N-type on off sequence alignment voltage action effect with it is defeated Go out power for timing on the contrary, U_c1＞ U_c2When select N-type on off sequence, increase inverter mid-point voltage；U_c1＜ U_c2When select P Type on off sequence, reduces the mid-point voltage of inverter.

First small sector, U_c1＞ U_c2Correspondence on off sequence OOO-OON-ONN；U_c1＜ U_c2Correspondence OOO-POO-PPO；

Second small sector, U_c1＞ U_c2Correspondence on off sequence PON-PNN-ONN；U_c1＜ U_c2Correspondence PNN-PON-POO；

3rd small sector, U_c1＞ U_c2Correspondence on off sequence PON-OON-ONN；U_c1＜ U_c2Correspondence PON-POO-PPO；

4th small sector, U_c1＞ U_c2Correspondence on off sequence PPN-PON-OON；U_c1＜ U_c2Correspondence PON-PPN-PPO；

Wherein, U_c1、U_c2Respectively direct current bus bar holds C₁Electric capacity C under the voltage and dc bus at two ends₂The electricity at two ends Pressure.

For other five big sector, by that analogy.

Compared with prior art, the invention has the advantages that and technique effect：

The method of the present invention can substantially reduce the amount of calculation of three level grid-connected inverter Power Controls, it is not necessary to increase Extra hardware circuit, cost is low；Inverter active power and reactive power ripple can be significantly reduced using the inventive method, together When can realize constant switching frequency, reduce input harmonics, with good practicality.

Brief description of the drawings

Fig. 1 is T-shaped three level grid-connected inverters structure chart.

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 inventive method.

Fig. 4-2 is the active power simulation waveform using the inventive method.

Fig. 4-3 is the reactive power simulation waveform using the inventive method.

Embodiment

The embodiment of the present invention is elaborated with example below in conjunction with the accompanying drawings.

Fig. 1 gives T-shaped three-level inverter structure chart, including three bridge arms in parallel, and two strings are included per phase bridge arm The IGBT switching tubes of connection, the IGBT that the midpoint side series connection both direction of each phase bridge arm is different is managed, and opposite side is connected with power network； Each bridge arm in parallel is terminated into same direct voltage source；The midpoint connection of input voltage source two neutral point clamp electric capacity in parallel One end of the different IGBT pipes of the both direction of each phase bridge arm；Each IGBT pipe is by control circuit drives.

Three level grid-connected inverter constant switching frequency model predictive control methods, embodiment includes four steps Suddenly：The first step, three-level space vector modulation method uses three Vector modulations, according to instantaneous power theory and direct Power Control Method determines object function；Second step, according to object function take minimum value determine reference vector where small sector position；3rd Step, calculates the difference action time of three vectors in a switch periods；4th step, determines to switch according to neutral point voltage balance Sequence.

Synthesized in the first step using the Vector Modulation of 3 level space vector three and determine the implementation process of object function For：The output level of each phase of the T-shaped inverter of three level has three kinds of states：Output voltage is equal to DC bus-bar voltage, output Voltage is equal to the half of DC bus-bar voltage, output voltage and is equal to 0, is set to P, O, N；Therefore 27 kinds of basis vectors point are had It is not：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 sector, and each big sector can be divided into four small again There are six kinds of resultant vectors sector, each big sector, and Fig. 3 is the polar plot of the first big sector, is fanned 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 selection zero vector v₀, small vector v₁, small vector v₂；

When reference vector is located at the second small sector, resultant vector selection small vector v₁, middle vector v₄, big vector v₃；

When reference vector is located at three small sectors, resultant vector selection small vector v₁, small vector v₂, middle vector v₄；

When reference vector is located at four small sectors, resultant vector selection small vector v₂, middle vector v₄, big vector v₅。

The object function determines method, specific as follows：

Negligible resistance R influence, under static α β coordinate systems, can be obtained with reference to instantaneous power theory

Wherein, u_α、u_β、i_α、i_β、e_α、e_βRepresent that inverter output phase voltage, phase current and line voltage are quiet in α β respectively 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 periods_i(i=1,2,3) is acted on respectively, if v_iDuring effect, the voltage of inverter For u_i(u_αi, u_βi), u_αi, u_βiFor u_iThe value fastened in α β static coordinates, action time is t_i。

And make

Then after a switch periods, the transformation relation of active power and reactive power is

Then object function is

Wherein, P_ref、Q_refThe respectively active power of combining inverter and reactive power set-point, P_j、Q_j、T_sDifference table Show current active power value, current reactive power value, switch periods；P_j+1、Q_j+1Respectively represent subsequent time active power value, The reactive power value of subsequent time.

In the second step according to object function take minimum value determine reference vector where small sector position implementation Journey is divided into two steps：

The first step, by 6 combinations point of 2 adjacent long vectors and zero vector in three level grid-connected inverter three dimensional vector diagrams Object function is not substituted into.By 6 circulations, obtain when J takes the vectorial combination of minimum value, obtain reference vectorThe big fan at place Zone position.

All small vectorial combinations of sector three in the big sector are substituted into object function, followed by 4 times by second step respectively Ring, obtains when J takes three vectorial combinations of minimum value, obtains reference vectorThe residing small fan in 3 level space vector figure Zone position.

The implementation process of difference action time that three vectors in a switch periods are calculated in 3rd step is：

Three vectorial combinations and changed power are substituted into following formula, the difference action time of three vectors is obtained.

Wherein, e_q=P_ref-P_j、e_p=Q_ref-Q_j。

Determine that the implementation process of on off sequence is according to neutral point voltage balance in 4th step：

For the first big sector, there are 4 small sectors, there are 6 vectors, there can be 8 on off sequences；

When inverter output power is just U_c1＞ U_c2When select p-type on off sequence, increase inverter mid-point voltage；U_c1 ＜ U_c2When select N-type on off sequence, reduce inverter mid-point voltage.

First small sector, U_c1＞ U_c2Correspondence on off sequence OOO-POO-PPO；U_c1＜ U_c2Correspondence OOO-OON-ONN；

Second small sector, U_c1＞ U_c2Correspondence on off sequence PNN-PON-POO；U_c1＜ U_c2Correspondence PON-PNN-ONN；

3rd small sector, U_c1＞ U_c2Correspondence on off sequence PON-POO-PPO；U_c1＜ U_c2Correspondence PON-OON-ONN；

4th small sector, U_c1＞ U_c2Correspondence on off sequence PON-PPN-PPO；U_c1＜ U_c2Correspondence PPN-PON-OON；

When inverter output power for it is negative when, p-type on off sequence and N-type on off sequence alignment voltage action effect with it is defeated Go out power for timing on the contrary, U_c1＞ U_c2When select N-type on off sequence, increase inverter mid-point voltage；U_c1＜ U_c2When select P Type on off sequence, reduces the mid-point voltage of inverter.

First small sector, U_c1＞ U_c2Correspondence on off sequence OOO-OON-ONN；U_c1＜ U_c2Correspondence OOO-POO-PPO；

Second small sector, U_c1＞ U_c2Correspondence on off sequence PON-PNN-ONN；U_c1＜ U_c2Correspondence PNN-PON-POO；

3rd small sector, U_c1＞ U_c2Correspondence on off sequence PON-OON-ONN；U_c1＜ U_c2Correspondence PON-POO-PPO；

4th small sector, U_c1＞ U_c2Correspondence on off sequence PPN-PON-OON；U_c1＜ U_c2Correspondence PON-PPN-PPO；

Wherein, U_c1、U_c2Respectively direct current bus bar holds C₁Electric capacity C under the voltage and dc bus at two ends₂The electricity at two ends Pressure.

For other five big sector, by that analogy.

Fig. 4-1,4-2,4-3 are the three level grid-connected inverter constant switching frequency Model Predictive Control sides using the present invention Simulation waveform during method, started control after 0.1 second, and wherein Fig. 4-1 is to export phase voltage and phase current waveform figure, and Fig. 4- 2 be active power oscillogram, and Fig. 4-3 is reactive power oscillogram, simulation result：Output voltage current harmonics is small, with preferable Harmonic restraining function, combining inverter active power and reactive power ripple be small, with preferable dynamic and static state performance, fully card Understand the practicality of the present invention.

Above-described embodiment is preferably embodiment, but embodiments of the present invention are not by above-described embodiment of the invention Limitation, other any Spirit Essences without departing from the present invention and the change made under principle, modification, replacement, combine, simplification, Equivalent substitute mode is should be, is included within protection scope of the present invention.

Claims (5)

1. a kind of three level grid-connected inverters constant switching frequency model predictive control method, it is characterised in that include following step Suddenly：

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 object function；

S2, taken according to object function minimum value determine reference vector where small sector position；

S3, three vectors calculated in a switch periods difference action time；

S4, on off sequence determined according to neutral point voltage balance.

2. three level grid-connected inverter constant switching frequency model predictive control method according to claim 1, its feature exists In the step S1 is specific as follows：

The output level of each phase of the T-shaped inverter of three level has three kinds of states：Output voltage is equal to DC bus-bar voltage, output Voltage is equal to the half of DC bus-bar voltage, output voltage and is equal to 0, is set to P, O, N；Therefore 27 kinds of basis vectors point are had It is not：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 sector, and each big sector is divided into four small sectors, each big fan Qu Youliu kind resultant vectors, the sector according to where reference voltage vector selects corresponding resultant vector, specific as follows：

When reference vector is located at the first small sector, resultant vector selection zero vector v₀, small vector v₁, small vector v₂；

When reference vector is located at the second small sector, resultant vector selection small vector v₁, middle vector v₄, big vector v₃；

When reference vector is located at three small sectors, resultant vector selection small vector v₁, small vector v₂, middle vector v₄；

When reference vector is located at four small sectors, resultant vector selection small vector v₂, middle vector v₄, big vector v₅；

Negligible resistance R influence, under static α β coordinate systems, can be obtained with reference to instantaneous power theory

$\left\{\begin{array}{c}\frac{dP}{dt}=\frac{3}{2}\{e_{\mathrm{\α}}\[\frac{(u_{\mathrm{\α}}-e_{\mathrm{\α}})}{L}+{\mathrm{\ωi}}_{\mathrm{\β}}\]+e_{\mathrm{\β}}\[\frac{(u_{\mathrm{\β}}-e_{\mathrm{\β}})}{L}-{\mathrm{\ωi}}_{\mathrm{\α}}\]\}\\ \frac{dQ}{dt}=\frac{3}{2}\{e_{\mathrm{\β}}\[\frac{(u_{\mathrm{\α}}-e_{\mathrm{\α}})}{L}+{\mathrm{\ωi}}_{\mathrm{\β}}\]-e_{\mathrm{\α}}\[\frac{(u_{\mathrm{\β}}-e_{\mathrm{\β}})}{L}-{\mathrm{\ωi}}_{\mathrm{\α}}\]\}\end{array}\right.$

Wherein, (u_α, u_β)、(i_α, i_β)、(e_α, e_β) represent that inverter output phase voltage, phase current, line voltage are quiet in α β respectively 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 T_sInside there are three vector v_iAct on respectively, wherein i=1,2,3；If v_iDuring effect, the electricity of inverter Press as u_i, (u_αi,u_βi) it is u_iThe coordinate fastened in α β static coordinates, action time is t_i；

And make

$\left\{\begin{array}{c}{f}_{pi}=\frac{dP}{dt}\\ f_{qi}=\frac{dQ}{dt}\end{array}\right.|(u_{\mathrm{\α}}=u_{\mathrm{\α}i},u_{\mathrm{\β}}=u_{\mathrm{\β}i},i=1,2,3)$

Then object function J is

$J=\underset{i=1}{\overset{3}{\mathrm{\Σ}}}\[{(P_{ref}-P_j-f_{pi}{T}_s)}^2+{(Q_{ref}-Q_j-f_{qi}{T}_s)}^2\],$

Wherein, P_ref、Q_refThe respectively active power of combining inverter and reactive power set-point, P_j、Q_j、T_sRepresent to work as respectively Preceding active power value, current reactive power value, switch periods.

3. three level grid-connected inverter constant switching frequency model predictive control method according to claim 2, its feature exists In the step S2 is specific as follows：

The first step, generation respectively is combined by 6 of 2 adjacent long vectors and zero vector in three level grid-connected inverter three dimensional vector diagrams Enter object function；By 6 circulations, obtain when J takes the vectorial combination of minimum value, obtain reference vectorThe big sector position at place Put；

All small vectorial combinations of sector three in the big sector are substituted into object function by second step respectively, by 4 circulations, are asked Go out when J takes three vectorial combinations of minimum value, obtain reference vectorThe residing small sector position in 3 level space vector figure Put.

4. three level grid-connected inverter constant switching frequency model predictive control method according to claim 3, its feature exists In 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 obtained₁、t₂、t₃：

$\left\{\begin{array}{c}{t}_1=\frac{(f_{q1}-f_{q3})e_p+(f_{p3}-f_{p2})e_q+(f_{p2}{f}_{q3}-f_{p3}{f}_{q2})T_s}{(f_{q2}-f_{q3})f_{p1}+(f_{q3}-f_{q1})f_{p2}+(f_{q1}-f_{q2})f_{p3}}\\ t_2=\frac{(f_{q3}-f_{q1})e_p+(f_{p1}-f_{p3})e_q+(f_{q1}{f}_{q3}-f_{q3}{f}_{p1})T_s}{(f_{q2}-f_{q3})f_{p1}+(f_{q3}-f_{q1})f_{p2}+(f_{q1}-f_{q2})f_{p3}}\\ t_3=T_s-t_1-t_2\end{array}\right.$

Wherein, e_q=P_ref-P_j、e_p=Q_ref-Q_j。

5. three level grid-connected inverter constant switching frequency model predictive control method according to claim 4, its feature exists In the step S4 is specific as follows：

For the first big sector, there are 4 small sectors, there are 6 vectors, there can be 8 on off sequences；

When inverter output power is just U_c1＞ U_c2When select p-type on off sequence, increase inverter mid-point voltage；U_c1＜ U_c2 When select N-type on off sequence, reduce inverter mid-point voltage；

First small sector, U_c1＞ U_c2Correspondence on off sequence OOO-POO-PPO；U_c1＜ U_c2Correspondence OOO-OON-ONN；

Second small sector, U_c1＞ U_c2Correspondence on off sequence PNN-PON-POO；U_c1＜ U_c2Correspondence PON-PNN-ONN；

3rd small sector, U_c1＞ U_c2Correspondence on off sequence PON-POO-PPO；U_c1＜ U_c2Correspondence PON-OON-ONN；

4th small sector, U_c1＞ U_c2Correspondence on off sequence PON-PPN-PPO；U_c1＜ U_c2Correspondence PPN-PON-OON；

When inverter output power is bears, p-type on off sequence and N-type on off sequence alignment voltage action effect and output work Rate is timing on the contrary, U_c1＞ U_c2When select N-type on off sequence, increase inverter mid-point voltage；U_c1＜ U_c2When selection p-type open Sequence is closed, reduces the mid-point voltage of inverter；

First small sector, U_c1＞ U_c2Correspondence on off sequence OOO-OON-ONN；U_c1＜ U_c2Correspondence OOO-POO-PPO；

Second small sector, U_c1＞ U_c2Correspondence on off sequence PON-PNN-ONN；U_c1＜ U_c2Correspondence PNN-PON-POO；

3rd small sector, U_c1＞ U_c2Correspondence on off sequence PON-OON-ONN；U_c1＜ U_c2Correspondence PON-POO-PPO；

4th small sector, U_c1＞ U_c2Correspondence on off sequence PPN-PON-OON；U_c1＜ U_c2Correspondence PON-PPN-PPO；

Wherein, U_c1、U_c2Respectively direct current bus bar holds C₁Electric capacity C under the voltage and dc bus at two ends₂The voltage at two ends；

For other five big sector, by that analogy.