CN104852620A - Three-phase voltage type pwm inverter control method - Google Patents

Abstract

The invention provides a three-phase voltage type PWM inverter control method. The three-phase voltage type PWM inverter control method includes following steps: firstly, a three-phase voltage type PWM inverter mathematical model is established; secondly, the three-phase voltage type PWM mathematical model is analyzed based on a synthetic vector via the introduction of the thought of the synthetic vector; thirdly, a control strategy obtained by analysis based on the synthetic vector is converted to a synchronous rotation d-q coordinate system, and a decoupling control method of a current inner loop of the three-phase voltage type PWM inverter without inductance parameters is obtained; and fourthly, a voltage outer loop control strategy of the three-phase voltage type PWM inverter is designed. According to the three-phase voltage type PWM inverter control method, no-inductance-parameter complete decoupling of the current inner loop is realized, and the control performance is guaranteed.

Description

Three-phase voltage type PWM inverter control method

Technical field

The present invention relates to electrical engineering field, specifically a kind of three-phase voltage type PWM inverter control method.

Background technology

Along with the development of power electronic technology, can realize energy in bidirectional flow, the three-phase voltage type PWM inverter of unit power inverter operation, low output current harmonics function is used widely.Along with the variation of application scenario, also more and more higher to the requirement of its dynamic and static performance, the control strategy improving three-phase voltage type PWM inverter control performance has become the focus of research.The Double closed-loop of voltage and current strategy that current three-phase voltage type PWM inverter extensively adopts.Due in synchronous coordinate system, exchange variable and be broken down into meritorious variable and idle variable, when stable state, they are all DC component, and meritorious variable and idle variable can obtain independentastatic control.Analysis for current control system performance is generally be based upon on the thorough decoupling zero basis of system, and namely in dynamic process, biphase current is independent of each other.But current status feedback decoupling control item notice road Inductor exact value conventional in traditional double Closed-loop Control Strategy, by the impact of inductance measurement error, system can not thoroughly decoupling zero, can have influence on the control performance of whole system.The double-loop control strategy that generally speaking three-phase voltage type PWM inverter adopts also exists following shortcoming: one, need know Inductor exact value during current inner loop Controller gain variations; Two, inevitably there is error between the measured value of inductance and inductance exact value; Three, when error appears in inductance parameters, current inner loop can not thoroughly decoupling zero, and control performance can be deteriorated, and along with the raising of synchronizing frequency, this phenomenon is particularly evident.

Summary of the invention

For defect of the prior art, the object of this invention is to provide a kind of three-phase voltage type PWM inverter control method, it is for three-phase voltage type PWM inverter, grid-connected inverters with not grid-connected be directly connected with resistive load time, devise outer voltage and current inner loop control strategy, wherein outer voltage adopts constant voltage control strategy, the running status of inverter is decided by the set-point changing outer voltage, outer voltage output valve is as the reference value of current inner loop, under embodiment of the present invention three-phase voltage-type inverter operates in unity power factor state.Current inner loop is based on the thought of resultant vector, achieve the uneoupled control without inductance parameters, when adopting this strategy, Inductor parameter will not be contained in current inner loop decoupling zero item, thus make the dominant pole of closed-loop control system not by the impact of physical condition, can be configured in Anywhere as required.

According to an aspect of the present invention, a kind of three-phase voltage type PWM inverter control method is provided, it is characterized in that, comprise the following steps:

Step one: set up three-phase voltage type PWM inverter Mathematical Modeling;

Step 2: by introducing the thought of resultant vector, the basis of resultant vector being analyzed the Mathematical Modeling of three-phase voltage type PWM, obtains based on the current inner loop decoupling control policy under resultant vector;

Step 3: under the current inner loop decoupling control policy based on resultant vector of gained in step 2 is transformed into synchronous rotary d-q coordinate system, obtain the current inner loop decoupling control method of three-phase voltage type PWM inverter without inductance parameters;

Step 4: design three-phase voltage type PWM inverter outer voltage control strategy, the output valve controlled by outer shroud is as the reference value of current inner loop uneoupled control in step 3.

Preferably, described three-phase grid-connected inverter comprises six switches, and on off state is defined as follows formula:

K=a, b, c in formula, wherein a, b, c represent ac electric three-phase respectively.

Preferably, described three-phase voltage type PWM inverter Mathematical Modeling d-q mark system under adopt as shown in the formula:

$\left\{\begin{array}{c}{\mathrm{Ri}}_d+L\frac{{\mathrm{di}}_d}{\mathrm{dt}}=u_d+{\mathrm{wLi}}_q-e\\ {\mathrm{Ri}}_q+L\frac{{\mathrm{di}}_q}{\mathrm{dt}}=u_q-{\mathrm{wLi}}_d-e\end{array}\right.$

In formula: L represents net side filter inductance; R represents power switch pipe loss equivalent resistance and ac filter inductance equivalent resistance sum, and w represents the angular frequency of three-phase main-frequency of ac; u _d, u _qto represent under static three phase coordinate systems that abc AC three-phase voltage is transformed into dq two phase voltage value under synchronous rotary two phase coordinate system; e _d, e _qto represent under static three phase coordinate systems that abc nets side three-phase alternating voltage and is transformed into dq two phase voltage value under synchronous rotary two phase coordinate system; i _d, i _qto represent under static three phase coordinate systems that abc nets side three-phase current and is transformed into dq biphase current value under synchronous rotary two phase coordinate system.

Preferably, in described step 3, the output valve of current inner loop is as the modulation signal of PWM, controls the output valve of PWM inverter, is also final output signal of the present invention.

Compared with prior art, the present invention has following beneficial effect:

One, current inner loop control design case method is simple, and principle is also uncomplicated, without the need to knowing inductance value at alternating side.

Two. adopt offseting of controller zero point and dominant pole, thus the dominant pole of closed-loop control system is not affected by physical condition.

Three, be transformed in synchronously rotating reference frame by the control strategy in resultant vector, Mathematical Modeling is simple, is easy to Digital Realization.

Accompanying drawing explanation

By reading with reference to following attached figureto the detailed description that non-limiting example is done, other features, objects and advantages of the present invention will become more obvious:

figure1 is the circuit of three-phase voltage type PWM inverter figure.

figure2 is the current decoupled control frames based on resultant vector figure.

figure3 be under synchronous rotary d-q coordinate system without inductance parameters L uneoupled control frame figure.

figure4 is three-phase voltage type PWM inverter controller chassises figure.

figure5 is signals of the system simulation model of three-phase voltage type PWM inverter when being incorporated into the power networks figure.

figure6 be three-phase voltage type PWM inverter not grid-connected and be directly connected with resistive load time the signal of system simulation model figure.

figure7 be three-phase voltage type PWM inverter when being incorporated into the power networks based on the present invention propose the signal of control strategy a phase voltage current waveform figure.

figure8 be three-phase voltage type PWM inverter when being incorporated into the power networks based on the present invention propose the signal of control strategy system power waveform figure.

figure9 is that three-phase voltage type PWM inverter is not grid-connected when being directly connected with resistive load based on the present invention proposes the signal of control strategy three-phase voltage waveform figure.

figure10 is that three-phase voltage type PWM inverter is not grid-connected when being directly connected with resistive load based on the present invention proposes the signal of control strategy system power waveform figure.

Embodiment

Below in conjunction with specific embodiment, the present invention is described in detail.Following examples will contribute to those skilled in the art and understand the present invention further, but not limit the present invention in any form.It should be pointed out that to those skilled in the art, without departing from the inventive concept of the premise, some distortion and improvement can also be made.These all belong to protection scope of the present invention.

Three-phase voltage type PWM inverter control method of the present invention comprises the following steps:

Step one: set up three-phase voltage type PWM inverter Mathematical Modeling, as figureshown in 1, three-phase grid-connected inverter comprises six switches, on off state is defined as follows formula (1):

K=a, b, c in formula (1), wherein a, b, c represent ac electric three-phase respectively.

Grid side electromotive force is the pure sine wave electromotive force of three phase equilibrium symmetries, sets up the three-phase voltage type PWM inverter Mathematical Modeling under three-phase static coordinate system, as shown in the formula (2) according to Kirchhoff's second law:

In formula: e _a, e _b, e _crepresent net side three-phase voltage;

I _a, i _b, i _crepresent net side three-phase current;

L represents net side filter inductance;

U _a, u _b, u _crepresent AC three-phase voltage;

R represents power switch pipe loss equivalent resistance and ac filter inductance equivalent resistance sum.

Of ac is become when Mathematical Modeling AC in three phase static symmetrical coordinates system is, be unfavorable for Control System Design, therefore can it be converted to the three-phase voltage type PWM inverter Mathematical Modeling under the d-q of electrical network fundamental frequency synchronous rotary mark system by coordinate transform, first-harmonic sinusoidal variable is converted to DC Variable, simplified control system design difficulty, realize astatic control, as shown in the formula (3):

$\left\{\begin{array}{c}{\mathrm{Ri}}_d+L\frac{{\mathrm{di}}_d}{\mathrm{dt}}=u_d+{\mathrm{wLi}}_q-e\\ {\mathrm{Ri}}_q+L\frac{{\mathrm{di}}_q}{\mathrm{dt}}=u_q-{\mathrm{wLi}}_d-e\end{array}\right.---\left(3\right)$

In formula: w represents the angular frequency of three-phase main-frequency of ac;

U _d, u _qto represent under static three phase coordinate systems that abc AC three-phase voltage is transformed into dq two phase voltage value under synchronous rotary two phase coordinate system.

E _d, e _qto represent under static three phase coordinate systems that abc nets side three-phase alternating voltage and is transformed into dq two phase voltage value under synchronous rotary two phase coordinate system.

I _d, i _qto represent under static three phase coordinate systems that abc nets side three-phase current and is transformed into dq biphase current value under synchronous rotary two phase coordinate system.

Step 2: three-phase voltage type PWM inverter designs based on the current inner loop decoupling control policy of resultant vector, by introducing the thought of resultant vector, the basis of resultant vector is analyzed the Mathematical Modeling of three-phase voltage type PWM, obtains based on the current inner loop decoupling control policy under resultant vector.

According to the Mathematical Modeling (3) of three-phase voltage type PWM inverter under d-q rotating coordinate system, adopt and have inductance parameters decoupling control policy, current regulator adopts pi regulator, and current inner loop governing equation is such as formula (4):

$\left\{\begin{array}{c}{u}_d^{*}=(k_p+\frac{k_i}{S})(i_d^{*}-i_d)-\mathrm{wL}{i}_q+e_d\\ u_q^{*}=(k_p+\frac{k_i}{S})(i_q^{*}-i_q)+\mathrm{wL}{i}_d+e_q\end{array}\right.---\left(4\right)$

Due to the symmetry of current inner loop d-q axle, therefore PI Controller gain variations is become the same.

Based on the value relating to grid side inductance parameters L during current inner loop uneoupled control under synchronous d-q coordinate system.In practical situations both, error is had between inductance measurements and actual value.By the impact of inductance measurement error, system decoupling can not be thorough, and when synchronizing frequency rises, the impact aggravation of current coupling, can have influence on the control performance of system.

Resultant vector changes the electric current link of two-output impulse generator into single-input single-output current model, by studying its transfer function in static two phase coordinates, changing controller zero point and being system is mainlimit, thus the method making it offset realizes the uneoupled control of electric current.Component under static two-phase α β coordinate system and synchronous rotary d-q coordinate system is respectively f _aand f _b, then defining resultant vector is formula (5):

By the Mathematical Modeling of three-phase voltage type PWM inverter under three phase coordinate systems static in formula (2), can derive three-phase voltage type PWM inverter under static two-phase α β coordinate system based on the Mathematical Modeling of resultant vector such as formula (6):

$L\frac{d{i}_{\mathrm{\α\β}}}{\mathrm{dt}}+R{i}_{\mathrm{\α\β}}=u_{\mathrm{\α\β}}-e_{\mathrm{\α\β}}---\left(6\right)$

When formula (6) is transformed under synchronous rotary d-q coordinate system, differential operator d/dt differential operator d/dt+jw replaces, can obtain three-phase voltage type PWM inverter under synchronous rotary d-q coordinate system based on the Mathematical Modeling of resultant vector such as formula (7):

$(\frac{d}{dt}+jw){\mathrm{Li}}_{dq}+{\mathrm{Ri}}_{dq}=u_{dq}-e_{dq}---\left(7\right)$

The expression formula of formula (6) in s territory is such as formula shown in (8):

$i_{\mathrm{dq}}=(u_{\mathrm{dq}}-e_{\mathrm{dq}})\frac{1}{\mathrm{sL}(R+\mathrm{jwL})}=(u_{\mathrm{dq}}-e_{\mathrm{dq}})\frac{1}{L[s+(\frac{R}{L}+\mathrm{jw})]}---\left(8\right)$

In synchronous coordinate system, current regulator adopts PI to control, and when not adding decoupling zero item, based on resultant vector, the open-loop transfer function of current control system in α β rest frame is such as formula shown in (9):

$G_{o1}\left(s\right)=\frac{k_p}{L}\frac{s+\frac{k_i}{k_p}-\mathrm{jw}}{(s-\mathrm{jw})(s+\frac{R}{L})}---\left(9\right)$

There is inductance parameters current inner loop uneoupled control by the dominant pole of the feedback compensation modernization system of current status, the dominant pole of system is disappeared with controller zero point mutually, thus the dominant pole of closed-loop control system is not affected by physical condition, what now transform is the dominant pole of system, and the zero point of controller is constant.Theoretical according to this, also can zero point of structural control device, the dominant pole of keeping system is constant, the zero point of controller and the dominant pole of system is offseted, can obtain required control effects equally.

According to formula (8), can the dominant pole of system be-R/L-jw in synchronous coordinate system.In order to offset with the dominant pole of system, necessary structural control device, the zero point of orecontrolling factor device is-k _i/ k _p-jw, now, when only needing to ensure CONTROLLER DESIGN parameter, makes k _i/ k _pcontrol effects required for=R/L just can obtain.Adopt the controller chassis of system during such scheme figureas figureshown in 2.

Now, based on figurethe open-loop transfer function of 2 gained under static two-phase α β coordinate system is formula (10):

$G_{o2}\left(s\right)=\frac{k_p}{L}\frac{s+\frac{k_i}{k_p}}{(s-\mathrm{jw})(s+\frac{R}{L})}---\left(10\right)$

According to figurepI Controller gain variations can be formula (11) by 2:

$C_{\mathrm{dq}}=\frac{k_p}{s}[s+(\frac{k_i}{k_p}+\mathrm{jw})]=k_p[1+(\frac{k_i}{k_p}+\mathrm{jw})\frac{1}{s}]---\left(11\right)$

Therefore formula (12) can be obtained:

$u_{\mathrm{dq}}^{*}=e_{\mathrm{dq}}+C_{\mathrm{dq}}(i_{\mathrm{dq}}^{*}-i_{\mathrm{dq}})---\left(12\right)$

Step 3: under the current inner loop decoupling control policy based on resultant vector of gained in step 2 is transformed into synchronous rotary d-q coordinate system according to formula (6), the current inner loop decoupling control method of three-phase voltage type PWM inverter without inductance parameters can be obtained.

Formula (13) can be obtained by formula (5):

$\left\{\begin{array}{c}{u}_{\mathrm{dq}}^{*}=u_d^{*}-j{u}_q^{*}\\ i_{\mathrm{dq}}^{*}=i_d^{*}-j{i}_q^{*}\\ u_{\mathrm{dq}}=u_d-j{u}_q\\ i_{\mathrm{dq}}=i_d-j{i}_q\\ e_{\mathrm{dq}}=e_d-j{e}_q\end{array}\right.---\left(13\right)$

Convolution (11), (12), (13) can obtain formula (14):

Arrangement can obtain formula (15):

$\left\{\begin{array}{c}{u}_d^{*}=(k_p+\frac{k_i}{s})(i_d^{*}-i_d)-\frac{{\mathrm{wk}}_p}{s}(i_q^{*}-i_q)+e_d\\ u_q^{*}=(k_p+\frac{k_i}{s})(i_q^{*}-i_q)-\frac{{\mathrm{wk}}_p}{s}(i_d^{*}-i_d)+e_q\end{array}\right.---\left(15\right)$

Can be found out in controller no longer containing inductance parameters L by formula (14).According to formula (14) can set up as figurecontroller chassis shown in 3 figure, achieve full decoupled without inductance parameters L of current inner loop, ensure control performance.

In step 3, the output valve of current inner loop is as the modulation signal of PWM, controls the output valve of PWM inverter, is also final output signal of the present invention.

Step 4: design three-phase voltage type PWM inverter outer voltage control strategy, the output valve controlled by outer shroud is as the reference value of current inner loop uneoupled control in step 3, specific as follows:

Voltage control adopts constant voltage to control, AC three-phase voltage u _a, u _b, u _cwith three-phase current i _a, i _b, i _cu can be obtained after d-q conversion _d, u _qand i _d, i _q.When the inversion stable operation of system unit power factor, get d axle and a phase homophase, 90 °, the advanced d axle of q axle, grid-connected side three phase sine voltage e during steady operation _a, e _b, e _cdecomposition value under d-q coordinate system is designated as e _d=381.4V, e _q=0, so q axle set point is zero, d axle set point when constant voltage controls for 381.4V.The output of outer voltage is as the reference value of current inner loop.

Three-phase voltage type PWM inverter controller chassis figureas figureshown in 4.Based on constant voltage outer shroud control, without inductance parameters current inner loop control three-phase voltage type PWM grid-connected and not grid-connected be directly connected with resistive load time application, outer voltage adopts constant voltage to control, current inner loop adopts the decoupling control policy without inductance parameters, no longer containing inductance parameters in current controller.Have in the current inner loop control strategy of inductance parameters and comprise inductance value at alternating side, and there is error in the measured value of inductance parameters and exact value, when there is error in the inductance value measured, current inner loop can not thoroughly decoupling zero, along with the rising of synchronizing frequency, the impact aggravation of current coupling, the control performance of system will be deteriorated.And the impact of inductance parameter measuring error is avoided without inductance parameters current inner loop decoupling control policy, the dominant pole of three-phase voltage type PWM inverter closed-loop control system is not by the impact of physical condition simultaneously. figure5 is three-phase voltage type PWM inverter system simulation models when being incorporated into the power networks. figure6 be three-phase voltage type PWM inverter not grid-connected and be directly connected with resistive load time system simulation model.Concrete simulation parameter as table 1shown in:

table 1the relevant parameter of three-phase voltage type PWM inverter

Parameter	Numerical value
		Frequency/the Hz of grid-connected three-phase alternating voltage	50
Line voltage effective value/the V of grid-connected three-phase alternating voltage	380
		DC voltage source voltage/V	800
Inductor L/mH	0.02
		AC resistance R/ Ω	0.1
Switching frequency f/kHz	10
		Bearing power P/kW	30

The present embodiment will verify validity and the accuracy of put forward control strategy from following two kinds of invertor operation situations.

(1) the grid-connected unity power factor inverter operation of three-phase voltage type PWM inverter;

(2) three-phase voltage type PWM inverter not grid-connected being directly connected with resistive load is run.

System responses is as attached in specification figureshown in.Wherein, figure7, figure8 is the system responses under (1) state, can find out when inverter be in be incorporated into the power networks state time, voltage and current in phase, reactive power is zero, active power maintains a stationary value, and this is consistent with emulating the unity power factor inverter operation set. figure9, figuresystem responses under 10 correspondences (2) state, can find out when inverter not grid-connected and be directly connected with resistive load time, three-phase voltage waveform is perfectly sinusoidal wave, and phase mutual deviation 120 °, the reactive power of system is zero, active power maintains a stationary value, consistent with set unity power factor inverter operation state.

The present invention is based on the thought of resultant vector, reach by transformation current inner loop controller and be zero point system is mainlimit offsets, and devises a kind of current inner loop decoupling control method without inductance parameters, and achieving three-phase voltage type PWM inverter system control performance does not affect by physical factor.This control strategy takes full advantage of discrete mathematical model simultaneously, calculates simple, easy Digital Realization.

Above specific embodiments of the invention are described.It is to be appreciated that the present invention is not limited to above-mentioned particular implementation, those skilled in the art can make various distortion or amendment within the scope of the claims, and this does not affect flesh and blood of the present invention.

Claims (4)

1. a three-phase voltage type PWM inverter control method, is characterized in that, comprises the following steps:

Step one: set up three-phase voltage type PWM inverter Mathematical Modeling;

Step 2: by introducing the thought of resultant vector, the basis of resultant vector being analyzed the Mathematical Modeling of three-phase voltage type PWM, obtains based on the current inner loop decoupling control policy under resultant vector;

Step 3: under the current inner loop decoupling control policy based on resultant vector of gained in step 2 is transformed into synchronous rotary d-q coordinate system, obtain the current inner loop decoupling control method of three-phase voltage type PWM inverter without inductance parameters;

Step 4: design three-phase voltage type PWM inverter outer voltage control strategy, the output valve controlled by outer shroud is as the reference value of current inner loop uneoupled control in step 3.

2. three-phase voltage type PWM inverter control method according to claim 1, is characterized in that, described three-phase grid-connected inverter comprises six switches, and on off state is defined as follows formula:

K=a, b, c in formula, wherein a, b, c represent ac electric three-phase respectively.

3. three-phase voltage type PWM inverter control method according to claim 1, is characterized in that, described three-phase voltage type PWM inverter Mathematical Modeling d-q mark system under adopt as shown in the formula:

$\left\{\begin{array}{c}{\mathrm{Ri}}_d+L\frac{{\mathrm{di}}_d}{\mathrm{dt}}=u_d+w{\mathrm{Li}}_q-e\\ {\mathrm{Ri}}_d+L\frac{{\mathrm{di}}_q}{\mathrm{dt}}=u_q-{\mathrm{wLi}}_d-e\end{array}\right.$

In formula: L represents net side filter inductance; R represents power switch pipe loss equivalent resistance and ac filter inductance equivalent resistance sum, and w represents the angular frequency of three-phase main-frequency of ac; u _d, u _qto represent under static three phase coordinate systems that abc AC three-phase voltage is transformed into dq two phase voltage value under synchronous rotary two phase coordinate system; e _d, e _qto represent under static three phase coordinate systems that abc nets side three-phase alternating voltage and is transformed into dq two phase voltage value under synchronous rotary two phase coordinate system; i _d, i _qto represent under static three phase coordinate systems that abc nets side three-phase current and is transformed into dq biphase current value under synchronous rotary two phase coordinate system.

4. three-phase voltage type PWM inverter control method according to claim 1, is characterized in that, in described step 3, the output valve of current inner loop is as the modulation signal of PWM, controls the output valve of PWM inverter, is also final output signal of the present invention.