CN101807861A - Method for rectifying three-phase active power factor - Google Patents

Abstract

The invention discloses a three-phase active power factor rectification method for realizing the three-phase power factor correction and the three-phase input current harmonics reduction, which comprises the following steps: obtaining an input current average value of two-phase in the n-th PWM period; regulating the obtained control parameter via a PI based on the output voltage; calculating the equivalent rated load resistance on each phase AC side, the equivalent rated load resistance on each phase AC side in the rated power and the duty cycles of three bidirectional switches in the next PWM control period, finally outputting three bidirectional switch duty cycle control signals to control three corresponding bidirectional switches by a DSP control system at the beginning of the next PWM control period. The invention adopts a DSP (Digital Signal Processor) as the control core to realize the three-phase active power factor rectification without an input voltage sensor approaching to the unity power factor.

Description

A kind of method for rectifying three-phase active power factor

Technical field

The present invention is a kind of method that realizes three-phase activity coefficient adjustment, reduces the three-phase input current harmonic wave, belongs to electrical technology field.

Background technology

At present, general rectifying three-phase active power factor device all needs to detect input ac voltage, realizes control to input current waveform by the waveform of following the tracks of input voltage, thereby realizes improving power factor and reduce Harmonics of Input.This method at first detects three-phase input ac voltage signal, with this signal reference signal as input current after nursing one's health, detect input current then, thereby change the PWM realization raising input power factor reduction input current harmonics of control main circuit power pipe according to the difference of input current and reference signal.This method need be used three voltage sensor senses three-phase input voltages, has increased the control system cost, and simultaneously, the signal errors of three voltage sensors or the interference of conduction pathway all can influence the control effect.In single-phase, rectifying three-phase active power factor device, use monocycle control method and can realize need not input voltage sensor, but all be the method that adopts analog circuit control.Because the method that the analog circuit control method adopts analogue device to build hardware circuit formation control circuit realizes, this circuit is once determining, relevant parameter in the control system then can't be regulated, and along with problems such as parameter drift appear in the aging meeting of the element in the control circuit, the control effect of system can be received influence.

Summary of the invention

The present invention proposes a kind of numerically controlled no input voltage sensor, effective method for rectifying three-phase active power factor of control of being suitable for.

The technical solution used in the present invention is: the main circuit with 6 rectifier diodes inserts three-phase input power supply by three input PFC inductance, three two-way power switch, three two-way power switch in the main circuit insert the DSP control system by drive circuit, at first obtain n interior input current average value of PWM cycle of two-phase; Regulate the Control Parameter that obtains through PI according to output voltage; Calculate the equivalent nominal load resistance of every cross streams side; The equivalent nominal load resistance of every cross streams side when calculating rated power; Calculate the duty ratio of the next PWM control cycle of three bidirectional switchs again, last DSP control system is controlled three corresponding bidirectional switchs with above-mentioned three the bidirectional switch duty cycle control signal outputs that obtain of step when next PWM control cycle begins.

The present invention adopts DSP as the control core, three-phase three switch three lever circuit are as main circuit topology, according to the AC side equivalent resistance under the input average current that samples, the rated condition, desired output direct voltage, actual output dc voltage, go out the duty ratio of three bidirectional switch PWM of next PWM control cycle by the derivation of equation, thereby realize no input voltage sensor rectifying three-phase active power factor near unity power factor.

Description of drawings

Fig. 1 is the inventive circuit theory diagram, wherein, and e _ae _be _cBe the input three phase mains, L _aL _bL _cBe that three input power factors are proofreaied and correct PFC inductance, K _aK _bK _cBe three two-way power switch, D ₁～D ₆Be 6 rectifier diodes, C ₁C ₂Be output filter capacitor, U _DcBe the voltage of detected output dc bus.

Fig. 2 is the schematic diagram of certain phase input current.

Fig. 3 is certain biphase current oscillogram.

Embodiment

The rectifier of Fig. 1 has 6 rectifier diode (D ₁～D ₆) main circuit by three input PFC inductance (L _aL _bL _c) access three-phase input power supply e _a, e _b, e _c, three two-way power switch K _a, K _b, K _cAn end common point insert two output capacitance C ₁, C ₂Mid point, DSP control system input pwm signal drives the back through drive circuit and controls three two-way power switch K in the main circuit _a, K _b, K _c

As Fig. 1, need in the circuit three bidirectional switch K _a, K _b, K _cDuty ratio control, by obtaining three bidirectional switch K to the controlling models analysis _a, K _b, k _cN+1 PWM duty ratio

Concrete steps are as follows:

1) obtains n interior input current average value＜i of PWM cycle of two-phase _{a n}With＜i _{b n}

2) according to output voltage U _DcRegulate the Control Parameter K that obtains through PI _UCalculate the equivalent nominal load resistance of every cross streams side $R^{\mathrm{\Δ}}=\frac{{220}^2}{P^{\mathrm{\Δ}}}\×3,$ P ^ΔRated power for rectifier; The equivalent nominal load resistance R of every cross streams side when calculating rated power ^Δ

3) calculate three bidirectional switch K _a, K _b, K _cThe duty ratio D of next PWM control cycle _N+1:

$D_{n+1}=T_{\mathrm{\α\β}/\mathrm{abc}}\left[\begin{array}{c}-\frac{3}{2}{K}_U\frac{R^{\mathrm{\Δ}}}{V^{\mathrm{\Δ}}}{\⟨i_a\⟩}_n\\ \frac{\sqrt{3}}{2}{K}_U\frac{R^{\mathrm{\Δ}}}{V^{\mathrm{\Δ}}}{\⟨i_a\⟩}_n+\sqrt{3}{K}_U\frac{R^{\mathrm{\Δ}}}{V^{\mathrm{\Δ}}}{\⟨i_b\⟩}_n\\ \frac{\sqrt{3}}{2}\end{array}\right]$

In the formula:

$D_{n+1}=\left[\begin{array}{ccc}{D}_{a_{n+1}}& D_{b_{n+1}}& D_{c_{n+1}}\end{array}\right],$ Be the duty ratio of n+1 each bidirectional switch of PWM control cycle,

V ^ΔBe the VD value of expectation, $T_{\mathrm{\α\β}/\mathrm{abc}}=\left[\begin{array}{ccc}1& 0& \frac{1}{\sqrt{2}}\\ -\frac{1}{2}& -\frac{\sqrt{3}}{2}& \frac{1}{\sqrt{2}}\\ -\frac{1}{2}& \frac{\sqrt{3}}{2}& \frac{1}{\sqrt{2}}\end{array}\right]$

4) three bidirectional switch K when next PWM control cycle begins, step 3) being obtained of DSP control system _a, K _b, K _cThree corresponding bidirectional switchs of duty cycle control signal output control.

2, about the preparation method of a, n PWM of b two-phase input current average value in the cycle:

In analog control circuit, can adopt the method that the electric current in the control cycle is carried out integration to obtain the mean value of a switch control cycle input current, and in digital control if adopt the digital integration method to ask the mean value of input current, then require the A/D sample frequency far above switch control cycle frequency, this requirement to hardware system is very high, and the present invention proposes the mean value that a kind of cycle synchronisation double sampling method can obtain accurate input current.

As Fig. 2, n cycle PWM cycle begins to finish i to (n+1) Ts from nTs constantly _LBe that power tube is opened electric current constantly, i _HBe that power tube turn-offs electric current constantly, the mean value that can obtain input current in n cycle is:

${\&lang;i\&rang;}_n=\frac{i_L+i_{\mathrm{<figure-callout\; id="2"\; label="H"\; filenames="H2009102322808E00021.png"\; state="\{\{state\}\}">H</figure-callout>}}}{2}$

For obtaining the mean value of following formula, the step of the concrete method of sampling of cycle synchronisation double sampling method is as follows:

1) standby sampled point, the mid point that defines the rising of input current as Fig. 2 are that the mid point of M1, decline is that M2 is, these two points are as standby sampled point.

2) determine sampled point, according to n cycle PWM cycle duty ratio D _nSize is determined sampled point, works as D _nDetermined that M2 was a sampled point at＜15% o'clock; As 15%≤D _nDetermined that M1 and M2 were sampled point at≤85% o'clock; Work as D _nDetermined that M1 was a sampled point at＞85% o'clock.

3) average current calculates, and the electric current that samples according to above-mentioned method is defined as With

It is as follows to obtain n cycle PWM cycle average current:

${\&lang;i\&rang;}_n=\left\{\begin{array}{cc}{\&lang;i_{{\mathrm{<figure-callout\; id="2"\; label="M"\; filenames="H2009102322808E00021.png"\; state="\{\{state\}\}">M</figure-callout>}}_2}\&rang;}_n& D_n<15\%\\ \frac{{\&lang;i_{{\mathrm{<figure-callout\; id="1"\; label="M"\; filenames="H2009102322808E00021.png"\; state="\{\{state\}\}">M</figure-callout>}}_1}\&rang;}_n+{\&lang;i_{{\mathrm{<figure-callout\; id="2"\; label="M"\; filenames="H2009102322808E00021.png"\; state="\{\{state\}\}">M</figure-callout>}}_2}\&rang;}_{\mathrm{<figure-callout\; id="2"\; label="n"\; filenames="H2009102322808E00021.png"\; state="\{\{state\}\}">n</figure-callout>}}}{2}& 15\%\&le;D_n\&le;85\%\\ {\&lang;i_{{\mathrm{<figure-callout\; id="1"\; label="M"\; filenames="H2009102322808E00021.png"\; state="\{\{state\}\}">M</figure-callout>}}_1}\&rang;}_n& D_n>85\%\end{array}\right.$

This processing method is a kind of one-period double sampling method of importing average current, at each once sampling current value of mid point of the rising and the decline of electric current, handles according to the situation of duty ratio again, can largely reduce the interference of power switch pipe switch.

Adopting rectification effect that this method realizes as shown in Figure 3, is respectively a, the b biphase current oscillogram of model machine rectifier input among Fig. 3, and the effective value of a, b two-phase all is 14.5A.

Claims (2)

1. a method for rectifying three-phase active power factor has 6 rectifier diode (D ₁～D ₆) main circuit by three input PFC inductance (L _aL _bL _c) access three-phase input power supply (e _ae _be _c), three two-way power switch (K _aK _bK _c), three two-way power switch (K in the main circuit _aK _bK _c) insert the DSP control system by drive circuit, it is characterized in that adopting following steps:

1) obtains n interior input current average value＜i of PWM cycle of two-phase _{a n}With＜i _{b n}

2) according to output voltage U _DcRegulate the Control Parameter K that obtains through PI _UCalculate the equivalent nominal load resistance of every cross streams side $R^{\mathrm{\&Delta;}}=\frac{{220}^2}{P^{\mathrm{\&Delta;}}}\&times;3,$ P ^ΔRated power for rectifier; The equivalent nominal load resistance R of every cross streams side when calculating rated power ^Δ

3) calculate three bidirectional switch (K _aK _bK _c) the duty ratio D of next PWM control cycle _N+1:

$D_{n+1}=T_{\mathrm{\&alpha;\&beta;}/\mathrm{abc}}\left[\begin{array}{c}-\frac{3}{2}{K}_U\frac{R^{\mathrm{\&Delta;}}}{V^{\mathrm{\&Delta;}}}{<i_a>}_n\\ \frac{\sqrt{3}}{2}{K}_U\frac{R^{\mathrm{\&Delta;}}}{V^{\mathrm{\&Delta;}}}{<i_a>}_n+\sqrt{3}{K}_U\frac{R^{\mathrm{\&Delta;}}}{V^{\mathrm{\&Delta;}}}{<i_b>}_n\\ \frac{\sqrt{3}}{2}\end{array}\right]$

In the formula: V ^ΔBe the VD value of expectation, $T_{\mathrm{\&alpha;\&beta;}/\mathrm{abc}}=\left[\begin{array}{ccc}1& 0& \frac{1}{\sqrt{2}}\\ -\frac{1}{2}& -\frac{\sqrt{3}}{2}& \frac{1}{\sqrt{2}}\\ -\frac{1}{2}& \frac{\sqrt{3}}{2}& \frac{1}{\sqrt{2}}\end{array}\right]$

4) three bidirectional switch (K when next PWM control cycle begins, step 3) being obtained of DSP control system _aK _bK _c) three corresponding bidirectional switchs of duty cycle control signal output control.

2. a kind of method for rectifying three-phase active power factor according to claim 1 is characterized in that: n interior input current average value＜i of PWM cycle of two-phase _{a n}With＜i _{b n}Preparation method be:

1) mid point of the rising of definition input current is that the mid point of M1, decline is that M2 is as standby sampled point;

2) according to n cycle PWM cycle duty ratio D _nSize is determined sampled point, works as D _nDetermined that M2 was a sampled point at＜15% o'clock; As 15%≤D _nDetermined that M1 and M2 were sampled point at≤85% o'clock; Work as D _nDetermined that M1 was a sampled point at＞85% o'clock.

3) calculate input current average value:

${<i>}_n=\left\{\begin{array}{cc}{<i_{M_2}>}_n& D_n<15\%\\ \frac{{<i_{M_1}>}_n+{<i_{M_2}>}_n}{2}& 15\%\&le;D_n\&le;85\%\\ {<i_{M_1}>}_n& D_n>85\%\end{array}\right.$

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