CN102055326A - Method for controlling process of turning off soft switch and soft switch - Google Patents

Abstract

The invention discloses a method for controlling the process of turning off a soft switch. When any main power switch tube in the soft switch needs to be turned off, the method comprises the following steps of: turning on an auxiliary switch tube with different position from the main power switch to be turned off on an axle arm, then charging energy to an LC (Liquid Crystal) second-order resonance circuit, and determining the ending time of energy charging for meeting the requirement that the maximum value of the resonance current is equal to the current load current; when the ending time for the energy charging is reached, ending the energy charging, turning off the auxiliary switch tube with different position from the main power switch to be turned off on the axle arm, and turning on an auxiliary switch tube with same position as the main power switch tube to be turned off on the axle arm; and determining that the time when the resonance circuit is zero, and starting from the moment and after 1/4 resonance period, turning off the auxiliary switch tube with same position as the main power switch tube to be turned off on the axle arm and the main power switch tube to be turned off simultaneously. The invention discloses the soft switch simultaneously. Due to application of the technical scheme disclosed by the invention, extra loss in the process of turning off the soft switch can be reduced.

Description

A kind of soft switch turn off process control method and a kind of soft switch

Technical field

The present invention relates to soft switch technique, particularly a kind of soft switch turn off process control method and a kind of soft switch.

Background technology

Usually, the large power inverter power source of 100KW-1000KW all adopts insulated gate bipolar transistor (IGBT, Insulated Gate Bipolar Transisitor) as device for power switching, the switching frequency of IGBT self can reach more than the 20KHz.But because the output current of inverter is bigger, the switching loss high frequency response under is also bigger, so limited the actual switch frequency of IGBT, generally about 2K, and needs the radiator of outfit bulky.This makes the output waveform of inverter have severe distortion, and harmonic component increases greatly; In addition, switch I GBT under the condition of big electric current can produce strong electromagnetic interference.Therefore, hope can make the IGBT switch of " softly ", to avoid the problems referred to above.

For this reason, propose a kind of soft switch technique in the prior art, Fig. 1 is the circuit topological structure schematic diagram of existing soft switch.As shown in Figure 1, S ₁And S ₄Be master power switch pipe, S _1xAnd S _4xBe auxiliary switch, S ₁And S ₄Series connection constitutes main switch brachium pontis, S _4xAnd S _1xSeries connection constitutes the auxiliary switch brachium pontis, wherein, and S ₁And S _4xLay respectively at the last brachium pontis of place brachium pontis separately, S ₄And S _1xLay respectively at the following brachium pontis of place brachium pontis separately; Two brachium pontis are connected in parallel between the dc bus, are connected with one between its mid point by resonant inductance L _rWith the resonance capacitor C _rThe LC second order resonant circuit of forming; C _dBe dc-link capacitance, be connected in parallel between the dc bus.

The operation principle of soft switch shown in Figure 1 is: before the master power switch pipe carries out switch, by handling auxiliary switch, cause LC second order resonance, with the load current i that flows in the master power switch pipe _aProgressively transfer in the LC second order resonant circuit along the sinusoidal variations rule, make load current i _aOnly reverse flow is through the inverse parallel diode of master power switch pipe, thereby realizes Zero Current Switch master power switch pipe.

The general controls mode is as follows: suppose that the master power switch pipe is in off state, load current i _aDirection as shown in Figure 1, this moment load current i _aMust be by master power switch pipe S ₁The inverse parallel diode be back to dc bus, therefore, master power switch pipe S ₁Be Zero Current Switch, and master power switch pipe S ₄Realize that Zero Current Switch then will be by means of auxiliary switch S _4x

Fig. 2 is existing master power switch pipe S ₄The process that turns on and off schematic diagram.As shown in Figure 2, opening master power switch pipe S ₄Before, at first open auxiliary switch S _4x, utilize resonant capacitance C _rLast energy stored causes LC second order resonant circuit free harmonic vibration; t ₂Constantly, resonance current i _xEqual load current i _a, load current i _aThe LC second order resonant circuit of all flowing through at this moment, turn-offs auxiliary switch S _4xAnd open master power switch pipe S simultaneously ₄, the most of energy in the LC second order resonant circuit feeds back to dc bus.

Turn-offing master power switch pipe S ₄Before, need open auxiliary switch S earlier equally _4x, utilize DC bus-bar voltage u _d(be dc capacitor C _dOn voltage) excitation second order resonant tank; At t ₅～t ₆Constantly, dc bus charges into energy to LC second order resonant circuit; At t ₇～t ₉Constantly, resonance current i _xBegin to surpass load current i _a, turn-off auxiliary switch S this moment _4xWith master power switch pipe S ₄, resonant energy is stored in capacitor C _rIn.

But as can be seen from Figure 2, there is an obvious defects in above-mentioned control mode, promptly when turn-offing the master power switch pipe, and resonance current i _xPeak value need be more than or equal to specified load current i _a, to guarantee in full-load range, realizing zero-current switching; Yet in the most of the time, inverter all can not operate under the full-load conditions, that is to say, and under low loading condition, the resonance current i in the turn off process _xPeak value be far longer than current load current i _a, the resonance current i that this is bigger _xWhen flowing through auxiliary tube switching tube and master power switch pipe, extra loss will be caused.

Summary of the invention

In view of this, main purpose of the present invention is to provide a kind of soft switch turn off process control method, can reduce the excess loss in the soft switch turn off process.

For achieving the above object, technical scheme of the present invention is achieved in that

A kind of soft switch turn off process control method comprises two master power switch pipe S in the described soft switch ₁And S ₄And two auxiliary switch S _1xAnd S _4x, described S ₁And S ₄Series connection constitutes main switch brachium pontis, described S _4xAnd S _1xSeries connection constitutes the auxiliary switch brachium pontis, wherein, and described S ₁And S _4xLay respectively at the last brachium pontis of place brachium pontis separately, described S ₄And S _1xLay respectively at the following brachium pontis of place brachium pontis separately; Described two brachium pontis are connected in parallel between the dc bus, are connected with a LC second order resonant circuit that is become with the resonance capacitance group by resonant inductance between the mid point of described two brachium pontis; Simultaneously, comprise further in the described soft switch that one is parallel to the dc-link capacitance between the described dc bus; When needs turn-offed arbitrary master power switch pipe, this method comprised:

Open and wait to turn-off the auxiliary switch that the master power switch pipe is positioned at different brachium pontis position, charge into energy, and be defined as satisfying the energy that the resonance current maximum equals current load current and charge into the finish time to described LC second order resonant circuit;

When arriving energy and charge into the finish time, finish energy and charge into, turn-off and turn-off the auxiliary switch that the master power switch pipe is positioned at different brachium pontis position, and open with described and wait to turn-off the auxiliary switch that the master power switch pipe is positioned at identical brachium pontis position with described waiting;

Determine that resonance current is zero constantly, and constantly, behind 1/4 harmonic period, turn-off simultaneously and describedly wait to turn-off the master power switch pipe and wait to turn-off the auxiliary switch that the master power switch pipe is positioned at identical brachium pontis position with described from this.

Preferably, describedly be defined as satisfying energy that the resonance current maximum equals current load current and charge into and comprise the finish time:

A, according to the current function of state of described LC second order resonant circuit

Calculate described resonant capacitance C _rOn function of voltage u _x(t)=-u _d(1-cos ω (t-t ₅)) and described resonant inductance L _rOn current function

Wherein,

Described u _dThe expression DC bus-bar voltage, described t ₅Expression with wait to turn-off the master power switch pipe and be positioned at the opening the moment of auxiliary switch of different brachium pontis position;

B, according to the result of calculation in the steps A, be defined as satisfying the resonance current maximum and equal current load current, the energy that need charge into to described LC second order resonant circuit:

Wherein, described t ₆The expression energy charges into the finish time, described i _aRepresent current load current;

Further try to achieve: $t_6=\frac{1}{\mathrm{\&omega;}}\arccos (1-\frac{Z^2{i}_a^2}{2u_d^2})+{\mathrm{<figure-callout\; id="5"\; label="t"\; filenames="H2009102096012E0000031.png"\; state="\{\{state\}\}">t</figure-callout>}}_5.$

Preferably, described definite resonance current is to comprise in zero moment:

C, according to the current function of state of described LC second order resonant circuit

And the t that calculates ₆Moment resonant capacitance C _rOn voltage

With the resonance inductance L _rOn electric current

Calculate described resonant capacitance C _rOn function of voltage u _x(t)=u _x(t ₆) cos ω (t-t ₆)+Zi _x(t ₆) sin ω (t-t ₆) and described resonant inductance L _rOn current function

And according to the symmetry of resonance current waveform, moving on to resonance current by the initial point with the resonance current waveform is zero t constantly ₇The place is reduced to u respectively with it _x(t)=u _x(t ₇) cos ω (t-t ₇) and

D, described resonant capacitance C when determining that resonance current is zero _rOn voltage u _x(t ₇The Zi of)=- _aAnd described resonant inductance L _rOn current i _x(t ₇)=0;

The result of calculation of E, comprehensive step C and D obtains:

And further try to achieve:

A kind of soft switch comprises in the described soft switch: two master power switch pipe S ₁And S ₄And two auxiliary switch S _1xAnd S _4x, described S ₁And S ₄Series connection constitutes main switch brachium pontis, described S _4xAnd S _1xSeries connection constitutes the auxiliary switch brachium pontis, wherein, and described S ₁And S _4xLay respectively at the last brachium pontis of place brachium pontis separately, described S ₄And S _1xLay respectively at the following brachium pontis of place brachium pontis separately; Described two brachium pontis are connected in parallel between the dc bus, are connected with a LC second order resonant circuit that is become with the resonance capacitance group by resonant inductance between the mid point of described two brachium pontis; Simultaneously, comprise further in the described soft switch that one is parallel to the dc-link capacitance between the described dc bus;

Initial condition, to be positioned at the auxiliary switch of different brachium pontis position open-minded with waiting to turn-off the master power switch pipe, charges into energy to described LC second order resonant circuit;

Charge into the finish time what determine for satisfying the energy that the resonance current maximum equals current load current, finish energy and charge into; Simultaneously, wait to turn-off the auxiliary switch that the master power switch pipe is positioned at different brachium pontis position and turn-off, wait to turn-off the master power switch pipe to be positioned at the auxiliary switch of identical brachium pontis position open-minded with described with described;

At the resonance current of determining is zero to rise constantly, behind 1/4 harmonic period, waits to turn-off the master power switch pipe and is positioned at the auxiliary switch of identical brachium pontis position and describedly waits to turn-off the master power switch pipe and turn-off simultaneously with described.

As seen, adopt technical scheme of the present invention, control the size that fills into the energy in the LC second order resonance electricity loop when turn off process begins according to the size of load current, the peak value that makes the energy that charges into just in time satisfy resonance current equals current load current, and carry out the switching of switching tube, thereby reduced the excessive excess loss that resonance current caused at the peak point of resonance current.

Description of drawings

To make clearer above-mentioned and other feature and advantage of the present invention of those of ordinary skill in the art by describing the preferred embodiments of the present invention in detail below with reference to accompanying drawing, in the accompanying drawing:

Fig. 1 is the circuit topological structure schematic diagram of existing soft switch;

Fig. 2 is existing master power switch pipe S ₄The process that turns on and off schematic diagram;

Fig. 3 is the flow chart of the inventive method embodiment;

Fig. 4 is master power switch pipe S of the present invention ₄The process that turns on and off schematic diagram;

Fig. 5 (a)～5 (d) is different resonance current flow path schematic diagrames constantly among the method for the invention embodiment.

Embodiment

At problems of the prior art, the present invention proposes a kind of brand-new soft switch controlling schemes, because problems of the prior art mainly are caused by turn off process, therefore scheme of the present invention is only improved at existing turn off process, promptly control the size that fills into the energy in the LC second order resonance electricity loop when turn off process begins according to the size of load current, the peak value that makes the energy that charges into just in time satisfy resonance current equals current load current, and carry out the switching of switching tube, thereby avoid the excessive excess loss that resonance current caused at the peak point of resonance current.

In order to make technical scheme of the present invention and advantage clearer,, the present invention is further elaborated below in conjunction with drawings and Examples.Should be appreciated that specific embodiment described herein only in order to explanation the present invention, and be not used in qualification the present invention.

Fig. 3 is the flow chart of the inventive method embodiment.Suppose to need in the present embodiment to turn-off master power switch pipe S ₄, as shown in Figure 3, may further comprise the steps:

Step 301: open auxiliary switch S _4x, charging into energy to LC second order resonant circuit, and be defined as satisfying the resonance current maximum and equal current load current, energy charges into the finish time.

Fig. 4 is master power switch pipe S of the present invention ₄The process that turns on and off schematic diagram.As shown in Figure 4, t wherein ₀～t ₄Identical in the corresponding opening process, specific implementation and prior art, repeat no more.At t ₅Constantly, open auxiliary switch S _4x, at this moment, energy is from dc-link capacitance C _dFill into LC second order resonant circuit, resonance current i _xFlow according to path shown in the dotted line among Fig. 5 (a).

In addition, except initially powering on constantly resonant capacitance C _rOn will have a smaller initial voltage:

$u_x=\left(t_5\right)=-\sqrt{u_d^2+u_{\mathrm{xm}}^2}+u_d$

Wherein, u _XmExpression t ₀Moment resonant capacitance C _rGo up residual voltage, u _dThe expression DC bus-bar voltage.

In order to make the energy that charges into that certain redundancy be arranged, and simplify and calculate, can ignore this initial voltage, and hypothesis u _x(t ₅)=0, i _x(t ₅)=0, thus the function of state that can obtain LC second order resonant tank is as follows:

$\left\{\begin{array}{c}{C}_r\frac{{\mathrm{du}}_x}{\mathrm{dt}}=i_x\\ L_r\frac{{\mathrm{di}}_x}{\mathrm{dt}}=-u_x-u_d\end{array}\right.---\left(2\right)$

Solve:

$\left\{\begin{array}{c}{u}_x\left(t\right)=-u_d(1-\cos \mathrm{\&omega;}(t-t_5))\\ i_x\left(t\right)=-\frac{u_d}{Z}\sin \mathrm{\&omega;}(t-t_5)\end{array}\right.---\left(3\right)$

Wherein, $\mathrm{\&omega;}=\frac{1}{\sqrt{L_r{C}_r}},$ $Z=\sqrt{\frac{L_r}{C_r}}.$

In order to make resonance current i _xPeak value equal current load current i _a(because the frequency of switch is very high, thus load current in a switch periods, can be similar to think constant), the energy of input LC second order resonant tank should satisfy:

$\frac{1}{2}{L}_r{i}_a^2=\frac{1}{2}{L}_r{i}_x^2(t_6-t_5)+\frac{1}{2}{C}_r{u}_x^2(t_6-t_5)=C_r{u}_d^2[1-\cos \mathrm{\&omega;}(t_6-t_5)]---\left(4\right)$

Because as resonance current i _xPeak value equal current load current i _aThe time, resonant capacitance C _rOn will not have voltage, that is to say that the energy in the LC second order resonant tank only is present in resonant inductance L _rOn, its energy is

Suppose that it is t that energy charges into the finish time ₆, energy so

To be equal to t ₆To t ₅Time period interior resonance capacitor C _rWith the resonance inductance L _rOn the energy summation, promptly as shown in Equation (4).

According to formula (3) and (4), can try to achieve:

$t_6-{\mathrm{<figure-callout\; id="5"\; label="t"\; filenames="H2009102096012E0000031.png"\; state="\{\{state\}\}">t</figure-callout>}}_5=\frac{1}{\mathrm{\&omega;}}\arccos (1-\frac{Z^2{i}_a^2}{2u_d^2})$

Or $t_6=\frac{1}{\mathrm{\&omega;}}\arccos (1-\frac{Z^2{i}_a^2}{2u_d^2})+t_5---\left(5\right)$

t ₆One be positioned constantly Scope in.

Further try to achieve t ₆Moment resonant capacitance C _rOn voltage and resonance inductance L _rOn electric current as follows:

$\left\{\begin{array}{c}{u}_x\left(t_6\right)=-\frac{Z^2{i}_a^2}{2u_d}\\ i_x\left(t_6\right)=-\frac{u_d}{Z}\sqrt{1-{(1-\frac{Z^2{i}_a^2}{2u_d^2})}^2}\end{array}\right.---\left(6\right)$

Step 302: when the arrival energy charges into the finish time, finish energy and charge into, turn-off auxiliary switch S _4x, and after Dead Time finishes, open auxiliary switch S _1x

At this moment, resonance current i _xTo flow according to path shown in the dotted line among Fig. 5 (b), and constantly be resonant capacitance C _rReverse charging.

At this moment, the function of state of LC second order resonant tank is as follows:

$\left\{\begin{array}{c}{C}_r\frac{{\mathrm{du}}_x}{\mathrm{dt}}=i_x\\ L_r\frac{{\mathrm{di}}_x}{\mathrm{dt}}=-u_x\end{array}\right.---\left(7\right)$

Solve:

$\left\{\begin{array}{c}{u}_x\left(t\right)=u_x\left(t_6\right)\cos \mathrm{\&omega;}(t-t_6)+{\mathrm{Zi}}_x\left(t_6\right)\sin \mathrm{\&omega;}(t-t_6)\\ i_x\left(t\right)=-\frac{1}{Z}{u}_x\left(t_6\right)\sin \mathrm{\&omega;}(t-t_6)+i_x\left(t_6\right)\cos \mathrm{\&omega;}(t-t_6)\end{array}\right.---\left(8\right)$

Wherein, $\mathrm{\&omega;}=\frac{1}{\sqrt{L_r{C}_r}},$ $Z=\sqrt{\frac{L_r}{C_r}}.$

Step 303: determine that resonance current is zero the moment, and from this constantly, behind 1/4 harmonic period, turn-off auxiliary switch S simultaneously _1xWith master power switch pipe S4.

Suppose resonance current i _xBe that moment of 0 is t ₇, can determine t so ₇Moment resonant capacitance C _rOn voltage and resonance inductance L _rOn electric current as follows:

$\left\{\begin{array}{c}{u}_x\left(t_7\right)=-{\mathrm{Zi}}_a\\ i_x\left(t_7\right)=0\end{array}\right.---\left(9\right)$

For ease of determining t ₇Constantly, can be with resonance current i _xThe initial point of waveform move on to t ₇The place is according to the symmetry of waveform, t ₇～t ₆Time be equal to from t ₇The time be carved into resonant capacitance C _rBuild-up of voltage to u _x(t ₇) time, so have:

$\left\{\begin{array}{c}{C}_r=\frac{{\mathrm{du}}_x}{\mathrm{dt}}=i_x\\ L_r\frac{{\mathrm{di}}_x}{\mathrm{dt}}=-u_x\end{array}\right.---\left(7\right)$

Solve (result after formula 8 is simplified):

$\left\{\begin{array}{c}{u}_x\left(t\right)=u_x\left(t_7\right)\cos \mathrm{\&omega;}(t-t_7)=-{\mathrm{Zi}}_a\cos \mathrm{\&omega;}(t-t_7)\\ i_x\left(t\right)=-\frac{1}{Z}{u}_x\left(t_7\right)\sin \mathrm{\&omega;}(t-t_7)=i_a\sin \mathrm{\&omega;}(t-t_7)\end{array}\right.---\left(10\right)$

Wherein, $\mathrm{\&omega;}=\frac{1}{\sqrt{L_r{C}_r}},$ $Z=\sqrt{\frac{L_r}{C_r}}.$

And further can get in conjunction with formula (6):

$-{\mathrm{Zi}}_a\cos \mathrm{\&omega;}(t_7-t_6)=u_x\left(t_6\right)=-\frac{Z^2{i}_a^2}{2u_d}---\left(11\right)$

That is: $t_7-t_6=\frac{1}{\mathrm{\&omega;}}\arccos \frac{{\mathrm{Zi}}_a}{{2u}_d}$

Or $t_7=\frac{1}{\mathrm{\&omega;}}\arccos \frac{{\mathrm{Zi}}_a}{2u_d}+t_6---\left(12\right)$

From t ₇Constantly begin resonance current i _xTo flow according to path shown in the dotted line among Fig. 5 (c), and continuous and current load current i _X4The change of current.At this moment, the function of state of LC second order resonant circuit is as follows:

$\left\{\begin{array}{c}{C}_r\frac{{\mathrm{du}}_x}{\mathrm{dt}}=i_x\\ L_r\frac{{\mathrm{di}}_x}{\mathrm{dt}}=-u_x\end{array}\right.---\left(7\right)$

Behind 1/4 harmonic period, be assumed to be t8 constantly, will have:

$\left\{\begin{array}{c}{u}_x\left(t_8\right)=0\\ i_x\left(t_8\right)=i_a\end{array}\right.---\left(13\right)$

From t ₈Constantly begin, turn-off master power switch pipe S simultaneously ₄With auxiliary switch S _1x, resonance current i _xAlong S _4xThe inverse parallel diode upwards flow, simultaneously gradually to master power switch pipe S ₁The change of current of inverse parallel diode, shown in the dotted line among Fig. 5 (d).At this moment, the function of state of LC second order resonant circuit is as follows:

$\left\{\begin{array}{c}{C}_r\frac{{\mathrm{du}}_x}{\mathrm{dt}}=i_x\\ L_r\frac{{\mathrm{di}}_x}{\mathrm{dt}}=-u_x\end{array}\right.---\left(7\right)$

Solve:

$\left\{\begin{array}{c}{u}_x\left(t\right)=i_{a}Z\sin \mathrm{\&omega;}(t-t_8)\\ i_x\left(t\right)=i_a\cos \mathrm{\&omega;}(t-t_8)\end{array}\right.---\left(14\right)$

Wherein, $\mathrm{\&omega;}=\frac{1}{\sqrt{L_r{C}_r}},$ $Z=\sqrt{\frac{L_r}{C_r}}.$

Through the t behind 1/4 harmonic period ₉Shi Keyou

$\left\{\begin{array}{c}{u}_x\left(t_9\right)=i_{a}Z=u_{\mathrm{xm}}\\ i_x\left(t_9\right)=0\end{array}\right.---\left(15\right)$

So far, finish whole turn off process.

Need to prove, above-mentioned only with master power switch pipe S ₄Turn off process be that example describes, for master power switch pipe S ₁Turn off process, it realizes principle and master power switch pipe S ₄Identical, repeat no more.

In a word, adopt technical scheme of the present invention, control the size that fills into the energy in the LC second order resonance electricity loop when turn off process begins according to the size of load current, the peak value that makes the energy that charges into just in time satisfy resonance current equals current load current, and carry out the switching of switching tube, thereby reduced the excessive excess loss that resonance current caused at the peak point of resonance current.

The foregoing description only is used to illustrate, and is not limited to technical scheme of the present invention.All any modifications of being done within the spirit and principles in the present invention, be equal to and replace and improvement etc., all should be included within protection scope of the present invention.

Claims (4)

1. a soft switch turn off process control method comprises two master power switch pipe S in the described soft switch ₁And S ₄And two auxiliary switch S _1xAnd S _4x, described S ₁And S ₄Series connection constitutes main switch brachium pontis, described S _4xAnd S _1xSeries connection constitutes the auxiliary switch brachium pontis, wherein, and described S ₁And S _4xLay respectively at the last brachium pontis of place brachium pontis separately, described S ₄And S _1xLay respectively at the following brachium pontis of place brachium pontis separately; Described two brachium pontis are connected in parallel between the dc bus, are connected with a LC second order resonant circuit that is become with the resonance capacitance group by resonant inductance between the mid point of described two brachium pontis; Simultaneously, comprise further in the described soft switch that one is parallel to the dc-link capacitance between the described dc bus; It is characterized in that when needs turn-offed arbitrary master power switch pipe, this method comprised:

Open and wait to turn-off the auxiliary switch that the master power switch pipe is positioned at different brachium pontis position, charge into energy, and be defined as satisfying the energy that the resonance current maximum equals current load current and charge into the finish time to described LC second order resonant circuit;

When arriving energy and charge into the finish time, finish energy and charge into, turn-off and turn-off the auxiliary switch that the master power switch pipe is positioned at different brachium pontis position, and open with described and wait to turn-off the auxiliary switch that the master power switch pipe is positioned at identical brachium pontis position with described waiting;

Determine that resonance current is zero constantly, and constantly from this, behind 1/4 harmonic period, turn-off simultaneously described with wait to turn-off the master power switch pipe and be positioned at the auxiliary switch of identical brachium pontis position and describedly wait to turn-off the master power switch pipe.

2. method according to claim 1 is characterized in that, describedly is defined as satisfying energy that the resonance current maximum equals current load current and charges into and comprise the finish time:

A, according to the current function of state of described LC second order resonant circuit

Calculate described resonant capacitance C _rOn function of voltage u _x(t)=-u _d(1-cos ω (t-t ₅)) and described resonant inductance L _rOn current function

Wherein,

Described u _dThe expression DC bus-bar voltage, described t ₅Expression with wait to turn-off the master power switch pipe and be positioned at the opening the moment of auxiliary switch of different brachium pontis position;

B, according to the result of calculation in the steps A, be defined as satisfying the resonance current maximum and equal current load current, the energy that need charge into to described LC second order resonant circuit:

Wherein, described t ₆The expression energy charges into the finish time, described i _aRepresent current load current;

Further try to achieve:

3. method according to claim 2 is characterized in that, described definite resonance current is to comprise in zero moment:

C, according to the current function of state of described LC second order resonant circuit

And the t that calculates ₆Moment resonant capacitance C _rOn voltage

With the resonance inductance L _rOn electric current

Calculate described resonant capacitance C _rOn function of voltage u _x(t)=u _x(t ₆) cos ω (t-t ₆)+Zi _x(t ₆) sin ω (t-t ₆) and described resonant inductance L _rOn current function

And according to the symmetry of resonance current waveform, moving on to resonance current by the initial point with the resonance current waveform is zero t constantly ₇The place is reduced to u respectively with it _x(t)=u _x(t ₇) cos ω (t-t ₇) and

D, described resonant capacitance C when determining that resonance current is zero _rOn voltage u _x(t ₇The Zi of)=- _aAnd described resonant inductance L _rOn current i _x(t ₇)=0;

The result of calculation of E, comprehensive step C and D obtains: And further try to achieve:

4. a soft switch comprises in the described soft switch: two master power switch pipe S ₁And S ₄And two auxiliary switch S _1xAnd S _4x, described S ₁And S ₄Series connection constitutes main switch brachium pontis, described S _4xAnd S _1xSeries connection constitutes the auxiliary switch brachium pontis, wherein, and described S ₁And S _4xLay respectively at the last brachium pontis of place brachium pontis separately, described S ₄And S _1xLay respectively at the following brachium pontis of place brachium pontis separately; Described two brachium pontis are connected in parallel between the dc bus, are connected with a LC second order resonant circuit that is become with the resonance capacitance group by resonant inductance between the mid point of described two brachium pontis; Simultaneously, comprise further in the described soft switch that one is parallel to the dc-link capacitance between the described dc bus; It is characterized in that,

Initial condition, to be positioned at the auxiliary switch of different brachium pontis position open-minded with waiting to turn-off the master power switch pipe, charges into energy to described LC second order resonant circuit;

Charge into the finish time what determine for satisfying the energy that the resonance current maximum equals current load current, finish energy and charge into; Simultaneously, wait to turn-off the auxiliary switch that the master power switch pipe is positioned at different brachium pontis position and turn-off, wait to turn-off the master power switch pipe to be positioned at the auxiliary switch of identical brachium pontis position open-minded with described with described;

At the resonance current of determining is zero to rise constantly, behind 1/4 harmonic period, waits to turn-off the master power switch pipe and is positioned at the auxiliary switch of identical brachium pontis position and describedly waits to turn-off the master power switch pipe and turn-off simultaneously with described.

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