CN104578806A - Cascade bilateral soft switch DC/DC circuit topology - Google Patents

Abstract

The invention discloses a cascade bilateral soft switch DC/DC circuit topology. The cascade bilateral soft switch DC/DC circuit topology comprises a preceding stage boosted circuit, an auxiliary circuit, a post-stage push pull transformer and a full-bridge circuit, which are connected in series in sequence, wherein the auxiliary circuit comprises a resonant inductor Lr, a resonant capacitor Cr2, an auxiliary switch VT2 containing an anti-parallel body diode VD2, fast recovery diodes VD9 and VD10, and a relay K; one end of the resonant inductor Lr is connected with the negative electrode of the fast recovery diode VD9; the other end of the resonant inductor Lr is respectively connected with the positive electrode of the fast recovery diode VD10 and the drain electrode of the auxiliary switch VT2; the source electrode of the auxiliary switch VT2 is connected with the anode of the fast recovery diode VD10; the negative electrode of the fast recovery diode VD10 is connected with one end of the relay K; the other end of the relay K is respectively connected with the negative electrode of the resonant capacitor Cr2 and the anode of the fast recovery diode VD9. The cascade bilateral soft switch DC/DC circuit topology is simple and reliable in control, simple in circuit structures, easy to realize, low in device cost, low in switch loss, low in voltage stress of the switch, high in conversion efficiency and low in circuit conduction loss.

Description

Cascade two-way Sofe Switch DC/DC circuit topology

Technical field

The invention belongs to electric vehicle engineering field, particularly electric automobile circuit topology.

Technical background

The circuit topology of current two-way DC/DC converter is generally divided into two classes: a class is non-isolation type, and main feature is that transformer configuration is simple, and volume is little, lightweight, and power is little, and efficiency is high, but is only applicable to the occasion of low-power without the need to electrical isolation; Another kind of, be isolated form, low-pressure side and on high-tension side electrical isolation is not only solved by introducing transformer, and the power of converter is increased substantially, but large-power occasions often produces the problems such as switching tube stress is large, switching loss is serious, electromagnetic performance is poor to be difficult to solve.

Summary of the invention

It is simple that the object of the invention is to provide a kind of structure, is easy to realize, and switching loss is few, the cascade two-way Sofe Switch DC/DC circuit topology of what device cost was low be applicable to electric automobile.

The present invention is achieved by the following technical solutions.

Cascade of the present invention two-way Sofe Switch DC/DC circuit topology, it comprises prime booster circuit, auxiliary circuit, rear class push-pull transformer, full-bridge circuit, is connected in series successively between them.It is characterized in that described auxiliary circuit comprises resonant inductance L _r, resonant capacitance C _r2, include inverse parallel body diode VD ₂auxiliary switch VT ₂, fast recovery diode VD ₉, VD ₁₀, relay K; Wherein, resonant inductance L _rone end be connected in fast recovery diode VD ₉negative electrode, resonant inductance L _rthe other end respectively with resonant capacitance C _r2positive pole, auxiliary switch VT ₂drain electrode be connected, auxiliary switch VT ₂source electrode and fast recovery diode VD ₁₀anode be connected, fast recovery diode VD ₁₀negative electrode be connected in one end of relay K, the other end of relay K respectively with resonant capacitance C _r2negative pole, fast recovery diode VD ₉anode be connected.

Described prime booster circuit comprises low-pressure side DC power supply u _l, filter capacitor C ₁, boost inductance L ₁, include inverse parallel body diode VD ₁main switch VT ₁, clamp capacitor C _r1;

Wherein, low-pressure side DC power supply u _lpositive pole and boost inductance L ₁one end be connected, boost inductance L ₁the other end be connected in main switch VT ₁drain electrode, main switch VT ₁source electrode and low-pressure side DC power supply u _lnegative pole be connected, filter capacitor C ₁forward is parallel to low-pressure side DC power supply u _l, clamp capacitor C _r1forward is parallel to main switch VT ₁drain-source pole, main switch VT ₁drain electrode as the cathode output end of prime booster circuit, main switch VT ₁source electrode as the cathode output end of prime booster circuit.

Described auxiliary circuit comprises resonant inductance L _r, resonant capacitance C _r2, include inverse parallel body diode VD ₂auxiliary switch VT ₂, fast recovery diode VD ₉, VD ₁₀, relay K;

Wherein, resonant inductance L _rone end as the electrode input end of auxiliary circuit, be connected in the cathode output end of prime booster circuit, resonant inductance L _rthe other end respectively with resonant capacitance C _r2positive pole, auxiliary switch VT ₂drain electrode be connected, auxiliary switch VT ₂source electrode as the negative input of auxiliary circuit, respectively with cathode output end, the fast recovery diode VD of prime booster circuit ₁₀anode be connected, fast recovery diode VD ₁₀negative electrode be connected in one end of relay K, the other end of relay K respectively with resonant capacitance C _r2negative pole, fast recovery diode VD ₉anode be connected, fast recovery diode VD ₉negative electrode be connected in the cathode output end of prime booster circuit, and as the cathode output end of auxiliary circuit, fast recovery diode VD ₁₀anode as the cathode output end of auxiliary circuit.

Described rear class push-pull transformer comprises and includes inverse parallel body diode VD ₃power switch pipe VT ₃, include inverse parallel body diode VD ₄power switch pipe VT ₄, the transformer of former limit three port (two Same Name of Ends), secondary two-port (Same Name of Ends);

Wherein, the Same Name of Ends in the middle of transformer primary side, as the electrode input end of rear class push-pull transformer, is connected with the cathode output end of auxiliary circuit, power switch pipe VT ₃drain electrode be connected in another Same Name of Ends of transformer primary side, power switch pipe VT ₃source electrode as the negative input of rear class push-pull transformer, respectively with cathode output end, the power switch pipe VT of auxiliary circuit ₄source electrode be connected, power switch pipe VT ₄drain electrode be connected in the non-same polarity of transformer primary side, power switch pipe VT ₃, VT ₄partner and recommend switching tube, the Same Name of Ends of transformer secondary is as the cathode output end of rear class push-pull transformer, and the non-same polarity of transformer secondary is as the cathode output end of rear class push-pull transformer.

Described full-bridge circuit comprises pulsactor L ₂, relay K, capacitance C ₂, include inverse parallel body diode VD ₅, export junction capacitance C ₅power switch pipe VT ₅, include inverse parallel body diode VD ₆, export junction capacitance C ₆power switch pipe VT ₆, include inverse parallel body diode VD ₇, export junction capacitance C ₇power switch pipe VT ₇, include inverse parallel body diode VD ₈, export junction capacitance C ₈power switch pipe VT ₈, filter capacitor C ₀, high-pressure side DC power supply u _h;

Wherein, pulsactor L ₂one end as the electrode input end of full-bridge circuit, be connected with the cathode output end of rear class push-pull transformer, pulsactor L ₂the other end be connected in capacitance C ₂positive pole, relay K is parallel to pulsactor L ₂, capacitance C ₂negative pole respectively with power switch pipe VT ₅source electrode, power switch pipe VT ₇drain electrode be connected, power switch pipe VT ₅drain electrode respectively with power switch pipe VT ₆drain electrode, filter capacitor C ₀positive pole, high-pressure side DC power supply u _hpositive pole be connected, power switch pipe VT ₇source electrode respectively with power switch pipe VT ₈source electrode, filter capacitor C ₀negative pole, high-pressure side DC power supply u _hnegative pole be connected, power switch pipe VT ₈drain electrode as the negative input of full-bridge circuit, respectively with cathode output end, the power switch pipe VT of rear class push-pull transformer ₆source electrode be connected, power switch pipe VT ₅, VT ₇the leading-bridge of composition full-bridge circuit, power switch pipe VT ₅, VT ₇the lagging leg of composition full-bridge circuit.

Feature of the present invention and technique effect:

1, all switching tubes in circuit are PWM control mode, and low-pressure side drive circuit, without the need to electrical isolation, controls simple and reliable;

2, auxiliary circuit is only made up of a switching tube and simple passive device, and complexity reduces greatly, and whole circuit structure is simple, and be easy to realize, device cost is low;

3, all switching tubes in circuit all can realize Sofe Switch, not only reduce switching loss, reduce the voltage stress of switching tube, also effectively improve conversion efficiency;

4, during boosting inverter, main switch VT ₁with recommend switching tube VT ₃, VT ₄three only has a conducting at any time, and auxiliary switch VT ₂operating time extremely short, so the on-state loss of circuit is also less.

Accompanying drawing explanation

Fig. 1 is cascade of the present invention two-way Sofe Switch DC/DC circuit topology.

Circuit topology when Fig. 2 is boosting inverter.

Work wave when Fig. 3 is boosting inverter.

Circuit topology when Fig. 4 is the conversion of step-down pressure.

Work wave when Fig. 5 is decompression transformation.

Embodiment

Cascade of the present invention two-way Sofe Switch DC/DC circuit topology see accompanying drawing 1, reverse operating state when forward operating state when it is divided into boosting inverter in actual applications and decompression transformation, when boosting inverter, high-pressure side DC power supply u _hits load form must be converted to, i.e. the impedance of motor; When decompression transformation, low-pressure side DC power supply u _lits load form must be converted to, i.e. the impedance of storage battery.For ease of understanding, unified by unloaded for its load form work process at this.

Below in conjunction with accompanying drawing and operation principle, the specific embodiment of the present invention is described in detail.

Concrete boosting inverter principle is as described below.

When automobile is when starting, accelerating or climbing, controller cuts out high-pressure side VT ₅~ VT ₈drive singal, relay K close, make pulsactor L ₂be shorted, the auxiliary circuit of low-pressure side is switched on, see accompanying drawing 2.C ₂as capacitance, suppress the magnetic bias effect of booster circuit.Low-pressure side voltage is first by main switch VT ₁with boost inductance L ₁the booster circuit formed boosts to certain value, and then push-pull transformer boosts again, finally by VD ₅~ VD ₈full-bridge rectification exports.

To simplify the analysis, following hypothesis is done: all elements are perfect condition; Ignore the leakage inductance of transformer.Work wave during converter boost conversion is see accompanying drawing 3, and half period can be divided into 8 mode, and the course of work of rear half period is substantially identical with front half period, just changes to the difference that another recommends pipe work, therefore half period before only introducing.

Mode 1 (t ₀~ t ₁): make t ₀before moment, switching tube VT ₁, VT ₂and VT ₄turn off, VT ₃conducting, system is in stable state, and booster circuit is through recommending pipe VT ₃power is sent in full bridge rectifier.T ₀moment, VT in auxiliary circuit ₂electric current I _vT2be zero, at L _reffect under VT ₂realize ZCS open-minded.In this stage, flow through L _relectric current I _lrstart from zero linear increase, and VT ₃electric current I _vT3reduce gradually.

$I_{\mathrm{VT}3}=\frac{u_H}{{\mathrm{nL}}_1}-\frac{u_H/n-u_L}{L_1}{t}_{01}---\left(1\right)$

$I_{\mathrm{Lr}}=\frac{u_L}{L_1+L_r}{t}_{01}---\left(2\right)$

In formula: u _hfor converter high-pressure side both end voltage, u _lfor converter low-pressure side both end voltage, n is transformer voltage ratio.

Mode 2 (t ₁~ t ₂): t ₁moment, L _r, C _r1between there is resonance, C _r1electric discharge, I _lrcontinue to increase.Until t ₂moment, C _r1electric discharge is zero, I _vT3also zero is dropped to.I _lrreach maximum, and equal L ₁electric current I _l1.

$t_{12}=\frac{\mathrm{\π}}{2}\sqrt{L_r{C}_{r1}},Z_{r1}=\sqrt{L_r/C_{r1}}---\left(3\right)$

$I_{\mathrm{Lr}\max }=I_{L1}=\frac{u_H}{{\mathrm{nZ}}_{r1}}---\left(4\right)$

Mode 3 (t ₂~ t ₃): t ₂in the moment, resonance terminates, I _lrthrough anti-paralleled diode VD ₁, VD ₃and VD ₄conducting afterflow, this stage constant current hold.VT ₁because both end voltage is zero by clamper, therefore it is open-minded to realize ZVS; VT again ₃electric current I _vT3be zero, so VT ₃zCS can be realized turn off.

Mode 4 (t ₃~ t ₄): t ₃moment, I _lrbecause of L _reffect can not sport zero, but L _ralmost share VT ₂whole voltage, so at this VT in a flash ₁zVS open VT ₂there is the effect of no-voltage clamper, VT ₂zVS can be realized turn off.This stage, by L _r, C _r2and VD ₉form resonant tank, C _r2start charging.Through 1/4th harmonic period, i.e. t ₄moment, I _lrbe zero, C _r2be full of electricity.

$t_{34}=\frac{\mathrm{\π}}{2}\sqrt{L_r{C}_{r2}},Z_{r2}=\sqrt{L_r/C_{r2}}---\left(5\right)$

Mode 5 (t ₄~ t ₅): C afterwards _r2start electric discharge, and and L _r, VT ₁, VD ₁₀form resonant tank, I _lrstart from scratch and increase in the other direction.T ₅moment, C _r2electric discharge is zero, L _rthrough VT ₁, VD ₂conducting afterflow, resonance terminates, duration and t ₃₄equal.

$u_{\mathrm{cr}2}=u_L-Z_{r2}{I}_{\mathrm{Lr}}\sin (t_{45}/\sqrt{L_r{C}_{r2}})---\left(6\right)$

Mode 6 (t ₅~ t ₆): this stage only has VT ₁a switching tube is conducting state, and auxiliary circuit quits work, and low voltage side battery is to L ₁charging.

Mode 7 (t ₆~ t ₇): t ₆moment, due to buffer capacitor C _r1voltage can not suddenly change, VT ₁achieve ZVS to turn off.And C _r1charged, at boost inductance L ₁effect under, charging current I _l1substantially constant.Again because VT ₄both end voltage by VD ₄clamper is zero, so VT ₁the VT when ZVS turns off ₄zVS is open-minded immediately, is L ₁freewheeling path is provided.

Mode 8 (t ₇~ t ₈): this stage is the course of work of common booster converter, i.e. battery and boost inductance L ₁jointly provide energy to high-pressure side.

Concrete decompression transformation principle is as described below.

When automobile is when slowing down, braking or dallying, controller cuts out low-side switch pipe VT ₁~ VT ₄drive singal, relay K disconnect, make pulsactor L ₂seal in high-pressure side, auxiliary circuit does not work, see accompanying drawing 4.C ₅~ C ₈for the output junction capacitance of switching tube, switching tube VT ₅~ VT ₈with phase shift work pattern, L ₂and C ₂effectively can expand loading range and reduce secondary duty-cycle loss, exporting through diode VD ₃and VD ₄full-wave rectification, filter inductance L ₁realize the recycling of energy and the charging to low-pressure side storage battery.

To simplify the analysis, suppose as follows: all elements are perfect condition, and L ₁>>L _lk/ n ².Work wave during converter decompression transformation is see accompanying drawing 5, u _pfor primary voltage of transformer, I _pfor primary side current of transformer, u _rfor transformer secondary voltage, half period can be divided into 6 mode, the course of work of rear half period and front half period full symmetric, therefore half period before only introducing.

Mode 1 (t ₀~ t ₁): make at t ₀before moment, switching tube VT ₅and VT ₈be in conducting, I _plinear rising, secondary side diode VD ₃and VD ₄equal conducting, is in commutation course.T ₀in the moment, the change of current terminates, VD ₄turn off, VT ₅and VT ₈continue conducting, I _pstart electric capacity C ₂charging, its voltage u _c2linearly change.T ₁in the moment, turn off VT ₅, I _preach maximum.This stage has:

$(L_{\mathrm{lk}}+L_2+n^2{L}_1)\frac{{\mathrm{dI}}_p}{\mathrm{dt}}=u_H-{\mathrm{nu}}_L---\left(7\right)$

$u_{c2}=\frac{{\mathrm{nI}}_p}{C_2}t-u_{c2}\left(0\right)---\left(8\right)$

Mode 2 (t ₁~ t ₂): VT ₅have no progeny in pass, shunt capacitance C ₅, C ₇with L ₂, L _lk, L ₁there is resonance, C ₇start electric discharge, C ₅charging, I _pthen from VT ₅transfer to C ₅, C ₇in.

$(C_5+C_7)\frac{{\mathrm{du}}_{c7}}{\mathrm{dt}}=C\frac{{\mathrm{du}}_{c7}}{\mathrm{dt}}=-I_p---\left(9\right)$

Due to L ₁relatively enough large, can be similar to and think I _p=I _o/ n is invariable, I _ofor secondary side output current.U _c7at I _peffect lower linear decline,

$u_{c7}=U_p-\frac{I_o}{\mathrm{nC}}{t^{\′}}_{12}---\left(10\right)$

By formula (10) known u _palong with u _c7continuous decline and reducing, until t ₂moment u _c7=0, I _pstart through anti-paralleled diode VD ₇conducting afterflow.

$t_{12}^{\′}=\frac{n{\mathrm{Cu}}_p}{I_o}---\left(11\right)$

Mode 3 (t ₂~ t ₃): t ₂moment, due to VD ₇conducting, switching tube VT ₇voltage clamping be zero, achieve ZVS open-minded.

Mode 4 (t ₃~ t ₄): t ₃moment, VT ₈at shunt capacitance C ₆, C ₈cushioning effect under ZVS turn off.After this, primary current I _pwith secondary current I _oall start to decline.Work as I _obe less than output inductor electric current I _l1time, I _l1in unnecessary electric current to VD ₄flowing.In commutation course, rectifier diode VD ₃and VD ₄conducting simultaneously, both sides voltage is all zero, and transformer is equivalent to short circuit, therefore the C of primary side ₆, C ₈with L _lk, L ₂there is resonance, C ₈charging, C ₆electric discharge.

$(C_6+C_8)\frac{{\mathrm{du}}_{c8}}{\mathrm{dt}}=I_p,(L_{\mathrm{lk}}+L_2)\frac{{\mathrm{dI}}_p}{\mathrm{dt}}=-u_{c8}---\left(12\right)$

By formula (12) known I _pthe while of ever-reduced, u _c8continuous increase.Until t ₄moment, I _p=0, then

$t_{34}^{\′}=\sqrt{(L_{\mathrm{lk}}+L_2)C}{\sin }^{-1}(u_{c8}/I_p{Z}_2),Z_2=\sqrt{(L_{\mathrm{lk}}+L_2)/C}---\left(13\right)$

Mode 5 (t ₄~ t ₅): t ₄moment, diode VD ₆conducting afterflow.C ₂polarity of voltage because of with I _pidentical and become reverse BV source, L ₂exit saturation condition, hinder I _preverse increase, makes it maintain nought state.Thus switching tube VT ₆realize ZCS open-minded.Until t ₅moment, diode VD ₆and VD ₇naturally turn off, I _pstart oppositely to increase.

Mode 6 (t ₅~ t ₆): t ₆moment, I _preach reverse maximum, diode VD ₃in electric current drop to zero and turn off, electric current I _l1all transfer to VD ₄in, commutation course terminates.

For realizing embodiments of the invention, be described further by following Sofe Switch condition analysis and parameter designing.

The Sofe Switch condition of boosting inverter is as follows.

In order to realize VT ₁zVS open-minded, C _r1the voltage at two ends can not rise too fast, i.e. t>=t _off, generally get (2 ~ 3) t _off(t _offfor main switch VT ₁turn-off time), C _r1need meet the following conditions:

$C_{r1}\frac{{\mathrm{du}}_{\mathrm{cr}1}}{\mathrm{dt}}=I_{\max },$ u _H/u _cr1＝n (14)

In formula: I _maxfor maximum input average current, can be obtained by formula (14):

$C_{r1}=\frac{{\mathrm{nI}}_{\max }}{u_H}(2~3)t_{\mathrm{off}}---\left(15\right)$

In order to not affect working method and the auxiliary switch VT of booster circuit PWM ₂sofe Switch, must to VT ₂operating time limit, i.e. t ₀~ t ₃time period is unsuitable long, is generally no more than the switch periods of 10%, therefore resonant inductance L _rneed meet:

$t_{03}=\frac{n{L}_r}{u_H}{I}_{\max }+\frac{\mathrm{\π}}{2}\sqrt{L_r{C}_{r1}}\≤0.1T_2---\left(16\right)$

In formula: T ₂for VT ₂switch periods.In addition, VT ₁realize ZVS to turn off, that t ₃~ t ₅the resonant process of time period must ensure C _r2electric discharge is zero, therefore resonant capacitance C _r2then need to meet:

$u_L\cos (t_{34}/\sqrt{L_r{C}_{r2}})=u_L-Z_{r2}{I}_{\mathrm{Lr}}\sin (t_{45}/\sqrt{L_r{C}_{r2}})---\left(17\right)$

The Sofe Switch condition of decompression transformation is as follows.

In order to realize the ZVS of leading-bridge switching tube, the primary voltage of transformer should drop to zero in Dead Time.So switching tube VT ₅and VT ₇zVS only need switching tube conducting and shutoff interval greater than t ' ₁₂:

$T_{D1}=\frac{\mathrm{\π}}{2}\sqrt{(L_{\mathrm{lk}}+L_2+n^2{L}_1)(C_5+C_7)}>\frac{n(C_5+C_7)u_p}{I_o}---\left(18\right)$

For the ZCS of lagging leg switching tube, then require to be stored in pulsactor L ₂with blocking capacitor C ₂in energy enough make primary side current of transformer be reset to zero.So:

$\frac{L_2{I_p}^2}{2}\≥\frac{(C_6+C_8){u_{c8}}^2}{2}+C_2{u_{c2}}^2---\left(19\right)$

And the duty-cycle loss time should meet following formula:

$T_{D2}=\frac{n{I}_o{L}_{\mathrm{lk}}}{u_p+u_{c2}}<t_{34}^{\&prime;}---\left(20\right)$

The parameter designing of circuit topology is as follows.

(1) number of turn of transformer and no-load voltage ratio: get high side voltage ripple during decompression transformation within 10%, then the umber of turn N of transformer primary side _p:

$N_p=\frac{u_H\&times;{10}^8}{K_f{f}_s{B}_m{A}_e}---\left(21\right)$

$A_e=\frac{P_T\&times;{10}^6}{2\mathrm{\&eta;}{f}_s{B}_m\mathrm{\&delta;}{K}_m{K}_c}---\left(22\right)$

In formula: K _frepresent form factor, generally get 4.44 (sine waves) or 4 (square waves); f _sfor the switching frequency of phase-shifting full-bridge switching tube; B _mfor maximum magnetic flux induction density; A _efor core center column section amasss; η represents conversion efficiency, gets 0.9; δ is current in wire bulkfactor, is generally 2.0A/mm ²; K _mfor the copper activity coefficient of magnetic core window, get 0.5; K _cfor iron space factor, get 1; P _tfor rated power.Consider the duty-cycle loss problem of phase-shifted full-bridge converter, first suppose secondary maximum duty cycle D _maxbe 0.9, then secondary requires the minimum voltage u of output _sminfor:

$u_{s\min }=\frac{u_{o\max }+v_D+v_{L1}}{D_{\max }}---\left(23\right)$

In formula: u _omaxfor secondary maximum output voltage; v _dfor rectifying tube forward voltage drop; v _l1for the direct current pressure drop of filter inductance.The turn ratio n of transformer is:

$n=\frac{\mathrm{\&eta;}{u}_H-\mathrm{\&Delta;}{v}_1}{u_{s\min }}---\left(24\right)$

In formula: Δ v ₁for the pressure drop that the switching tube of transformer primary side, pulsactor and capacitance etc. are total.Therefore draw the umber of turn N of transformer secondary _s=N _p/ n.In addition, transformer parameter also must meet boosting inverter, and the input voltage value making booster circuit complete once boosting is u _in, output voltage values is u _o, relation is as follows:

u _o＝2nu _inD _T(25)

In formula: D _tfor recommending the duty ratio of pipe.Make the tube voltage drop of circuit during boosting inverter, electric capacity pressure drop, winding pressure drop etc. for Δ v ₂, verification method can be thought at u _intime minimum, obtain required output voltage just can meet arbitrary situation under boosting no-load voltage ratio relation, known by inference by formula (15):

$n\&GreaterEqual;\frac{u_o+{\mathrm{\&Delta;v}}_2}{2u_{\mathrm{in}\min }{D}_T}---\left(26\right)$

(2) boost inductance L ₁: in booster circuit, boost inductance directly determines the ripple Δ I of input current _lsize.When boosting power output is maximum, when input voltage is minimum, Δ I _lmaximum, L ₁value also maximum.

${\mathrm{\&Delta;I}}_{L\max }=\frac{0.1P_T}{\mathrm{\&eta;}{u}_L}---\left(27\right)$

$L_{1\max }=\frac{u_L}{{\mathrm{\&Delta;I}}_{L\max }}\frac{u_o-u_L}{u_o}{T}_s---\left(28\right)$

In formula: T _sfor main switch VT ₁switch periods.Due to L ₁filter inductance will be made, so also need inductance value when considering step-down when step-down.During step-down, output circuit is full-wave rectifying circuit, therefore secondary current ripple frequency is 2 times of former limit switching tube.Relation is as follows:

$L_1=\frac{u_L}{2\left(2f_s\right)\left(0.1I_o\right)}(1-\frac{u_L}{u_{o\max }/n-v_D-v_{L1}})---\left(29\right)$

So convolution (18), (19) consider the value that can obtain L1.

(3) filter capacitor C ₀, C ₁: in order to meet the requirement of commutating voltage and low-and high-frequency ripple, generally get the AC ripple Δ v0=50mv of output voltage.During boosting inverter, export and eliminate filter inductance, by means of only C ₀filtering ripple.If capacitance current is 20% of output current, then have:

$C_0=\frac{0.2I_0}{8{\mathrm{\&Delta;v}}_0}{T}_s---\left(30\right)$

During decompression transformation, export as full-wave rectification, have:

$C_1=\frac{u_L}{8L_1{\left(2f_s\right)}^2{\mathrm{\&Delta;v}}_0}(1-\frac{u_L}{u_{o\max }/n-v_D-v_{L1}})---\left(31\right)$

(4) pulsactor L ₂: in order to realize the ZVZCS of phase-shifting full-bridge, L ₂high-frequency loss and heat radiation all can be comparatively large, so L ₂voltagesecond product too high without the need to designing, such duty-cycle loss is just very little.Solution formula is as follows:

$u_{c2}{T}_{D2}=u_{c2}(\frac{T}{2}-\frac{\mathrm{DT}}{2}-\mathrm{\&Delta;T})---\left(32\right)$

$u_{c2}=\frac{n{I}_o\mathrm{DT}}{4C_2},\mathrm{\&Delta;T}=\frac{n{I}_o{L}_2}{u_{c2}}---\left(33\right)$

In formula: D, T are respectively duty ratio and the switch periods of lagging leg switching tube, Δ T is the time interval of two switching tube turn-on and turn-off in lagging leg.

(5) capacitance C ₂: can not eliminate completely because the output pulse width of converter is inconsistent, feedback loop is asymmetric etc., so bias phenomenon certainly exists, and during boosting inverter, the magnetic bias of push-pull configuration is even more serious.Capacitance when this gets boosting inverter.

$C_2=\frac{1}{L_{\mathrm{lk}}{w}^2}=\frac{1}{L_{\mathrm{lk}}{\left(2\mathrm{\&pi;}{f}_s\right)}^2}---\left(34\right)$

In sum, the circuit parameter of embodiment is determined as follows.

u _L＝24V，u _H＝380V，P _T＝3.5KW，f _s＝50KHZ，n＝5，L ₁＝100uH，L ₂＝560uH，L _r＝25uH，L _lk＝11uH，C ₀＝100uF，C ₁＝298uF，C ₂＝0.47uF，C _r1＝47nF，C _r2＝220nF。

Claims (5)

1. a cascade two-way Sofe Switch DC/DC circuit topology, comprises prime booster circuit, auxiliary circuit, rear class push-pull transformer, full-bridge circuit, is connected in series successively between them, it is characterized in that described auxiliary circuit comprises resonant inductance L _r, resonant capacitance C _r2, include inverse parallel body diode VD ₂auxiliary switch VT ₂, fast recovery diode VD ₉, VD ₁₀, relay K; Wherein, resonant inductance L _rone end be connected in fast recovery diode VD ₉negative electrode, resonant inductance L _rthe other end respectively with resonant capacitance C _r2positive pole, auxiliary switch VT ₂drain electrode be connected, auxiliary switch VT ₂source electrode and fast recovery diode VD ₁₀anode be connected, fast recovery diode VD ₁₀negative electrode be connected in one end of relay K, the other end of relay K respectively with resonant capacitance C _r2negative pole, fast recovery diode VD ₉anode be connected.

2. cascade according to claim 1 two-way Sofe Switch DC/DC circuit topology, is characterized in that described prime booster circuit comprises low-pressure side DC power supply u _l, filter capacitor C ₁, boost inductance L ₁, include inverse parallel body diode VD ₁main switch VT ₁, clamp capacitor C _r1; Wherein, low-pressure side DC power supply u _lpositive pole and boost inductance L ₁one end be connected, boost inductance L ₁the other end be connected in main switch VT ₁drain electrode, main switch VT ₁source electrode and low-pressure side DC power supply u _lnegative pole be connected, filter capacitor C ₁forward is parallel to low-pressure side DC power supply u _l, clamp capacitor C _r1forward is parallel to main switch VT ₁drain-source pole, main switch VT ₁drain electrode as the cathode output end of prime booster circuit, main switch VT ₁source electrode as the cathode output end of prime booster circuit.

3. cascade according to claim 1 two-way Sofe Switch DC/DC circuit topology, is characterized in that described auxiliary circuit comprises resonant inductance L _r, resonant capacitance C _r2, include inverse parallel body diode VD ₂auxiliary switch VT ₂, fast recovery diode VD ₉, VD ₁₀, relay K; Wherein, resonant inductance L _rone end as the electrode input end of auxiliary circuit, be connected in the cathode output end of prime booster circuit, resonant inductance L _rthe other end respectively with resonant capacitance C _r2positive pole, auxiliary switch VT ₂drain electrode be connected, auxiliary switch VT ₂source electrode as the negative input of auxiliary circuit, respectively with cathode output end, the fast recovery diode VD of prime booster circuit ₁₀anode be connected, fast recovery diode VD ₁₀negative electrode be connected in one end of relay K, the other end of relay K respectively with resonant capacitance C _r2negative pole, fast recovery diode VD ₉anode be connected, fast recovery diode VD ₉negative electrode be connected in the cathode output end of prime booster circuit, and as the cathode output end of auxiliary circuit, fast recovery diode VD ₁₀anode as the cathode output end of auxiliary circuit.

4. cascade according to claim 1 two-way Sofe Switch DC/DC circuit topology, is characterized in that described rear class push-pull transformer comprises and includes inverse parallel body diode VD ₃power switch pipe VT ₃, include inverse parallel body diode VD ₄power switch pipe VT ₄, the transformer of former limit three port (two Same Name of Ends), secondary two-port (Same Name of Ends); Wherein, the Same Name of Ends in the middle of transformer primary side, as the electrode input end of rear class push-pull transformer, is connected with the cathode output end of auxiliary circuit, power switch pipe VT ₃drain electrode be connected in another Same Name of Ends of transformer primary side, power switch pipe VT ₃source electrode as the negative input of rear class push-pull transformer, respectively with cathode output end, the power switch pipe VT of auxiliary circuit ₄source electrode be connected, power switch pipe VT ₄drain electrode be connected in the non-same polarity of transformer primary side, power switch pipe VT ₃, VT ₄partner and recommend switching tube, the Same Name of Ends of transformer secondary is as the cathode output end of rear class push-pull transformer, and the non-same polarity of transformer secondary is as the cathode output end of rear class push-pull transformer.

5. cascade according to claim 1 two-way Sofe Switch DC/DC circuit topology, is characterized in that described full-bridge circuit comprises pulsactor L ₂, relay K, capacitance C ₂, include inverse parallel body diode VD ₅, export junction capacitance C ₅power switch pipe VT ₅, include inverse parallel body diode VD ₆, export junction capacitance C ₆power switch pipe VT ₆, include inverse parallel body diode VD ₇, export junction capacitance C ₇power switch pipe VT ₇, include inverse parallel body diode VD ₈, export junction capacitance C ₈power switch pipe VT ₈, filter capacitor C ₀, high-pressure side DC power supply u _h; Wherein, pulsactor L ₂one end as the electrode input end of full-bridge circuit, be connected with the cathode output end of rear class push-pull transformer, pulsactor L ₂the other end be connected in capacitance C ₂positive pole, relay K is parallel to pulsactor L ₂, capacitance C ₂negative pole respectively with power switch pipe VT ₅source electrode, power switch pipe VT ₇drain electrode be connected, power switch pipe VT ₅drain electrode respectively with power switch pipe VT ₆drain electrode, filter capacitor C ₀positive pole, high-pressure side DC power supply u _hpositive pole be connected, power switch pipe VT ₇source electrode respectively with power switch pipe VT ₈source electrode, filter capacitor C ₀negative pole, high-pressure side DC power supply u _hnegative pole be connected, power switch pipe VT ₈drain electrode as the negative input of full-bridge circuit, respectively with cathode output end, the power switch pipe VT of rear class push-pull transformer ₆source electrode be connected, power switch pipe VT ₅, VT ₇the leading-bridge of composition full-bridge circuit, power switch pipe VT ₅, VT ₇the lagging leg of composition full-bridge circuit.