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第四章开关过程与缓冲技术§4-2有损缓冲电路电感电流断续的缓冲电路§4-3无损缓冲电路电感电流连续的缓冲电路§4-1开关损耗与器件应力关断缓冲电路开通缓冲电路§4-1开关损耗与器件应力总损耗P=导通损耗Pon+阻断损耗Poff+开关损耗Ps(Ps=40~80%P)延迟时间—Is小,可略上升时间存储时间—Us小,可略下降时间Ps上升时间tup下降时间tdo一般80%updottdoupCCCSCECCECSTttUIdtuidtuiE0061)(每周期损耗SdoupCCCSSfttUIP)(61开关功率损耗iCuCEMNUCCICS开关轨迹onttUuttIiupCCCEupCSC)(1offttUuttIidoCCCEdoCSC))(1电阻负载容性负载开通过程uCEiCiCpONpONuCEiCpOFFpOFFuCEiCuCEMN感性负载关断过程安全ON:限制di/dt—开通/串联缓冲;OFF:限制du/dt—关断/并联缓冲;降低(转移)S损耗,改变开关轨迹。缓冲电路(SnubberCircuit)有损缓冲电路无损缓冲电路部分开关损耗转移到缓冲电路(总值不变)电流、电压、热应力Stress§4-2有损缓冲电路(感性负载含有L滤波)1iL断续时的缓冲电路uLiBRBRCUCCuRuCEτ=L/RTsCCLCCCERiuUuttttiBiCuCEuLUCCCCLRiuUCCiCuCEMNUCCICSdoCSLtILU大→二次击穿小→不击穿Em(LIcs2/2)消耗于T、R峰值加续流管iLiBRBRCUCCuCEiDiCDCLiiiiCuCEUCCIC2NIC1MICMtiBiLICMiCiDtRR允许短路时间但关断损耗仍然较大加电容(仅为修正关断轨迹)iLiBRBRCUCCuCEiCC开通过程恶化!iCuCEMNUCCICS综合利用D与C的作用→同时修正开关轨迹?RCD缓冲电路iCuCEMNUCCICSRSRCiLiBRBRCUCCiDuCSCSDSRS★参数计算:△关断时,为RLC二阶响应根据临界阻尼条件:SSCCLR2024CSSRLC△导通时,应保证在最短导通时间内Cs充电至Ucc3minONtSONsCtR3min2iL连续时的缓冲电路(Buck为例)无缓冲工作波形UiCDTLRuoLiCiDittiCuCEUiOLiUuUIL2IL1D导通D恢复存储uL=0uL0D导通DLCiiiiCuCEIL1D恢复D导通D导通uL0IL2开、关过程损耗均大!RCD关断缓冲电路①临界电容Cs缓冲UiCDTLRuoLiDiDsCsRs经tDOCs大,uCE↑UiCs小,uCE↑Ui→D导通L≈恒流源,关断初,D阻断,经存储时间iC↓→iDS↑,Cs充电,限制du/dt。设:iC线性下降uCEiCILUitDO)/(DOLCttIi12021ttCIdtiICuuDOSLtCLSCECsDO)(iSDOLCsDOUCtIutt2/:iDOLSUtIC20/612240022//OFFtDOiLSLDOCCEOFFEtUICItdtiuEDO20/DOiLOFFtUIE设:导通时Cs能量全耗于Rs242102/RONDOLiiSRONEtIUUCE20/DOLiRONtIUERCD关断缓冲电路②大电容缓冲UiCDTLRuoLiDiDsCsRsuCEiCILUitDOtFUDODODOLCttttttIi01)/(FUtCLSCsdtiICu01)()()(121220SDOFUiDOLSCttUtIC1DOFUtt/FUtOFFCCEOFFEdtiuE0012162122102OFFiSRONEUCE由iFUCsUtu)(RCD关断缓冲电路③小电容缓冲UiCDTLRuoLiDiDsCsRsuCEiCILUitDOtFUDOtCLSCsdtiICu01)()/(DOLCttIi120SSCC)(1342020DOtOFFCCEOFFEdtiuE221202OFFiSRONEUCE★关断损耗α1时最小最小值应在α1的抛物线上讨论iCuCEα1α=1α1★开关损耗α=2/3时最小RONOFFTSEEE11341126123113202020OFFOFFOFFTSEEEE)()()(03420)(OFFTSEddE949500//minminSSOFFTSCCEEEα.2.4.6.81.2.4.6.8101.21.6ES-TEON-REOFF0.35~1★电容参数在最小导通时间内Cs电荷应放尽RCD关断缓冲电路的另一种接法UiCDTLRuoLiDsCsRs参数选取1350~.iDOLSSSUtICCC).~.()~.(500601120020★电阻参数SONSSSONCtRRCt)~()~(minmin5353频率越高,电阻越小,开通附加电流越大。电阻值与损耗无关。RLD开通缓冲电路UiCDTLRuoLiDiDsRsLsL≈恒流源,开通初,D导通/恢复,经上升时间tUP:uCE由Ui↓→0uL由0↑→Ui限制di/dt经tUPLs大,iC↑IL→D导通,tUPtFU,α1Ls小,iC↑IL→D阻断,tUPtFU,α1设:uCE线性下降uCEiCILUitUPtFUuCEiCILUitUPtFUuCEiCILUitUPRLD开通缓冲电路临界电感缓冲由对偶原理:uCEiCILUitUPCEiLuUuiUPiCEUttUuUPSitCEiSCtLtUdtuULiUP2120)(LUPCIti)(LUPiSItUL20开通关断并联串联电压电流电容电感上升下降……★开关损耗α=2/3时最小949500//minminSSOFFTSLLEELUPiSSItULL).~.()~.(50060112001350~.min/)~(OFFSStLR53在最小关断时间内Ls电流应回零电阻值与损耗无关;频率越高,电阻越大,关断附加电压越大。复合缓冲电路UiCDTLRuoLiDiDs2Rs2LsDs1Rs1CsiLiCRBRSUCCiDDSCSLSiSRLLLDLCCCRSDSCSLSUiCDTLRuoLiDiDs2Rs2LsDs1Rs1Cs§4-3无损缓冲电路有损缓冲电路SiSOFFfUCP221SLSONfILP221由S移出Ui、RLS、Rs热?无损缓冲电路1无损关断缓冲电路与RCD并联缓冲相似UiDTLRuoLiCiD11Ci2Ci1LiD2D3CBuck例1Cu2CuiULCiiLCCCiiii21onDD21/DOtOFF关断过程1Cu2CuCEu0iU0onDDOiLStUICCC).~.(//5006021221/SCCCttiCuC1/C2UituCEtiL1无损关断缓冲电路UiDTLRuoLiCiD11Ci2Ci1LiD2D3C开通过程Ui、D3、L1、C1、C2回路串联谐振iMaxCCUu21/否则D1、D2导通★最小导通时间≥谐振周期112CLtONminSSCLf210/12212CtLONmin★开通最大附加电流0210LRtexUitLifCsin1001LCS/112LCUiiMaxfCttiCuC1/C2UiD恢复附加tuCEtiL无损关断缓冲电路另一种形式自行分析UiDTLRuoD1D2D3CC2C1L12无损开通缓冲电路与RLD串联缓冲相似DTLRuoCN1DsN2LUPiItUL).~.(500601★在最小关断时间内应保证次级电流回零,剩余能量为零211222NUNILUILtiiOFFminminOFFitUNILN11222222112121ILIL221221KIILLminOFFitILU222N★关断最大附加电压12NNUUfCEiN2不能过小ifCEKUU3变压器隔离缓冲电路关断过程开通过程aLCuiUonD1DOtOFFCi1iCEuCiuUCu0否则经N1、Ui、D2、Ls回路放电21/NUNUuOiC若N2电流=0时iCUuT、D2、Ls、Cs回路谐振,当iCUuD1导通,Ls、Cs能量回馈LSDii1SiLU/按速率下降到0iCUu最终漏感★除一般无损缓冲意义外,吸收漏感能量,防止开关器件过压TRuoCN1N2D1D2LsLaUiCsuc1iCiFlyback例3变压器隔离缓冲电路参数选取:TRuoCN1N2D1D2LsLaUiCsuc1iCi否则加大Cs但开通时谐振附加电流亦增大★关断时,Cs、La能量守恒转移到Cs22122)(212121OiSCSaiSUNNUCILUC221212)/(/2NNUNNUUILCOOiCSaS★验证关断后Uce最大值是否超限★Ls由最小导通时间≥谐振周期确定SSONCLt2minSSCLf210/SONSCtL2min22SSCSOiBRCECLIUNNUU21SSCL/为谐振阻抗
本文标题:现代电力电子技术4-Snubber
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