0N的半桥LLC论述.pdf

Design considerations for a HalfDesign considerations for a Half-Bridge LLC resonant converterBridge LLC resonant converter2AgendaAgendaWhy an HB LLC converterConfigurations of the HB LLC converter and a resonant tankOperating states of the HB LLCHB LLC converter modeling and gain characteristicsPrimary currents and resonant cap dimensioningSecondary rectification design and output cap dimensioningResonant inductance balanceTransformer winding dimensioning and transformer construction3The LCD and PLASMA TV market is growing each year.These and also other markets call for an SMPS unit that can provide these features:-Output power from 150 W up to 600 W-Universal mains-Active or passive PFC(given by needed power)-Limited width and space,no fan:limited air flow-Low standby power consumption-Consumer Electronics market:fierce competitionThe above requirements can be fulfilled with an SMPS that provides:High power densitySmooth EMI signatureCost effective solution with minimum component countWhy an LLC series resonant converter?Why an LLC series resonant converter?4Benefits of an LLC series resonant converterBenefits of an LLC series resonant converterType of serial resonant converter that allows operation in relatively wide input voltage and output load range when compared to the other resonant topologiesLimited number of components:resonant tank elements can be integrated to a single transformer only one magnetic component neededZero Voltage Switching(ZVS)condition for the primary switches under all normal load conditionsZero Current Switching(ZCS)for secondary diodes,no reverse recovery lossesCost effective,highly efficient and EMI friendly solutionfor high and medium output voltage converters5AgendaAgendaWhy an HB LLC converterConfigurations of the HB LLC converter and a resonant tankOperating states of the HB LLCHB LLC converter modeling and gain characteristicsPrimary currents and resonant cap dimensioningSecondary rectification design and output cap dimensioningResonant inductance balanceTransformer winding dimensioning and transformer construction6Configurations of an HB LLC Configurations of an HB LLC single res.capsingle res.cap-Higher input current ripple and RMS value-Higher RMS current through the resonant capacitor-High voltage(600 1500 V)resonant capacitor needed-Low cost-Small size/easy layout7Compared to the single capacitor solution this connection offers:-Lower input current ripple and RMS value(1/2)-Resonant capacitors handle half RMS current-Capacitors with half capacitance are used-Low voltage ratings(450 V)for the resonant capacitors when clamping diodes D3,D4 perform an easy and cheap overload protectionConfigurations of an HB LLC Configurations of an HB LLC split res.capsplit res.cap8Resonant tank configurations Resonant tank configurations discrete solutiondiscrete solutionResonant inductance is located outside of the transformerAdvantages:-Greater design flexibility(designer can setup any Lsand Lmvalue)-Lower radiated EMI emissionDisadvantages of this solution are:-Complicated insulation between primary and secondary windings-Worse cooling conditions for the windings-More components to be assembled9Leakage inductance of the transformer is used as a resonant inductance.Advantages:-Low cost,only one magnetic component is needed-Usually smaller size of the SMPS-Better cooling conditions for transformer windings-Insulation between primary and secondary side is easily achievedDisadvantages:-Less flexibility(achievable Ls inductance range is limited)-Higher radiated EMI emission-LLC with integrated resonant tank operates in a slightly different way than the solution with discrete Ls-Strong proximity effect in the primary and secondary windingsResonant tank configurations Resonant tank configurations integrated solutionintegrated solution10AgendaAgendaWhy an HB LLC converterConfigurations of the HB LLC converter and a resonant tankOperating states of the HB LLCHB LLC converter modeling and gain characteristicsPrimary currents and resonant cap dimensioningSecondary rectification design and output cap dimensioningResonant inductance balanceTransformer winding dimensioning and transformer construction11sssLCF=21)(21minmssLLCF+=+=LLC converter can operate:a)between Fminand Fsc)above Fsb)direct in Fsd)between Fminand Fs-overloade)below FminOperating states of the LLC converter Operating states of the LLC converter Two resonant frequencies can be defined:Discrete resonant tank solution12c)Operating waveforms for Fop Fs Discrete resonant tank solutionCBADEFOperating states of the LLC converter Operating states of the LLC converter 13-Integrated resonant tank behaves differently than the discrete resonant tank-leakage inductance is given by the transformer coupling-Llkparticipates only if there is a energy transfer between primary and secondary-Once the secondary diodes are closed under ZCS,Llkhas no energySecondary diodes are always turned OFF under ZCS condition in HB LLC.The resonant inductance Lsand magnetizing inductance Lmnever participate inthe resonance together as with discrete resonant tank solution!mlkLLM=1Operating states of the LLC converter Operating states of the LLC converter Integratedresonant tank solution14sssLCF=21msLCF=21minLLC converter can again operate:a)between Fmin and Fsc)above Fsb)direct in Fsd)between Fmin and Fs overloade)below FminTwo resonant frequencies can be defined:Integratedresonant tank solutionOperating states of the LLC converter Operating states of the LLC converter 15AgendaAgendaWhy an HB LLC converterConfigurations of the HB LLC converter and a resonant tankOperating states of the HB LLCHB LLC converter modeling and gain characteristicsPrimary currents and resonant cap dimensioningSecondary rectification design and output cap dimensioningResonant inductance balanceTransformer winding dimensioning and transformer construction16LLC converter modeling LLC converter modeling equivalent circuitequivalent circuitLLC converter can be described using firs fundamental approximation.Only approximation accuracy is limited!Best accuracy is reached around Fs.Transfer function of equivalent circuit:212ZZZVVnGinoutac+=+=Z1,Z2are frequency dependent=LLC converter behaves like frequencydependent divider.The higher load,the Lmgets to be more clamped by Rac.Resonant frequency of LLC resonant tank thus changes between Fsand Fmin.17Real load resistance has to be modified when using fundamental approximation because the real resonant tank is driven by square wave voltage.ORMSacII22_=ORMSacVV 22_=Considering the fundamental component of the square wave,the RMS voltage is:In a full-wave bridge circuit the RMS current is:LOORMSacRMSacacRIEIVR22_88=The AC resistance Racca be expressed as:LLC converter modeling LLC converter modeling equivalent circuitequivalent circuit1802ZRnQL=ssCLZ=0smLLk=Resonant tank equationsResonant tank equationssssLCF=21)(21minmssLLCF+=+=Quality factor:Characteristic impedance:Lm/Ls ratio:Minimum resonant frequency:Series resonant frequency:Load dependent!infoutVVVG)(2+=Gain of the converter:190.00.20.40.60.81.01.21.41.61.82.00.00.20.40.60.81.01.21.41.61.82.0f/fsvoltage gainQ=0.05Q=0.5Q=1Q=2Q=3Q=4Q=5Q=10Q=20Q=50Q=100Q=200Lm/Ls=6Region 2Region 1Region 3Normalized gain characteristicNormalized gain characteristicRegion 3:ZCS regionRegion 1 and 2:ZVS operating regionsQ=0.05 Heavy loadZCSZVSQ=200 Light load20Gain characteristic discussionGain characteristic discussion-The desired operating region is on the right side of the gain characteristic(negative slope means ZVS mode for primary MOSFETs).-Gain of the LLC converter,which operates in the fsis 1(for discrete resonant tank solution)-i.e.is given by the transformer turns ratio.This operating point isthe most attractive from the efficiency and EMI point of view sinusoidal primarycurrent,MOSFETs and secondary diodes optimally used.This operating point can be reached only for specific input voltage and load(usually full load andnominal Vbulk).Gain characteristics shape and also needed operating frequency range is givenby these parameters:-Lm/Lsratio-Characteristic impedance of the resonant tank-Load value-Transformer turns ratio21How to obtain gain characteristics?How to obtain gain characteristics?Use fundamental approximation and AC simulation in any simulation softwarelike PSpice,Icap4 etc.Racis the parameter!1 V amplitude AC supplyDirect gain plot for given Rac22Simulation schematic for discrete solutionSimulation schematic for integrated solutionDiscrete and integrated tank gain differencesDiscrete and integrated tank gain differences23Full load Q and k factors optimization Full load Q and k factors optimization Proper selection of these two factors is the key point for the LLC resonantconverter design!Their selection will impact these converter characteristics:-Needed operating frequency range for output voltage regulation-Line and load regulation ranges-Value of circulating energy in the resonant tank-Efficiency of the converterThe efficiency,line and load regulation ranges are usually the most importantcriteria for optimization.Quality factor Q directly depends on the load.It is given by the Lsand Cscomponents values for full load conditions:ssLCLRnQ=2240.0000.0500.1000.1500.2000.2501.00E+041.00E+051.00E+06Frequency HzGain-Q=2Q=3Q=4n=8,Ls/Lm=6,Q=parameter,Rload=2.4 GminGmaxfQ=4fQ=3Needed gains band for full load regulation-Higher Q factor results in larger Foprange-Characteristic impedance has to be lower for higher Q and given load=higher Cs-Low Q factor can cause the loss of regulation capability!-LLC gain characteristics are degraded to the SRC for very low Q values.Full load Q and k factors optimization Full load Q and k factors optimization 25-The k=Lm/Lsratio dictates how much energy is stored in the Lm.-Higher k will result in the lover magnetizing current and gain of the converter.-Needed regulation frequency range is higher for larger k factor.0.0000.0500.1000.1500.2000.2501.00E+041.00E+051.00E+06Frequency HzGain-k=2k=4k=6k=8k=10GmaxGminNeeded gains band for full load regulationfk=6fk=2n=8,Cs=33nF,Ls=100uH,Lm=parameter,Rload=2.4 Full load Q and k factors optimization Full load Q and k factors optimization 26Practically,the Ls(i.e.leakage inductance of the integrated transformer version)has only limited range of values and is given by the transformer construction(forneeded power level)and turns ratio.The Q factor calculation is then given by the wanted nominal operating frequency fs.The k factor has to be then calculated to assure gains needed for the outputvoltage regulation(with line and load changes).The k factor can be set in such a way that converter wont be able to maintainregulation at light loads skip mode can be easily implemented to lover no loadconsumption.Full load Q and k factors optimization Full load Q and k factors optimization 27AgendaAgendaWhy an HB LLC converterConfigurations of the HB LLC converter and a resonant tankOperating states of the HB LLCHB LLC converter modeling and gain characteristicsPrimary currents and resonant cap dimensioningSecondary rectification design and output cap dimensioningResonant inductance balanceTransformer winding dimensioning and transformer construction28Fsw=FsPrimary currents Primary currents single resonant capsingle resonant capIIN,IDM1ICs Time2.780ms2.782ms2.784ms2.786ms2.788ms2.790ms2.792ms2.794ms2.796ms2.798msV(Cs2:2)0V100V200V300V400VVCs Time3.26000ms3.26400ms3.26800ms3.27200ms3.27600ms3.28000ms3.28400ms3.25665ms3.28740ms-I(IDM1)-2.0A-1.0A-0.0A1.0A2.0AIDM2 Time3.26000ms3.26400ms3.26800ms3.27200ms3.27600ms3.28000ms3.28400ms3.25665ms3.28740ms-I(IDM2)-2.0A-1.0A-0.0A1.0A2.0A+222222_1681swmbulkoutRMSCfLVnIIs msLprimaryCInIII+=+=sec Time2.8160ms2.8200ms2.8240ms2.8280ms2.8320ms2.8360ms2.8400msI(Cs2)I(L5)-I(TX1)-2.0A-1.0A-0.0A1.0A2.0A29 Time1.3200ms1.3240ms1.3280ms1.3320ms1.3360ms1.3400ms1.3440ms1.3479msI(Cs)-2.0A-1.0A-0.0A1.0A2.0A Time1.3200ms1.3240ms1.3280ms1.3320ms1.3360ms1.3400ms1.3440ms1.3479msI(Cs2)-2.0A-1.0A-0.0A1.0A2.0A Time1.9680ms1.9720ms1.9760ms1.9800ms1.9840ms1.9880ms1.9648ms-I(V1)-1.00A0A1.00A2.00A-1.49A2.54A Time1.320ms1.325ms1.330ms1.335ms1.340ms1.345ms1.350msV(Cs2:2)0V100V200V300V400VIINICs2VCs2ICs1 Time3.26000ms3.26400ms3.26800ms3.27200ms3.27600ms3.28000ms3.28400ms3.25665ms3.28740ms-I(IDM1)-2.0A-1.0A-0.0A1.0A2.0AIDM1IDM2 Time3.26000ms3.26400ms3.26800ms3.27200ms3.27600ms3.28000ms3.28400ms3.25665ms3.28740ms-I(IDM2)-2.0A-1.0A-0.0A1.0A2.0APrimary currents Primary currents split resonant cap split resonant cap Fsw=Fs30Single and split resonant capacitor solutions-24 V/10 A applicationComparison of Primary CurrentsComparison of Primary Currents1.08 A2.16 AIIN_Pk0.76 A1.07 AIIN_RMS0.76 A1.52 AICs_RMS1.08 A2.16 AICs_PkSplit CapsSingle CapParameterSplit solution offers 50%reduction in resonant capacitor current and 30%reduction in input rms currentSelect resonant capacitor(s)for current and voltage ratings31-Body diode is conducting during the dead time only(A)-MOSFET is conducting for the rest of the period(B)-Turn ON losses are given by Qg(burned in the driver not in MOSFET)-MOSFET turns OFF under non-zero current=turn OFF lossesPrimary switches dimensioning Primary switches dimensioning Time3.26800ms3.27200ms3.27600ms3.28000ms3.28400ms3.26620ms3.28707ms-I(IDM1)(V(M1:g)-V(bridge)/10V(M2:g)/10-1.0A0A1.0A2.0AAB32MOSFET RMS current calculation-The body diode conduction time is negligible-Assume that the MOSFET current has half sinusoid waveform+222222_16161swmbulkoutRMSswitchfLVnII swmbulkOFFfLVI8Turn OFF current calculation-Assume that the magnetizing current increases linearly-Turn OFF losses(EOFF IOFF)can be find in the MOSFET datasheetPrimary switches dimensioningPrimary switches dimensioningOFFdsONRMSswitchtotalswitchPRIP+2_33AgendaAgendaWhy an HB LLC converterConfigurations of the HB LLC converter and a resonant tankOperating states of the HB LLCHB LLC converter modeling and gain characteristicsPrimary currents and resonant cap dimensioningSecondary rectification design and output cap dimensioningResonant inductance balanceTransformer winding dimensioning and transformer construction34Secondary Rectifier DesignSecondary Rectifier DesignSecondary rectifiers work in ZCSPossible configurations:a)Push-Pull configuration for low voltage/high current outputb)Bridge configuration for high voltage/low current outputc)Bridge configuration with two secondary windings for complementary output voltagesAdvantages:-Half the diode drops compared to bridge-Single package,dual diode can be used-Space efficientDisadvantages:-Need additional winding-Higher rectifier breakdown voltage-Need good matching between windingsPush-Pull Configuration35Equations24 V/10 A outputRMS diode current4_=outRMSDII2_outAVGDII=2_=outPKDIIAVG diode currentPeak diode currentAIRMSD85.7_=AIAVGD5_=AIPKD7.15_=12 V/20 A outputAIPKD4.31_=AIAVGD10_=AIRMSD7.15_=Secondary Current Calculations Secondary Current Calculations PushPush-PullPullTo simplify calculations,assume sinusoidal current