(精品)bridgelessPFC(1208)

,LITE,ON,Power Electronics Lab.(Beijing),Power Conversion BU,P&C SBG,单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,Bridgeless PFC,Vivian sun,Bridgeless PFC,The purpose,-For higher power range,the bridge power loss is high,especially at low line condition.For example,the bridge power loss of 1200W PS is about 24W.,-The bridgeless PFC topology can reduce total power loss,improve efficiency and thermal performance.,Bridgeless PFC,The comparison of bridge and bridgeless PFC,The design process,Power loss calculation,Design tools,The comparison of bridge and bridgeless PFC,Topology,Power Loss and Parts Count,Current Sensing,Iac,Sensing,Floating Ground,The topology of bridge PFC,The Topology of Bridgeless PFC,Bridgeless PFC Operation,Comparison of Bridge and Bridgeless PFC,Current Sensing,Current Sensing,Current Sensing,Iac,Sensing(bridge),Iac,Sensing(bridgeless),The Floating Ground of Bridgeless PFC,With a coupled choke as boost inductor,no capacitor can link L and N to power GND,otherwise the choke will be shortened.So the power GND is floating with the switches on and off at a switching frequency.,The Comparison of Efficiency,Design Specifications,Vin,=90264VAC,Vo=380VDC,Po=1200W,Fs=100kHz,PF0.98(Full load&high line),Eff,92%,Block Diagram,Boost Inductor Design,Peak input current at low line,I,pk,:,Duty cycle at low line D:,Boost Inductor Design,Boost inductance L:,Delta I is 20%peak current,Select,L=300uH,(initial inductance),Boost Inductor Design,Magnetic core:Arnold MS-185060-2 or,Dongbu,S184-086A,Magnetic material:,sendust,(,kool,Mu,),Al=86mH/1000T,Bs=0.95T,We choose:N=60,According design tools,the maximum magnetic force is 120,Oersteds,and the flux density is 0.56T(2/3)Bs.,Power Stage Design,Output capacitor selection(holdup time 20ms),Select C,out,=660uF(two 330uF/450V capacitor in parallel),Main switch selection,Two STW26NM60(600V/30A)in parallel,Boost diode selection,Low reverse current and fast reverse recovery diode shall be selected.SDT12S06 or STTH1506TTI is preferred.,Control Circuit Design,Using UCC3818 as the PFC controller,Voltage Loop Design,Current Loop Design,Critical Point of Bridgeless PFC,Voltage Loop Design 1,The pole is placed at the crossover frequency,is about 1020Hz,the zero is placed at the one tenth of the crossover frequency.,The power stage gain is given by:,Voltage Loop Design 2,Voltage loop,The voltage a,mplifier configuration as right:,Vref,=7.5,so we choose:,R125=R126=R127=332k,R129=19.6k,Vout,=(332*3+19.6)*7.5/19.6=388V,The second,harmanic,voltage on the output capacitor is:,The gain of the voltage amplifier is:,Voltage Loop Design 3,Voltage loop(continued),The value of,Cf,is determined by:,The pole is place at the frequency:,Current Loop Design 1,Current loop,The gain of the power stage is:,The current amplifier gain is:,Current Loop Design 2,Current loop(continued),The crossover frequency is 5KHz10KHz,the zero is placed at the crossover frequency to give a phase margin of 45 degrees.And a pole is placed at one-half the switching frequency to reduce switching noise.,Critical point of Bridgeless PFC,Due to the floating power GND,IAC cant be achieved by rectified line voltage directly in this circuit.We know IAC is|,Vin,|/R,so we just need have|,Vin,|.In this circuit,we can achieve|,Vin,|by filtering Vo*(1-D).D is the duty cycle of the driving signal of switches.,Critical point of Bridgeless PFC,The net introduces one pole at:,The pole must be located at a frequency high enough not to distort the input waveform and at the same time,low enough to filter the switching frequency.We select,fp,=10kHz,R1=600k,R2=7.5k,C=2200pF,Power Loss Calculation,Boost inductor,Power Loss Calculation,Main Switches,Power Loss Calculation,Power Loss Calculation,Boost Diode,