Research On Single-phase Zero-voltage-switching On-board EV Charger

As a key component of electric vehicle power system,the on-board charger’s(OBC)efficiency is an important index.The on-board charger is generally composed of a prestage power factor correction(PFC)circuit and a post-stage isolated DC/DC converter,which respectively realizes unit power factor correction and battery charging control.The front-stage PFC circuit is generally hard-switching,the switching loss restricts the conversion efficiency and power density of the front-stage PFC circuit.At the same time,the post-stage phase-shifted full-bridge circuit has drawback such as limited soft switching range,which causes the conversion efficiency to drop.In order to improve the conversion efficiency and power density,this article introduces the active clamping soft-switching technology into the on-board charger to realize the soft-switching operation of the front-stage PFC circuit and expand the soft switching range of the full-bridge phase-shift DC/DC converter.The article proposes a single-phase soft-switching on-board charger circuit and a soft-switching modulation strategy(ZVS-PWM),analyzes the operating principle of the soft-switching on-board charger circuit,derives the soft-switching constrain conditions,and gives the selection range of auxiliary branch switch’s duty cycle under different power.On the basis of theoretical analysis,an experimental model of the single-phase soft-switching on-board charger with rated power of 3.3k W and switching frequency of 75 k Hz is designed and built,and the modulation principle is verified.Experiments show that the on-board charger’s all switches can achieve zero voltage switching-on in a wide operating range,the soft-switching range of the full-bridge phase-shift DC/DC converter is also extended.The overall efficiency of the experimental model at the rated operating point reaches 97%.