High-Efficiency and Low-Stress ZVT–PWM DC-to-DC Converter for Battery Charger

High-Efficiency and Low-Stress ZVT–PWM DC-to-DC Converter for Battery Charger Ying-Chun Chuang and Yu-Lung Ke,Senior Member,IEEE

Abstract—This work presents a novel highly efficient and low-stress battery charger with a resonant switch converter—based on resonance and zero-voltage-transition soft-switching theory—that reduces defects associated with high voltage and high current stresses caused by the resonance of traditional resonant circuits.The novel battery charger meets the requirement that all circuit components must operate with zero-voltage switch-ing.Experimental test results indicate that the proposed battery charger reduces the temperature of an active power switch,and switching losses are less than those obtained using a traditional pulsewidth-modulation converter as a battery charger.

Index Terms—Battery chargers,soft-switching,zero-voltage-transition(ZVT).

I.I NTRODUCTION

E LECTRONIC equipment is essential to daily life.Accord-

ingly,developing reliable battery chargers is extremely important.An effective charging technique is efficient,prolongs the life cycle of batteries,and rapidly charges batteries.In 1970,N.R.M.Rao developed the conventional pulsewidth-modulation(PWM)power converter,using PWM technology to control power switches and produce a step-up or step-down output voltage.The PWM control principle is to regulate the time a switch switches on by setting the switching frequency of an active power switch.Consequently,the converter’s output voltage is controlled by varying the pulsewidth of the trigger signal on the power switch.This approach of controlling the pulse trigger signal on the power switch using a simple circuit design has been widely utilized to control power switch topol-ogy in various converters.

Fig.1shows switching losses in a traditional PWM power converter,where V C(t)is the voltage drop between the collector and the emitter in a transistor,and i c(t)is the currentflow through the collector[1]–[4].This conventional PWM power converter increases the efficiency of a traditional linear power converter;however,the switching frequency must be increased to decrease the volume and weight while simultaneously in-creasing the switching stress,di/dt and dv/dt surge,switching losses,and electromagnetic interference(EMI).

A traditional PWM power converter has a nonideal switching process.The resonant power converter that uses the capaci-tor parallel to the power switch can be applied to overcome the aforementioned disadvantages.The voltage is a sinusoidal waveform during the switching instant of the power switch

Manuscript received October25,2007;revised February4,2008.First published March21,2008;last published July30,2008(projected).

The authors are with the Department of Electrical Engineering,Kun Shan University,Tainan71003,Taiwan,R.O.C.(e-mail:chuang@.tw; yulungke@;yulungke@.tw).

Digital Object Identifier

10.1109/TIE.2008.921218

Fig.1.Switching losses in a traditional PWM power

switch.

Fig.2.Switching losses in a resonant power switch.

when resonance occurs,thereby decreasing the area of overlap

between the voltage and current,reducing the switching losses

[5]–[12].Fig.2displays the switching loss of a resonant power

converter.The area of overlap between the voltage and current

in a resonant converter is substantially decreased during the

switching instant(Figs.1and2).The principal advantage of

the resonant converter is that reducing the voltage or current

on the power switch to zero decreases the switching loss from

the power switch and effectively hinders EMI.However,based

on Fig.2,the voltage or current with sinusoidal wave that

results from the application of resonant technology increases

the voltage/current stress on the component.Marked conduc-

tion loss is simultaneously generated,as the circuit components

have parasitic resistance.Therefore,the zero-voltage-transition

(ZVT)/zero-current-transition(ZCT)soft-switching power con-

verter is then created to further improve resonant converter

performance.

By using available devices and circuit technologies,PWM

converters have been generally designed to operate with a

high switching frequency.However,a high switching frequency

increases switching losses.The switching loss at turn off is prin-

cipally caused by converter leakage inductance.As the power

switch is turned on,switching losses are generally caused by the

abrupt discharge of energy stored in the parasitic capacitance

of active power switches.Several resonant converters have

been developed that decrease switching losses for active power

switches in switched-mode converters.However,due to the

resonant nature of current and voltage waveforms,operating

resonant converters typically involves high circulating energy,

which results in a significant increase in conduction losses.

The ZVT–PWM technique,which decreases switching losses, 0278-0046/$25.00©2008IEEE