Study Of A Novel Soft-switching Bi-directional DC/DC Converter Based On PWM

Bi-directional DC-DC converters allow the transfer of power between two DC sources in either direction. They are increasingly used in applications such as DC uninterruptible power supply, aerospace power system, DC motor drive systems and hybrid-energy electric vehicles, armored car power system, etc. High power bi-directional DC-DC converters are a difficult problem in power electronics field.The main function of bi-directional DC-DC converter applied in some big car carried power system is the transfer of power between two DC sources in either direction:(1) transfer dc 270v into dc 48v to charge storage battery, its main technology parameters: power rating:5kw; electrical source voltage: 270V± 10%(DC); output voltage rating :dc 48v;rated current: 102A;capacity of over loading:150A,2 minutes; efficiency > 85% ;and safeguarding functions of over voltage, lack of voltage, over current, etc.(2) transfer dc 48v into dc 270v to charge storage battery, its main technology parameters: power rating:5kw; electrical source voltage: 48V±10%(DC); output voltage rating :dc 270v;rated current:28A;capacity of overloading:40A,2 minutes; efficiency >85%;and safeguarding functions of over voltage, lack of voltage, over current, etc.According to above special needs, a new topology of bi-directional DC-DC converter is put forward in the dissertation in order to allow the transfer of power between two DC sources in either direction. Bridge bi-directional DC-DC converter that is easier realized soft switching is applied in high & medium powers. Two sorts of soft-switching modes (ZVS &ZVZCS) of bi-directional PWM DC-DC converter is analyzed by the numbers. Control strategy of PS-FB-ZVZCS-PWM is applied in the dissertation.Characteristics of the new topology: The topology is a phase-shifted full-bridge ZVZCS PWM (PS-FB-ZVZCS-PWM) bi-directional DC-DC converter with isolated transformer and passive network. There is a PS-FB-ZVZCS-PWM converter receptively from two sides. Therefore, thenew topology is simple.Theory analysis, Pspice simulation, experiment of the new topology and its control strategy based on PS-FB-ZVZCS-PWM bi-directional DC-DC converter are introduced. Results of Pspice simulation & experiment are also presented. All of active switches in the new converter with PIC singlechip, UC3875, passive resonance network, saturation inductance can achieve soft switching in both forward and backward operation modes, so switching losses of the converter is reduced. The new converter maintains soft switching in wide load rang. Moreover, Synchronous rectifier operation makes conduction losses of the converter reduced. As a result, weight and volume of the converter will be reduced largely, and the converter will have high power density.