Research Of FB-ZVZCS-PWM Converter With Wide Range Input

Switching power supply is more and more universal in human's life. As one ofthe topologies of switching power supply, full bridge topology is used widely inhigh-power applications because of its relatively lower voltage and current stress ofthe switches. Although this circuit has been in a mature stage, there are still somedrawbacks, for example the limit of maximum duty cycle, and realizing softswitching at light loads difficultly. It leads to the limit of the input voltage range.Based on this shortcoming, a thorough study is made. And this extends the rangesof the input voltage in some degree which has some theoretical and practical value.The full bridge phase-shifted converter with its primary side of the transformerin series with saturated inductor and blocking capacitor to realize ZCZVS is used asthe research object, and the control strategy is average current mode. By theanalysis of the working principle, a conclusion is obtained that the loss of dutycycle is smaller in the constant current input mode than the constant voltage outputmode. This phenomenon is leaded because of the difference of the operating powerin essence.Digital power supply is the development tendency of the switching powersupply. TAfter the T TelaborativeT T analysis of the use of digital signal processorTMS320F2812 in the full bridge phase-shifted converter, Tthis article proposes twomethods of generating driving waveforms. In order to control the phase angle, onemethod is to change the data in the TUniversal Timer. The other is to change thevalue of the comparator in the EV module. At the same time, this article does someimprovement on the traditional PI T Talgorithm, which reduces the computing time ofthe regulator and improve the performance of the T Tdynamic response.TWhen Tfull bridge phase-shifted converter is used in the applications of highinput voltage and light loads, the switches of the Tleading leg are hard to realizezero-voltage switching, which limit the maximum input voltage. However in theapplications of low input voltage and heavy loads, the switches of the lagging legare hard to realize zero-current, which limit the minimum input voltage. Afterelaborate researches, we find that when the parameters are fixed, there are mainlytwo factors that limit the range of the input voltage. One factor is that the dead timeof the conventional phase-shifted controlling chips are fixed which leads that boththe situation of high input voltage, light load and the situation of low input voltage,heavy loads could not be taken into account simultaneously. The other is that thevalue of the saturated inductor could not adjust to both the situation of high input voltage, heavy loads and the situation of low input voltage, heavy loads. In view ofthis situation, the article proposes two methods to extend the range of input voltage.One scheme is to make use of the flexibility of DSP, accommodating the dead timeof the leading leg in real time. The second method is to use the super ability ofcomputing of DSP, through proper additional circuits to control the magnetizationtime of the saturated inTductor.TA test prototype with the maximum power of 10.5kW is designed. Thisprototype works well and has a relatively high efficiency. It extends the range ofthe converter's input voltage and verifiesT that the theoretical analysis is correctT.