Study on Discontinuous Current Mode of Phase-Shifted Full-Bridge Zero-Voltage-Switching PWM Converter

Phase-shifted full-bridge zero-voltage switching PWM converters work in discontinuous current mode (DCM), when the current of output filter inductor is discontinuous in one switching period. The oscillation of inductance voltage is found in DCM converter. The operation principle in this mode is described in detail in the paper to research the oscillation phenomenon. Critical continuous condition is introduced to distinguish between these two models: discontinuous current mode and continuous current mode (CCM). The condition for CCM is deduced mathematically. The output filter inductor is equivalent to LC paralleled resonant circuit by considering its parasitic parameters. The voltage and current expression of resonance are given. The resonant characters are influenced by parameters´ variety. The influence rule, which is concluded comprehensively, is studied in simulation. The analysis is verified experimentally. Useful advice to make the oscillation down is proposed at last.