Time-domain steady-state analysis of fixed-frequency series resonant converters with phase-shift modulation

Frequency modulation is often used in series resonant converters (SRC) to gain voltage regulation, which brings challenges for EMI filter and switch driver design. Also the desirable zero voltage switching (ZVS) cannot be maintained at light load conditions. This paper presents time-domain steady-state analysis of fixed-frequency SRC with phase-shift modulation. Three modes of operation are identified based on resonant tank current, a discontinuous and two continuous modes. Analytical expressions for all variables in each mode, ZVS conditions, and the mode boundaries are demonstrated. Exact formulae for current zero crossing moments are reported. Also the condition for existence of three or two modes is provided.