Analysis and control of phase-shifted series resonant converter operating in discontinuous mode

DC-DC series resonant converter operating in Discontinuous Conduction Mode (DCM) offers advantages in terms of low switching losses, high power density, and low control complexity. The low switching loss feature is lost when the converter operation shifts from DCM to Continuous Conduction Mode (CCM). This paper presents an in-depth analysis of such a converter operating in DCM and derives two boundary conditions under which the converter shifts to CCM. The fixed-frequency phase-shifted pulse width modulation is used to adjust the effective duty cycle and regulate the output voltage. Steady state analysis for above resonant frequency operation is also presented in this paper. The derived boundary conditions aid the design of the converter using which DCM operation and hence the soft switching feature is ensured at all operating points. Limits of these boundary conditions are verified using simulation and experimental results on a prototype converter.