Multi-harmonic small-signal modeling of digitally controlled dc-dc series resonant converters

This paper addresses the problem of small-signal modeling of digitally controlled dc-dc series resonant converters when controlled using a combination of phase shift and pulse width modulation. Examples of such combined modulation techniques have been recently proposed as part of online efficiency optimization controllers, in which the regulator acts on both the phase shift between the input and output legs and the duty cycle of one of the converter legs. This paper extends the dynamic phasor approach, employed for instance when a pure phase shift control is used, to a more general multi-harmonic model which accounts for the effects of duty cycle modulation on both the baseband components and the switching frequency components. Theoretical findings confirm the need for an extended model in order to fully capture the converter dynamics. Simulations and experimental results are presented to validate the approach