Generalized Optimal Trajectory Control for Closed Loop Control of Series-Parallel Resonant Converter

The series parallel resonant converter (SPRC) is known to have combined the merits of the series resonant converter (SRC) and the parallel resonant converter (PRC). However, the series PRC (SPRC) has a three-element LCC structure with complex transient dynamics and without control of the resonant circuit's dynamics, the converter's closed loop bandwidth to switching frequency ratio will be much reduced compared to that of pulsewidth modulation converters. In this paper, the generalized optimal trajectory control (GOTC) for the SPRC is presented. It allows the nonlinear resonant circuit of the SPRC having an arbitrary starting state to reach a desired steady state in one cycle with two optimally controlled switching instances. It is a generalized form of optimal trajectory control (OTC) which is restricted to transitions between steady states. Based on GOTC, a traditional controller with inner current and outer voltage state-feedback is designed for an SPRC based dc–dc converter. The GOTC based feedback controller allows use of higher feedback gains compared with one using OTC or frequency control and gives higher closed loop bandwidth. This results in either better disturbance rejection for the converter or the possibility of reducing output filter sizing. Experimental results confirm the theoretical claims.