Improved pulse density modulation for high-frequency series resonant inverter with transformer-coupled load

Abstract

An improved method to determine the pulse density modulation (PDM) pattern is proposed for the high-frequency series resonant inverter (SRI) with a load-matching transformer. A simple discrete-time model of SRI is derived and the constraints given by a load-matching transformer are analysed. Using the model and constraints, the optimal PDM pattern is derived. The output current ripple is much reduced with this method and the transformer saturation problem can also be avoided. The results of a prototype experiment verify that the unwanted spectral component in the output current is effectively decreased by the optimal pattern. It is believed that the proposed technique is useful for practical applications such as the high-frequency power supply of an induction heating system.