Power inverter control for induction heating by pulse density modulation with improved power factor

This paper describes the design and analysis of a new pulse density modulation (PDM) control strategy adapted for resonant inverters for induction heating applications. PDM is introduced to overcome the drawbacks of the classical control modes such as PWM, FM and phase shift. One characteristic of PDM is that it operates at resonant frequency with zero-voltage and zero-current switching for a wide range of output power variations. The PDM strategy allows to vary the power and to reduce switching losses and electromagnetic noises. Fixed length switching patterns are used and are chosen to maximize power factor while keeping controller implementation simple. Simulation results obtained using the power system blockset in the Matlab/Simulink environment and experimental results are presented to illustrate the effectiveness of the new pulse density modulation control strategy.