High-frequency inverter with phase-shifted PWM and load-adaptive PFM control strategy for industrial induction-heating

The authors describe a control scheme incorporated in the voltage-fed full-bridge series resonant high-frequency inverter using static induction high power transistors (SITs), which is based on a load-adaptive variable frequency modulated phase-shift PWM (pulse-width modulation) control strategy. The operating principle of the load-adaptive variable frequency PWM series resonant inverter system with a new control scheme is described along with its operating characteristics in steady state. The 20 kW-200 kHz prototype inverter system suitable for induction heating in industry is demonstrated, including a specially designed power transformer. SIT stacks with a water cooling system, and a building-block assembly for high-power use. Experimental results and simulation results are presented. Finally, an improved variable frequency PWM series resonant inverter topology incorporating partially inserted capacitive lossless snubbers is proposed for soft switching and compared with the inverter mentioned above