Enhanced asymmetrical modulation for half-bridge series resonant inverters in induction heating applications

This paper presents a method that improves the reliability of half-bridge (HB) series resonant inverters (SRI) for high-frequency induction heating applications. Many industrial processes, like induction heat treatments, are very repetitive. This cyclical operation represents a strong limitation of the inverter's reliability, mainly due to the accelerated stress of the power semiconductors. This method consists in an enhanced asymmetrical pulse width modulation (EAPWM) that allows distributing the losses across the components, thereby reducing the cyclic increase in junction temperature of the power devices, and thus achieves a reliability that is more than twice as high as that achieved using traditional modulation methods. The work methodology includes a theoretical study of the HB inverter and a complete analysis of losses. The presented design rules have been used to implement a 25 kW, 100 kHz inverter. The use of silicon carbide (SiC) MOSFET transistors allows reaching an efficiency greater than 99%. The analytical results obtained have been experimentally validated by testing the inverter on an induction heating test bench. This paper presents an enhanced Asymmetrical Modulation for Half-Bridge Series Resonant Inverters in Induction Heating Applications to improve system reliabilityimage