Series resonant multi-inverter with discontinuous-mode control for improved light-load operation

Operation under light-load conditions is a general issue when developing power converters, as it can lead to system instability and/or decreased performance. This topic is especially important for resonant converters, as the efficiency significantly degrades when the operation point is set out of the resonant conditions. Considering the importance of efficiency for the power converter reliability, the environmental impact, and the regulation concerns, a major effort to improve the operation under light-load conditions is justified. Domestic induction heating is an application example where the variable load and the output power requirements imply the operation under a wide range of conditions, including long-term light-load operation. The aim of this paper is to propose an improved control scheme for the series resonant multi-inverter, a cost-effective topology to supply multiple inductive loads, based on the discontinuous-mode operation. Two different control strategies are proposed: regenerative control (RC) and direct conduction control (DCC). An analytical study is performed and the main simulation results are presented. Besides, an experimental series resonant multi-inverter prototype is used to validate the simulation results.