A Fixed-Frequency Single-Phase Resonant Direct AC–AC Converter Integrating Variable Inductor Technique for High-Frequency Induction Heating Applications

This paper presents a new prototype of a single-ended single-phase class-E direct ac-ac converter for induction heating (IH) applications, which is the first proposal for the application of variable inductor (VI) technology to a direct ac-ac converter, thereby achieving fixed-frequency control with a wide soft-switching (SSW) range. Combining VI technology enhances IH system flexibility and resolves issues of mechanical noise and electromagnetic interference (EMI) caused by variable frequency modulation, which are prevalent in conventional IH methods. This paper analyzes the proposed converter’s operation, explaining the VI control strategy for fixed-frequency power regulation, with key VI parameters designed using a reluctance model. Furthermore, experimental verification with a 850W/50kHz prototype confirms the fundamental performance capabilities of the proposed direct ac-ac converter. This evaluation demonstrates the high-frequency load power regulation and power conversion efficiency, and further confirms the implementation of SSW. The proposed converter achieved a high efficiency of 96.0%, which is significant for reducing energy loss of IH systems.