Investigation of Dual Coil Induction Heating for Enhanced Temperature Distribution Optimization

Optimizing temperature distribution is one of the crucial tasks in induction heating technology, especially, for small devices with constraints on compactness, efficiency, and cost. The optimization solely using coil shape parameters, referred to as 'traditional coil design', cannot provide a satisfactory solution with highly limited structural constraints of lateral or vertical size. A multi-coil system where each set of coils is fed by multiple inverters enables control of the magnitude and phase of exciting currents, providing an alternative approach to enhance the design flexibility. However, additional inverters increase both the volume of a driving circuit and the cost of products, so this approach has a risk of reducing applicability to personal electronics. This article proposes a dual coil system, consisting of primary and secondary coils, to enhance the flexibility for temperature distribution optimization. The impact of primary and secondary coil currents on heat source distribution and efficiency are analyzed, and an equivalent circuit model representing both coils and a workpiece is introduced to provide the main concept of the proposed dual coil system. The effect of circuit parameters on resonance characteristics of the dual coil system are studied for a sensitivity analysis of design parameters. Finally, the optimization flow is proposed and applied to a case study model to demonstrate its superiority compared to the traditional coil design. Potential challenges are discussed to provide insights for further model development.