Field analysis and high frequency conversion for multi-coils induction heating appliances

Abstract

Today, induction heating is becoming a viable alternative to conventional cooking methods by providing a quiet, safe and low radiation cooking environment. Nevertheless, the commonly used single coil induction heater suffers from the problems of localized thermal distribution and fast aging of the induction pan. The design of multi-coils induction heater outperforms the conventional single coil products by enhancing power capability and providing uniform thermal distribution. The objective of this research is to realize a uniform distribution of field patterns in commercial products through systematic and in-depth investigation of the multi-coils technique for induction heating appliances. The thermal impacts of electromagnetic proximity effects in induction cooker with multi-coils are comprehensively studied. An analytical computation method is developed and implemented with different effecting parameters, so as to analyze the thermal impacts of proximity effects and eddy currents distribution in the system. For enhancing heating performance of the induction cooker with Chinese wok, Variable Turn Pitch (VTP) coils are designed and applied to address the localized eddy currents distribution problem of single coil system. Corresponding analytical equations are given to illuminate the design process of the VTP coils. The thermal field distribution on the wok is experimentally validated to be remarkably improved by applying the VTP coils. To improve electrical efficiency of high-power induction cooker for commercial applications, its control strategies are thoroughly studied. Various control algorithms for the power regulation are studied in detail. In particular, the loss analysis of switches facilitates comparing the obtained results by adopting different control methods. Consequently, an optimized hybrid power regulation strategy is proposed in this research. The experimental results sufficiently verify the validity and reliability of the proposed control strategy. Moreover, induction cookers with distributed multi-coils are proposed and investigated to improve their heating performances. Multi-coils solutions including 7-circle coils, hexagon like 7-coils, and square 9-coils are designed and investigated to replace the traditional single coil design. A switched exciting method for driving the multi-coils is adopted for obtaining optimized performance. The testing results on the prototype verify that the proposed solution is capable of providing more uniform and better thermal distribution. A novel cordless ironing system by implementing multi-coils induction heating techniques is proposed and investigated in this research. The coils solution is thoroughly investigated and determined based on thermal performance analysis. In addition, the inductances characteristics of the coils are studied by analytical computation and Finite Element Method (FEM) analysis, given that the iron is placed above the coils at different locations on the ironing board. The experimental results on the prototype amply prove the theoretical analysis and also confirm the feasibility of the proposed induction iron system. To sum up, this research has accomplished comprehensive analysis and in-depth studies in various aspects including magnetic field, thermal field, control strategies, and practical applications of multi-coils induction heating techniques. The research outcomes provide meaningful theoretical findings as well as feasible application solutions of induction heating appliances with multi-coils.