Load Estimation for Induction Heating Cookers Based on Series RLC Natural Resonant Current

Abstract

In domestic induction heating applications, cookware can be considered an equivalent load in a series resistor–inductor–capacitor resonant converter. Therefore, the electrical parameters of an equivalent circuit change according to the cookware material, size and the cookware position on the heating coil. This study proposes an online estimation method for detecting the cookware status, determining the material and estimating the equivalent heating resistance of cookware on an induction heating cooker (IHC) for power control. The proposed method could turn off the circuit in abnormal situations such as low equivalent heating coverage rate or non-ferromagnetic cookware and adjust the power in normal situations. In the method, a half-bridge series resonant converter (HBSRC) generates two test patterns with three resonant voltage pulses to detect cookware every 10 ms, only the current feedback information is needed to avoid the calculation loads and times necessary for complex signal operations in software. To verify the proposed method, a digital signal processor based HBSRC with 1000 W was constructed. The maximum errors between the estimated and measured resistance and inductance were 7.14% and 2.91%, respectively. Moreover, power control in emulated user operation reveal that the proposed method and control system can effectively estimate load online to detect cookware status and determine whether to turn off or vary the heating power for an IHC.

Modelling and Simulation of Quasi-Resonant Inverter for Induction Heating under Variable Load

“…However, while in more complex resonant inverters, the current in the resonant tank is managed by the control strategy of two or more switches, allowing an efficient control in the desired frequency range, in a singleswitch inverter the design of the converter has to be tightly coupled with the analysis of the coil-workpiece system. Finally, some direct online load identification techniques have been developed to evaluate the load in real induction heating systems with full-bridge or half-bridge inverters [10,11]. Still, these methods require to process current measurements in real time, augmenting the complexity of the systems.…”