Quantitative Design and Implementation of an Induction Cooker for a Copper Pan

The nonferromagnetic pans with a low equivalent resistance are desired to generate sufficient power for heating by larger eddy current. First, Maxwell 3D is used to estimate the equivalent heating resistance of a copper pan and select the optimal number of turns for a induction coil by Litz wire according to its size limitations and efficiency. Furthermore, the optimal resonant frequency is determined by maximizing the heating efficiency. Finally, the electric parameters are obtained to construct a simulation environment for the design of control strategies. A full-wave rectifier, buck converter, and half-bridge resonant converter are cascaded to construct the converter. Because of low equivalent resistance and high quality factor of the copper pan, a high slope ratio of the resonant current to the frequency is obtained. Therefore, the resonant converter is operated at a fixed switching frequency to reduce low-frequency oscillations of the resonant current. The buck converter is used to control the DC link voltage with third-harmonic injection, which enables heating power control, increases heating power and satisfies the standard, IEC-61000-3-2 Class A. Moreover, a resonant frequency estimator is developed to detect the resonant frequency for various positions of the pan on the induction coil to determine the optimal heating frequency. Finally, TMS320F28075-based converter with 100 A of peak resonant current is built. The heating effect and power loss on a copper pan is then measured, and the maximum heating efficiency is 69%. The measurement results verify the effectiveness of the proposed induction cooker and exhibits excellent agreement with the simulated results.