Simple Power Control Method for Induction Heating Cookers Using Fundamental Frequency Power under Asymmetrical Pulse-Width Modulation

To simplify power calculation, this article proposes a simple power control method based on fundamental frequency power (FFP) for induction heating cookers in both dc or ac input systems. FFP is calculated from the estimated equivalent resistance and the peak value of the fundamental frequency resonant current, which is obtained through peripheral circuits to reduce the computational load on the digital signal processor (DSP). By employing Fourier series, the characteristics of the resonant tank under asymmetrical pulsewidth modulation at a fixed switching frequency are derived. Therefore, the power is dominated by FFP in the dc input system, while in the ac input system, sideband frequency powers which are near to the fundamental frequency must be considered. However, the power control error (PCE) when only using FFP may increase at lower power levels. Consequently, a power compensation coefficient K is introduced and validated through variance analysis, thereby reducing PCE. Finally, a DSP-based half-bridge series resonant converter was implemented to validate the proposed method. The proposed method successfully controls power and achieves PCEs lower than 6.9% and 7.5% at different power levels compared to measured results of a power meter in both dc or ac input systems, respectively.