Resonance Tracking Control at Fixed Frequency for Electromagnetic Induction-based Systems

Electromagnetic induction-based systems are widely utilized in everyday life. The efficiency of these systems, which rely on resonance, decreases when variations in inductance cause deviations from the resonant condition. Traditionally, this issue has been addressed by adjusting the operating frequency to match the resonant frequency. However, for applications such as wireless power transfer systems or induction heating, operating at a fixed frequency is often preferred. A variable capacitor is an effective solution for maintaining resonance at a fixed frequency. However, variable capacitors are typically designed for low-current applications. Those capable of handling high currents require specialized designs and are not commonly used in general-purpose applications. Moreover, they tend to be larger in size and significantly more expensive. Therefore, a novel resonant tracking control method employing quasi variable capacitors is proposed as an effective solution for these systems. The proposed quasi variable capacitor, by simply adding a switch, does not result in an increase in size or cost. Moreover, since resonance can be maintained through PWM control, the circuit remains uncomplicated. This paper explains the operating principle of the proposed quasi variable capacitor and analyzes its circuit characteristics. As a result, it is demonstrated that stable operation is achieved while maintaining resonance at a fixed frequency. Furthermore, it is shown that power control can also be easily accomplished.