Single-Phase High-Frequency Resonant Direct AC–AC Converter With Constant Off-Time Pulse Coding Modulation for Fluid Water Induction Heating

Induction heating (IH) has been widely applied in both industrial and domestic environments as a clean, efficient, energy-saving, and high safety electric heating technology. This paper proposes a new pulse modulation for single-phase direct ac–ac converters in fluid water IH systems, which is defined as constant off-time pulse coding modulation (COT-PCM). The proposed pulse modulation is suitable for fixed-frequency power control in a direct ac–ac converter, featuring high performances of skin effect, reduction of input (utility line) current fluctuations, and minimization of the size and capacity of the filtering components. Furthermore, this approach can overcome the technical issues of conventional pulse modulations such as pulse frequency modulation (PFM) and pulse density modulation (PDM) such as audible noises with respect to power controller. The essential performances of the proposed pulse modulation are demonstrated by an experiment based on a 2 kW-40 kHz prototype for a fluid water IH appliances in home and consumer appliances. The high-frequency load power regulation, power control range & resolution, power conversion efficiency, and soft-switching of a bidirectional switch are revealed, after which the validity is evaluated from a practical point of view.