A High Frequency Inverter for Variable Load Operation

Inverters operating at high frequency (HF, 3-30MHz) are important to numerous industrial and commercial applications such as induction heating, plasma generation, and wireless power transfer. A major challenge in these applications is that the load impedance can vary dynamically in both real and complex components over a wide range, making it difficult to maintain high-efficiency soft-switched operation. The constraints that a variable load impedance place on high frequency inverter design results in systems that are often bulky, expensive, and inefficient. This paper presents the design, physical prototype, controller, and experimental results of a high-frequency variable load inverter that is able to directly drive widely variable loads with high efficiency. The prototype can deliver 1kW into a 22 ohm load at 95.4% efficiency as well as deliver significant power to a wide range of both capacitive and inductive loads.