Dual 1.5-MHz 3.5-kW versatile half-bridge series-resonant inverter module for inductive load characterization

This paper presents the challenges encountered and the solutions adopted during the construction of a versatile high-frequency series-resonant half-bridge voltage-fed inverter module. It is being used as the large-signal generator for an inductive load characterization test-bench which permits to obtain measurements in a real working situation over a wide frequency and output power operating conditions for a variety of loads. Square wave operation is established slightly above resonance under Zero Voltage Switching conditions to acquire near sinusoidal current and low losses. Output power is controlled by means of a variable DC bus and resonant conditions are fixed for each operating frequency by means of two adjustable resonant capacitor banks. The control of every test-bench block and the triggering waveform generation is performed digitally by means of a Field Programmable Gate Array. The modular approach and the flexible control implementation enable the utilization of several modules in parallel connection or full-bridge configuration widening the possibilities of load excitation. Final prototype covering the required operation range has been designed, and two modules have been constructed and evaluated for operation in half-bridge and full-bridge configurations showing rugged and stable operation during characterization of induction heating loads.