This paper planned a high ability LLC resonant inverter for induction heating use by using asymmetrical voltage cancellation control. The planned control method is realize in a full-bridge topology for induction heating use. The operating frequency is automatically adjusted to maintain a small constant lagging phase angle under load parameter variation.
The output power is controlled using the asymmetrical voltage cancellation method. The LLC resonant tank is plan without the use of output transformer. This results in an increase of the net efficiency of the induction heating system. The validity of the planned method is verified through computer simulation and hardware experiment at the operating frequency of 93 to 96 kHz.
Fig. 1. Full-bridge series and parallel resonant inverter.
EXPECTED SIMULATION RESULTS
Fig. 2. Voltage and current waveforms at 100 % duty cycle
Fig. 3. Simulation results with α=70o
This work planned the full-bridge LLC resonant inverter for induction heating use. The phase-locked loop allows resonant density tracking under load limit variation. The analytical expression of the output power as a function of the shifted phase angle is given in this work.
Based on the derived expression, the asymmetrical voltage cancellation can be used to control output power to the induction coil. Simulation and experimental studies are performed to verify the planned control method. The resonant density tracking and the adjustment of pulse voltage together ensure the maximum power transfer to the load throughout the heating cycle with minimal loss.
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