Harmonics Suppression using a GaN-based Flying-Capacitor Multilevel Inverter with PWM Operation at 13.6 MHz

This paper discusses a flying-capacitor multilevel inverter (FCMI) with PWM operation at 13.6 MHz industrial, scientific, and medical (ISM) frequency band to eliminate the inverter output filter in wireless power transfer (WPT) systems. The inverter utilizes GaN HEMT to enable switching at such the high frequency with an acceptable power loss. Full-bridge three-level topology with phase-shifted carrier SPWM makes it possible to reduce the voltage stress and the required switching frequency to one-half and one-fourth, respectively. This paper also introduces two series RLC balancing circuits with phase-toground connection to achieve capacitor voltage balance in any condition. The developed inverter has been verified in experiments. As a result, it achieved an efficiency as high as 70.65% under a 12-W output power operating condition. Moreover, the inverter effectively suppressed the low-order harmonic distortion in the output current to 2.04%, leading to an output filter-less configuration.