Flying-capacitor Linear Amplifier for Wireless Power Transfer Systems with Flying-capacitor Voltage Balancing

In this paper, a flying-capacitor linear amplifier (FCLA) for wireless power transfer systems is proposed. The proposed circuit has an n-series FCLA with only N-ch MOSFETs and an unfolder. The flying capacitor (FC) voltages are balanced by selecting the operation state of each MOSFET with phase-shifted carriers. FCLA outputs a continuous voltage that does not contain the harmonics that cause current harmonics. Due to this, the radiation noise from the transmission coils is reduced. The operation of the WPT system with the proposed 16-series FCLA is demonstrated in a simulation. The proposed FCLA output the sinusoidal voltage to the resonance circuit. In addition, the harmonics of the primary coil current are analyzed. From this result, the FCLA significantly reduces the current harmonics than the conventional two-level inverter. Then, The FC voltage balance is verified using the prototype with a 2-series FCLA. From the experimental results with a small-scale prototype, the proposed circuit outputs full-wave rectified sinusoidal output voltage with balanced FC. Furthermore, the harmonics of the unfolder output voltage are analyzed. From the analyzed result, the third-order harmonics are reduced by 19.8dB due to FCLA with MOSFET in the active-state in comparison with the theoretical value of harmonics of square wave voltage.