Single-Stage PWM Converter for Dual-Mode Control of Capacitive Wireless Power Transmission

In capacitive wireless power transfer system, effective capacitance of the energy link between the transmitter and receiver changes according to variations in separation distance or degree of alignment in electrodes, which would modify the resonant frequency and degrade the system performance. To compensate for such a change, it is necessary to track the resonance frequency. In this case, frequency control scheme cannot be used for the output voltage regulation. Conventionally, additional DC/DC converter has been adopted in the front of the transmitter or in the back of the receiver for this regulation purpose; however, it increases system complexity and decreases power efficiency. This paper proposes a new single stage topology that can achieve output voltage regulation as well as resonant frequency tracking. By combining asymmetric pulse width modulation scheme with a buck-boost converter, the output voltage is regulated by duty cycle control and the energy link variation can be compensated by frequency control, which is suitable for the wireless power transfer system in practical user scenario. Furthermore, as the proposed circuit uses only two additional components, the transmitter circuit is compact. For verification, the proposed circuit has been tested by a 50W prototype hardware.