Exploitation of MOSFET‐based AC switches in capacitive impedance matching networks in inductive wireless power transfer systems

Abstract

This paper investigates the exploitation of MOSFET based AC switches in capacitive impedance matching networks (IMN) for inductive wireless power transfer (WPT). The IMN optimum capacitance has been chosen for a 200 kHz resonant frequency. The activation of tuning capacitor on the tuning branch is achieved with the use of MOSFET AC switches in order for the WPT system to achieve maximum power transfer efficiency. The MOSFET AC switch is modelled as an internal parasitic resistor and capacitor connected in parallel. A WPT analytical model is developed to study the effects of the MOSFET’s parasitic elements on the WPT system’s efficiency and is verified experimentally. Various MOSFET switches and relays have been implemented as the IMN switching elements and compared when tested under the same conditions. It is concluded that MOSFET AC switches which have low on-resistances and small parasitic capacitances are desirable as they have a smaller impact on the efficiency. Additionally, parasitic capacitances of MOSFET AC switches need careful consideration for different resonant frequencies as they can affect the overall IMN tuning capacitance especially when they are turned off. Comparing to commonly used relay switches, MOSFET based AC switches have similar switching performance but are significantly smaller in size.