Efficient and cost-effective wireless CC/CV charging for electric vehicles: A bipolar duty cycle approach

Inductive Power Transfer (IPT) has gained significant popularity in recent times, particularly in electric vehicle (EV) battery charging applications. To achieve optimal battery charging, it is imperative to implement both constant current (CC) and constant voltage (CV) modes of operation. Traditionally, CC/CV modes are attained through conventional phase shift techniques, frequency modulation schemes, the use of active converters, and additional compensator circuits and coils. However, these conventional methods not only reduce system efficiency but also escalate overall costs and control complexity on the onboard side. This article proposes a novel bipolar duty cycle control strategy for a series-series resonant IPT system, aiming to achieve CC/CV modes of operation. The proposed control strategy increases the number of switches operated with zero voltage switching, compared to other fixed-frequency phase shift control strategies across a wide load range. Furthermore, the article provides a detailed procedure for implementing the voltage and current compensator. Additionally, it describes the construction of a one-kilowatt laboratory prototype using Sic devices, presenting the obtained results. The peak measured DC-DC efficiency of 93.8 % is achieved at a distance of 150 mm, and the efficiency has also been evaluated under misalignment conditions.