Primary side control strategies for battery charging regulation in wireless power transfer systems for EV applications

Resonant inductive-based wireless power transfer (WPT) for battery charging has potential applications in electric vehicles (EVs). The EV battery charging process requires the regulation of both charging voltage and current. Duty ratio or frequency control is generally preferred to manage the power flow between the transmitter and receiver coils in the WPT system. In the case of WPT charging, misalignment between the coils and parameter variations are unavoidable issues that result in changes to the output power. Therefore, it is essential to control the power flow to maintain constant current (CC) and constant voltage (CV) modes during battery charging. To address these challenges, various primary-side control techniques, such as asymmetric clamped mode (ACM), asymmetric duty cycle (ADC), and phase-shift (PS) fixed frequency control strategies, have been proposed for WPT systems. This paper conducts a comparative analysis of these control methods, considering their output voltage ranges and their ability to maintain zero-voltage switching (ZVS) for the entire control range. Furthermore, the paper presents a generalized design for reduced-order small signal modelling, utilizing an extended describing function. The designed controller, based on small signal modelling, will undergo real-time testing to evaluate its dynamic performance in the series-series resonant converter.