Design of a dual-loop controller for in-motion wireless charging of an electric bus

In this paper, a 25-kW Wireless Power Transfer (WPT) system is considered for in-motion charging of an electric bus. The goal of this research is to derive a control strategy for the primary side of a wireless Electric Vehicle (EV) charger, with the objective to achieve fast dynamics and full control over the primary coil current and the amount of transferred power. To this aim, a dual-loop controller has been proposed which utilizes two feedback PI controllers combined with two feed-forward controllers to set targeted steady state operation points. Using Generalized State Space Averaging (GSSA) approach, the primary side of the wireless charger system is modeled. This includes full-bridge inverter, LCC compensation circuit and primary track or coil. By using this small-signal model, two closed loop digital PI controllers have been designed to ensure fast and accurate response of the track current controller, as well as control of the power flow transferred to the secondary side. In order to increase the reliability of the system, two feed-forward controllers have been added to the PI controllers. For the current controller (inner loop) the feed-forward controller is based on a sigmoid phase angle profile, and for the power controller (outer loop), it is derived based on an analytical equation relating transferred power and primary track current. The simulation and experimental results demonstrate expected operation of the entire control system for a typical load profile observable in inmotion charging applications.