A New Resonator Design for Wireless Battery Charging Systems of Electric Bicycles

This article presents a new resonator design scheme for wireless battery charging systems of electric bicycles (EBs). The newly designed method is established based on a switched series (S)-series parallel (SP)/S compensation scheme and Helmholtz coils for the transmitting coils. The Helmholtz coils are adopted to ensure that the mutual inductance between the transmitting and receiving coils is invariant. For this reason, the switched S-SP/S compensation scheme can be used to implement load-independent constant current (CC) and constant voltage (CV) charging for the battery loads instead of using the conventional LCL or LCC compensation schemes. The advancements of the proposed design, as compared to the conventional methods for wireless EB charging, are more than constant mutual coupling and elimination of compensated inductors. The communication channel between the transmitter and receiver, additional user-end converter, and complicated control algorithms can also be annihilated. Simulation results using Maxwell verify that the mutual inductance of the proposed resonator is constant. Experimental results validate that the output current and voltage can be well-regulated to track the references at 1.2 A and 24 V, respectively, at different load conditions. Especially, the maximum efficiency can reach 97.17% in the CC charging mode, whereas 91.17% in the CV charging stage. The maximum output power is 115 W on the load side. This design can be generalizable to other power levels to meet different charging demands.