Inductively Coupled Wireless Charging System with Multiple Electric Bicycle Loads

Abstract

Recharging of an electric bicycle involves direct connections from an electrical power outlet and this makes the charging process cumbersome. This can be simpli ed by using Inductive Power Transfer (IPT) wireless charging technology. IPT is a method that enables power to be transferred between two mutually coupled coils across an air gap. This thesis focuses on developing a low cost eet IPT charging system for electric bicycles. In this thesis, magnetic couplers that can t within a bicycle while providing su cient output power and low magnetic leakage are rst investigated. The bicycle kickstand is chosen to mount the couplers because it is close to the ground and this reduces the amount of magnetic radiation on the torso of users. Various magnetic coupler con gurations are considered and designed to meet the requirements. A DD-Solenoid magnetic coupler con guration is shown to be the best as it provides the highest power output capability with the lowest magnetic leakage with the chosen tolerance bands. A Double Coupled IPT System is proposed in this thesis where an intermediary coupler is inserted between the primary and pickup to provide individual control of each charging dock. This ensures that no magnetic elds are generated by the magnetic couplers when a bicycle is absent from the charging dock. An intermediary coupler con guration, consisting of an LCL network with an AC switch, is proposed and analysed. A 400 W prototype have been built for experimental validation and a single branch, consisting of an intermediary and a pickup, achieves 88% e ciency. A low-cost single-phase IPT power supply, which produces amplitude modulated track currents, was designed to power the Double Coupled IPT system. This amplitude modulation causes the pickup to produce pulse currents for battery charging. In order to assess the e ects of such pulse currents on typical batteries used in bicycles, a battery cycling experiment was undertaken where two batteries were cycled 2000 times with pulse shaped and DC currents. The results showed that pulse charging appears to be similar to conventional DC charging with little di erences when the average charging rate was kept the same and this suggests that the pulse currents generated from such an IPT system can be safely used for battery charging applications.