Simulation-Assisted Design of a Bidirectional Wireless Power Transfer With Circular Sandwich Coils for E-Bike Sharing System

Abstract

A wireless power transfer (WPT) system with bidirectional power flow control for charging batteries and drawing electric power from batteries is presented in this paper for e-bike sharing applications. The proposed WPT consists of a bidirectional DC-DC converter and a sandwiched coil set, which includes primary winding with ferrite pad in charging stations and a movable secondary coil without ferrite pad, which is inserted into the primary coils to receive or transmit energy, on the e-bike. Hence, the proposed coil set could provide high coupling factor, better tolerance of misalignment, and a compact size that enables easy installation in the current mechanism of bike-sharing systems. The Maxwell 3D is adopted to design coil sets, which are based on the known resistance of Litz wire, and the effect of the ferrite pad and misalignment are analyzed to achieve good performance. To select a suitable converter, the characteristics of predesigned coils are simulated using Maxwell 3D, MATLAB and PSIM. Then, a full-bridge CLLC converter with the same resonant frequency for charging and discharging modes is chosen to provide minimal loss by using the synchronous rectifier on the 48-V side and voltage gain without the loading effect. Finally, a digital signal processor-based digitally controlled CLLC converter is constructed to verify the performance of the proposed WPT, which can provide 200 to 48 V/500 W charging and discharging functions with constant current/constant voltage modes and fast-response current control. In addition, the maximum efficiency is 96% at 52 V and 75% rated load in charging mode. INDEX TERMS Wireless power transfer (WPT), bidirectional DC-DC converter, e-bike sharing applications, sandwich coil, Maxwell 3D, full-bridge CLLC converter.

Review on Control Techniques for EV Bidirectional Wireless Chargers

“…In [64], we can find a study about how to configure the ferromagnetic material in two circular coils used in an e-bike wireless charger. As for the control, when charging the battery, the Constant Voltage and Constant Current modes are implemented.…”

“…There is no study about the reactive power, which is also modified according to the parameters. [61] Full-bridge Full-bridge Series-Series I, II [62] Eight-switch leg Eight-switch leg Series-Series I, II [63] Half-bridge Half-bridge CLC-LC All (two-switch leg) (two-switch leg) (Uncontrolled Q) [64] Full-bridge Full-bridge Series-Series I, II…”

“…• Coupler design. Little attention has been paid to the coil design in bidirectional wireless chargers, with just some proposals in [64,77] addressing this topic. Since the power flow is in both senses, the coil design must attend to the magnetic field leakage and variations of the coupling coefficient due to misalignment for the battery charging and discharging process.…”

Efficient finite element modelling of litz wires in toroidal inductors

“…IET Power Electronics published by John Wiley & Sons Ltd on behalf of The Institution of Engineering and Technology [8,9]. However, engineers face difficulties in accurately defining winding resistance for complex winding structures as a function of frequency during the optimization stage of magnetic components [10].…”

“…Hence, a comprehensive understanding of the frequency dependent phenomenon in litz wire is a key to the optimal design of magnetic components [8, 9]. However, engineers face difficulties in accurately defining winding resistance for complex winding structures as a function of frequency during the optimization stage of magnetic components [10].…”