Design and development of a wireless charging system for electric vehicles in smart grid

• Main Author: Lim, Gerald Lip Giap
• Other Authors: So Ping Lam
• Format: Final Year Project
• Language: English
• Published: 2014
• Subjects: DRNTU::Engineering
• Online Access: http://hdl.handle.net/10356/61284
• Institution: Nanyang Technological University

This report presents an adaptive wireless charging system for electrical vehicles. Three important aspects of the wireless charging system are being considered. Consisting of frequency tuning for maximum power transfer efficiency, impedance matching for maximum output power and single- inductor multiple-output (SIMO) DC/DC converter for balance charging. The electromagnetic resonant coupling technology is being used for high power transfer efficiency. By varying air gap between the transmitter coil and the receiver coil, the mutual inductance will be changed. The theoretical analysis shows that varying air gap or/and load impedance results in shifting the optimal operational frequency and the reduction of power transfer efficiency. Model predictive control (MPC) is utilised to obtain optimal operational frequency. More, through varying load leads impedance mismatch, the maximum output power condition becomes invalid. A novel PI impedance matching network is developed to keep maximum output power under a range of load impedance variations. The final stage of the wireless charging system is a DC/DC converter for balance charging. A practical charging method is individual charging based on status of each battery. In order to realise individual battery charging, SIMO DC/DC converter is being used. Smaller size and low cost are the advantages of SIMO DC/DC converter, however it has cross regulation problem. Therefore, a model predictive voltage control method is developed for SIMO DC/DC converter as such the converter will be operating in the continuous conduction mode (CCM) to suppress the cross regulation. MPC strategy has the capability to track the reference voltage automatically, so that it is being used to control the inverter in the execution of the frequency tuning by following the reference frequency. The MPC employed dynamic tracking property which aids SIMO DC/DC converter to reduce the impact of cross regulation. Therefore, the MPC is used in inverter for frequency tuning and the SIMO DC/DC converter for balance charging A simulation model is built using Matlab/Simulink to evaluate the performance of the wireless charging system. The current simulation results show that the maximum wireless power transfer efficiency is 93% with resonant frequency tuning, and the maximum power transferred to the load is stably maintained with a novel PI impedance matching network, and the cross regulation of SIMO DC/DC converter is significantly reduced with MPC control.