Wireless power transfer for electric vehicles using variable capacitor technique in compensated circuit

Abstract

The Wireless Power Transfer (WPT) systems provide a platform by which the electric energy from the power grids can be conveyed to Electric Vehicles (EVs) by only using the electromagnetic fields, i.e. without necessarily the contacts. Other enhancements that WPT offers include: its ability to address some issues inherent in the "plug-in" charging technique like vulnerability to vandalism, power inefficiencies, and the dangers of exposed connectors as well as loose wires, among other things. Additionally, this technology makes it convenient for EVs to be charged while they are moving or parked. Comprehensive research has been carried out in the last decades in the development of wireless power transfer technologies for electric vehicles. Literature review in the field of wireless power transferred has revealed that inductive resonance with series-series compensation circuit is the most efficient compensated circuit in inductive resonant technology as it plays important role in the system resonance. The resonance frequency is the key point which could be disturbed because of external and internal disturbance of the inductor values. To overcome this limitation a variable capacitor technique is used to achieve the required resonance frequency. A proposed variable capacitor technique implemented in wireless power transfer circuit is designed, simulated and practically implemented with 87.75% efficiency. In this research the fixed capacitor in the proposed compensation circuit is replaced with a controlled variable capacitor in order to achieve a fine-tuned resonance frequency. Also, the speed of selecting the required tuned capacitor is achieved using high frequency (100kHz). The main idea is to select different values of the resonant capacitor in order to achieve different resonance frequencies. Inductor coil design is also presented in this research using Ansys Electronic software in order to find the optimum inductor and optimum airgap used in the design of the variable-capacitor compensated circuit. A circuit using the proposed technique is built in the lab to verify the design and simulation results. Overall, this research is based on static wireless charging.