Electric vehicles (EVs), which are becoming increasingly popular, can be charged by either wired or wireless means. The latter, based on wireless power transfer (WPT) technology, is convenient and safe, but pad misalignment is one of the major concerns as it causes a reduction in charging power level, prolonging the charging process. Therefore, wireless charging systems with high tolerance to pad misalignment are necessary. This study proposes a three-phase bi-directional wireless power transfer (BD-WPT) system with a control scheme that offers high tolerance to pad misalignment in EV charging applications. The system uses simple coil designs for pads and utilises the magnetic coupling among pads to compensate for the power variation. A comprehensive mathematical model, incorporating all magnetic cross-coupling effects, is presented to investigate the charging performance of the system under pad misalignment and different pad spacings. To demonstrate the validity of the proposed system, theoretical and simulated results are presented, benchmarking against a single phase WPT system, and in comparison to a prototype 1.3 kW three-phase BD-WPT system. Results are convincing and indicate that the proposed three-phase BD-WPT system with small pad spacing is more tolerant to wide pad misalignment in EV charging applications.
Bi-directional inductive power transfer (BD-IPT) systems are preferable for applications such as Electric Vehicles (EVs) and wireless integration of EVs with the utility grid (V2G). In particular, poly-phase BD-IPT systems are used in high power applications and for rapid charging of EVs but their performance is severely compromised by the cross-coupling effects between phases and the misalignment of charging pads or coils. This paper therefore presents a generalized mathematical model to investigate the cross-coupling effects caused by pad-misalignments and corresponding impacts on the power flow of ploy-phase BD-IPT systems used for EV charging. Using the proposed model, the charging behavior of an EV, based on a 3-phase BD-IPT system, is investigated under different operating conditions, analyzing the sensitivity of power flow and direction to cross coupling.Results are presented in comparison to simulations to demonstrate the accuracy of the proposed mathematical model and as well as to show that the changes in power flow and direction can be somewhat compensated for by the individual control of phases.
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