Model of Misalignment Tolerant Inductive Power Transfer System for EV Charging

This paper presents a study on the behaviour of the currents in a 1-D resonator array of inductive power transfer (IPT) systems that can be used for electric vehicle (EV) charging. The resonator array is used to ease misalignment issues between the receiver and the transmitter and to improve the transmission distance. Besides, IPT systems with resonator arrays may offer the possibility of dynamic charging. The analysis is performed assuming a generic position of the receiver over a 1-D array. A theoretical model - tolerant to the misalignment of the receiver - has been developed and experimentally verified. The model is used to determine the currents in the system. The obtained results highlight significant stresses on the circuit components that must be considered in the design stage of the apparatus, especially when a large power is transferred, such as in the case of EV charging.

I. Introduction

Recently, inductive power transfer (IPT) systems have been used in a broad range of applications, with a growing interest for electrical vehicle (EV) charging. These systems offer many advantages as avoiding electrical contact and being able to transfer energy in environments with rough conditions. Traditional IPT systems for EV applications are usually composed of two coupled coils, with different shape and geometry depending on the design optimization. The main drawbacks of these systems are usually related to the misalignment conditions, being them characterized by a high leakage magnetic field. This leads to a sharp decrease in efficiency, as well as safety concerns, due to the high magnetic field in the proximity. Several studies suggest particular arrangements for the windings allowing these drawbacks to be mitigated, according to [1]–[3]. An alternative solution for the stationary charging of EV which does not require the positioning of the on-board receiver coil in a particular position may rely on the use of resonator arrays [4], [5]. This extends the region where the receiver circuit can pick up energy from the magnetic field by means of the addition of intermediate relay coils. Making the coils resonate at the operating frequency allows the power to be transferred from the source coil to the receiver one with an efficiency adequate to EV battery charging. Moreover, the use of resonator arrays may point to dynamic charging. However, the effects of the power reflected by the receiver on the currents in the array resonators due to mismatch of the impedance have not been sufficiently investigated yet. In this paper, it is shown that the currents in the array of an IPT system may be significant, especially for high power systems such as those used in EV charging. This is a crucial aspect to take into account during the design stage of this type of systems. By means of magneto-inductive wave (MIW) theory [6]–[8] an explanation of the mechanism producing the increase in the currents is given.