A Hybrid Bi-directional Wireless EV Charging System Tolerant to Pad Misalignment

Abstract

Electric vehicles (EVs) are becoming increasingly popular as a means of future transport for sustainable living. However, wireless charging of EVs poses a number of challenges related to interoperability, safety, pad misalignment etc. In particular, pad-misalignments invariably cause changes in system parameters which in turn lead to increase in losses as well as reduction in power throughput, making the charging process long and inefficient. Consequently, wireless charging systems that are less sensitive to pad-misalignments have become preferable. This paper, therefore, presents a hybrid Wireless Power Transfer (WPT) system that charges EVs at constant rate despite large misalignments between charging pads. The proposed charging system uses a combination of two different resonant networks to realize a constant and efficient charging process. A mathematical model is also developed, showing as to how the two resonant networks can be combined to compensate for pad-misalignments.

Existing System

Frequency Control Method.

Proposed System

The proposed hybrid WPT system uses two LCL and CL resonant networks, connected in parallel, as compensation for each side. Bipolar charging pads, consisting of two coil windings with a center tap, are used for primary and secondary. Alternatively, two pairs of non-polarized pads, similar to the pads can also be used instead of bipolar pads in the proposed hybrid topology. The two resonant networks are fed by the same converter, but connected separately to one of the bifilar windings in each charging pad. A mathematical model is presented to characterize the behavior of the hybrid system as well as to show how the unique characteristics of each resonant network can be exploited to maintain a constant charging profile without requiring primary and/or pick-up regulation, overcoming the effects of 3D pad misalignments. The proposed hybrid system, therefore, only require simple protection and control circuitry and could potentially work without any position sensors (or with a much simpler positioning system) reliably. This will not only reduce the total cost of wireless EV charging systems but also it will make the system more versatile.

Architecture

EV charging system