Leakage Flux Control of Mismatched IPT Systems

Inductive power transfer (IPT) is becoming increasingly popular in stationary and taxi rank electric vehicle (EV) charging with many pad topologies available. Multicoil topologies, such as a bipolar pad (BPP) or double d quadrature pad, are particularly suited as the primary pad due to the pads' interoperability characteristics and ability to couple power with wider tolerances. Appropriately designed IPT systems that can transfer power with good efficiency within leakage flux limits are a particular concern to manufacturers as standards restrict the field levels which users are allowed to be exposed to and EV manufacturers prefer smaller secondary pads. BPPs have been shown to be interoperable with both polarized and nonpolarized secondary pads and this paper focuses on such a primary coupling to double D pad secondaries in locations requiring much wider tolerances than fixed parking lots. This paper shows that leakage flux is heavily influenced by the proximity of the energized coils in the primary and that leakage reductions of up to 50% are possible if a BPP is used and coils are appropriately energized when delivering 3.3 kW in misaligned conditions. It also shows that a secondary regulator is needed to improve both the efficiency and the leakage flux.