Multiple coil pair geometric designs for inductive wireless power transfer

Abstract

The inductance coil of the transmitter and receiver coils plays a significant role in the inductive wireless power transfer (IWPT) charging system for electric vehicles (EVs). The dynamic wireless charging (DWC) system is based on the inductive coupling between an electrified road transmitter track and a receiver coil embedded underneath the EV chassis. Most researchers design the coil pair with the same coil geometric designs for the transmitter and receiver coils which is the conventional way of IWPT charging system. Hence, this research investigates a new coil pair combination that utilises different coil geometric designs to compare if the new proposed combination can be as efficient as the conventional coil pair. The proposed coil pairs are expected to show a slightly lower efficiency when compared to the established existing coil pair. The transmitter coil is made of double-D (DD) geometric, whilst the receiver coil is made of a circular geometric design. A 2000 mm long DD transmitter coil is designed along with five circular receiver coils with 400 mm outer dimensions (D_out). There are five proposed coil pairs (T-R1, T-R2, T-R3, T-R4, T-R5), all of which have the same dimension for the DD transmitter coil and circular receiver coils’ outer diameter (D_out) but having different circular receiver coil inner diameter (D_in) among the five of them. These variations are significant as different EV manufacturers might have different preferences on designing and building inductance coils. Intensive calculations are done for coil parameters and geometric properties for the five proposed coil pairs. The coil parameters calculations are done to calculate the electrical parameters for the IWPT circuit’s components. Meanwhile, the geometric properties calculations are done to calculate the suitable dimensions and coil turns number of the proposed coil pairs. For the performance analyses simulations, the power transmission efficiency (PTE), magnetic flux density (MFD), and transmitted power (P_tx) are analysed further using the JMAG Designer software. The compatibility of the proposed coil pairs is simulated for three different conditions, which are air-gap, lateral misalignment, and vertical movement conditions. All the proposed coil pairs showed a good result in terms of their compatibility. Each has a PTE greater than 60%, which follows a test conducted by UC Berkeley on the dynamic charging concept, and the MFD is within the standard limits. The MFD at several observation points under different conditions are analysed to meet the level defined in the ICNIRP standard. T-R4 has the best PTE, MFD, and P_tx performances, whereas T-R1 demonstrated the most unsatisfactory performances. When the performance analyses were completed, it was determined that all five proposed coil pairs exceeded or met the PTE and MFD performance standards. These results conclude that the DD transmitter coil and circular receiver coil are compatible to couple. This coil pair is a new combination of existing coil geometric designs that have never been reported in the literature. Thus, this study is establishing opportunities to improve this technology and investigating the feasibility of designing a coil pair that meets the preferred needs of multiple EV models in a more efficient and effective manner.