Remote systems, such as vehicles, have been introduced that include locomotion power derived from electricity received from an energy storage device such as a battery. For example, hybrid electric vehicles include on-board chargers that use power from vehicle braking and traditional motors to charge the vehicles. Vehicles that are solely electric generally receive the electricity for charging the batteries from other sources. Battery electric vehicles (electric vehicles) are often proposed to be charged through some type of wired alternating current (AC) such as household or commercial AC supply sources. The wired charging connections require cables or other similar connectors that are physically connected to a power supply. Cables and similar connectors may sometimes be inconvenient or cumbersome and have other drawbacks. Wireless charging systems that are capable of transferring power in free space (for example, via a wireless field) to be used to charge electric vehicles may overcome some of the deficiencies of wired charging solutions. As such, wireless charging systems and methods that efficiently and safely transfer power for charging electric vehicles are desirable.
Wireless power transfer systems may utilize inductive power transfer (IPT) to transfer power between a wireless charging system base and a mobile device pickup. IPT systems have a base unit which includes a tuned induction coil and drive circuitry and a mobile device which includes a similarly tuned induction coil and receive circuitry. Power may be transferred between the charging system base and the mobile device pickup due to coupling between the tuned induction coils. In single direction power transfer, energy is transferred from the base unit induction coil by way of a generated electromagnetic field within which the mobile device induction coil needs to be positioned. For efficient energy transfer the mobile device induction coil will typically be positioned close above and substantially co-axial to the base unit induction coil so as to achieve a strong degree of coupling between the electromagnetic field and the mobile device induction coil.
Many IPT systems also include a physical core made of a material having a high electromagnetic permeability. A commonly used material is ferrite. The physical core is highly permeable to electromagnetic fields and therefore greatly increases the magnitude of the generated electromagnetic field.
Some IPT systems include induction coils positioned above a ferrite core in the manner of a backing. A further advantage of using a ferrite core as a backing is that the electromagnetic field that surrounds the induction coil is constrained to the ferrite backing material on that side of the induction coil. The reason for this is that it is much easier for the electromagnetic field to travel through the ferrite material than air or other less permeable components.
Due to the ferrite's effect on the electromagnetic field produced by the induction coil, the presence of the ferrite also has a large influence on the inductance of the induction coil and therefore the coupling frequency. If the ferrite material exhibits a large variation in permeability then the induction coil will exhibit a similarly large variation in inductance and tuning making it difficult to achieve consistent tuning.
WO 2010/090539 discloses an IPT system for powering electric vehicles in which a base (usually the primary) coil consists of two separate co-planar coils positioned above a core formed from parallel bars of a material of high electromagnetic permeability, such as ferrite. In this arrangement, there is no straight path through the core that passes through the coils. As such, the coils act as pole areas and lines of electromagnetic flux arc between them in the form of a “flux pipe” above the coils, a zone of high flux concentration. Advantageously, the arrangement results in little leakage of flux below the coils on the side of the core.
Single homogeneous slabs or bars of highly electromagnetically permeable materials of the size typically required for use in wireless power transfer systems are fragile, difficult to obtain, expensive and may not provide suitable consistent permeability.
It is an object of the disclosed embodiments to address the foregoing problems or at least to provide the public with a useful choice. Further aspects and advantages of the present disclosure will become apparent from the ensuing description which is given by way of example only.