Inductive Charging—Making Recharging Easier

rate providing the battery pack with 90% of the charge in about five minutes.

The power to the charging station will have to be made available at multitiered prices. During the off-peak hours, the cost will be lucrative to encourage users of EVs to charge the vehicles. During the shoulder or in-between peak and off-peak hours, the price will be higher. And during the peak hours, the price for charging the EV will carry an additional premium to provide charging opportunities to users in a must have situation.

INDUCTIVE CHARGING—MAKING RECHARGING EASIER

As the demand for the EVs continues to rise, it is important to make it easy to charge the EV. The recharging of consumer and commercial EVs require:

• Simple, easy to use, and intuitive methods • Flexible infrastructure for all vehicle and utility power levels • Safe for all-weather operations • Reliable and long-lasting or durable equipment operation

Most EVs will be charged at least once during the day. This will average out to 3,000 to 7,000 charge cycles during the 10-year life of the vehicle. The conventional electrical outlet cannot meet the heavy-duty cycle requirement of the EV battery pack. During the inadvertent connecting and disconnecting from and to the charge port, large electrical arcs may be drawn, which can be fatal at times. It is essential to use a safe coupling method to charge the EV and prevent all forms of direct electric connection between the electric utility power outlet and the battery pack inlet port. In addition, it is essential to ensure that there are no moving parts associated with the charging mechanism. The charge coupler should offer minimum contact resistance and be rugged enough to withstand the weight of an EV, resistant to the weather elements.

Inductive charging is a coupling process that transfers electrical energy from the electric utility charge port to the EV battery pack through an electromagnetic connection rather than physical or direct connection. Operating on the principle of a transformer, the electrical energy transfer takes place by linking the electromagnetic fields between two separate inductors. The primary and the secondary inductor are

coils of conductive wire that are wound to contain the magnetic field with the ferrite material.

A simple inductive coupler consists of a copper coil wound around a ferrite core to direct the magnetic field. When electric current flows through the primary coil, the resulting magnetic field induces an alternating voltage through the magnetic field and into the secondary coil. Thus the circuit is completed. The AC current is then converted to DC and stored in the battery pack.

During the inductive charging process, the onboard vehicle charging port closes mechanically after the coupler is inserted. Thus there are no moving parts associated with the charging process. Since the inductive charger serves as an isolation transformer, it provides electrical isolation between the EV and the utility grid. In addition, the coupler has a double-insulated coil. Both the inductive coupling and the power cable are electrically cold. Power is applied only when the coupler is inserted and locked into the receptacle port, and communication between the EV charge inlet port and the utility outlet port has been established. In addition, the necessary diagnostic tests must be completed successfully, before the power is applied to the cable and the coupler.

Since there is no direct electrical contact, the inductive coupler/port can be operated safely under water. The charge coupler and the charge port are coated with nonconductive protective material and so no water, dirt, ice, or snow will affect the unit or interrupt the safe operation of the inductive charger. Since the orientation is intuitive, there are no additional alignment requirements. The inductive coupler is lightweight and easy to handle. Conventional industrial electrical cables and connectors are heavy, having complex key insertion systems and require an insertion force of 20 to 30Nmtr and a high twist-to-lock force of 5 to 10Nmtr.

The one-size-fits-all connector for different utility service lines and battery voltages allows for easy charging. A single-sized inductive coupler with the high-frequency switching electronics can accommodate charging levels ranging from 1 to 150kW power levels. Thus the inductive charger and coupler with high frequency switching electronics can accommodate charging over the power levels from 1 to 150kW. This makes it possible for consumers to charge the battery pack at home and at work with a 240V AC, 6.6kW system. This quick charge takes place in 12 minutes from 80% SOC at 50kW from a 600V AC industrial service line or charge at 1.5kW with an onboard charger from any 120V AC outlet. Power is transferred through an inductive system at high frequencies (80 to 300kHz), making it possible for the coupler and port to be kept at the same size.