A new technique to wirelessly charge moving objects

Imagine if you could transfer power wirelessly, charging an electric car or robot without the need for wires, and even without the object needing to stop. This dream is becoming one step closer to reality as researchers from North Carolina State University have developed a new technique to wirelessly transmit power from a stationary source to a moving object.

There are several wireless power transfer techniques in existence that work on the principle of transferring energy from one coil (transmitter) to another coil (receiver). One current approach uses a much larger transmitter coil than receiver coil, meaning there is a constant coupling between coils. However, this is inefficient because much of the transmitter coil is not coupled with the receiver and the large transmitter emits a strong magnetic field which can be dangerous.

New research used segmented coils, a different technique in which there are several transmitter coils, each one a similar size to the receiver coil. This increases efficiency (energy transfers more efficiently between coils of the same size) and addresses safety concerns, since each coil only produces a low-level electromagnetic field.

The team designed a system so that when the receiver comes into range, it couples with a transmitter coil. This specific transmitter coil then increases the current going through it automatically, increasing the magnetic field around it and therefore increasing the energy it can transfer by 400%. When the receiver passes out of range, the transmitter coil returns to normal levels of current. This allows one transmitter coil to increase the power going to the receiver without the other transmitter coils dangerously increasing in current.

The team have currently created a working prototype that will now be scaled up. Its efficiency will also need to be increased: currently it transmits energy at 0.5kW, but the aim is to increase this to around 50kW, allowing it to be used in real-world situations.

The paper, “Reflexive Field Containment in Dynamic Inductive Power Transfer Systems,” is published online in IEEE Transactions on Power Electronics.