VHF rectification for fleet and HGV wireless charging solutions

This project aims to develop VHF rectification as a key part of fleet and HGV wireless charging solutions. Inductive Power Projection Ltd is the project lead, and Warwick Manufacturing Group is to provide the academic support.

There are wide-ranging socio-political issues concerning road transportation's greenhouse gas emissions, and the UK's strategy is to encourage broad adoption of EVs. Cable-free wireless power transfer (WPT) (also known as inductive power transfer) can potentially overcome the drawbacks of wired EV chargers, and represents a potentially transformational method for improving the EV operation and user experience. Aside from its convenience, WPT can significantly downsize the onboard EV battery, and has potential for dynamically charging EVs on the move. Although WPT solutions are being widely explored, charging rates are slow because the power density is low; and while manufacturers claim WPT is market ready, the transmission distance (reach) is poor, and angular misalignment of transmitter/receiver coils regularly results in batteries not receiving full charge. However, the greatest challenge is with heavy-duty vehicles. These require much higher charge-rates and more reach than WPT can currently offer. The only way to solve the charge-rate problem, as well as the reach and misalignment problems, is to significantly increase power density in the magnetic field.

Power density can be increased in several ways, but the state-of-the-art copper-coil based WPT systems are already highly optimised. Increased operating frequency will meet the technical challenge but leads to unacceptable power losses and therefore more operating costs. There's no way out for conducting coils. The emerging 2nd-generation frequency standard for automotives is 85kHz, rising from 20kHz with 1st-generation. A "difficult region" exists above 85kHz. Nevertheless, there's a strong business need to significantly increase charging rates, reach and robustness to misalignment tolerance of WPT systems by increasing the power density, at reduced costs. To this end, we offer a completely new capability using VHF technology that transcends the "difficult region" and delivers greatly enhanced power densities.

Until now, nobody has been able to formulate high-power VHF-WPT, but rectification is a major barrier and needs to be addressed before the commercial potential of our technology can be realised. Power diodes already used in WPT can't switch fast enough. VHF diodes that can switch fast enough are used in the context of smaller signals where moderate efficiency is tolerable. This project will therefore start to build a new capability for high-powered VHF rectifier solutions for VHF-WPT.