Scalable Architectures for High Frequency and Very High Frequency Wireless Power Transfer

Abstract

Wireless charging is already taking hold with abundant commercial products that operate at around a hundred kHz. Currently, high frequency (HF, 30 MHz) and very high frequency (VHF, 30-300 MHz) wireless power transfer (WPT) stand out because of better passive components, faster transient response, better combination with communications, and higher receiver input voltages. However, current WPT systems are not fully scalable for different applications with different power levels and transfer distances in the wireless power world.

The thesis investigates scalable architectures for HF and VHF WPT, which can scale the power level and transfer distance while maintaining the efficiency with an application range from watts for biomedical and consumer electronics to tens of watts for robots and drones, breaking the trade-offs among devices, power, frequency, and transfer distance. The vision is to provide energy anytime and everywhere for electronic devices in the wireless power world.

To fully utilize the fast switching speed of Gallium nitride (GaN) at HF-VHF, an ultrafast and isolated gate driver is investigated with variable frequencies, variable duty cycles, and arbitrarily long on- and off- times. It can be scaled for different active devices with the ultimate speed of below 270 ps rise and fall times.

To mitigate the EMI (electromagnetic interference) and EMC (electromagnetic compatibility) problems at HF-VHF, a magnetic field cancellation method is presented for the encircled circuits inside WPT coils to make miniaturized devices operate properly under strong magnetic fields. The fundamental magnetic field for the encircled circuits can be reduced to 1 % compared to that without cancellation.

To design robust and resilient WPT systems, a classic circuit topology CMCD is brought back to the renaissance, which can work as both inverter and rectifier. It can absorb parasitics and be modeled as a purely second-order system, which does not require multi-resonant tuning in the higher-order ZVS resonant converters. The straightforward design reveals the advantages of a wide load range and small input current ripple at the same time.

With CMCD as a building block, the vision of a wireless power world can be possible. A single CMCD inverter coupled with a CMCD rectifier, i.e. a singleton system, fulfills the low power and short transfer distance applications. A segmented CMCD inverter coupled with a segmented CMCD rectifier, i.e. a segmentation system, fulfills the high power and long transfer distance applications. The segmented CMCD power converters aggregate the magnetic flux and corresponding power together from each identical and synchronous module by electrically connecting the resonance, which also physically increases the coil size at HF-VHF and extends the transfer distance and power level but maintains the efficiency of the optimized singleton system.

In the end, the thesis concludes the contributions and illustrates the future directions of HF and VHF power conversion and transmission.