As a power supply method with high spatial freedom, megahertz (MHz) wireless power transfer (WPT) has great potential in particular application fields. The role and importance of WPT are described from the perspective of interdisciplinary. This article starts with WPT systems’ performance at different frequencies, emphasizes the basic composition and working principle of MHz systems, and focuses on a comprehensive review of recent years on inverters, rectification, impedance compression, dynamic impedance matching, coupling structure design, and multiload model establishment. Meanwhile, different technologies are summarized, compared, and classified. Current challenges and future development trends are discussed.

Efficient and simple modulation of output power is demanding for radio frequency plasma and wireless power transmission,magnetic resonance imaging systems. In this article, a power modulation strategy that can improve the linearity, power capability and efficiency simultaneously is proposed. The control modes ofon/offand Outphasing are combined to ensure shallow phase depth in a wide power range. Hybrid modules composed of load independent class Φ2structure and symmetrical class Φ2structures are adopted ason/offmodules and PS module to match the proposed control scheme, which are able to provide constant output voltage while remaining zero voltage switching (ZVS) state under resistive-inductive and resistive-capacitive load separately. Theon/offmodule is uniquely designed to behave as a static load when turned off. With the cooperation of control strategy and circuit architecture, the proposed system is able to regulate power linearly with optimal efficiency and minimal voltage and current stress. An implementation with four modules, 13.56 MHz, 25–200 W inverter system is demonstrated, the output power can be seamlessly and linearly controlled with efficiency always within 82%–93.5%. The heat dissipation in prototype is uniform, and is feasible to expand to a higher power compared with other control and circuit structures.

To solve the power supply problem of the high-voltage side detection module in HVDC applications, a multi-relay wireless power transfer (WPT) system with an operating frequency of 800 kHz is designed. This paper establishes the model of multi-relay WPT system and derives the expressions of the efficiency and output power. By analyzing the influence of the insulator metal flanges and optimizing the coil spacing, the energy transfer efficiency of the system can be improved. A 1.1m prototype with 8 resonant coils and 2 metal flanges is built and the experimental results verify the influence of metal flanges on the multi-relay WPT system and the feasibility of optimized arrangement of coils.

This paper presents a regulated 24V-to-1V series-capacitor buck converter to achieve single-stage high step-down dc-dc power conversions with high efficiency and high power density. Many of the challenges faced by conventional buck converters are overcome by this converter topology. The switching losses and noise of all switching elements in this topology are sufficiently reduced because the voltage stress of switches is reduced to one-fourth of the input source voltage at switching periods. By taking advantage of the benefits from the series-capacitor buck converter topologies, all switching elements of the converter allow for low withstand voltage MOSFETs with low drain-source on-state resistance and low gate charge total characteristics. Further, the use of coupled inductors can achieve a small steady-state current ripple and enhance transient response to the load steps. The effectiveness of the topology is verified by a 24V-1V/20A prototype with a peak efficiency of 91.6%.

In order to further improve the boost ratio of the traditional impedance source inverter, and to improve the DC bus voltage spikes during switching transient caused by the leakage inductance of the coupled inductor. A new high-step up and low-spikes impendence inverter based two coupled inductors is proposed. By using two T-type coupled inductors to replace the inductance in the classic Z-source inverter, the proposed inverter can flexibly control the turns ratio of the two coupled inductors to obtain a much higher boost ratio. The DC bus voltage spike absorption circuit composed of several passive components effectively recovers the leakage inductance energy and suppresses the DC bus voltage spikes. In order to show the characteristics of the proposed topologies, the operating principles, analysis are shown in this paper. Experimental results verify the feasibility of the proposed inverters.

In this paper, an isolated synchronous rectification DC-DC converter based on GaN HEMT is proposed, which can achieve soft-switching characteristics and reduce the conduction loss of the rectifier. In conventional rectifier converter, fast-recovery schottky diodes are used for resonant rectification, and the diode forward voltage drop results in larger diode conduction losses, which causes the power converter to be less efficient. To solve this problem, the proposed topology, whose rectifier diode is replaced by a synchronous switch, adopts synchronous rectification, which helps to improve the efficiency of power converters. Meanwhile, the transformers with magnetic core are also replaced by coreless planar transformers to reduce the volume. Thus, the system efficiency and power density can be improved. To achieve soft switching and reduce switching losses, the driving circuit of the rectifier circuit is optimized and the detailed design method of the proposed converter is analyzed. In tens of megahertz, the GaN HEMTs are adopted to reduce the driving loss, switching loss and conduction loss. A 20MHz prototype based on the proposed topology is designed in this paper. The experimental results verify the feasibility of the proposed converter and corresponding design method.