开关功率变换器的功率密度是其小型化和轻量化的关键，因而提高开关频率是其发展的必然趋势。超高频开关功率变换器可以极大地提升功率密度，但其由开关和寄生参数引起的损耗较大，降低了电能变换的效率。本项目首先对超高频开关功率变换器的电路结构开展研究，通过谐振网络补偿、阻抗压缩和适应电流变化的软驱动策略，分别降低谐振逆变器、整流器和驱动电路的损耗；接着基于时域反射法提取系统中的精确寄生参数，进而建立变换器不同工作状态下的损耗模型，满足损耗估计在精度和复杂度上的要求；最后针对不同的变换器工作状态，通过状态变量和控制变量的调节来提高变换器稳态和瞬态下的效率，并保证软开关正常工作。本项目将完善超高频开关功率变换器的低损耗电路结构和损耗模型，初步构建变换器损耗估计和最优效率控制的理论框架，特别是最优效率状态变量控制和基于瞬态效率优化的控制策略，可以为开关功率变换器功率密度和效率的提升提供一定的理论依据和示范。

Power density is the key to decrease size and weight of power converter, therefore, it is imperative to increase the switching frequency. Converter power density can be greatly improved by using very high frequency power conversion strategy. However, relatively high power loss can be caused by the switch and parasitic parameters, which decreases the efficiency. This project will study low-loss circuit scheme for very high frequency power converter. Through harmonic compensation, resistance compression network and current-adaptive resonant driving strategy, power loss of resonant inverter, rectifier and driving circuit will be reduced. Furthermore, accurate parasitic parameters will be extracted through time domain reflectometry method, and they are used to build the power loss model suitable for different operation conditions. Based on the model, feedback is established to regulate converter states and control signals, which optimizes both steady state efficiency and transient efficiency of the converter, and ensures soft switching. This project will improve low-loss circuit scheme and model of very high frequency power converter, and explore fundamentals for power loss estimation and maximum efficiency control, especially for maximum efficiency state variable controller and transient efficiency optimizing strategy. The achievements will provide a demonstration to improve the power density and efficiency of switched mode power converter.