Optimization On A Three-phase Magnetically Coupled Resonant Wireless Power Transfer System

Recently,extensive attention has been paid to wireless power transfer(WPT),due to its superiority on convenience of being cordless,safety during power charging.Magnetically coupled resonant(MCR)WPT technology has become one of the most promising technologies,as it can still keep high transmission efficiency in the mid-range distance.Comparing with the single-phase MCR WPT system that the transmission power and efficiency fluctuate sharply with varying spatial locations of the coils,the multi-phase system can effectively reduce the sensitivity of system to spatial locations,and decrease the resonant current in each phase,which is suitable for the applications with relatively high power and arbitrary spatial locations of coils.In this thesis,a three-phase MCR WPT system with cylinder-shaped coils was investigated and the equivalent circuit model was built to derive the formula of the three-phase input current and the output power.Mutual inductance model was also built to obtain the mutual inductance function that merely relates to the coil turns and the angular misalignment of receiving coil.Based on the equivalent circuit model,this thesis analyzed the influential factors on zero-voltage-switching(ZVS)conditions of power switches in the driver inverter,including the phase-shifted angle,the coil turns and the angular misalignment.Further,coil turns were optimized to ensure the power switches realize ZVS within the full range of angular misalignment.Meanwhile,the equivalent circuit model was simplified to investigate optimal output power characteristics of the system that was defined as the one with high amplitude and minor fluctuations within the full range of angular misalignment.Based on the theoretical analysis of the simplified model,the coil turns and control strategy of the phase-shifted angle were optimized to ensure the system realize the optimal output power characteristics.Further,the load characteristic was explored for follow-up studies to improve the system performance.Finally,a prototype had been built and tested to evaluate the accuracy of theoretical analysis and confirm the validity of the proposed optimization schemes that ensure the system realize ZVS and improve the output power characteristics.