Design Of Resonant Compensator And Efficiency Optimization For WPT System Applied To Modern Trams

The modern tram has many characteristics,such as strong capacity for carrying passengers,low pollution,low energy consumption,short construction period and low cost.In order to solve the urban traffic problems and build a modern urban public transportation system,modern tram has been developed in some cities of China.Wireless power transfer(WPT)technology provides a new supply power model to the tram:Based on this background,this paper studies to improve WPT power supply technology,so that it can be more efficient and more suitable for the modern tram that use super capacitor as energy storage.Firstly,this paper introduces the main circuit structure and working principle of the WPT system for modern tram,including the inverter,coupling coil,resonant compensation and power conversion part in secondary side.Several feasible schemes are compared and analyzed to choose suitable circuit topology and modeling method.The theoretical basis is provided for the subsequent design of the resonant compensation topology and the method of efficiency optimization.Secondly,this paper focuses on how to design a resonant compensation topology and to improve the efficiency.SS compensator is commonly used in WPT system.But it has some disadvantages in cascade buck circuit that DC bus voltage of secondary side varies with buck duty cycle.For that reason,LCC compensator is proposed.It has the characteristics of quasi constant voltage output in the secondary side and makes the control more flexible.The voltage gain can also be designed according to the need without being limited to the parameters of the coil.In this paper,the design method of the parameters of the LCC compensation topology is analyzed in detail and the design formula is given.To introduce secondary side coil inductance parameter design based on the quality factor,the input voltage and current waveforms of rectifier can be ensured no oscillation.After that,the system efficiency expression based on LCC compensator is derived.The effect of super capacitor charging power and mutual inductance on the system efficiency is analyzed.Based on the above analysis and combined with the characteristics of the modern tram,a dynamic charging power adjustment strategy is given,which takes the maximum efficiency as the goal and the parking charging time as the limiting condition.This strategy is verified by the simulation.Finally,1kW and 50kW wireless power transfer experiment platforms are built.The rationality of parameter design for LCC compensation topology,quasi-constant voltage characteristic and the efficiency optimization strategy are verified by the experiment.The 50kW platform is introduced in detail for the main circuit design and control circuit design.Some experiments are done on the platform.