Research On Dynamic Wireless Power Supply Technology Employing Bipolar Primary Rail

According to the structure of the transmitting coil,the primary rail of dynamic wireless power supply(DWPS)systems can be divided into long coil type,array coil type,and bipolar type.Considering advantages such as strong misalignment tolerance,high power density,small occupied road space and good electromagnetic compatibility(EMC),etc.,the bipolar rail is more suitable for large-scale application in the field of electric vehicles(EVs).At present,the key problems of DWPS system using the bipolar rail are coupling zero compensation,system resonance state control,fast response of system control strategy,system output stability control,and efficiency improvement,etc.This paper mainly discusses the above key issues,specifically,including the following aspects:Firstly,in the DWPS system using the bipolar rail,the conventional single-phase receiver faces the problems of discontinuous power transmission,low average transmission power,and low efficiency.To solve these problems,in this paper,a novel multi-phase receiver structure is proposed.By adding the one-phase or multi-phase receiving coil,the zero coupling area of the conventional single-phase receiver is compensated so that the average transmission power and efficiency are improved.In addition,aiming at the problem of large amount and high cost of core,a novel "Π" type primary rail and the corresponding frame type core structure of the receiver are proposed,which greatly reduces the amount of core at the receiver.Meanwhile,the design method and optimization procedure of the two-phase and multi-phase receiver are given.Secondly,in general,the self-inductance and mutual inductance of the primary and secondary coil fluctuate greatly during the movement of the receiving coil.With the operating state of the EV,the load also varies greatly.So the resonant frequency fluctuates with the equivalent load on the primary side.By analyzing the output characteristics of the primary side power inverter,a switching control algorithm for resonant state tracking and constant current(CC)output is proposed.With the feedback of the system state,the system state space and the switching plane are established.By adjusting the position and slope of the system switching plane in the state space,the switching action of the switching device in primary inverter is controlled to ensure that the output voltage and current of the inverter are in phase.It is also possible to regulate the output current by adjusting the equivalent duty cycle of the inverter output voltage.The proposed control method realizes the resonance state tracking in real time and improves the system efficiency and the power factor of the system.In addition,the primary coil current is also stabilized.On one hand,the magnetic field above the rail is constant.On the other hand,a stable induced voltage can be obtained in the secondary coil.Thirdly,when the bipolar rail is applied,the coupling coefficient and the load are constantly changing,resulting in the unstable output voltage and current.Aiming at the above problem,an impedance matching method based on the optimal current ratio is proposed.Using two sets of auxiliary measuring coils,the relative position of the receiver and the primary coil is provided,and the output current of each phase is calculated.The system efficiency is improved under the fixed output current.In addition,in order to adapt to the wide variation of mutual inductance and the load,the cascaded active rectifier-Buck impedance matching topology is adopted to achieve impedance matching in the range of 0~+∞.Finally,an experimental setup of the DWPS system is built.During the experiment,the output power and efficiency of the proposed two-phase receiver and the conventional single-phase receiver are compared.The transfer efficiency improvement of the proposed two-phase receiver is verified.The experimental system control hardware platform is designed to validate the primary side resonance state tracking and CC output control algorithm.Using the proposed impedance matching method based on the optimal current ratio,the improvement of the system efficiency and the CC output characteristic are validated.