Research On Misalignment Tolerance Of Electric Vehicle Wireless Power Transfer

Electric Vehicle-Wireless Power Transfer（EV-WPT）technology has become a hot topic nowadays due to its high speed development.Compared with wired power transfer,WPT technology is safe,reliable,flexible in power transfer,high environmental affinity,and has a broad development prospect.In the process of electric vehicle wireless power transfer,the magnetic couplers coil inevitably misalignment and the load resistance value keeps changing,which leads to the reduction of the system output current and transmission efficiency.Therefore,it is essential to investigate the WPT system with misalignment tolerance and constant output current values.That is a EV-WPT system with misalignment tolerance.The main research work of this paper is as follows:1)Study of variable load resistance and misalignment tolerance of compensation circuits for EV-WPT system.Comparing the misalignment tolerance of four basic compensation circuits,the mathematical models of SS（Series-Series）,LCL-LCL,and LCC-LCC compensation circuits are modeled to analyze the input current,output current of the circuit,the parameter resonance conditions and transmission efficiency,the results shows that the output currents of SS and LCC-LCC topological circuits are inversely proportional to the mutual inductance and positively proportional to the mutual inductance.The SS and LCC-LCC hybrid topology circuit is designed according to its output characteristics,and the analysis shows that the hybrid topology circuit has the misalignment tolerance of variable-load constant-current output when ignoring the cross mutual inductance.2)The coil model is established for SS and LCC-LCC hybrid topology circuit.Firstly,a single type coil mutual inductance model is built,and the parametric simulation analysis shows that the square coil has better misalignment tolerance than the circular coil.Secondly,a DDQ（double D quadrant coil）type coil model based on a square coil is established,and the simulation shows that the magnetic induction intensity of the coil varies uniformly under different misalignment,which is applicable to the wireless power transfer of electric vehicles.Finally,according to the variation curve of mutual inductance of DDQ type coil,the cross mutual inductance of the system in X direction and Z direction is always zero,which satisfied constant current output and misalignment tolerance.3)Optimized design of hybrid compensation circuit parameters for EV-WPT systems.For the problem that different values of hybrid circuit parameters affect the output misalignment tolerance of the system,this paper proposed a particle swarm optimization method to optimize the parameters of the system hybrid topology circuit.The parameters of the hybrid topology circuit are selected to maximize the variation range of the mutual inductance of the coupling coil by satisfying the variation rate of the output current gain value within a certain range.The misalignment tolerance of the system after parameter optimization are analyzed,and it is verified that the parameter optimization method proposed in this paper can effectively improved the misalignment tolerance of the system.4)Verify the misalignment tolerance of the EV-WPT system in this paper.The wireless power transfer system is simulated in the PSIM software,and finally the experimental platform of the wireless power transfer system is built to analyze the misalignment tolerance and the system transmission efficiency in the X-direction and Z-direction.According to the experimental results,when the system load varies and the magnetic couplers coil is shifted in a certain range along the X and Z directions,the rate of change of the system output current is always within a certain deviation range.In this paper,the WPT system does not rely on a complex closed-loop control strategy to achieve a constant current output and misalignment tolerance.