Research On Interoperability Evaluation And Improvement Technology For Magnetic Coupler Of Wireless Electric Vehicle Charging

Wireless electric vehicle charging（WEVC）technology is booming because of safety and convenience.The interoperability between different products has become an important factor affecting technology popularization.The interoperability refers to the ability to output rated power with specified efficiency when different ground assemblies（GAs）and vehicle assemblies（VAs）are matched.As the core of power transmission,it is essential to accurately evaluate and improve the interoperability of different magnetic couplers.Compared with the evaluation through system power/efficiency,transforming the product interoperability evaluation into the evaluation between products and the reference magnetic coupler（RMC）is an effective means to improve evaluation standardization.However,a series of problems emerge,such as the difficulty of design and verification of RMC,the lack of evaluation accuracy,and the poor interoperability between different types of magnetic couplers.Aiming at the above problems,this paper studies the multi-objective optimization of RMC,equivalence verification between RMC and national standards,high-precision interoperability evaluation method and interoperability improvement technique.Aiming at the difficulty of RMC design,this paper analyzes the design objectives and constraints of RMC.Different from the general design,the RMC needs to realize the relative optimization of multiple indexes under the constraints of national standards.The constraints of RMC are given.Taking the coupling coefficient,total loss and weight as the design objectives,the multi-objective optimization design method of RMC is proposed.To calculate the nonlinear influence of winding,magnetic core and aluminum plate on the output characteristics,the model of mutual inductance and coupling coefficient is obtained.The calculation method of winding resistance based on image current equivalence is proposed for the loss model,avoiding much finite element simulation.The experimental results show that the design schemes can improve the coupling coefficient,loss and weight,respectively.The proposed design method can provide a theoretical reference for the RMC with different power levels.Aiming at the equivalence verification of reference magnetic coupler with different parameters,this paper considers that the equivalence can be verified by the output consistency when interoperating with the national standard magnetic coupl er.The characteristic value of fundamental mutual inductance C_FMI is defined.Then,the gauge device is introduced to measure the fundamental mutual inductance and calculate C_FMI,solving the problem that the magnetic parameters are not easy to measure.To improve the consistency of the relative variation between the measur ed value of fundamental mutual inductance and national standard s,the structural parameters of the gauge device are designed,and a simplified gauge device containing only PCB coil is proposed.Experiments show that the proposed method and test equipment can effectively verify whether the designed GA is equivalent to national standards.To improve the shortcomings of the existing interoperability evaluation techniques,such as lack of comprehensive evaluation criteria and low accuracy,the evaluation method based on the detuning factor and load factor is proposed.The relationship between the two evaluation factors and the output characteristics is established.Combined with national standards,the interoperable impedance region boundary function is calculated.Meanwhile,to reduce the phase difference measurement error of high-frequency signals,a high-precision impedance calculation method based on the power orthogonal decomposition algorithm is proposed.The input power is used to calculate the impedance t o avoid measurement error and further improve the evaluation accuracy.Aiming at the problem that the power and efficiency decline when different types of magnetic couplers interoperate,the interoperability improvement strategy based on flux regulation is studied.For the occasion where the product schemes are fixed,taking the rectangular and DD type magnetic coupler as examples,an adaptive matching method of GA position is proposed.The input current is used to determine the GA position,and a perturbation and observe algorithm is designed to guide the GA to move to the high coupling region.For the occasion where the products can be redesigned,a reconfigurable transmitter（RT）consist ing of two overlapping coils is designed,and a power efficiency cooperative control strategy based on optimal current ratio is proposed.By adjusting the flux amplitude and direction,the RT can output the rated power with maximum efficiency when interoperating with different receivers within the national standard misalign ment.