Magnetic Channel Estimation Based On Multi-coil MCR-WPT System

The magnetic coupling resonance wireless power transfer(MCR-WPT)technology realizes wireless charging by virtue of the theory of power exchange during electromagnetic resonance,and the strong interaction of magnetic field makes it reach a high level in both transmission efficiency and transmission power.Therefore,it has become one of the most concerning aspects in the field of wireless power transfer.However,for the multi-coil system,since the complicated coupling relationship between magnetic fields,the characteristics of the magnetic channel need to be further studied.This paper mainly studies the multi-coil MCR-WPT system.Based on the traditional one-to-one wireless power transmission technology,adding transmission nodes can expand the transmission distance in the space,while supporting the access of more devices,so that the system can be better applied to different scenarios.Due to the dynamics of the system and various coil designs,the magnetic field is intricate,which puts forward a severe challenge to achieve high-power and high-efficiency charging on the device.From the perspective of exploring the characteristics of the magnetic channel,this paper primarily includes two research contents:the estimation of mutual inductance information in the multi-coil system and the influence of frequency on transmission performance and its selection.The innovations of each part of the research content are as follows:1.Synchronous mutual inductance estimation algorithm based on the least square methodThe cross-coupling in the multi-coil system makes the mutual inductance estimation more complicated.Aiming at the inefficiency of the existing one-to-one mutual inductance estimation scheme in the multi-coil system,this paper proposes a synchronous mutual inductance estimation algorithm,which can estimate all mutual inductances directly related to the receiving coils at the same time,and has a certain versatility in the series-series compensation wireless power transmission system,because they are not limited by the number and shape of the coils.Due to the dynamic nature of the system,some parameters of the model are not fixed,but change irregularly with time.In order to adjust in time to adapt to changes,the state of the system must be monitored at all times,so the system is modeled in the time domain.In a short time interval,the mutual inductance to be solved can be regarded as approximately constant,which is an approximate treatment for a dynamic system.By analyzing the circuit,it is found that the response of the current system is equal to the linear combination of the current excitation acting on each part of the system,that is,there is a certain relationship between the input and output of the system and the electrical parameters.Therefore,when other fixed electrical parameters are known and the input and output can be measured,the above relationship can be used to fit the collected data using the least square algorithm.2.Frequency characteristic research and frequency selection strategy designIn a multi-coil MCR-WPT system,especially when there are relay coils,it is more and more difficult to analyze and optimize the system performance as the number of coils increases,and the optimization goal of the current research is single.To solve this problem,this paper analyzes the output power and transmission efficiency from the perspective of frequency,and gives the solution of the frequency corresponding to the maximum power and efficiency in theory,which provides a theoretical basis for optimizing the system through frequency modulation.Based on the above research,a frequency selection strategy is proposed for a multi-coil MCR-WPT system with relay,and the effectiveness of the strategy is verified by simulation and experiment.When the system parameters remain unchanged,the frequency corresponding to the maximum power transmission and maximum efficiency transmission of the system does not change with time,and the performance gap between each other is relatively large.Therefore,the strategic goal is to optimize transmission efficiency as much as possible under the premise of ensuring that the system is working in resonance.The specific implementation is to take the result of quantitative analysis as the input of the strategy,set a certain threshold and allowable error for a range search(several frequency points can limit the search range and improve the search efficiency),and finally use the output result as the power supply operating frequency.