Research On Efficiency Improvement Technology Of Inductive Power Transfer Systems With Discrete Loads

With the merits of flexibility and safety,inductive power transfer(IPT)technology has been widely employed in many applications,such as consumer,medical,transportation,energy,manufacturing and other industries,to replace the plug-in/out system for mobile electrical device charging.However,compared with the plug-in/out system,extra intermediate energy conversion links in the IPT process lead to large power loss,overheating and low economic benefits,and also give the limitation of the further development of IPT technology.Thus,how to improve the transmission efficiency is still an important scientific problem.With the development of IPT technology in discrete load applications,such as rice cookers,reefer containers and multi-stage constant-current constant-voltage charged batteries,the disadvantages of traditional impedance matching methods for continuous load,such as complex system structure,poor universality,high loss and cost,and difficulty in soft switching,are highlighted.Besides,the characteristics of different discrete loads are not same.How to optimize the IPT systems for discrete loads with different characteristics has become one of the key problems to be solved.Additionally,various discrete loads have distinct requirements on IPT system output.How to design IPT system to meet the requirements has become another problem to be solved.Therefore,the goal of this paper is to improve the transmission efficiency of IPT systems without significant increasement on the system structure and control complexity for discrete load applications.The main work is as follows:(1)Reconfigurable IPT systems can reconstruct their system circuits and alter their operating modes through switches.Due to the similar characteristics among reconfigurable IPT systems and discrete loads,reconfigurable IPT systems are regarded as an available option for discrete load impedance matching.However,when the characteristics of a reconfigurable IPT system and a discrete load are not matched with each other,transmission efficiency decreases.Therefore,based on the statistical characteristics of discrete loads and the operating mechanism of reconfigurable IPT systems,a time-weighted efficiency model of reconfigurable IPT systems in discrete load application scenarios is established,and the key factors affecting the time-weighted efficiency are investigated.The model can provide a theoretical criterion for the optimization design of reconfigurable IPT systems.(2)The traditional impedance matching methods convert the load impedances into the optimal load resistance to achieve impedance matching,and can lead to unstable system outputs,complex system structures,and terrible system performances in the applications of the discrete loads with small relative extreme deviation.Thus,for the discrete loads,the key factors affecting the optimal load resistance of an IPT system are analyzed,and the approach of regulating the optimal load resistance is studied.Then,an optimal load resistance switching method of the IPT systems based on series/parallel reconfigurable coil is proposed from the perspective of magnetic coupler reconfiguration.The method can achieve impedance matching without additional impedance conversion circuit,and has no effect on the input and output of the systems.(3)In order to satisfy the requirements on high freedoms and wide ranges of impedance matching in the applications of the discrete loads with large relative extreme deviation,the impedance transformation characteristics of typical compensation circuits are investigated.The LCL(Inductor-Capacitor-Inductor)compensation circuit is found with the abilities to enlarge or reduce the load impedance,and realize accurate impedance matching without any reactive power.Then an impedance matching method of the IPT systems based on a switchable LCL circuit is proposed from the perspective of compensation circuit reconfiguration.By sharing components of high-quality factor,both the component number and the power loss of the compensation circuit are reduced.The method has the advantages of high design freedom,wide transformation range,and low energy loss.(4)For the discrete loads with medium relative extreme deviation and requirement on variable output,the operating principle,input-output and impedance transformation characteristics of the multiple gain reconfigurable rectifier are analyzed.Then the power loss model of the IPT system based on the multiple gain reconfigurable rectifier is established,and a corresponding efficiency improvement method is proposed.At the same time of achieving approximate impedance matching,the requirements on variable system outputs are met by reconstructing the inverter and rectifier of the system.Besides,the regulation on the conduction angle of the inverter is not required with the method,thus difficulties in soft switching are effectively solved even with wide-range variable outputs.(5)In order to solve the problem that transmission efficiency is reduced due to the unbalance currents in the multiple-paralleled-litz-wire(MPLW)-based magnetic coupler in high current applications,the multi-harmonic circuit model of the MPLW-based IPT system is established.The key factors affecting the phases and amplitudes of the unbalance currents are quantitatively analyzed,and the principle of the coil parameter difference suppression is summarized,and then unbalance current suppression coil winding methods are proposed.The methods can effectively reduce the power loss of the MPLW-based magnetic coupler.This dissertation focuses on the reconfigurable IPT systems,aiming at the different discrete load applications,from ‘the discrete loads with small relative extreme deviation’ to‘the discrete loads with large relative extreme deviation’,to ‘the discrete loads with medium relative extreme deviation and requirement on variable output’,and then to ‘high current application scenario’,gradually puts forward a variety of IPT system efficiency improvement methods,effectively solves the problems existing in the reconfigurable IPT systems with different discrete loads,and provides a theoretical basis for promoting the development of reconfigurable IPT technology.