Study On Efficiency Optimization Of Magnetic-field Coupled Wireless Power Transfer System

The wireless power transfer(WPT)technology is a technology that realizes the transmission of electric energy by means of an invisible soft medium in space.This technology can effectively solve some problems of traditional power transmission,such as unsafety,unreliability,inconvenience and so on,and has great market demand and research value.Currently available WPT technology mainly includes magnetic field coupling type,electric field coupling type,electromagnetic radiation type and ultrasonic type.Among them,the magnetic field coupling type has the broadest application prospects and can be used in consumer electronics,household appliances,medical equipment,electric vehicles and many other fields.Therefore,the magnetic field coupled WPT technology is chosen to be studied in this thesis,and the WPT in the following refers to the magnetic field coupled WPT.At present,low system efficiency is a major problem that restricts the development and promotion of WPT technology.Based on this,this thesis conducts research on how to improve and optimize the efficiency of the WPT system,with a view to contributing to the development of WPT technology.The main work of this thesis is as follows:1)In order to provide the theoretical basis for the subsequent research,the characteristics of the WPT system are studied firstly in this thesis.The series/series(S/S)compensated WPT system(S/S WPT system)is the most basic WPT system.Therefore,it is selected as the research object.In the study,for convenience,a new analysis idea is adopted,and the compensation capacitance is set as a variable to analyze the characteristics of the system.After analysis,the following conclusions are drawn.Output is current source when input is voltage source and output is voltage source when input is current source under the condition the capacitance compensates for self-inductance.But output is voltage source when input is voltage source and output is not voltage or current source when input is current source under the condition the capacitance compensates for leakage inductance.Input impedance is purely resistive when the capacitance compensates for self-inductance.And input impedance is partially inductive when the capacitance compensates for leakage inductance.System efficiency is optimal when the capacitance compensates for self-inductance.In terms of efficiency,the system has a corresponding optimal equivalent load resistance whatever the compensation.Finally,the conclusions are verified by experiments.2)For the S/S WPT system,the capacitance compensating for self-inductance is the most commonly used compensation method.The S/S WPT system based on self-inductance compensation has a maximum efficiency point,and its efficiency can be improved through the maximum efficiency point tracking control.Therefore,the maximum efficiency point tracking control method for this system is studied,and a new tracking control method is proposed in this thesis.This method realizes the tracking of the maximum efficiency point by making the primary and secondary coil currents be a specific ratio.Compared with the existing methods,this method is simpler and more attractive in practical applications.Finally,the effectiveness of this method is verified by experiments.3)Because the LCC/S compensation network can make the WPT system have some unique and excellent characteristics,the LCC/S compensated WPT system(LCC/S WPT system)has attracted widespread attention in recent years.In order to improve the efficiency of the LCC/S WPT system,this thesis analyzes the efficiency characteristics of the system.In this analysis,the equivalent series resistance of the compensation inductor is considered,and the case where the input impedance is inductive is also considered.Through analysis,it is found that the LCC/S WPT system also has a maximum efficiency point,and the maximum efficiency point tracking control can also be used to improve the efficiency of this system.Therefore,this thesis studies the maximum efficiency point tracking control method of the LCC/S WPT system,and proposes a new tracking control method according to the characteristics of the system at the maximum efficiency point.This method can avoid some shortcomings of the existing perturbation and observation method,and has good practicability.Finally,the correctness of the theoretical analysis and the effectiveness of the proposed tracking control method are verified by experiments.4)As a kind of power supply,the WPT system usually needs to be able to realize constant output voltage.When the coupling coefficient and load resistance are both variable,adding a DC/DC converter to the system to achieve output voltage regulation is a common way,but this will reduce the efficiency of the system.Therefore,this thesis studies the compensation network and proposes a new type of three-element compensation network.The compensation network can effectively reduce the sensitivity of the output voltage of the WPT system to the coupling coefficient and load resistance,so that the WPT system can achieve high efficiency while achieving output voltage stabilization.Finally,the effectiveness of the compensation network is verified by experiments.5)In some practical applications,the coupling coefficient in the WPT system can be fixed.In the case of constant coupling coefficient,the constraint condition of compensation capacitance for the S/S WPT system to realize constant output voltage is derived in this thesis.With the constraint condition,the effects of compensation capacitance on system characteristics are analyzed.Based on the analysis,an optimal design strategy for compensating capacitance is presented in order to make the system have the highest possible efficiency while achieving constant output voltage.Finally,the correctness of the theoretical analysis is verified by experiments.