| Wireless power transfer(WPT)systems have received widespread attention due to flexibility,convenience,simple maintenance,high reliability and environmental adaptability.However,the misalignment of the primary and secondary sides is often unavoidable in actual occasions,which leads to a significant deterioration in output voltage and efficiency.This defect seriously hinders the further development of WPT systems.Therefore,it is necessary to improve the misalignment tolerance of WPT systems from two aspects.One is to reduce the falling speed of the coupling coefficient with the increase of the offset distance;the second is to adopt closed-loop design to make systems transmit energy smoothly even if the coupling coefficient changes.The thesis starts with the magnetic coupling structure and uses a flat solenoid magnetic coupler.The two major reasons for its excellent perf ormance of misalignment tolerance are elaborated from the perspective of magnetic field lines.The magnetic core is further simplified and the structure of discrete flat solenoid is determined.Secondly,a parameter optimization method is proposed for high misalignment tolerance using variable-controlling method,obtainiing the best parameters under given constraints.Simulation results show that the performance of misalignment tolerance of the designed coupler in the horizontal and vertical directions is much better than other traditional anti-offset structures.WPT systems can not use the traditional transformer model because of severe magnetic leakage.Thus,two equivalent models of leakage inductance are d educed and the S/S compensation topology based on the equivalent model of leakage inductance is proposed.This is to achieve the purpose of constant voltage output and easy realization of soft switching.In the thesis,the fundamental gain analysis method is used to derive the voltage gain under S/S topology,and the input impedance angle,harmonics and stress of components are analyzed in depth.Finally,the frequency characteristic curves of voltage gain and input impedance angle are simulated to determine the value of parameters and frequency varia tion range.Based on the analysis of the frequency characteristics of the S/S compensation topology,the author finds out a method.By adjusting the operating frequency to resonant frequency of compensation capacitors and leakage inductances during the offset,the purpose of constant voltage output can be achieved.Thus,an efficient WPT system with high misalignment tolerance based on frequency modulation control is proposed and its digital closed-loop control program is designed.Bluetooth is used in systems to implement wireless data transmission.In order to achieve the closed-loop control,the thesis takes the lead in introducing the extended description function(EDF)method to accurately model systems and gets the small-signal equivalent model and transfer function.Based on the block diagram of closed-loop control,the design of the controller is carried out and the type III compensation is determined.The designed controller and related parameters make systems stable in the offset range.Then the analog controller is discretized to realize the digital PI control of systems.Finally,based on theoretical analysis,the paper builds a simulation model with an output power of 200 W.When the air gap is 40 mm and its own length and width are 206 mm × 200 mm,it achieves horizontal misalignment tolerance of 220 mm,vertical misalignment tolerance of 80 mm and vertical misalignment tolerance of 70 mm,and the efficiency is as high as 96.59%. |
