Research On Power Conversion Control Of Permanent Magnet Linear Generator

The free piston stirling linear generation system can realize the direct conversion of all kinds of heat energy to electric energy by coupling the power piston of the free piston stirling engine(FPSE)and the mover of the linear motor.It has been applied in space power supply,biomass generation,solar thermal generation,factory waste heat generation,cogeneration and other fields.In order to solve the problems of large fluctuation of output electric energy and self starting of free piston stirling linear generation system,Two-stage electric energy conversion control mode which combines three-phase AC/DC and bidirectional DC/DC is adopted,to make the generation system output stable DC power.Based on the bidirectional energy flow characteristic of two stages power transformation topology,the current displacement double closed loop control is adopted to realize the self starting of generation system.Firstly,the nonlinear mathematical model of free piston stirling engine and the linear mathematical model of three-phase permanent magnet linear motor are established,and the modeling and simulation work are completed on MATLAB/Simulink.In order to improve the performance of frequency and displacement tracking,PR(proportional resonance)controller is used instead of PI controller in traditional position loop,and the corresponding simulation verification is completed.Secondly,according to the frequency and amplitude variation characteristics of the output voltage of the linear generator,in order to realize the unit power factor control of the AC side of the generator and the stability and controllable of the DC side voltage,the hysteresis SVPWM current control strategy with high robustness and dynamic response is applied to the rectifier.The principle and implementation of the control strategy are described in detail.The modeling of three-phase voltage source rectifier(VSR)and the selection of inductance and capacitance of key energy storage elements are completed.The performance of the designed three-phase VSR is verified by simulation.Thirdly,the bi-directional DC/DC part of the power generation system uses the non-isolated bi-directional buck/boost topology.The design of the key energy storage elements,such as inductance,capacitance is completed.Based on the state space average method,the small signal model of the converter under two working modes is established,and the controller of the current-voltage double closed-loop control strategy is designed,and the simulation of the converter is carried out.Finally,a test platform is built to simulate the free piston stirling engine,and the hardware design and software compilation of the control system with TMS320F28335 as the main control core are completed.The performance of AC/DC and DC/DC converters is tested on the experimental platform.The feasibility and accuracy of the topology and control strategy are verified by the experimental and simulation results.