Performance Analysis Of Permanent Magnet Linear Generator For Free Piston Engine System

With the rapid development of automobile,free piston engine has gradually become the development direction of automobile engine.It is driven by compressed air or fuel oil,and composed of free piston and linear generator of thermal-mechanical-electrical energy conversion system,its structure is simple and its power generation efficiency is high.As a core energy conversion device in a free-piston linear engine system,the linear generator will greatly affect the power generation stability and power generation efficiency of the whole system.Therefore,it is of great significance to study linear generators.This paper studied the electromagnetic performance of permanent magnet linear generators for free piston engine systems.Firstly,in order to study the speed change trend of generator mover and verify the accuracy and feasibility of the finite element simulation method,a prototype of a flat permanent magnet linear generator for a compressed air driven free piston engine was tested.The motion velocity curve,and comparative analysis simulation and experimental results,verified the accuracy and feasibility of the finite element simulation method.Secondly,a cylindrical permanent magnet linear generator for free piston engine was designed.The permanent magnets with the shape of the structure were used to model the generators of the new permanent magnets and the traditional rectangular permanent magnets and simulate the electromagnetic performance.The results showed that compared with the traditional rectangular permanent magnet structure generator,the new shape permanent magnet structure generator had better overall performance when moving at constant speed,and the air gap magnetic density harmonic component was less;The harmonic distortion rate of the no-load induced electromotive force was lower at 2.53%,which was 2.16% lower;the voltage regulation rate was lower at 9.59%,which was 5.2% lower;the generator power density was higher.When the speed was changed,the induced potential waveform was better and the output power was larger.The study of the instantaneous power during the motion of the generator showed that the instantaneous power in the process of increasing the speed was smaller than the instantaneous power at the same speed during the decreasing process.Finally,the influence of generator structure parameters on force characteristics was analyzed.It was found that compared with the traditional rectangular structure permanent magnet generator,the no-load detent force of the permanent magnet generator and the electromagnetic force fluctuation with load were smaller.And proper adjustment of the pole arc coefficient and the length of the edge permanent magnet could effectively reduce the detent force and reduce the electromagnetic force fluctuation,which was beneficial to the stable operation of the generator.