As a promising linear energy conversion system, the free piston internal combustion powertrains system (FPICPS) has many advantages such as compact structure, short energy transmission chain and high fuel flexibility. The main parts of FPICPS consists of a two-stroke combustion engine, a permanent magnet linear synchronous machine system (PMLSMS) and a gas spring chamber. However, FPICPS has special structure of no mechanical constraints, and the extra degree poses a huge technical challenge for a series of operation processes such as start-up, continuous stable generation, emergency braking, overcoming misfire and unstable operation caused by potential disturbance. This paper concentrates on research on the precise, controllable and instant response characteristics of force of PMLSMS. It was found that the power adjustment controller on PMLSMS side can switch the operating mode under generation and motorized state with negligible delay compared to relay. So technically feasible control variable of force for PMLSMS was chosen and coupled with a force of PMLSMS controller design to implement a series of operation processes by identifying current operating status and different types of system mode, which could be applied in future FPICPS control system designs for different operating modes. The controller performance was seen to be satisfactory for switching between different operating modes without delay and of great significance in improving the robustness of FPICPS and improving the combustion efficiency by MATLAB/SIMULINK. Therefore, it may be beneficial to the application of FPICPS as range extenders in the way that synergize advantages of the free piston engine and functional control logic of the stable operation, promising in hybrid vehicles.
Keywords free-piston internal combustion powertrains system (FPICPS); permanent magnet linear synchronous machine system (PMLSMS); operation mode; power adjustment controller; force of PMLSMS controller; hybrid vehicles.