Modeling and Control of a Portable Two-Stroke Free-Piston Engine Generator

The free-piston engine generator (FPEG) is a novel energy conversion system, which is known to have greater thermal efficiency than conventional engine. The free-piston moves freely in the cylinder without crankshaft. It must be controlled to overcome challenges in the starting process, risk of misfire, and unstable operation. A multidisciplinary model of the prototype is presented in this paper. The features and working principle of FPEG is demonstrated. A PID algorithm is designed to control the current of the FPEG, and pulse-width modulation (PWM) is utilized to adjust the target current of the system. The top turning centers (TTC) and bottom turning centers (BTC) of free-piston are considered as control objectives. Simulation results show that TTC, BTC and the trajectory of free-piston are well controlled.