Robust and optimal control of free piston linear generator by variable piston trajectory tracking throughout entire operating process

Free piston linear generator (FPLG) shows advantages in freedom of piston motion and fuel adaptability due to the removal of mechanical constraints imposed by the crankshaft. However, the real-time matching of multiple forces over the whole process represents a substantial challenge for control. Previously, a piston trajectory control strategy is proposed which can track various reference piston trajectories. In this paper, a piston trajectory generator is proposed to generate different reference piston trajectories based on operation states including starting, transition, combustion and stopping. The switching of reference piston trajectories throughout the entire operating process enables seamless transition between operation states. Moreover, the combustion trajectory based on polynomial trajectory is optimized by genetic algorithm, with the objective of enhancing system efficiency. The simulation results show that the optimal polynomial trajectory significantly improves system performance, as it matches the operating characteristics of FPLG. The piston trajectory generator is implemented into a single-piston FPLG prototype. The experimental results show that the system achieves control of piston motion over the entire operating process. Moreover, the method is demonstrated to enhance the indicated thermal work and electric output work of one cycle from 134.66 J to 58.27 J–172.71 J and 80.57 J, respectively.