Hybrid controller design of a free-piston energy converter

Abstract

A Free Piston Energy Converter (FPEC) is a combination of a linear combustion engine and a linear electrical machine. It is a potential technology for series hybrid vehicles, as well as stationary power generation applications. In a free piston energy converter, the piston is not connected to a crank-shaft. Instead, the piston movement is "free" and controlled by a linear hydraulic or electric machine. The major advantages of such a design over the conventional ones are the simpler engine layout and much improved conversion efficiency. Unlike other traditional modeling method, in this paper, the free piston converter is modeled as a hybrid automaton. A hierarchical hybrid controller is designed based on this model. The hybrid controller includes a discrete controller which is in charge of switching actions and a continuous controller which compute the electro-magnetic force. High-fidelity simulation results are provided to illustrate the applicability and performance of developed control law.