A novel stable control strategy of single cylinder free-piston linear generator

This paper presents a novel control strategy for a single cylinder free-piston linear generator (FPLG) to stabilize the operation process when combustion fluctuation occurs. The FPLG is composed of an internal combustion engine (ICE), a linear Voice Coil Motor (VCM) and a mechanical spring which is assembled between the ICE and the VCM and functions as a rebounding device. When the piston is in expansion stroke, a two-stage control strategy is employed to guarantee the accuracy of bottom dead center (BDC) position of the piston. In compression stroke, a one-stage reference electromagnetic force is enough to control the TDC on account of the accurate control of BDC. The electromagnetic force of the VCM is controlled by the armature current through following the energy balance equation. The dead point position errors, in-cylinder pressure and piston velocity are regard as a feedback to the control loop to regulate electromagnetic force. A simulation model built in MATLAB/Simulink is used to verify the effectiveness of this control strategy. The results validate that this strategy can achieve stable operation with the variation of ±6 mg fuel mass in combustion process. The settling time is less than 0.1s.