Power Extraction for Free Piston Linear Generator

Free-piston linear generators (FPLG) produce electrical alternate voltages which exhibit a double frequency modulation: the lower frequency depends on the mechanical oscillation of the piston and the higher one is determined by the electromagnetic generation and the number of pole pairs. This paper proposes a control strategy for providing the maximum power extraction from FPLG aimed at charging a battery with a desired electrical current profile. The control scheme is based on a dynamic averaged model of the active three-phase power converter which connects the voltage generation, dependent on the piston velocity, and the battery. The desired dc battery current is obtained by using a double frequency rotation of the model and by designing feedforward and feedback components of the modulation signals from the steady state and dynamic model of the system, respectively. Simulation results show the effectiveness of the proposed solution in tracking the reference battery current profile.