Non-linear and multi-domain modelling of a permanent magnet linear synchronous machine for free piston engine generators

Abstract

• The motivations for continued FPE and LEM development are established. • A non-linear and multi-domain model of the PMLSM is presented. • Incorporation of the PMLSM in an FPEG multi-domain model is demonstrated. • Model validation with data captured from an experimental FPEG is conducted. • Simulation results indicate the model captures the dominant dynamics of the PMLSM. The Free Piston Engine (FPE) can be considered a viable and promising option in future low-carbon technology development. When coupled to the Linear Electric Machine (LEM) to produce electrical energy, its characteristic non-linear dynamics typically have been described as linear when considering a systems-level modelling approach. This paper presents a multi-domain model of a Permanent Magnet Linear Synchronous Machine (PMLSM) for Free Piston Engine Generators (FPEG) and offers a detailed non-linear mathematical description of the machine dynamics. The model was implemented in a free-piston expander system and validated against experimental data from a test rig that has identical parameters. The simulation results indicate a strong correlation to the experimental data, which captured the dominant dynamics of the PMLSM and prove the satisfactory accuracy and performance of the model, together with a similar voltage and current output trace, indicating a cyclic energy output error of approximately 10 %. This paper aims to extend the current knowledge and literature within FPEG PMLSM design by considering the inherent non-linearity and multi-directional nature of the system dynamics and its interactions with multi-physical domains.