Cooperative Control of Two Free-Piston Engine-Generators for Vibration Reduction

The free-piston engine-generator (FPEG) is a promising power unit in vehicle-mounted energy conversion systems. However, inertial-force excitation caused by free-piston reciprocating motion remains a major constraint on its practical application. To address this issue, a hierarchical control architecture consisting of a single-engine motion control layer and a two-engine synchronization control layer is proposed for an opposed two-engine FPEG system. The single-engine motion control layer combines iterative learning control with displacement feedback and adaptive compensation with velocity feedback to regulate dead-center positions. The two-engine synchronization control layer introduces a Combustion State Observer (CSO) to estimate cycle-to-cycle indicated-work variations caused by stochastic combustion fluctuations and guide differential fuel-injection compensation. A simulation verification framework is established to evaluate the proposed strategy under compound disturbances. Relative to the single-engine case, the cooperative scheme achieves a 99.6% mean-square force reduction while maintaining 43.3% indicated thermal efficiency. The residual RMS inertial force is further reduced by 38.1% compared with the master–slave baseline. These results demonstrate that the CSO-based cooperative synchronization strategy is effective in reducing inertial-force excitation in two-engine FPEG systems.