Control-Based Design of Free-Piston Stirling Engines
In this approach, Stirling engines are recast and reinterpreted from a dynamic systems and controls perspective by viewing the interacting dynamic system elements in the context of designing a feedback loop. Initial work indicates that a non-standard control design problem emerges. For the engine to produce power, there must exist at least two complex-conjugate closed-loop poles in the right-half plane. Therefore, the control-based design of free-piston Stirling engines requires seeking instability and instability robustness. Instability in a linear sense implies an engine that produces power, whereby the true nonlinear system will seek a limit cycle.
Stirling engines have unfortunately fallen far short of their historical promises due primarily to low power density – a heavy engine producing small amounts of useable power – particularly at the sub 10kW scale. The free-piston variety of Stirling engine is recognized as possibly holding the key to increasing power density without sacrificing the Stirling engine’s characteristic high efficiency.
- E. J. Barth and M. E. Hofacker, “SGER: Green Energy via Control-Based Design of Free-Piston Stirling Engines”. NSF CMMI Grantees Conference, June 22-25, 2009, Honolulu, HI.