Based upon our review of published NASA papers and reports, compared with other teamsÂ’Stirling machine controllers, our controller appears uniquely capable of precisely controlling piston motions (i.e., amplitude, mean position offset, frequency) and phase-synchronization with other machines. Our robust active controller implements a novel nonlinear control algorithm to maintain stable machine operation despite model parameter uncertainty and unmodeled dynamics. However, to date, we have only evaluated the performance of our controller as part of software simulations of Stirling machines. The virtual controller performance has been extensively studied through two NASA SBIR Phase I projects. The next logical step in developing this controller is transitioning from present virtual model simulations to real processor hardware. The migration to hardware always introduces new and unexpected problems. Therefore, we propose validating our control algorithm using a simple linear motor on the lab benchtop. We will derive the motor test hardware from convertor alternator/ piston/ cylinder components from a past NASA SBIR Phase II project. The effort will include the selection of a physical processor board, deploying the control algorithm to the board, and initial controller integration with the power stage, sensors, and linear motor. Lastly, we will subject the hardware system to a range of test scenarios and parameter sweeps to confirm the robustness of our controller to maintain desired piston motion. As a performance reference, we will update our virtual system model throughout the project. This hardware demonstration will test our performance predictions and help guide the future development of the standalone controller for use with other linear free-piston machines. Anticipated
Benefits: Our controller can support dynamic radioisotope power system (DRPS) Stirling convertors at any power level – offering reliable, efficient, and robust control of one or more convertors under off-nominal conditions. We could adapt the controller for NASA cryocooler applications to directly cool space sensors and reliquefy vapor for zero-boiloff fluid storage. The proposed controller could also be applied to linear gas compressor/ liquid pump or other linear actuator applications. Our controller could support convertors for terrestrial remote power applications requiring high reliability (e.g., navigation or communications equipment in off-grid areas). The controller could support cryocoolers for commercial CubeSat/ SmallSat or other missions requiring cooling multiple heat loads, possibly at different temperatures.
