Hierarchical Multi-Timescale MPC for Control of Off-Grid Renewable Energy Powered Ammonia Plant with Storage

Electrifying industrial processes powered by renewable energy (RE) presents unique control challenges due to the multi-timescale dynamics and signals inherent in these systems. The coupling of the fast-timescale dynamics of the RE subsystems and the slow-timescale dynamics of industrial end-use systems creates a complex control problem. Further, variability in RE resources in both fast and slow timescales introduces an additional challenge for the storage dispatch that the controller must also consider. This paper presents a multi-timescale model predictive controller (MT-MPC) designed for an off-grid RE-powered electrified ammonia plant. The MT-MPC effectively manages storage dispatch and provides dynamic control of the end-use subsystem at slow timescales while also managing control of the fast-timescale RE subsystem with the time-varying RE resource input. The MT-MPC outperforms two single-timescale MPCs designed for only the fast or slow timescales, showing that the electrified ammonia plant benefits from multi-timescale control and that the MT-MPC is a promising controller to address that need.