Closing the loop: experimental validation of a predictive multi-timescale controller for hybrid battery-hydrogen storage systems

This research explores the effect of higher penetration of variable renewables on energy fluctuations at various time scales and the necessity of energy storage systems for balancing power supply. This paper presents an experimentally verified predictive multi-timescale control method for a hybrid energy storage system (HESS) consisting of lithium iron phosphate (LFP) batteries, vanadium redox flow battery (VRFB), and hydrogen storage. Laboratory-scale HESS was tested for over 500 hours for four scenarios of grid operations including renewable smoothing, load following, ancillary services, and seasonal shifting. In order to perform coordinated operation, control method relies on a hierarchical model predictive control (MPC) structure with mixed-integer linear programming (MILP) used for day-ahead scheduling and receding horizon optimization applied to real-time dispatch. Experimental results have shown that application of predictive control helps to decrease the ramp rate of the grid by 59% and LFP cycling by 42%. Efficiency of the experimental HESS was 92.3% for LFP batteries, 74.8% for VRFB, and 35.4% for hydrogen P2G2P which gave a total efficiency of the system 65.4%. Cost of energy was estimated as £0.106/kWh while CO2 emissions decreased by 95.8% compared to diesel system.