Control-oriented DC-link harmonic mitigation in cyclic operated reversible solid oxide electrolyser plants

This paper presents a model-based, analytical control design for the multiple bidirectional DC–DC converters interfacing individual stacks in a full-scale, cyclically operated reversible solid oxide electrolyser plant to mitigate DC-link harmonics. The distributed synchronous cycling of the rSOE stacks excites low-frequency harmonics and induces DC-link oscillations that degrade stability and power quality. To analyze and mitigate these effects, we develop a control-oriented, linearized small-signal model of the rectification stage, DC distribution network, and converter–stack subsystems, assembled into a plant-level state-space representation. This model enables analytical PI control design for closed-loop pole placements, where there is an inherent trade-off in the control design between dampening DC-link oscillations and maintaining fast reference tracking performance. Simulation results validate the model’s fidelity and demonstrate that the proposed control design strategy effectively reduces DC-link oscillations while preserving acceptable tracking dynamics. A baseline study shows that traditional control methods fail to capture critical plant dynamics, potentially leading to instability.