Stress-informed Control of Medium- and High-head Hydropower Plants to Reduce Penstock Fatigue

Abstract: The displacement of conventional generation in favor of stochastic renewable requires increasing regulation duties from the remaining dispatchable resources. In high- and medium-head hydropower plants (HPPs), providing regulation services to the grid and frequently changing the plant's set-point causes water hammer, which engenders pressure and stress transients within the pressurized conduits, especially the penstock, damaging it in the long run. This paper proposes a model predictive control (MPC) that explicitly models the hydraulic transients within the penstock. It achieves to reduce the mechanical loads on the penstock wall, and, consequently, fatigue effectively. Thanks to a suitable linearization of the plant model, the optimization problem underlying the MPC scheme is convex and can be solved with off-the-shelf optimization libraries. The performance of the proposed controller is tested with numerical simulations on a 230MW medium-head HPP with Francis turbine providing primary frequency control. Simulation results show substantially reduced penstock fatigue, existing approaches outperformed, and problem resolution times compatible with real-time control requirements.