Optimal control of conventional hydropower plant retrofitted with a cascaded pumpback system powered by an on-site hydrokinetic system

Highlights: • Presents an optimal control for a conventional hydropower plant fitted with a cascaded pumpback retrofit. • A comparison of the pumping energy of the cascaded and the classical model is presented. • Potential daily pumping energy saving of up to 48.18% is achieved with cascaded model. • A daily optimal increase in energy production of 31–48% in dry season and 66.45% in rainy season is realised. - Abstract: This paper presents an optimal control strategy for a hydropower plant retrofitted with a hydrokinetic-powered cascaded pumpback system in dry season. Pumpback operation aims at recycling a part of the down-stream discharge back to the main dam to maintain a high water level to optimise the energy value of the available water. The problem is formulated as a multi-objective optimisation problem to simultaneously minimise the grid pumping energy demand, minimise the wear and tear associated with the switching frequency of the pumps, maximise the restoration of the volume of the dam through pumpback operation and maximise the use of on-site generated hydrokinetic power for pumping operation. The performance of the proposed cascaded model is compared with the classical single pump pumped storage model. Simulation results based on a practical case study shows that the cascaded pumpback model can reduce the pumping energy demand by up to 48.18% and increase the energy yield of the resultant system by up to 47.10% in dry season.