The increasing accommodation of intermittent renewable energies into power grids creates needs for additional flexibility in power generation. In the field of hydropower research, this has translated into significant attention paid to the larger control possibilities brought by power electronics converters. Through theoretical analysis and transient simulations, the present paper investigates the power control of a pump-as-turbine fed by a reservoir, and driving an induction machine, itself connected to the grid through a full-scale power converter. The modelling of each part of the system is thoroughly discussed and two control strategies are considered, namely the direct control of power through the electromagnetic torque, and the indirect control of power through the rotational speed. Theoretical analysis and transient simulations show that the first control strategy may lead to unstable operation, depending on the system and control parameters, while the second ensures the system stability.
Mercier, T., Hardy, C., Van Tichelen, P., Olivier, M., & De Jaeger, E. (2019). Control of variable-speed pumps used as turbines for flexible grid-connected power generation. Electric Power Systems Research, 176(105962), 9. https://doi.org/10.1016/j.epsr.2019.105962 (Original work published 2019)