  This paper deals with the design of controllers for variable speed hydropower (VSHP) plants with the objective of optimize the plants' performance. The control objectives imply enabling fast responses to frequency deviations while keeping the electric and hydraulic variables within their constraints. A model predictive controller (MPC) was developed to coordinate the turbine controller with the virtual synchronous generator (VSG) control of the power electronics converter. The simulation results show that the VSG is able to deliver fast power responses by utilizing the rotational energy of the turbine and the generator. The MPC controls the guide vane opening of the turbine to regain the nominal turbine rotational speed. If this is not possible due to the constraints of the hydraulic system, the MPC adjusts the power output of the VSHP by changing the VSG power reference. The proposed control system allows the VSHP to provide fast frequency reserves (FFR). 
Optimized Control of Variable Speed Hydropower for Provision of Fast   Frequency Reserves