  This paper presents the development of a non-linear model predictive
controller (MPC) for controlling variable speed hydropower (VSHP) plants. The
MPC coordinates the turbine controller with the virtual synchronous generator
(VSG) control of the power electronics converter to optimize the plant's
performance. The main objective is to deliver a fast power response to
frequency deviations by utilizing the kinetic energy of the turbine and
generator. This is made possible by allowing the turbine rotational speed to
deviate temporarily from its optimal speed. In addition, the efficiency should
be maximized while keeping the electric and hydraulic variables within their
constraints. The simulation results show that the proposed MPC is also able to
damp power oscillations in the grid, reduce water hammering in the penstock and
improve the future estimation of turbine head, turbine power and turbine flow.
This ensures that the turbine head does not exceed its limits and that the
overshoot in the turbine speed after a disturbance is reduced. Besides, the VSG
converter control enables a fast power response by utilizing the rotational
energy of the turbine and generator. Thereby, the VSHP can provide a
significant amount of fast frequency reserves (FFR) to the grid.
