As the share of wind and solar energy production increases, more flexible production and loads are required to control the balance of the grid. A potential use of Variable Speed Hydro Power (VSHP) is to provide this flxibility and compensates the production of variable renewables. The hypothesis is that VSHP can offer additional ancillary services, contributing to the frequency regulation and improving the grid stability by utilizing the rotational energy in the turbine and generator. This allows for higher Department of Electric penetration of renewables in the grid.

Objective: The focus of the PhD work is to investigate the interactions between the VSHP plant and the grid, and how variable speed operation can benefit the security and flexibility of the power system operation. The control possibilities is investigated from a system perspective while considering the limitations given by the water/turbine system.

Results and ongoing work
• A new hydraulic model for grid integration of VSHP are developed and tested against excising hydraulic models for grid integration of conventional power plants.
• This model is implemented and tested in a grid with both VSHP and conventional hydropower, including models of VSHP generator, generatorside converter, grid-side converter and a representatively test grid.
• Next, different methods for virtual inertia (VI) control methods for VSHP are compared
• A model predictive control (MPC) is under development. It is used together with VI for optimize the frequency support capabilities of the VSHP, while keeping the electric and hydraulic variables within their limits.