Variable speed pumped storage hydropower for integration of wind energy in isolated grids : case description and control strategies

This paper presents the use of variable speed pumped storage hydropower plants for balancing power fluctuations from wind power in an isolated grid. A topology based on a synchronous machine and a full scale back-to-back voltage source converter is suggested for obtaining variable speed operation of a pump-turbine unit. This topology has not been previously investigated for variable speed pumped storage power plants, but can now be considered relevant for small and medium sized pumped storage units because of the development of voltage source converter drives for higher voltage levels. A possible case for implementation of such a system is described based on the situation on the Faroe Islands, where controllable energy storage can help to allow for a higher share of renewable energy in the power system and by that to reduce the dependency on fossil fuels. Power control of the pumped storage unit by load following for direct compensation of the fluctuations in power output from a wind farm will limit the influence on the operation of the rest of the grid. By utilizing the pumped storage to take part in the primary frequency control of the power system, the frequency response to other changes in production or load will also be improved.reviewe