Modelling and benefits of combined operation of hydropower unit and battery energy storage system on grid primary frequency control

Increasing amount of renewable energy generation reduces predictability of power generation in electrical grids. Increased error between production and consumption power balance is shown as fluctuation in the grid frequency. Transmission system operators use frequency containment reserves for grid frequency control. To be able to operate as a frequency control reserve, the reserve unit must fulfill the requirements defining the dynamic response. Conventional hydropower plants have limited control bandwidth because of massive mechanical control actuators. However, battery energy storage systems (BESS) are coupled to the electrical grid with power electronics devices, which can operate on the frequency containment reserve market with negligible limitations in the output power ramp rate. Combined operation of a BESS and a hydropower plant is a solution for dynamic requirements of frequency control units. This paper covers the modelling of the combined system of a BESS and a hydropower plant. This model is used for testing the fulfillment of outlined FCR-N market technical requirements as well as for simulation of combined operation in grid frequency control.