Simulation of a Battery Energy Storage System for Fast Frequency Reserve Support.

Sammanfattning: Electricity providers has a growing interest in moving towards Renewable Energy Sources (RES) for power generation due to their attractive features. This has caused phasing out of coal, oil and nuclear power plants which use large synchronous generators for power production. These large rotational masses provide inertia to the electricity grid which compensate the sudden frequency instabilities of the grid. Therefore, lowering the system inertia opens up to frequency instabilities in the electricity grid.  As a solution for the lower system inertia, the concept of Fast Frequency Reserve (FFR) has been introduced. The timeframe of primary generation reserves can be too slow in case of a sudden frequency instability. Amongst the energy sources that can be used for FFR, this thesis work explores the possibility of a Battery Energy Storage System (BESS) to be used in FFR. To accomplish this objective, a total BESS system including power electronic converters for integration to the grid is designed in this work. The software of choice for simulation is Matlab/Simulink.  This work uses a hybrid battery model proposed by previous research which is a combination of runtime model and Thevenin model. A bidirectional Buck-Boost converter integrated with a current controller has been used as the DC-DC converter. An outer voltage control loop integrated with the inverter dq current controller has been used to connect the BESS to the gird. The function of each subsystem is observed to verify their functionality. The hybrid battery model is tested by comparing results with the battery model available in Simulink. Finally, power delivery to grid under FFR activation requirements is observed.  Results show that the hybrid battery model is a good approximation to represent a real battery cell in electrical grid applications. The simulation time can be reduced by replacing the series battery cell configuration used in this work with the Simulink battery model. The power delivery to the grid shows BESS is a reliable energy resource that can be used for FFR.