Primary frequency control by energy storage system : a Fourier transform procedure for the dynamic analysis of the grid

Non dispatchable Renewable Sources continue to increase in Installed capacity: in 2014 Wind Power was 14% (128 GW) of Total Power Capacity in Europe whereas Photovoltaic Systems (PV) accounted for 9% (88 GW). In 2020 Wind Power could reach 192 GW installed, instead PV could grow over 159 GW. Moreover, Sun and Wind Power sources are connected tothe Electric Grid through Static Power Converters and therefore, they do not contribute to the Rotating Inertia of the Grid. Moreover, Power mismatch between Load and Generation will increase due to the stochasticity of renewable primary source (wind velocity and Sun radiation). Therefore the frequency will divert from the nominal value of 50 Hz for very long periods and with high deviations. This situation could damage the behaviour of sensible Loads (like electronics components) and saturate Power Reserve of the Grid, endangering the system in case of a generator trip or some other big incident. Battery Energy Storage System (BESS) seems very well suited for Primary Frequency Control (PFC) in comparison to the Traditional Generation Plants due to its velocity and precision. Technology and Safety reasons make installations expensive and moreover severe State of Charge (SOC) dynamics can affect their useful life. Optimal use and design need to be assured. In the case of PFC, due to its finite efficiency, even if the frequency signal is symmetrical, the battery will tend to discharge progressively even following the normal symmetric Fixed Droop Power-Frequency curve. To assure the Service of PFC it will have to recharge itself by acquiring the energy from the grid, increasing the operational costs. The thesis is based on a novel procedure devoted to build a Test Grid with a frequency signal oscillating in a realistic way by manipulating the oscillations introduced by Wind, Sun, Load and Traditional Generation Sources. Velocity of oscillation is replicated by the use of the Fourier Transform of the frequency signal. Finally, BESS will be introduced in the Test Grid in order to validate their effectiveness in the frequency control. After being characterized in capacity and efficiency a Variable Droop Strategy and a usual fixed one will be used to improve the frequency deviations and the battery SOC dynamics.