No abstract

The increasing presence of distributed generation (DG) in the electrical grid determines new challenges in grid operations, especially in terms of voltage and frequency regulation. Recently, several grid codes have required photovoltaic (PV) inverters to control their reactive power output in order to provide voltage regulation services, and the allocation of a certain amount of active power reserve for fast frequency response (FFR) service during under-frequency contingencies is needed. This requirement involves a significant waste of energy for PV systems, due to the necessity to constantly operate in de-loaded mode, under normal operating conditions. In addition, the variability of the irradiance can affect the correct amount of active power reserve that the system can provide in the moments after an under-frequency occurrence. The increasing number of battery energy storage systems (BESSs), coupled to PV systems, can be used to provide a worthy contribution to this frequency regulation service. The aim of this paper is to analyze the efficiency of active power reserve provided by a BESS connected to the DC bus of a non-ideal grid-connected PV inverter, taking into account the impact of reactive power control. For this purpose, the contribution of BESSs to frequency regulation is discussed and, starting from an existing model of real inverter, an analytical formulation for active power reserve evaluation is presented. Results concerning the impact of reactive power control are also given. Finally, the possibility for a low voltage (LV) grid with aggregated PV systems and BESSs to contribute to grid active power reserve is considered. Different voltage control strategies are compared, defining a helpful new parameter.

The aim of this study is to analyze the different decentralized voltage control strategies, based on the reactive power control of photovoltaic inverters. The study focuses on evaluating their impact in terms of reactive power demanded from the grid, due to the regulation, and active losses in the network and in the photovoltaic inverters. In a second step, the presence of battery energy storage systems in the network is considered and further analysis are performed, in order to take into account the overvoltage mitigation by peak shaving of the photovoltaic generation. All the simulations are performed in MATLAB/SIMULINK, where the model of a single-phase low-voltage distribution network with distributed generation sources is implemented.