SOC-Based BESS Control Logic for Dynamic Frequency Regulation in Microgrids with Renewables

In recent years, power systems have been characterized by significant changes. The shift from centralized generation to non-dispatchable distributed generation needs crucial actions to maintain the network security and stability. In such a scenario, battery energy storage systems (BESS) are expected to have a key role for frequency restoration processes, thanks to their rapid response to frequency deviations. In this paper, an innovative control logic based on BESS management is proposed for dynamic frequency restoration in microgrids (μGs) with renewables. In addition to the BESS management, a new function, which is the State of Charge (SOC) Management Control (SMC), is developed. The SMC logic allows keeping the BESS SOC within the 'energy restoration band' as the SOC interval where the BESS is certainly able to participate to the frequency restoration process after system imbalances. This allows ensuring the needed amount of energy restoration reserves during the μG operation for next frequency deviation events. In simulation testing, carried out in DIgSILENT Powerfactory environment, two μGs in grid-connected and islanded modes are investigated. Results show that the SMC logic increases the possibility for the BESS to participate to frequency restoration processes as compared with the case without the control logic, by ensuring a higher availability of energy reserves, thus improving the μGs reliability for both the analyzed configurations.