Electro-Mechanical Mode Identification of a BESS Integrated Grid System Through Subspace Identification Method

Increasing the penetration of renewable energy sources into an existing power system reduces the system's inertia, which can result in stability issues. Consequently, monitoring the different oscillatory modes resulting from an inverter-based generation's integration to a grid is of great concern. Most renewable energy sources operate based on maximum power point tracking (MPPT), because of economic reasons, since they are strongly dependent on weather conditions, which are intermittent and fluctuate. Battery energy storage systems (BESS) can provide a solution to the stochastic nature of renewable energy sources, because of a BESS's capability to store energy, support bidirectional energy exchange, provide geographical independence, and support fast output response. In this paper, a BESS along with a photovoltaic (PV) system are connected to a power grid via grid following and grid forming control architectures to study the oscillatory modes. A subspace identification method is used to identify oscillatory modes and their damping ratios from the measured voltage dynamics are obtained for the test system.