Dynamic Analysis of Energy Storage Integrated Systems Considering Bidirectional Power Flow and Different Control Loops of Energy Storages

Dynamics of inverter-based resources, particularly renewable energies, have been extensively analyzed. However, bidirectional active power flow in these scenarios has not received significant attention. With the rapid development of energy storages (ESs), the power flow may undergo a notable reversal. It is crucial to clarify the impact of bidirectional active power flow on the dynamics of energy storage integrated systems (ESISs) to ensure stable operations. This study primarily focuses on small signal stability of grid-following ESs, involving two well-known control loops: DC voltage control and active power control. The established model is used to theoretically verify that the impact of ESs on the dynamics of ESISs is negative as the active power amplitude of ESs increases, regardless of direction. The identified cause is the transformation from x–y to d–q coordinates when implementing the control loops of ESs under grid-following control (GFL). Therefore, increased rated power and connected numbers of ESs should be approached with caution, because they may lead to subsynchronous oscillations. The conclusions are demonstrated through a simple and large-scale ESISs.