Nonlinear adaptive backstepping controller design for controlling bidirectional power flow of BESSs in DC microgrids

In this paper, a nonlinear adaptive backstepping controller
is designed to control the bidirectional power flow (charging/
discharging) of battery energy storage systems (BESSs) in a DC
microgrid under different operating conditions. The controller is
designed in such a manner that the BESSs can store the excess energy
from the renewable energy sources (RESs) in a DC microgrid after
satisfying the load demand and also feeding back the stored energy
to the load when RESs are not sufficient. The proposed controller is
also designed to maintain a constant voltage at the DC bus, where
all components of DC microgrids are connected, while controlling
the power flow of BESSs. This paper considers solar photovoltaic
(PV) systems as the RES whereas a diesel generator equipped with
a rectifier is used as a backup supply to maintain the continuity of
power supply in the case of emergency situations. The controller is
designed recursively based on the Lyapunov control theory where
all parameters within the model of BESSs are assumed to be
unknown. These unknown parameters are then estimated through
the adaptation laws and whose stability is ensured by formulating
suitable control Lyapunov functions (CLFs) at different stages of
the design process. Moreover, a scheme is also presented to monitor
the state of charge (SOC) of the BESS. Finally, the performance
of the proposed controller is verified on a test DC microgrid under
various operating conditions. The proposed controller ensures the DC
bus voltage regulation within the acceptable limits under different
operating conditions.