Distributed secondary control of energy storage units in a droop-controlled DC microgrid

In the control and management of an energy storage system consisting of multiple energy storage units, bus voltage regulation, load power sharing, and energy level balancing are important objectives. To achieve these objectives, we propose a distributed secondary control scheme for each energy storage unit in a droop-controlled multi-bus DC microgrid. This control scheme is composed of two auxiliary control inputs. By constructing a distributed voltage observer based on the dynamic average consensus algorithm of a first-order multi-agent system, we design the first auxiliary control input such that global voltage regulation is achieved. Moreover, based on the leaderless consensus algorithm of a second-order multi-agent system, we design the second auxiliary control input such that proportional power sharing and state-of-energy balancing are simultaneously achieved. Through simulation studies in MATLAB/Simulink, we validate the effectiveness of the proposed control scheme and highlight the appealing feature of state-of-energy balancing over state-of-charge balancing for a battery energy storage system.