Stability preservation and power management in autonomous microgrids using adaptive nonlinear droop scheme

This paper proposes sharing active and reactive power in autonomous voltage source inverter (VSI)-based microgrids with no physical communication links. In decentralized VSI-based microgrids, when the demand or generation changes, the output voltage of distributed generation units and the frequency of the system will also change. This study presents a novel adaptive nonlinear droop (ANLD) scheme for preserving network stability, improving the system's dynamics, and controlling power sharing in multibus microgrids in a decentralized manner. Subcontrollers are modeled in a state space and combined together so that a complete dynamic model of the network can be developed. Note that controller coefficients are optimized to improve small-signal stability and to obtain a good operating point. To this end, an optimization problem is formulated and solved using the particle swarm optimization method. For the purposes of comparison, the proposed ANLD method and three other schemes are applied to two case studies: a 5-bus microgrid and a modified 37-bus IEEE microgrid. The stability margin analysis and time response simulations prove that the proposed algorithm performs much better and can be applied to large-scale microgrids.