With the development of distributed renewable generations, a large number of distributed generations (DGs) are connected to the microgrid. Therefore, distributed cooperative algorithms are more suitable for optimal dispatch of the microgrid than centralized algorithms. This paper proposes a novel distributed cooperative control method for optimal dispatch of microgrids, considering line losses and time delay. First, the optimization model of the microgrid considering line losses is established, and optimality conditions are obtained. Second, a novel distributed optimization method considering line losses is proposed, where the primary control is to achieve optimal dispatch, and the secondary control is to achieve frequency regulation. Third, the stability of the system under time delay is analyzed, and the robust stability conditions are obtained. Finally, simulation results verify the the effectiveness of the proposed method.

Classical droop control and virtual impedance methods play crucial roles in improving the system voltage/frequency stability and autonomous power control. Usually, these two methods are often applied as a combination to facilitate load sharing under different line impedance among distributed generators (DGs) in microgrids. They have been developed in two separate concepts, but present strong similarities. In this paper, the comparison of basic droop control and virtual impedance methods is revisited from a new analogy perspective. By combing both of them, a unified multi-degree-of-freedom droop control is proposed with systematic consideration of steady-state power-sharing performance, dynamic performance, and universal applicability of complex line impedance, which is suitable for arbitrary transmission line impedance characteristics. Moreover, this study gives a clear mechanism analysis of virtual inductance to facilitate the P-f & Q-V droop control in complex resistive-inductive microgrid. Finally, the experiment results verify the feasibility of the proposed unified droop control.

The feasibility of battery energy storage system (BESS) in ameliorating power system transient stability has been proved. However, the required BESS capacity is large, which leads to high price. Meanwhile, the improving effect is significantly affected by fault location and BESS location. To address the problem, a distributed configuration of BESS, with a coordinated control method, is proposed in this paper. Firstly, an independent double-closed loop decoupling controller is designed for each BESS, so that the BESS unit can realize decentralized control according to its local correlation information. Secondly, particle swarm optimization is applied to optimize the control parameters of the distributed controllers to achieve coordinated control. Simulation results show that the distributed BESS controllers optimized by particle swarm optimization can better coordinate with each other, and the transient stability of the system is significantly improved.

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