title: A multi-mode operation control strategy for flexible microgrid based on sliding-mode direct voltage and hierarchical controls.
abstract: Multi-mode operation and transient stability are two problems that significantly affect flexible microgrid (MG). This paper proposes a multi-mode operation control strategy for flexible MG based on a three-layer hierarchical structure. The proposed structure is composed of autonomous, cooperative, and scheduling controllers. Autonomous controller is utilized to control the performance of the single micro-source inverter. An adaptive sliding-mode direct voltage loop and an improved droop power loop based on virtual negative impedance are presented respectively to enhance the system disturbance-rejection performance and the power sharing accuracy. Cooperative controller, which is composed of secondary voltage/frequency control and phase synchronization control, is designed to eliminate the voltage/frequency deviations produced by the autonomous controller and prepare for grid connection. Scheduling controller manages the power flow between the MG and the grid. The MG with the improved hierarchical control scheme can achieve seamless transitions from islanded to grid-connected mode and have a good transient performance. In addition the presented work can also optimize the power quality issues and improve the load power sharing accuracy between parallel VSIs. Finally, the transient performance and effectiveness of the proposed control scheme are evaluated by theoretical analysis and simulation results.
authors.affiliation: Marine Engineering College, Dalian Maritime University, Dalian 116026, People's Republic of China. Electronic address: zqj18@qq.com.
authors.forename: Qinjin
authors.initials: Q
authors.lastname: Zhang
authors.affiliation: Marine Engineering College, Dalian Maritime University, Dalian 116026, People's Republic of China. Electronic address: liuycdlmu@126.com.
authors.forename: Yancheng
authors.initials: Y
authors.lastname: Liu
authors.affiliation: Marine Engineering College, Dalian Maritime University, Dalian 116026, People's Republic of China. Electronic address: zhyt@newmail.dlmu.edu.cn.
authors.forename: Youtao
authors.initials: Y
authors.lastname: Zhao
authors.affiliation: Marine Engineering College, Dalian Maritime University, Dalian 116026, People's Republic of China. Electronic address: n.wang.dmu.cn@gmail.com.
authors.forename: Ning
authors.initials: N
authors.lastname: Wang
keywords: Adaptive sliding-mode control; Microgrid; Multi-mode operation; Seamless transition; Three-layer hierarchical structure; Virtual negative impedance