Review of Active and Reactive Power Sharing Strategies in Hierarchical Controlled Microgrids

Abstract

Microgrids consist of multiple parallel-connected distributed generation (DG) units with coordinated control strategies, which are able to operate in both grid-connected and islanded mode. Microgrids are attracting more and more attention since they can alleviate the stress of main transmission systems, reduce feeder losses, and improve system power quality. When the islanded microgrids are concerned, it is important to maintain system stability and achieve load power sharing among the multiple parallel-connected DG units. However, the poor active and reactive power sharing problems due to the influence of impedance mismatch of the DG feeders and the different ratings of the DG units are inevitable when the conventional droop control scheme is adopted. Therefore, the adaptive/improved droop control, network-based control methods and cost-based droop schemes are compared and summarized in this paper for active power sharing. Moreover, nonlinear and unbalanced loads could further affect the reactive power sharing when regulating the active power, and it is difficult to share the reactive power accurately only by using the enhanced virtual impedance method. Therefore, the hierarchical control strategies are utilized as supplements of the conventional droop controls and virtual impedance methods. The improved hierarchical control approaches such as the algorithms based on graph theory, multi-agent system, the gain scheduling method and predictive control have been proposed to achieve proper reactive power sharing for islanded microgrids and eliminate the effect of the communication delays on hierarchical control. Finally, the future research trends on islanded microgrids are also discussed in this paper.

MAS-Based Distributed Coordinated Control and Optimization in Microgrid and Microgrid Clusters: A Comprehensive Overview

“…The decentralized control does not rely on a MGCC and droop mechanism, so the error of a DG unit will not produce the failure of the entire system. Compared with the centralized control, these strategies have higher ability to tolerate the communication errors, and better plug-and-play performance, and can be easily extended to more DG units, which makes the system more scalable [144]. Nevertheless, there are still many problems that have not been effectively solved in the existing literatures.…”

Optimal Design and Real Time Implementation of Autonomous Microgrid Including Active Load

“…The active load input current (i lALDQ ) is converted from the common reference frame "DQ" to the active load reference frame dq AL using PLL. (20) where δ i is the angle between the dq active load frame and common reference frame DQ.…”

“…The details and characters of various control schemes were illustrated in [5]. Another updated revision for the power-sharing schemes was presented in [20]. It was stated that load demand and the controller power-sharing coefficients dominantly distress the low frequency modes; while filter parameters, load dynamics, and the controller parameters of the inner voltage and outer current controllers distress the medium and high frequency damped modes [5].…”

A Survey on Smart Agent-Based Microgrids for Resilient/Self-Healing Grids

“…Hybrid control, a more practical scheme, combines centralized and distributed control, as shown in Figure 3 [80,81]. Distributed energy sources are grouped within an MG; a centralized control is used within each group, while distributed control is applied to a set of groups.…”