Microgrids: Hierarchical Control and an Overview of the Control and Reserve Management Strategies

Abstract

T he increasing share of distributed generation (DG) units in electrical power systems has a significant impact on the operation of the distribution networks, which are increasingly being confronted with congestion and voltage problems. This demands a coordinated approach for integrating DG in the network, allowing the DG units to actively contribute to frequency and voltage regulation. Microgrids can provide such coordination by aggregating DG, (controllable) loads, and storage in small-scale networks, which can operate in both grid-connected and islanded mode. In this article, the islanded operating condition is considered. As in the conventional networks, a hierarchical control structure can be implemented in islanded microgrids. In recent years, many different concepts for primary, secondary, and tertiary control of microgrids have been investigated. These controllers can be classified as either local or centralized. In this article, the

Toward the Universal DC Distribution System

“…Oversizing the converters is an expensive solution which is sometimes employed for AC systems [33]. Also, a small nanogrid in islanded operation might not be able to produce high enough short-circuit currents, even with oversized converters.…”

Hybrid AC/DC Microgrid Mode-Adaptive Controls

“…These units are also named grid-following devices, as they do not regulate the bus but rather they "follow" their frequency and/or voltage [5,7].…”

“…These devices share the power variations occurring in the microgrid to decrease the variations of the bus frequency/voltage [5,7].…”

Review on the Coordination and Energy Management of Microgrids Broad Based on PQ Controller and Droop Control. Some Useful Information Is Given in This Paper

“…The micro source such as wind power and photovoltaic cells, which output power is influenced by the weather, have obvious intermittent [2]. Control of microgrids becomes a critical issue for ensuring reliable operation of the microgrid and each AC and DC microgrids have different hierarchical controls, but those could be generalize into three levels by referring to the hierarchical control which are classified as follows: (1) the primary control is based on the droop method, including an output-impedance virtual loop; (2) the secondary control allows the restoration of the deviations produced by the primary control and to improve power quality via unbalance and mitigation of harmonics in network; and (3) the tertiary control manages the power flow between the microgrid (MG) and the external electrical distribution system [3]. The PQ controller and droop control should be able to control and manage power properly in both operating mode, grid-connected mode and stand-alone mode.…”