Microgrid is an important and necessary component of smart grid development. It is a small‐scale power system with distributed energy resources. To realize the distributed generation potential, adopting a system where the associated loads and generation are considered as a subsystem or a microgrid is essential. In this article, a literature review is made on microgrid technology. The studies run on microgrid are classified in the two topics of feasibility and economic studies and control and optimization. The applications and types of microgrid are introduced first, and next, the objective of microgrid control is explained. Microgrid control is of the coordinated control and local control categories. The small signal stability and methods in improving it are discussed. The load frequency control in microgrids is assessed.

In this study, power system stabiliser (PSS), static VAR compensator (SVC), and thyristor controlled series capacitor (TCSC) controllers are simultaneously used to increase the stability and damping of the oscillations of a multi‐machine power system. By SVC, the transferrable power in the steady state can be increased and the voltage profile can be controlled along the line. TCSC can regulate line impedance and therefore, increase the transferred power of the system. PSS is added to excitation system to enhance the damping of electric power system during low frequency oscillations. SVC, TCSC, and PSS can combine with each other for further damping and stability; therefore, their coordination is very important. Then, adaptive velocity update relaxation particle swarm optimisation algorithm is used to optimise the parameters of PSS, SVC, and TCSC simultaneous controllers. The robustness of the proposed algorithm has been tested on 16‐machine 68‐bus power system.

Droop-based techniques have widely been utilized in controlling voltage source inverter based distributed generation units within a microgrid. Advantages of droop based control have been extensively discussed, while its effects on stability and power quality of the inverter based microgrids have not been explicitly studied. This paper addresses this gap by analyzing the stability of islanded microgrid with focusing on power quality problems. From this viewpoint, current paper studies the effect of parameters change on the stability margin of the microgrid using a bifurcation analysis approach. To this end, this work firstly derives a dynamic model of a microgrid including controllers of the inverter, network and loads. Based on this model, the loci of the system eigenvalues have been analyzed, showing that, by changing the droop coefficients, the Hopf and Period-Doubling bifurcation can occur in such a system. Furthermore, the droop tuning procedure may also cause the system to experience the flicker phenomenon in advance of the instability. Next, a virtual impedance-based solution is presented to avoid the flicker as well as instability problems. Finally, the efficacy of the proposed method is proved on a practical network.

Low voltage DC (LVDC) microgrids facilitate the integration of renewable energy systems and modern loads. However, they suffer from the lack of a sensitive, selective, reliable, and fast protection strategy. The low fault current of high-resistance faults makes fault detection and faulty zone identification challenging tasks for protection engineers. This paper proposes a protection scheme that is effective for both bolted and high-resistance faults at LVDC feeders. The developed strategy relies on two intelligent electronic devices at both ends of the protected zone, calculating the normalized superimposed component of the line current. By adding this component to the input of the periodically-forced harmonic oscillator (PFHO), both fault occurrence and fault direction can be simultaneously determined based on the oscillator state variable with only two possible values during stable and unstable modes. It eliminates the need for selection of various protection thresholds for different LVDC microgrid structures/topologies. The proposed protection strategy can classify pole-to-ground and pole-to-pole faults and is effective for both grid-connected and islanded LVDC microgrids. The reliable performance of the developed PFHO based protection is assessed on the simulation model of a ±750 V meshed LVDC microgrid with the TN-S grounding system.

Droop control is at the first level of the control hierarchy and does not require communication. Having high reliability, is usually used in inverter‐based microgrids. The microgrid can operate as an island, and it can also be connected to the main or auxiliary grid. By reviewing the extensive literature on the role of the controller in inverter‐based microgrids for the island mode of operation, in this study, the droop regulation strategy has been covered briefly and compactly. Droop regulation is an example of decentralized regulation in basic control, and its importance is revealed in the island mode of operation when it is possible to share power in all facilities without needing to communicate with other units. Disadvantages of common droop control, such as slow transient dynamics and low energy quality for non‐linear and unbalanced loads, have limited its use in advanced microgrids. Therefore, various methods to improve the common droop control have been investigated so far, some of which have been mentioned. This study highlights the application of droop control strategies in order to coordinate distributed generation units in the microgrid. About 180 published studies in this field have been reviewed, classified and indexed for quick reference.