Variation of frequency and voltage by load changes in a Microgrid is a challenge in droop control method. Centralized restoration frequency or voltage in a Microgrid requires communication link and therefore affects the advantage of decentralized droop control such as reliability, simplicity and inexpensiveness. This paper proposes a decentralized method that restores the frequency of a Microgrid without any communication link and maintains these advantages. The method detects signal changing by wavelet transform (WT) to synchronize distributed energy resource (DER) that interfaced by converter to Microgrid. Its operation principle and control method are explained and analyzed. The simulation results are presented to validate the effectiveness of the proposed method.

In Islanded Microgrids, circulating currents among parallel inverters pose significant challenges to system stability and efficient power distribution. Traditional droop control methods often struggle to manage these currents effectively, leading to inefficiencies and potential system damage. This study introduces an advanced fuzzy-robust droop control strategy that integrates fuzzy logic with robust droop control to address these challenges. By incorporating fuzzy logic, the proposed strategy enhances the adaptability of droop control to varying system conditions, improving the management of circulating currents and ensuring more accurate power sharing among inverters. Comprehensive mathematical modeling and extensive simulation analyses validate the performance of this control strategy. The results show that the fuzzy-robust droop control method significantly outperforms conventional approaches, achieving up to a 70% reduction in circulating currents. This improvement leads to a substantial reduction in power losses and enhances the dynamic response under varying load conditions. Additionally, the strategy improves voltage and frequency regulation, contributing to the overall stability and reliability of the Microgrid. The findings provide a robust solution to the longstanding issue of circulating currents, optimizing Microgrid operations, and paving the way for more efficient and resilient distributed energy systems. The advanced control strategy presented in this study not only addresses critical challenges but also demonstrates the potential for innovative methodologies to meet the growing demands of future energy infrastructures, where reliability and efficiency are essential.

Accurate load power sharing and voltage regulation are two critical control objectives to ensure power quality and reliable operation of Islanded Microgrids. Although voltage regulation can be achieved using a secondary control loop, the inaccuracy of reactive power sharing is a prominent issue due to the varying impedance of lines connected to distributed generation sources. One of the techniques for accurate sharing of reactive power is to modify the production reference voltage by the droop control method. In this paper, a control strategy is proposed to improve the accuracy of reactive power sharing among distributed generation units of Islanded Microgrids. The proposed control method was based on transient reactive current injection to modify the production reference voltage of the droop control method. The reactive power-sharing error was reduced by changing the reference voltage. In addition, the proposed controller did not require a communication link between distributed generation sources for implementation. The effect of the proposed controller on the stability of the system was demonstrated using the reduced-order small-signal model. To evaluate the performance and effectiveness of the proposed control strategy, it was implemented on an Islanded Microgrid consisting of three distributed generation units. The simulation results showed the proper performance and efficiency of the proposed method.

This paper applies a new state feedback control to a distributed secondary voltage and frequency control in an Islanded Microgrid. The problem is focused on the output consensus of the multi-agent systems, which is converted to a first-order dynamic system. The inverter-based distributed generations play as agents in the proposed control strategy. It is assumed that the distributed generators communicate through a communication network modeled by a directed graph (digraph). The distributed output consensus is used to design the secondary controllers. Such innovative controllers synchronize distributed generators' output voltages and frequencies to their reference values by a novel state feedback approach. Compared to the existing consensus protocols, the proposed method provides a different innovative solution to the secondary voltage and frequency control of Microgrids, which has a better response in case of communication failures. Finally, extensive and comparative simulations have been presented to verify the validity of the proposed control strategy and the system performance.

Power-electronic converters play a crucial role in the functioning of Microgrids. However, these converters, characterized by their low inertia, present a significant challenge to maintaining a consistent frequency in Islanded Microgrids. To address this issue, an innovative concept known as virtual inertia control has emerged as a promising solution for enhancing frequency stability in Islanded Microgrids. The virtual inertia control system does not perform well against disturbances and uncertainty related to Microgrid parameters. Therefore, to overcome these problems, it needs a suitable controller in its structure. In this paper, a linear quadratic regulator mode feedback controller based on deep learning is proposed to improve the performance of virtual inertia control in an Islanded Microgrid against disturbances and uncertainties in the system. The linear quadratic regulator controller uses measurements of system states and the integration of a deep network increases the accuracy and dynamic response of the feedback controller. This allows for fine-tuning of the control response, which exhibits significant robustness against uncertainty in system parameters and disturbances. To evaluate its effectiveness and compare it against alternative control approaches, comprehensive assessments have been conducted across multiple scenarios. The results indicate that the proposed method in the field of virtual inertia control surpasses previous approaches.

In this article, the control of interfaced converters of distributed generations (DGs) in order to improve Microgrid power quality with emphasis on voltage unbalance is considered. The control scheme of these converters is coordinated so that the DGs contribute to voltage unbalance compensation proportional to their rated power and by considering the residual capacity of each DG. The control structures presented in this article are classified into two categories: voltage_controlled mode (VCM) control scheme and current_controlled mode (CCM) control scheme. VCM units using capacitive virtual impedance contribute to voltage unbalance compensation, while in the control scheme of CCM units, a virtual admittance is implemented in order to compensate voltage unbalance with considering the residual capacity of the inverter. Also, VCM and CCM units contribute to reactive power sharing by droop and reverse droop control methods, respectively. Droop coefficients are adjusted considering the limited capacity of these inverters and the unbalance power. Finally, the results were then presented to show the effectiveness of the proposed control structure at different stages.

Microgrids as the "building blocks of smart grids" are predicted to play a major role in the future, as they are capable of improving the technical, environmental and economic fields in large power systems. This paper proposes a new formulation for the Islanded Microgrid reconfiguration in order to improve voltage stability index. The formulated problem is solved using harmony search algorithm. The increasing load ability index of Microgrids in the islanding mode is more important than the index of the grid-connected mode due to its operational limitations such as reactive power generation. In addition, this paper presented an improved indicator to estimate the voltage stability margin of Islanded Microgrid system based on the system's operational constraints both saddle node and limited induced bifurcations, called ascat_ VSIIMG. The cat_ VSIIMG which is validated by verified CPF method for IMGs is called the maximum load ability margin of IMG, lIMG. Performance and effectiveness of the proposed method are demonstrated on 33-bus test system. The results show that the implementation of appropriate IMG reconfiguration problem formulations will facilitate a successful integration of the Microgrid concept in power systems.

Increasing DC loads along with DC nature of distributed energy resources (DERs) raises interest to DC Microgrids. Conventional droop/non-droop power-sharing in Microgrids suffers from load dependent voltage deviation, slow transient response, and requires the parameters of the loads, system and DERs connection status. In this paper, a new nonlinear decentralized back-stepping control strategy for voltage control and load sharing of DC Islanded Microgrids is proposed. The proposed method is robust against the load variations and uncertainty in Microgrid parameters and has excellent dynamic and steady-state performance under different operating conditions. The major purpose of the proposed controller is to improve the transient performance of MG with load variations and constant power loads (CPLs). The local controller regulates the terminal voltage of DC-DC converter regarding the local quantities without needs to additional data of other system components. For simplicity, the proposed method is simulated with PSIM software on a DC Microgrid with two DGs. Different scenarios are studied to present the performance of the proposed method under different operating conditions. The results indicate the capability of the proposed method for voltage control and load sharing in DC Microgrids.