This study aims to introduce a new structure based on a nonlinear controller for controlling and analyzing the stability of the microgrids. In the proposed model, AC and DC resources and loads are located on two different sides. In addition, an AC/DC bidirectional interface converter is applied to supply loads by AC/DC sources. There are AC/DC products on both sides of the converter and each side can supply the load of the other side via a bidirectional interface converter and its load. Alternatively, an energy storage system is used for the system stability on the DC side. The nonlinear microgrid controller is designed to adjust the AC bus side frequency and the DC bus side voltage properly. In this structure, the coordinated optimal power exchange and precise regulation of control signals lead to constant improvement. Thus, system performance is improved. The results show that the proposed model is efficient for both reduction of the fluctuations and improvement of the system stability

In this paper, a virtual inertia control strategy based on linear feedback is presented that improves dynamic behavior of islanded dc microgrids interfaced with constant power loads (CPLs). In order to solve the stability challenges caused by low inertia and CPLs, the proposed control scheme is composed of a virtual capacitor and a virtual conductance. It is implemented in the inner loop control, i. e. current loop control to be fast enough emulating inertia and damping concept. In addition, the droop characteristic is modeled by using the virtual resistance which adjusts the steady-state response of the system. In this study a multi-level structure is considered, which comprises the source level, interface converter level, and common load level. In addition, an accurate small-signal model is used to investigate the stability of dc MG interlaced with CPLs, and then, an acceptable range of inertia response parameters is determined by using the root locus analysis. Performance of the proposed control structure is demonstrated through numerical simulations.

Coordinated control schemes are employed for both bidirectional DC/DC and AC/DC converters in this paper which are considered for connecting AC subgrid to DC one in hybrid AC/DC microgrids. Each subgrid consists of distributed generation units, which are photovoltaic systems working in maximum power point tracking mode, and local loads. Indeed, even though hybrid AC/DC microgrid has multiple merits over conventional microgrid, the interconnection of two different grids has some concerns such as complication, power management, and control. The coordinated control term in bidirectional AC/DC converter is formulated with regard to voltage of common bus and frequency of AC part. The common bus and DC subgrid voltages are utilized in the coordinated control term of bidirectional DC/DC converter. Modeling and simulating a hybrid AC/DC microgrid have been conducted in MATLAB/SIMULINK software. According to simulation results, the surveyed system can sustain its stability under the introduced coordinated control schemes. Hence, the proposed power management system based on coordinated control terms manage the power flow among DC and AC subgrids in addition to storage system.

In this paper, a new hierarchical robust control approach based on the combination of decentralized and distributed control is proposed for voltage control and power sharing in islanded DC microgrids by considering uncertainties and disturbances in the primary control loops and communication channels in the secondary layer. Uncertainties and disturbances are the main factors that can affect the stability of a microgrid. Unlike the previous methods, first by using a decentralized robust PI control structure based on Kharitonov's theory, the primary voltage control loop is robustly designed considering uncertainties and disturbances. By anticipating these changes and preventing them from entering the communication channel in the secondary layer, we compensate for the voltage deviations in the primary layer by using the distributed PI robust control structure. In addition to being simple and robust, the proposed controller is based on a new consensus and robust decentralized protocol, which has a higher convergence rate than the previous protocols and its performance is completely satisfactory under the conditions of uncertainties and large disturbances. Different simulations are performed in MATLAB/SimPowerSystems toolbox on a standard DC microgrid including four distributed generations and under different disturbances. The simulation results show the effectiveness of the proposed controller. In general, the proposed controller increases the reliability of microgrid by sending low data in communication channels.

In this paper, using the state-dependent Riccati equation (SDRE) technique, a suboptimal fault-tolerant control scheme is designed for a DC microgrid in the islanded mode. The objectives are the voltages control of the photo-voltaic cell, the battery, the capacitor bank, and the DC bus as well as on time fault detection. In the design procedure of the SDRE observer-controller, a nonlinear mathematical model is utilized to model the behavior of the microgrid in different working conditions. The performance of the microgrid is evaluated in the presence of uncertainties in its parameters and measurement noises. The obtained simulation results show that the proposed method is so effective in the fault detection, not detecting the disturbance instead of fault, and having a robust performance even in the presence of external disturbances.

Nowadays, the use of renewable energy sources has gained more attention due to their lower pollution ‎and cost compared to traditional fossil fuel generators. Microgrid (MG) structures are used for better ‎management of these resources. This article focuses on power control in three-terminal AC/DC hybrid ‎MGs. For this purpose, a network backup converter is used to improve power sharing and reduce power ‎quality disturbances. The components of the MG include distributed generation units, AC loads, DC ‎loads, energy storage system (battery), and parallel connecting converters. In the studied topology of ‎AC/DC hybrid MG in this article, there are two main converters: a grid-forming converter that acts as ‎an intermediary converter and is used to control the MG voltage, and a VSC converter that is located ‎between the DC link (including the DC MG and battery) and the AC MG. In this article, a control ‎system is implemented for a hybrid MG and simulations are performed in MATLAB software for ‎four different scenarios related to active and reactive power of the MG and loads. Simulation results ‎show that the energy management system and power control in the AC/DC hybrid MG have reduced ‎harmonics and improved system reliability in the MG.

DC microgrids have gained extensive attention in the recent years. In the islanded mode of operation power sharing between sources is required. The power sharing usually is provided by employing P-V droop characteristics while the voltage local property results in power sharing error. In this paper two decentralized approaches for resolving power sharing error are studied and compared. In the first approach, sources employ proper virtual resistance. In second approach, droop characteristics are realized in the Point of Common Coupling (PCC). It is shown that by using second approach, the voltage drop is reduced and equally the voltage quality is improved. It is discussed that the reason is bypassing the voltage drop associated with the sources output resistance in the second approach. Time domain simulations of a test DC microgrid are provided to verify the results.

In this paper a repetitive control (RC) approach to improve current sharing between parallel-connected boost converters in DC microgrids is presented. The impact of changes in line impedance on current sharing is investigated. A repetitive controller is designed and connected in series with current controller of the boost converters to control the switching signals such that by regulating of the output voltage of each converter, the circulating current is minimized. The performance of the proposed control strategy is validated through simulation.

Recently, environmental, economic and reliability oriented motivations facilitate cellular operation of smart power systems in the light of microgrid paradigm. Obviously, due to low inertia stack, high variety of generation units with various technical characteristics and different islanded and grid-connected operational modes, make the protection and control structures become new challenges. On the other hand, by integration of advanced metering and communication infrastructures in the microgrids, differential protection as the most reliable relaying logic, play a vital role in the protection structure of the microgrids. Owing to nature of occurring faults in the microgrids, high resistance faults have created a major problem in applying differential protection and directional fault. In this paper is used a new method for quick and accurate detection of fault in DC micro-grid, so that it detected internal fault from external fault, the performance of this new algorithm is also shown for increasing the fault resistance and compared with the conventional differential protection. The basis of new method is to use the Fault Component Current of the two sides of the study line and plot them on the  plan to identify the type of fault. In this paper simulation of internal and external fault in EMTP-ATP for different values of fault resistance is done and the implementation of the new algorithm and conventional differential protection is done in MATLAB. The simulation results indicate the accuracy and high speed of the operation of the new expressed method.

microgrids have played an important role in distribution networks during recent years. DC microgrids are very popular among researchers because of their benefits. However, protection is one of the significant challenges in the way of these microgrids progress. As a result, in this paper, a fault detection and location scheme for DC microgrids is proposed. Due to advances in Artificial Intelligence (AI) and the suitable performance of smart protection methods in AC microgrids, Recurrent Neural Networks (RNNs) are used in the proposed method to locate faults in DC microgrids. In this method, fault detection and location are done by measuring feeders current and main bus voltage. Furthermore, the performance of the proposed method is assessed in grid-connected and the islanded operation modes of the microgrid. The result has confirmed the efficiency of the proposed scheme. In this paper, MATLAB and DIgSILENT are used to design RNNs and DC microgrid simulation respectively.