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One of the main crises that the world will face is the over pollution of the environment due to the use of fossil fuels. This problem will be solved by replacing renewable energy sources (RESs). DC microgrids (DCMGs) provide the ability to exploit all the potential of RESs. But, high penetration of these sources reduces the inertia and damping of the DCMGs. Therefore, it makes DCMG vulnerable to fluctuations and disturbances. This challenge can be addressed by using distributed energy storage systems (DESS) in DCMGs and inertial simulations. To improve the inertia as well as to balance the charge/discharge of the DESS, the concept of a virtual supercapacitor based on the state of charge (SOC) is introduced. Under the proposed control strategy, DCMG inertia is provided and the SOC balance is maintained in charge and discharge mode. Due to the bidirectional power transmission capability, symmetrical structure and considering the protection purposes of dual half‐bridge converter (DHB) can be selected. A small signal has also been investigated to analyse the role of virtual inertia in stability. The simulation results in MATLAB/Simulink show the correct performance dynamics and high impact of the proposed scheme compared to conventional schemes. [ABSTRACT FROM AUTHOR]

With increasing energy demand, the use of renewable energy resources is increasing. Renewable energy sources require power electronic converters to get integrated into power grids. Multi‐terminal high voltage direct current (MT‐HVDC) systems are a promising solution for their grid integration. Using droop‐based controller strategies in power converter stations of MT‐HVDC grid, in addition, to providing power‐sharing, can support the frequency of the connected AC grids. However, power changes lead to direct voltage deviations, thereby disrupting the stability of the MT‐HVDC system. Here, a new control structure for the droop controller of the voltage source converter (VSC) controller is proposed which is named modified droop controller (M‐Droop). This method, in addition to power‐sharing, uses an appropriate control action to provide the required voltage stability. Here, analytical studies of the modified control strategy are reported. Moreover, through a developed MATLAB Simulink platform, its performance is verified in the events of transients, consisting of fault, variable load, and change in power generation. [ABSTRACT FROM AUTHOR]

High‐voltage direct current breaker is among the essential components of high‐voltage direct current grids. Such a breaker generally needs a direct current reactor to reduce the fault currents rate. However, direct current reactors have destructive effects on the multi‐terminal high‐voltage direct current grid dynamic stability, and in such a system, despite the variety of controllers, the system dynamics are highly sensitive to the operating point. Therefore, additional damping control will be needed. This paper proposes a modification to be applied to the traditional droop controller of high‐voltage direct current grids to cope with the influence of these large reactors, improving the direct voltage stability and decreasing power variations in the transient events by introducing a direct current power system stabilizer. The proposed method for direct voltage control has been investigated through the analytical model of the system. Stability improvement has been studied following the application of the proposed method by investigating zeros, poles, and frequency response analysis. Moreover, a method is proposed for optimal design and optimal placement of direct current power system stabilizer. The system analysis and time‐domain simulations demonstrate a decent damping improvement attained by the proposed method. All simulations and analytical studies are conducted on Cigré DCS3 test high‐voltage direct current grid in MATLAB/Simulink. [ABSTRACT FROM AUTHOR]

Direct voltage fluctuations due to the presence of relatively large DC reactors (as an essential part of HVDC breakers), lack of inertia, and unwanted frequency fluctuations in the AC side of HVDC grids, have major consequences on the stability of HVAC/HVDC grids. The use of the DC Power System Stabilizer (DC‐PSS) can damp and eliminate voltage oscillations caused by the presence of the DC reactors. However, DC‐PSS cannot address the issues of inertia and unwanted frequency fluctuations. A method to improve inertia is proposed here that can operate well with the droop controller, and DC‐PSS does not interfere with power‐sharing and does not interact with any of these elements. Since the presence of a droop controller in HVAC/HVDC grids associates with power and direct voltage, the method proposed here can improve direct voltage fluctuations by eliminating severe power peaks. Moreover, this method does not change the voltage level of the entire system, so there is no need to change the set‐points of controllers. In addition, all parameters of the controllers are tuned by an intelligent algorithm, and the Participation factor (PF) scheme is used to find the proper placement of the proposed controller. [ABSTRACT FROM AUTHOR]

Independence in energy generation, attention to environmental issues, limited fossil fuel sources, and easy access to renewable energy sources have led governments, industry, and engineering to use renewable energy sources for decades. Meanwhile, microgrids for residential, commercial, industrial, and military purposes are widely used using these resources. However, the use of these sources in microgrids is associated with the challenges of uncertainty and lack of inertia. Therefore, by using energy storage systems in DC microgrids, the mentioned challenges can be overcome by emulating inertia. The purpose of this paper is to present a virtual compounded DC machine (VCDCM). The governing equations of the compounded DC machine have been accurately studied and the desired characteristics of this machine have been used to emulate inertia through the control of the buck‐boost converter connected to the energy storage systems in the concept of VCDCM. Proposed scheme; in an islanded microgrid with maximum components and standards required; Simulated in the Simulink/MATLAB environment. The results obtained under different scenarios confirm the ability of the proposed scheme to stabilize the DC bus voltage. The magnitude of DC bus voltage deviation from the reference value when an error occurs has resulted in a significant reduction compared to conventional schemes. [ABSTRACT FROM AUTHOR]

This article presents a novel high-temperature superconductive (HTS) power flow controller and current limiter (PFCCL), which limits fault currents and manages power flow in the intended transmission line. The proposed device includes series HTS reactors, HTS controlling dc coil, recovery resistive coil, and power electronic switches, which protects the microgrid from the upstream ac grid, short-circuit faults, and it controls the power flow between a microgrid and the upstream grid. Performance of the proposed PFCCL is mathematically analyzed, utilizing MATLAB and Maxwell software, and then validated by laboratory scaled-down experimental setup. It is shown that the simulation results are in fair agreement with the developed experimental laboratory setup results. [ABSTRACT FROM AUTHOR]

This study focuses on the selection of the most effective location of direct current power system stabiliser (DC‐PSS) in multi‐terminal high‐voltage direct current (MT‐HVDC) grids that is applied to voltage source converter (VSC) to voltage stability enhancement and oscillation damping. Due to the adverse interaction between having multiple number of DC‐PSS, it is necessary to select the best location for installing DC‐PSS in MT‐HVDC grid. In this study, the participation factor (PF) method is used. This method assists to find which power converters are more sensitive and have a major impact on the instability of the entire system. In this approach, the whole of the system is modelled as a multi‐input multi‐output (MIMO) dynamic system. PFs related to each power converter are intended by the oscillatory mode sensitivity analysis against the components of the MIMO matrix of the system. The PF analysis determines which VSC station is more participating in the small‐signal instability of the system. In order to endorse the efficiency of the proposed method, time‐domain MATLAB simulations are conducted in Cigré MT‐ HVDC grid benchmark. [ABSTRACT FROM AUTHOR]

In this paper, an initial design and analytical electromagnetic field solution for Slotless and Dual Quasi‐Halbach (DQH) Permanent Magnet mover is proposed for reciprocating free piston alternator application. Utilizing presented analytical magnetic field solution, Air‐Gap magnetic flux characteristic, and generated voltage are estimated. Using 3‐D finite‐element method (FEM) proposed structure numerically investigated and obtained numerical results employed to confirm the derived analytical models. The analytical results are compared with FEM and show excellent agreement. In order to determine output voltage and power characteristics, the load testing has been performed by a resistive variable load. The obtained results from FEM analysis and analytical magnetic field solution show an enhancement in the proposed alternator performance compared with the alternator with Halbach magnetized configuration, by improving provided power. [ABSTRACT FROM AUTHOR]

Summary: A smart distribution system should be able to restore interrupted customers as quickly as possible after outages. By optimal allocation of switching and protective devices, it is possible to enhance the reliability and increase the restoration capacity of the loads after an outage. In this paper, by taking into account uncertainty in the load data, a novel practical method for the simultaneous planning of optimum location of switching devices including tie‐lines and remote‐control switches (RCSs), fault indicators, and cut‐out fuses is proposed. In this paper, a method for minimization of the costs associated with equipment investment and interruption cost has been proposed. Practical parameters such as geographical position and conditions of the understudy network and feeders, and the configuration and possible constraints of the real network from the experts' viewpoint, have been considered in this study. The actual characteristics of the network are extracted by utilizing the analytical hierarchical process (AHP), the geographic information system (GIS) data, and the event recording software. To optimize the problem, the multi‐objective nondominated sorting genetic algorithm II (NSGAII) is employed. The efficacy of the proposed method is proved through simulation of a real medium‐voltage (MV) feeder. [ABSTRACT FROM AUTHOR]