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Showing 25 results for Microgrid

A. Hajizadeh,
Volume 9, Issue 1 (3-2013)
Abstract

This paper presents modeling and control of a hybrid distributed energy sources including photovoltaic (PV), fuel cell (FC) and battery energy storage (BES) in a microgrid which provides both real and reactive power to support an unbalanced utility grid. The overall configuration of the microgrid including dynamic models for the PV, FC, BES and its power electronic interfacing are briefly described. Then controller design methodologies for the power conditioning units to control the power flow from the hybrid power plant to the unbalanced utility grid are presented. In order to distribute the power between power sources, the neuro-fuzzy power controller has been developed. Simulation results are presented to demonstrate the effectiveness and capability of proposed control strategy.
A. Zakariazadeh, Sh. Jadid,
Volume 10, Issue 2 (6-2014)
Abstract

Microgrid (MG) is one of the important blocks in the future smart distribution systems. The scheduling pattern of MGs affects distribution system operation. Also, the optimal scheduling of MGs will be result in reliable and economical operation of distribution system. In this paper, an operational planning model of a MG which considers multiple demand response (DR) programs is proposed. In the proposed approach, all types of loads can participate in demand response programs which will be considered in either energy or reserve scheduling. Also, the renewable distributed generation uncertainty is covered by reserve prepared by both DGs and loads. The novelty of this paper is the demand side participation in energy and reserve scheduling, simultaneously. Furthermore the energy and reserve scheduling is proposed for day-ahead and real-time. The proposed model was tested on a typical MG system in connected mode and the results show that running demand response programs will reduce total operation cost of MG and cause more efficient use of resources.
F. Namdari, M. Parvizi, E. Rokrok,
Volume 12, Issue 1 (3-2016)
Abstract

Integration of distributed generations (DGs) in power grids is expected to play an essential role in the infrastructure and market of electrical power systems. Microgrids are small energy systems, capable of balancing captive supply and requesting resources to retain stable service within a specific boundary. Microgrids can operate in grid-connected or islanding modes. Effective islanding detection methods are essential for realizing the optimal operation of microgrids. In this paper, a new passive islanding detection method is presented according to the change rate of DG’s voltage over active power index. This technique has been applied on inverter-based and synchronous-based microgrids. The efficiency of the proposed method is verified through a comprehensive set of simulation studies carried out in Matlab/Simulink.


E. Alizadeh, A. M. Birjandi, M. Hamzeh,
Volume 12, Issue 4 (12-2016)
Abstract

This paper proposes an autonomous and economic droop control scheme for DC microgrid application. In this method, a cost-effective power sharing technique among various types of DG units is properly adopted. The droop settings are determined based on an algorithm to individually manage the power management without any complicated optimization methods commonly applied in the centralized control method. In the proposed scheme, the system retains all the advantages of the traditional droop method while minimizes the generation costs of the DC microgrid. In the proposed method, all DGs are classified in a sorting rule based on their total generation cost and the reference voltage of their droop equations is then determined. The proposed scheme is applied to a typical DC microgrid consisting of four different types of DGs and a controllable load. The simulation results are presented to verify the effectiveness of the proposed method using MATLAB/SIMULINK software.


H. Shayeghi, A. Ghasemi,
Volume 12, Issue 4 (12-2016)
Abstract

Microgrids is an new opportunity to reduce the total costs of power generation and supply the energy demands through small-scale power plants such as wind sources, photo voltaic panels, battery banks, fuel cells, etc. Like any power system in micro grid (MG), an unexpected faults or load shifting leads to frequency oscillations. Hence, this paper employs an adaptive fuzzy P-PID controller for frequency control of microgrid and a modified multi objective Chaotic Gravitational Search Algorithm (CGSA) in order to find out the optimal setting parameters of the proposed controller. To provide a robust controller design, two non-commensurable objective functions are formulated based on eigenvalues-domain and time-domain and multi objective CGSA algorithm is used to solve them. Moreover, a fuzzy decision method is applied to extract the best and optimal Pareto fronts. The proposed controller is carried out on a MG system under different loading conditions with wind turbine generators, photovoltaic system, flywheel energy, battery storages, diesel generator and electrolyzer. The simulation results revealed that the proposed controller is more stable in comparison with the classical and other types of fuzzy controller.


M. Khalilzadeh, A. Fereidunian,
Volume 12, Issue 4 (12-2016)
Abstract

In this paper, a stochastic approach is proposed for reliability assessment of bidirectional DC-DC converters, including the fault-tolerant ones. This type of converters can be used in a smart DC grid, feeding DC loads such as home appliances and plug-in hybrid electric vehicles (PHEVs). The reliability of bidirectional DC-DC converters is of such an importance, due to the key role of the expected increasingly utilization of DC grids in modern Smart Grid. Markov processes are suggested for reliability modeling and consequently calculating the expected effective lifetime of bidirectional converters. A three-leg bidirectional interleaved converter using data of Toyota Prius 2012 hybrid electric vehicle is used as a case study. Besides, the influence of environment and ambient temperature on converter lifetime is studied. The impact of modeling the reliability of the converter and adding reliability constraints on the technical design procedure of the converter is also investigated. In order to investigate the effect of leg increase on the lifetime of the converter, single leg to five-leg interleave DC-DC converters are studied considering economical aspect and the results are extrapolated for six and seven-leg converters. The proposed method could be generalized so that the number of legs and input and output capacitors could be an arbitrary number.


A. A. Khodadoost Arani, B. Zaker, G. B. Gharehpetian,
Volume 13, Issue 1 (3-2017)
Abstract

The Micro-Grid (MG) stability is a significant issue that must be maintained in all operational modes. Usually, two control strategies can be applied to MG; V/f control and PQ control strategies. MGs with V/f control strategy should have some Distributed Generators (DGs) which have fast responses versus load changes. The Flywheel Energy Storage System (FESS) has this characteristic. The FESS, which converts the mechanical energy to electrical form, can generate electrical power or absorb the additional power in power systems or MGs. In this paper, the FESS structure modeled in detail and two control strategies (V/f and PQ control) are applied for this application. In addition, in order to improve the MG frequency and voltage stability, two complementary controllers are proposed for the V/f control strategy; conventional PI and Fuzzy Controllers. A typical low voltage network, including FESS is simulated for four distinct scenarios in the MATLAB/ Simulink environment. It is shown that fuzzy controller has better performance than conventional PI controller in islanded microgrid.


E. Alizadeh, A. Motie Birjandi, M. Hamzeh,
Volume 13, Issue 4 (12-2017)
Abstract

This paper proposes a decentralized control technique to minimize the total operation cost of a DC microgrid in both grid-connected and islanded modes. In this study, a cost-based droop control scheme based on the hourly bids of all participant distributed generators (DGs) and the hourly energy price of the utility is presented. An economic power sharing technique among various types of DG units is adopted to appropriately minimize the daily total operation cost of DC microgrid without a microgrid central controller. The DC microgrid may include non-dispatchable DG units (such as photovoltaic systems) and dispatchable generation units. Unlike other energy management techniques, the proposed method suffers neither from forecasting errors for both load demand and renewable energy power prediction modules, nor from complicated optimization techniques. In the proposed method, all DGs and the utility are classified in a sorting rule based on their hourly bids and open market price, and then the droop parameters are determined. The simulation results are presented to verify the effectiveness of the proposed method using MATLAB/SIMULINK software. The results show that the proposed strategy is able to be implemented in various operation conditions of DC microgrid with resistance to uncertainties.

S. Dolatabadi, S. Tohidi, S. Ghasemzadeh,
Volume 14, Issue 4 (12-2018)
Abstract

In this paper, a new active method based on traveling wave theory for islanding detection is presented. A standard power grid that combines a distributed generation source and local loads is used to test the proposed method. Simulations are carried out in MATLAB/Simulink and EMTP/rv which demonstrate fast response and zero non-detection zone (NDZ) of the method along with low perturbation.

S. M. Hoseini, N. Vasegh, A. Zangeneh,
Volume 16, Issue 2 (6-2020)
Abstract

In this paper, a robust local controller has been designed to balance the power for distributed energy resources (DERs) in an islanded microgrid. Three different DER types are considered in this study; photovoltaic systems, battery energy storage systems, and synchronous generators. Since DER dynamics are nonlinear and uncertain, which may destabilize the power system or decrease the performance, distributed robust nonlinear controllers are designed for the DERs. They are based on the Lyapunov stabilization theory and super-twisting integral sliding mode control which guarantees system stability and optimality simultaneously. The reference signals for each DER are generated by a supervisory controller as a power management system. The controllers proposed in this work are robust, have fast response times, and most importantly, the control signals satisfy physical system constraints. The designed controller stability and effectiveness are also verified using numerical simulations.

M. Sedighizadeh, S. M. M. Alavi, A. Mohammadpour,
Volume 16, Issue 3 (9-2020)
Abstract

Regarding the advances in technology and anxieties around high and growing prices of fossil fuels, government incentives increase to produce cleaner and sustainable energy through distributed generations. This makes trends in the using microgrids which consist of electric demands and different distributed generations and energy storage systems. The optimum operation of microgrids with considering demand-side management increases efficiency and reliability and maximize the advantages of using distributed generations. In this paper, the optimal operation scheduling and unit commitment of generation units installed in a microgrid are investigated. The microgrid consists of technologies based on natural gas that are microturbine and phosphoric acid fuel cell and technologies based on renewable energy, including wind turbine and photovoltaic unit along with battery energy storage system and plug-in electric vehicle commercial parking lot. The goal of the paper is to solve a multi-objective problem of maximizing revenues of microgrid operator and minimizing emissions. This paper uses an augmented epsilon constraint method for solving the multi-objective problem in a stochastic framework and also implements a fuzzy-based decision-maker for choosing the suitable optimal solution amid Pareto front solutions. This new model implements the three type of the price-based and incentive-based demand response program. It also considers the generation reserve in order to enhance the flexibility of operations. The presented model is tested on a microgrid and the results demonstrate the efficacy of the proposed model economically and environmentally compared to other methods.

M. Khajevand, A. Fakharian, M. Sedighizadeh,
Volume 16, Issue 3 (9-2020)
Abstract

Using distributed generations (DGs) with optimal scheduling and optimal distribution feeder reconfiguration (DFR) are two aspects that can improve efficiency as well as technical and economic features of microgrids (MGs). This work presents a stochastic copula scenario-based framework to jointly carry out optimal scheduling of DGs and DFR. This framework takes into account non-dispatchable and dispatchable DGs. In this paper, the dispatchable DG is a fuel cell unit and the non-dispatchable DGs with stochastic generation are wind turbines and photovoltaic cells. The uncertainties of wind turbine and photovoltaic generations, as well as electrical demand, are formulated by a copula-based method. The generation of scenarios is carried out by the scenario tree method and representative scenarios are nominated with scenario reduction techniques. To obtain a weighted solution among the various solutions made by several scenarios, the average stochastic output (ASO) index is used.  The objective functions are minimization of the operational cost of the MG, minimization of active power loss, maximization of voltage stability index, and minimization of emissions. The best-compromised solution is then chosen by using the fuzzy technique. The capability of the proposed model is investigated on a 33-bus MG. The simulation results show the efficiency of the proposed model to optimize objective functions, while the constraints are satisfied.

P. Bhat Nempu, J. N. Sabhahit,
Volume 16, Issue 4 (12-2020)
Abstract

The hybrid AC-DC microgrid (HMG) architecture has the merits of both DC and AC coupled structures. Microgrids are subject to intermittence when the renewable sources are used. In the HMG, since power fluctuations occur on both subgrids due to varying load and unpredictable power generation from renewable sources, proper voltage and frequency regulation is the critical issue. This article proposes a unique method for operating a microgrid (MG) comprising of PV array, wind energy system (WES), fuel cell (FC), and battery in HMG configuration. The control scheme of the interlinking converter (ILC) regulates frequency, voltage, and power flow amongst the subgrids. Power management in the HMG is investigated under different scenarios. Proper power management is accomplished within the individual subgrids and among the subgrids by the control techniques adopted in the HMG. The system voltage and frequency deviations are found to be minimized when the FC system acts as the backup source for DC subgrid, reducing the power flow through the ILC.

M. Keshavarz, A. Doroudi, M. H. Kazemi, N. Mahdian Dehkordi,
Volume 17, Issue 2 (6-2021)
Abstract

The droop control strategy is the most common approach for microgrids control but its application is limited due to frequency deviation following a load change. Complementary control strategy has then been proposed to solve the problem using a communication network. However, under this strategy, regular loads profile produces a continuous change of output power of all distributed generators (DGs) and their generation changes seem to be permanent. This also causes continuous data exchange between DGs through communication links. This paper shows the possibility of adapting the droop/isochronous control methodology used by synchronous generators in conventional power systems to provide frequency control and power balance to inverter-based distributed generation power systems. To this end, this paper presents a centralized complementary control framework for the management of power-sharing and sustaining frequency in its nominal range in microgrids using a hybrid droop-isochronous control system.  The proposed method is event-triggered based and communication between DGs is only needed when the output power of the isochronous generator exceeds its power limits. The method provides an efficient and reliable control system and has a simple concept, easy, and cost-effective implementation. Simulations in MATLAB/SimPower are performed on a typical microgrid under various conditions to evaluate the performance of the proposed controller.

A. Karimpour, A. M. Amani, M. Karimpour, M. Jalili,
Volume 17, Issue 4 (12-2021)
Abstract

This paper studies the voltage regulation problem in DC microgrids in the presence of variable loads. DC microgrids generally include several Distributed Generation Units (DGUs), connected to electrical loads through DC power lines. The variable nature of loads at each spot, caused for example by moving electric vehicles, may cause voltage deregulation in the grid. To reduce this undesired effect, this study proposes an incentive-based load management strategy to balance the loads connected to the grid. The electricity price at each node of the grid is considered to be dependent on its voltage. This guide moving customers to connect to cheaper connection points, and ultimately results in even load distribution. Simulations show the improvement in the voltage regulation, power loss, and efficiency of the grid even when only a small portion of customers accept the proposed incentive.

Shankarshan Prasad Tiwari, Ebha Koley,
Volume 18, Issue 4 (12-2022)
Abstract

In recent years, DC microgrid has attracted considerable attention of the research community because of the wide usage of DC power-based appliances. However, the acceptance of DC microgrid by power utilities is still limited due to the issues associated with the development of a reliable protection scheme. The high magnitude of DC fault current, its rapid rate of rising and absence of zero crossing hinders achieving reliable protection in DC microgrid. Further, the intermittency associated with the non-conventional distributed generators demands adaptiveness under varying weather conditions. In this paper, the above-mentioned issues are addressed by developing a bagging tree-based protection approach for a multi-terminal DC microgrid. The proposed scheme addresses the intermittency associated with renewable sources. It performs the functions of mode detection, fault detection/classification, and faulty section identification using local information of current and voltage signals only. The same avoids the communication network related drawbacks like data loss and latency.
 

Hamid Salarvand, Meysam Doostizadeh, Farhad Namdari,
Volume 18, Issue 4 (12-2022)
Abstract

Owing to the portability and flexibility of mobile energy storage systems (MESSs), they seem to be a promising solution to improve the resilience of the distribution system (DS). So, this paper presents a rolling optimization mechanism for dispatching MESSs and other resources in microgrids in case of a natural disaster occurrence. The proposed mechanism aims to minimize the total system cost based on the updated information of the status of the DS and transportation network (TN). In addition, the characteristics of the protection system in DS (i.e., relays with fixed protection settings), the constraints related to the protection coordination are examined under pre- and post-event conditions. The coordinated scheduling at each time step is formulated as a two-stage stochastic mixed-integer linear program (MILP) with temporal-spatial and operation constraints. The proposed model is carried out on the Sioux Falls TN and the IEEE 33-bus test system. The results demonstrate the effectiveness of MESS mobility in enhancing DS resilience due to the coordination of mobile and stationary resources.

M. Dodangeh, N. Ghaffarzadeh,
Volume 18, Issue 4 (12-2022)
Abstract

An intelligent strategy for the protection of AC microgrids is presented in this paper. This method was halving to an initial signal processing step and a machine learning-based forecasting step. The initial stage investigates currents and voltages with a window-based approach based on the dynamic decomposition method (DDM) and then involves the norms of the signals to the resultant DDM data. The results of the currents and voltages norms are applied as features for a topology data analysis algorithm for fault type classifying in the AC microgrid for fault location purposes. The Algorithm was tested on a microgrid that operates with precision equal to 100% in fault classification and a mean error lower than 20 m when forecasting the fault location. The proposed method robustly operates in sampling frequency, fault resistance variation, and noisy and high impedance fault conditions.

Mitesh Kumar, Shivam Shivam,
Volume 18, Issue 4 (12-2022)
Abstract

The idea of a microgrid is created by utilizing more diverse ac or dc distributed generation (DG) sources along with an energy storage system (ESS) and loads. The most efficient and reliable selection of ac and dc microgrids is a hybrid ac/dc microgrid. The hybrid microgrid largely overcomes the shortcomings of standalone ac or dc microgrids. A bidirectional interlinking converter (BIC) is utilized in the interface for controlling power flow between subgrids. In order to improve voltage and frequency regulation with effective power sharing, the BIC based on the proposed control scheme is implemented for power flow between ac and dc sub-grid in Islanding mode. The control scheme is modified based on conventional droop control with voltage and frequency variation in order to improve bus voltage and frequency regulation with effective power sharing for intermittent sources. The operation of the islanded hybrid ac/dc microgrid is performed with solar, wind, and energy storage system under variable generation and load conditions. In order to make robustness of the system, there are considered different cases for generation and load scenarios. In the transient state, the overshoot and settling time of frequency and voltage are improved, as well as the frequency and voltage regulations are found within the permissible limit in the steady state. Furthermore, the corresponding variations are shown in tabular form in the simulation result. The actual data of solar irradiance and wind speed have been taken from the National Renewable Energy Laboratory. The performance of the system is verified in MATLAB/Simulink environment.
 


Seyed Masoud Barakati, Farzad Tahmasebi,
Volume 19, Issue 3 (9-2023)
Abstract

Increasing the penetration of distributed generation (DG) systems in power systems has many advantages, but it also has problems, including interference with the proper functioning of the protection systems. This problem is severe in microgrid systems that contain many DGs. Overcurrent relays are one of the most critical protection equipment of protection systems. The DG sources significantly change the characteristics of fault currents and the protection designs as well as the coordination of overcurrent relays. This paper proposes a coordination method for directional overcurrent relays with dual adjustment to resolve the interference problem in the protection system of a microgrid in the presence of distributed generation sources based on the electronic power converter (inverter). This is done by considering the curve of different standard characteristics according to the IEC60255 standard in two operating modes, the grid-connected and islanded. A genetic optimization algorithm is used to reduce the total operating time of the relays. The simulation results verify the effectiveness of the proposed coordination method. The results show that the protection coordination scheme with dual adjustment relays and the use of combined characteristic curves can significantly reduce the operating time of the total relays.


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