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This paper endeavours a control scheme for optimal control of voltage and frequency of power inverter which relied upon distributed generation in cognitive microgrid using soft computational methods. It gives sound direction on how to control the active power flow, voltage-frequency regulation, and sharing of power among various components of MG. The classical voltage–frequency control strategy in parallel with the modern control method is well excavated in the present paper. Moreover, modulation techniques, variants of reference frames, power quality indices are covered blatantly. Thus, the paper gives fast insight and understanding to the engineers working in this niche area.

Summary Mass roll-out of plug-in hybrid electric vehicles (PHEVs) and significant penetration of renewable energy sources in distribution system play a major role in delivering low carbon environment. However, placing and utilizing these units randomly result in overloading, increased power loss, and reduced voltage profile. This paper responds to these technical challenges by using a strategic placement method for locating the distributed generation (DG) and the charging station (CS) of PHEVs in a multi-zone distribution system. For simultaneously scheduling of these units in each zone, the smart energy management framework is proposed in this paper. Apart from usual energy management constraints, this paper also incorporates the real-time constraints involving the capacity of PHEV batteries, the mobility pattern, and the power level of the charging infrastructure. The simulation studies are carried out for each hour of a day. To cope with this time constraint execution, particle swarm optimization algorithm-based approach is used. The proposed framework is tested in IEEE 33 and IEEE 69 bus radial distribution system. The obtained results imply that the presented energy management framework provides maximum profits for the vehicle owner, and meanwhile it fulfills preferences of the user in each zone simultaneously.

Microgrid implementation requires effective and efficient strategies for controlling the grid parameters. Various problems are encountered with the deployment of distributed generation in terms of reverse power, an imbalance between power generation and nonlinear load. This paper is focused on the existing controllers in terms of their merits and limitations. Furthermore, the state of the art of the local power distribution system especially on renewable energy resources along with energy storage methods is explored. Reliability and stability of power flow between sources and consumers via voltage source inverter are also considered. The emerging microgrid concept in islanding and grid-connected mode using different controller along with soft computing algorithm are presented. This paper gives the reader fast insight into the context of the controller and its application.

Islanding is a condition in which a microgrid or a portion of power grid, consisting of distributed generation (DG) sources, converter, and load, gets disconnected from the utility grid. Under this condition the DG sources in a microgrid must switch to a voltage control mode, in order to provide constant voltage to local loads. In grid connected mode, the microgrid works as current controller and injects power to the main grid, depending on the power generation and local load with suitable market policies. Providing constant voltage at a stable frequency with proper synchronization amongst each DG in a microgrid is a challenge. The complexity of such grid requires careful study and analysis before actual implementation. These challenges of microgrid are addressed using real time OPAL-RT simulation technology. Thus the paper describes an islanded microgrid with master slave controller for power balance, voltage/frequency regulation, and synchronization. Based on an advanced real-time platform named Real-Time Laboratory (RT-LAB), the impacts of the micro sources, load, and converters in an islanded microgrid is studied in this paper. The effectiveness of the proposed controller is analyzed through experimental results under balanced/unbalanced nonlinear loads condition.

The continuous development of microgrid’s technology creates favorable conditions for the access of distributed energy. Firstly, in order to consider the interests of the demand side and the power side, this paper presents a dual-layer optimal dispatching model of microgrid based on demand response. The objective of the first-layer optimization is to obtain the maximum load satisfaction and to optimize the load curve. The objective of the second-layer optimization is to make the microgrid system economical and environmentally friendly and to optimize the power utilization ratio. And a microsource control strategy based on the isolated microgrid is proposed, which can optimize the operation state of battery and improve the economy of the system. Finally, the Nondominated Sorting Genetic Algorithm-II (NSGA-II) is adopted to solve the optimal scheduling problem of the isolated microgrid. The simulation results indicate that the microsource scheduling strategy proposed in this paper can improve the operation economy and environmental conservation of the system. It can improve the reliability of microgrid power supply and reduce energy waste.

This paper discusses adding a spatial dimension to the design of community microgrid projects in the interest of expanding the existing discourse related to energy performance optimization measures. A multidimensional vision for designing community microgrids with higher energy performance is considered, leveraging urban form (superstructure) to understand how it impacts the performance of the system’s distributed energy resources and loads (infrastructure). This vision engages the design sector in the technical conversation of developing community microgrids, leading to energy efficient designs of microgrid-connected communities well before their construction. A new generation of computational modeling and simulation tools that address this interaction are required. In order to position the research, this paper presents a survey of existing software packages, belonging to two distinct categories of modeling, simulation, and evaluation of community microgrids: the energy infrastructure modeling and the urban superstructure energy modeling. Results of this software survey identify a lack in software tools and simulation packages that simultaneously address the necessary interaction between the superstructure and infrastructure of community microgrids, given the importance of its study. Conclusions represent how a proposed experimental software prototype may fill an existing gap in current related software packages.

Microgrid became one of the key spot in research on distributed energy systems. Since the definition of the microgrid is paradigm of the first time, investigation in this area is growing continuously and there are numerous research projects in this moment all over the world. The increased infiltration of nonlinear loads and power electronic interfaced distribution generation system creates power quality issues in the distributed power system. In this paper, a comprehensive survey on microgrid to improve the power quality parameters is taken as the main objective. Furthermore, the detailed investigations are explored in this paper for the enhancement of power quality issues with the help of an optimization technique, filters, controllers, FACTS devices, compensators, and battery storage.

Summary A MicroGrid (MG) can be operated in two main situations: grid-connected mode and autonomous mode. Power electronics (PE) are required to interface the DG units with the MG. This paper presents an optimal operating strategy and cost minimization scheme for an electronically weak-coupled MG. The major objective of the paper is to minimize the overall cost considering both the power system and the power electronics constraints in the two modes of operation. The paper presents steady-state models of power electronic converter/inverter systems for coupling distributed generation (DG) units to the grid based on Newton–Raphson method. A Matlab program is developed to represent the proposed algorithm. The program is tested in various network conditions and verified by applying it to an MG with three different DG units. The main contribution of the study is to ensure that the converter constraints are satisfied for both types using DC/AC inverter and AC/AC matrix converter. Copyright © 2013 John Wiley & Sons, Ltd.

Summary An essential part of the smart grid development is to connect the main transmission grid with microgrids that consist of distributed generation resources. The integration of microgrids and the transmission grid not only can improve the reliability of the power system operation but also can increase the competition of the electricity market. The effective trading between microgrid agents and a distribution company (DisCo) is consistent with the direction of smart grid development. Developing effective strategy to optimally schedule energy trading between microgrid agents and the DisCo will bring benefits to all parties and promote further development of distributed clean energy. By analyzing the operation characteristics of the electricity market with the addition of microgrid agents as new market participants, this paper presents a bi-level optimization model that aims to maximize the benefits of microgrid agents and a DisCo while considering transmission loss factors from various generators, duality role of the microgrid agents who can either buy electricity from the wholesale market at volatile prices or sell electricity into the market or to its local consumers. The model presented in this paper jointly optimizes the energy schedules of the microgrid agents and the DisCo and determines the bid/offer price at which the microgrid agent buys and sells electricity from/to the DisCo. At last, simulation results are provided to demonstrate the feasibility and application of the proposed two-level optimization model. Copyright © 2013 John Wiley & Sons, Ltd.

The use of green energy sources to feed DC microgrids is gaining prominence over traditional centralised AC systems. DC microgrids are characterised by the use of intermediate DC-DC converter which acts as power conditioning units. Hence, the choice of an appropriate DC-DC converter becomes significant as the overall system efficiency is strongly dependent on the converter’s performance. This paper proposes a novel high gain high power (HGHP) DC-DC converter for DC microgrid, which is of one of the significant step forward in the development of DC microgrids. The suitability of the proposed HGHP DC-DC converter is demonstrated by experimental tests of the 60V/1.1kV, 3kW converter; test results validate the converter’s suitability for DC distribution. A significant number of performance parameters of the proposed converter is compared with state of the art converter topologies demonstrating the superior capabilities of the proposed converter. This paper also portrays the potential benefits that could be reaped by trending towards DC instead of existing AC system. The advantages and challenges to be confronted in the foreseeable future while implementing sustainable DC microgrids are also highlighted. Finally, this paper encapsulates renewable energy fed DC microgrid system as an appropriate, technically feasible, economically viable and competent solution for efficiently utilising the sustainable energy sources.

Rwanda is an East African Community (EAC) nation with rapid and remarkable past development in different sectors and still with the ambitious targets and plans to be achieved in the coming years ahead. The government plans universal electricity access by 2024 with 52% grid connection and 48% off-grid connections. In the transport sector, the concept of electric vehicles has been initiated and started in order to contribute to the UN Paris agreement and decrease the reliance of the transport sector on gaseous fuels which are one source of air pollutants leading to climate change, premature deaths, and morbidity associated with poor air quality. With higher electricity demand than the generation of the Rwandan power grid, different energy strategies are being developed with the overall objective to achieve the targeted universal energy access. In order to overcome the aforementioned issue, this paper proposes an integration of solar PV microgrids for the satisfaction of electric vehicle (EV) technology in Rwanda. Using HOMER Grid software, a managed EV charging station is simulated to a grid connected solar PV microgrid with storage in order to assess the economic impact. The results show that the proposed technology can lower the levelized cost (LCOE) of electricity by 139.7%. This study can contribute to further research developments in either different perspectives related to the integration of distributed energy resources (DERs) with electric vehicles or studies related to affordable and environment-energy systems.

The frequency stability of multi-microgrids is easily affected by random load fluctuations and intermittent renewable resources. Additionally, geographically distributed generation equipment usually cannot adopt the “point-to-point” dedicated communication scheme to realize the information exchange considering the construction and computation costs. Therefore, a H∞-switching frequency control strategy for multi-microgrids based on edge computing framework is proposed in this paper. Firstly, an edge computing device is set up in each microgrid to collect the operation statuses of local participating equipment and generate the control instructions to ensure the real-time local frequency stability. Secondly, the multihop data transmission process in edge computing environment is described as a cascade queuing model. Then, the frequency control system in each microgrid is described as a switching model dependent on the varying time delays. Finally, via constructing a Lyapunov function, the constraints of the controller gains ensuring the H∞-damping performance for external load demands and the renewable outputs are derived at the same time. Simulation results show that compared with the traditional centralized control schemes, the peak value of our proposed edge computing framework is reduced by 32.51% compared with the traditional centralized control scheme. Moreover, under the same edge computing framework, the integral of absolute error (IAE) of frequency with the proposed H∞ control strategy can be reduced by 37.19% at least. Therefore, a better transient performance can be obtained with our proposed method.

In this paper, a constant frequency control strategy of a microgrid by coordinating energy router (ER) and energy storage system is proposed to solve the frequency fluctuation problem of microgrid, in which ER is the core of the energy management system. The interface converter of ER connected to the microgrid adopts the virtual synchronous generator (VSG) control, which adjusts the mechanical reference power in real time according to the state of charge (SOC) of the energy storage. The energy storage system adopts constant voltage and constant frequency (V/F) control to maintain the frequency and voltage stability of microgrid. The energy storage system with fast charge and discharge responds to the power fluctuation of the microgrid. ER maintains the stability of the energy storage capacity through bidirectional power regulation. When the energy storage system fails, the frequency and voltage droop characteristics of ER controlled by VSG will play a role in maintaining the stable operation of the microgrid. By the coordinating control strategy, the maximum efficiency of intermittent distributed energy can be guaranteed, and the stability, reliability, and grid-connection friendliness of the microgrid operation can be improved. Simulation results prove the effectiveness of the proposed control strategy.

In order to analyse the impact of renewable generation and load uncertainties on the economic operation optimization of the island microgrid, a multiobjective economic optimal dispatch model under uncertainty based on interval optimization is proposed in this paper. The mathematical model of distributed generation and the prediction model of wind speed and wave generation are established. The uncertainties of renewable generation and load are described by the interval mathematical method. On this basis, the interval multiobjective optimal dispatch model is presented. For the “battery disgusting” users on the island, the battery cost is regarded as a separate optimization objective, and a multiobjective optimization objective function to minimize the economic cost, battery cost, and pollution emission of the island microgrid is discussed. An island microgrid, composed of wind turbine, photovoltaic, wave energy generation, diesel generator, and energy storage system, is chosen as a case study. The NSGA-II algorithm is applied to solve the multiobjective optimal problem. The results for deterministic forecast data and load are analysed, and the optimal operation scheme is obtained by the improved multiobjective grey target decision-making method. The influence of renewable generation fluctuations ±10%, ±20%, and ±30% and the load fluctuations ±10% and ±20% on island microgrid operation optimization is discussed in detail, respectively. The relevant research results can provide a reference for formulating the operating scheme of the island microgrid.

The flexible operation of microgrids, along with the availability of distributed generation (DG) units, causes a variety of changes in short-circuit current levels, magnitudes, and directions, which has undesirable effects on the operation of protection systems. Conventional protection schemes use typical directional overcurrent relays (DOCRs) with limited operating capability, unable to respond to microgrid operations in the manner of short-circuit current changes. In this paper, a quaternary protection scheme implemented with dual-directional overcurrent relays (dual-DOCR) and a protection control strategy is developed for protecting against faults in microgrids, taking into account the existence of DGs and connection and disconnection of DG units. The optimal dual-DOCRs setting and coordination are formulated as an optimization problem solved by evolutionary programming to minimize the relay operating times. The proposed protection scheme is implemented with a centralized protection control system based on the smart grid concept to increase the adaptability of the dual-DOCRs, which have multiple relay setting groups in accordance with system state changes. The simulation case studies are performed using the IEEE 14-bus test system, which is modified as a meshed microgrid operation. Test scenarios, including possible operations of microgrids, DGs availabilities, and different fault events, are analyzed and discussed. The comparative studies and simulation results show that the proposed scheme provides efficient coordination between the primary and backup relays and increases the responsibility of the protection system, which can be observed from the significant reduction in the relay operating times, resulting in the enhancement of selectivity, sensitivity, and speed of microgrid protection systems.

The objective of this paper is implementation of multiagent system (MAS) for the advanced distributed energy management and demand side management of a solar microgrid. Initially, Java agent development environment (JADE) frame work is used to implement MAS based dynamic energy management of solar microgrid. Due to unstable nature of MATLAB, when dealing with multithreading environment, MAS operating in JADE is linked with the MATLAB using a middle ware called Multiagent Control Using Simulink with Jade Extension (MACSimJX). MACSimJX allows the solar microgrid components designed with MATLAB to be controlled by the corresponding agents of MAS. The microgrid environment variables are captured through sensors and given to agents through MATLAB/Simulink and after the agent operations in JADE, the results are given to the actuators through MATLAB for the implementation of dynamic operation in solar microgrid. MAS operating in JADE maximizes operational efficiency of solar microgrid by decentralized approach and increase in runtime efficiency due to JADE. Autonomous demand side management is implemented for optimizing the power exchange between main grid and microgrid with intermittent nature of solar power, randomness of load, and variation of noncritical load and grid price. These dynamics are considered for every time step and complex environment simulation is designed to emulate the distributed microgrid operations and evaluate the impact of agent operations.

Summary The power flow study is an exigency for planning, operation, and optimization of future smart microgrids. In this paper, an interior point-based power flow solution for balanced microgrids operating in islanded mode is presented. In the proposed method, the power flow problem is set up as a constrained interior-point optimization problem in which nonlinear power mismatch equations are iteratively solved without defining a slack bus. Unlike conventional power flow problems, the unknown frequency of the microgrid and droop equations for distributed generation units are also taken into account. Moreover, fixed, voltage-dependent, and frequency-dependent distributed loads are also considered. The computational efficiency of the proposed method is verified using two tools and tested with various case studies. The proposed method has a good convergence pattern and execution time for all types of distributed generation units and loads in islanded networks that are arbitrarily complex. Copyright © 2015 John Wiley & Sons, Ltd.

Summary Usually, distributed generations with natural energies bring negative effects to the utility grid. Microgrid with various power sources is able to eliminate these negative effects. A frequency domain-based method is proposed in this paper for configuration and control design of power sources in a grid-connected microgrid. First, the power sources are configured based on their frequency spectrum features. After that, the frequency domain-based power follow-up control is applied to the power sources, and the power at the point of common couple (PCC) is regulated to follow up a desired power value. Detailed theoretical analysis of the frequency domain-based method for configuration and power follow-up control of power sources are presented. Finally, a microgrid in a campus with multiple power sources is designed based on the proposed configuration method and control method. Frequency domain analysis and experimental results show that the power at PCC can be regulated to a desired value, i.e. the disturbances to the grid caused by loads and renewable resources in microgrid are successfully suppressed. Copyright © 2014 John Wiley & Sons, Ltd.

As renewable energy is widely integrated into the power system, the stochastic and intermittent power generation from renewable energy may cause system frequency deviating from the prescribed level, especially for a microgrid. In this paper, the load frequency control (LFC) of an island microgrid with photovoltaic (PV) power and electric vehicles (EVs) is investigated, where the EVs can be treated as distributed energy storages. Considering the disturbances from load change and PV power, an observer-based integral sliding mode (OISM) controller is designed to regulate the frequency back to the prescribed value, where the neural network observer is used to online estimate the PV power. Simulation studies on a benchmark microgrid system are presented to illustrate the effectiveness of OISM controller, and comparative results also demonstrate that the proposed method has a superior performance for stabilizing the frequency over the PID control.

Summary A microgrid can operate in two different operating modes, i.e. utility-grid connected mode or autonomous mode. In this paper, the operation of a microgrid with fully inverter-based renewable sources in transition from utility-grid connected mode to the autonomous mode is investigated. Energy storage device as a kind of buffering system might compromise microgrid autonomous operation due to the limited capacity; hence, available electric vehicles and responsive loads in the microgrid are used in primary frequency control upon separation from the utility grid. Secondary frequency control is performed by slow-response sources. In order to establish a readiness for upcoming disturbances, the state of charge of the energy storage device is held in a secure range by proper coordination and management of the electrical vehicles, responsive loads, energy storage devices and controllable microsources. The proposed control strategy is standalone and does not need any communication link in controlling the sources and loads. Copyright © 2014 John Wiley & Sons, Ltd.

Summary In a microgrid, the islanding condition occurs when the utility circuit breaker (CB) is opened. In this case, the microgrid is disconnected from the main grid. Therefore, the islanding condition can be detected by monitoring the variables that caused the utility CB to open. In this paper, the utility CB current is measured at the grid side, and the islanding condition is detected based on a feature extracted from the measured signal before the utility CB opening. Discrete wavelet transform is used to extract the features of the measured current, and then, the artificial neural network is trained in order to detect the islanding conditions based on the extracted features. Since the disturbances of distributed generation (DG) units or fault occurrence have no effect on the measured current, the proposed method is an effective one for islanding detection in distribution networks with high penetration of DGs. Copyright © 2014 John Wiley & Sons, Ltd.

Summary Industrial microgrids (IMGs) consist of factories with distributed energy resources (DERs) and electric loads that heavily rely on combined heat and power (CHP) systems. The new generations of IMGs are expected to also include renewable DERs and plug-in electric vehicles (PEVs) with different power ratings and charging characteristics. This paper proposes a profit-based security constrained unit commitment (PB-SCUC) formulation for IMGs with PEV charging and renewable DERs that includes both microgrid security and factories constraints as well as the PEV charging requirements. PB-SCUC will utilize the generators waste heat to fulfill thermal requirements and also consider the status of renewable DERs to decrease the overall cost of IMG. To demonstrate the effectiveness of PB-SCUC, detailed simulation results are presented and analyzed for an IMG consisting of 12 factories and 6 types of PEVs without/with photovoltaic generations operating in grid-connected and stand-alone modes. Copyright © 2014 John Wiley & Sons, Ltd.

Summary Industrial plants/commercial facilities with synchronous generation, seek reliable and continuous operation even at the time of grid outages. Thus, islanding detection methods have been proposed in the literature that can be used to change the operating mode of the employed distributed generators from grid-parallel to stand-alone. Among the few solutions previously presented for switching the control mode in the reverse event of reconnecting to the grid, the method presented in this paper is unique. This grid-reconnection detection technique is low cost, fast, and does not interact with the power quality of the island although it only uses one, locally measured, variable. The method implies processing of oscillatory modes in frequency signal and is independent of the autonomous island's boundary. The investigation also includes a discussion on similar event of merging of adjacent islands. Simulations confirm the successful discrimination between reconnection event and other switching/power quality events. Copyright © 2013 John Wiley & Sons, Ltd.

SUMMARY This paper proposes a new approach to distribution system named Three-wire Network (3-NET). Considering the integration of different distributed generation (DG) technologies as well as the diversity of loads, the idea of 3-NET is splitting a single power network into three qualitatively different networks: (i) a high quality direct current (DC) network; (ii) a conventional alternating current (AC) network; and (iii) a low quality DC network. By this configuration, the multi-stage conversion of energy from DG sources can be reduced, whereas loads can be supplied with different power quality and reliability levels as desired. In order to evaluate the potential benefits of 3-NET, the operational strategy is formulated in a market model; the reliability performance is investigated using Monte Carlo simulation and quantified in terms of interruption costs. In the case study, the proposed 3-NET is considered for integrating a certain amount of DG into a specific distribution system and then compared with another system approach: hybrid AC–DC microgrid. The simulation shows that although the operation costs can be slightly higher, the 3-NET shows a great improvement in reliability performance in comparison with the hybrid microgrid. Copyright © 2013 John Wiley & Sons, Ltd.

Summary In this paper, two-level decentralized optimization power dispatch control strategies are proposed in an islanded microgrid without communication network to ensure frequency security and economic benefit. First, the secondary-level decentralized optimization control strategy is designed only by using local measurement regarding frequency deviation. It is able to implement the optimal power dispatch for all dispatchable distributed generation units in a coordinated way in order to completely restore the system frequency with minimum operation cost. Then, the first-level decentralized droop compensation control strategy is designed to implement real-time optimal power sharing among all energy storage units in order to quickly compensate large supply–demand imbalance and ensure frequency security. Moreover, the proposed control strategies are proved to be able to meet the requirements of the “plug and play” operation in the absence of communication network. Simulation results verify the validity of the proposed method. Copyright © 2016 John Wiley & Sons, Ltd.