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Grid modernization and innovations in clean energy are leading to a rapid increase in the penetration of inverter-based resources (IBRs) like wind power and solar photovoltaic (PV) plants in the bulk power system (BPS). To study the implications on BPS dynamics and mitigate potential risks to grid reliability, the second-generation generic renewable energy system model has been developed earlier. However, this model has three modules with eighty-six user-defined parameters and eight control flags to facilitate the utility-scale solar PV plant operation in different control modes. It presents a major challenge to the transmission system planning engineers. There is a critical need to identify the key parameters of the dynamic model that are highly sensitive to grid events causing large-scale voltage and frequency disturbances. In this work, a sensitivity analysis based on modified Sobol method is proposed for identification of the key parameters in the utility-scale solar PV plant model. The total Sobol sensitivity index captures even the higher-order effects of the variations in the parameters. Validation of the identified key parameters was carried out on a modified IEEE 9-bus system and 200-bus synthetic grid using PSSE for plant-level control and local coordinated control operation of the solar PV plant.

The International Electrotechnical Commission (IEC) 62351-6 standard prescribes provisions to secure IEC 61850-8-1 generic object-oriented substation events (GOOSE) communications from cyber threats. The GOOSE authentication schemes recommended by IEC 62351-6 have shortcomings, such as long authentication-value computation times, large signature lengths, the usage of symmetric keys, and susceptibility to quantum computer attacks. To overcome these, this paper proposes the usage of the rainbow signature scheme (RSS), a quantum cryptographic method to secure GOOSE messages. The RSS offers fast signature generation and verification using asymmetric keys, making it very attractive to meet the time-latency and security requirements of the GOOSE protocol. The adaptation of the RSS cryptography method for its application to the GOOSE protocol is presented in this paper. The algorithms for key generation, signature computation and message verification are discussed in detail. A first-of-its-kind C library that incorporates security features within the GOOSE protocol in compliance with the IEC 62351-6–stipulated format, is developed. The superior features of the RSS in comparison with the other IEC 62351-6 security schemes are demonstrated.

The reactive power capability of distributed photovoltaic (PV) inverters could be exploited to mitigate voltage violations under high PV penetration in the distribution grid. Coordinating the reactive power dispatch of individual PV inverters to obtain desired voltage regulation performance is a major challenge. In this article, a decentralized method is proposed to enable PV inverters to autonomously regulate terminal node voltages. The proposed method minimizes the effect of a terminal node's reactive power contribution on the voltage profile of its respective parent-to-terminal node. This ensures that the interference between the voltage regulation of terminal nodes by individual PV inverters is minimized. The performance of the proposed decentralized scheme is verified by extensive powerflow simulations on the EPRI Circuit 24 test feeder in open-source distribution system simulation platform OpenDSS.

Faults in dc microgrids require quicker interruption than those in traditional ac power systems. This is due to the reduced stiffness of dc microgrids being powered by low inertia distributed energy resources interfaced through power electronic converters. For a high impedance fault, the limited magnitude of the fault current poses additional challenges in detection and identification of fault location in the system, with difficulty in distinguishing the fault condition from the normal operating condition. This article proposes a new cost-effective protection system for fast identification, selective isolation of short circuit and high impedance faults, and system restoration in such dc microgrids. It is achieved through proper coordination of source converters with intelligent three tie contactor switch units (ICU) and there are no solid-state circuit breakers in action. The high impedance faults are identified through multi resolution analysis of the locally measured current signals with discrete wavelet transform and K -nearest neighbor-based classifier at each source converter and contactor. The selectivity is achieved through adaptive resistance time curves set by the programmable relay units installed at each ICU node in the system.

Recently, prime-mover stalling phenomenon was observed in a synchronous generator-based distributed energy resource (DER) for large step load changes during experimental testing at the Consortium for Electric Reliability Technology Solutions Microgrid. It is found to highly impact the generator's survivability during transient overload conditions. The stalling occurs in synchronous generator-based DER because of a sustained imbalance between electrical load demand and mechanical power available from the prime mover, thus depleting the generator's stored kinetic energy. In particular, mechanical power capability of the prime mover and stored kinetic energy in the rotating mass are the causal factors. This article evaluates two different types of prime movers—reciprocating engine and combustion gas turbine—for the DER survivability. The characteristics of these two commonly used prime movers are investigated during transient overload conditions by simulation case studies using PSCAD/EMTDC software.

This study proposes a strategy for coordinated operation of networked microgrids (MGs), distributed energy resources (DERs), and volt-VAR control devices in the implementation of volt-VAR optimisation (VVO). The authors’ formulation is focused on implementing conservation voltage reduction, although it can be extended for any other VVO problems. They consider the voltage–power control modes of DERs contemplated in IEEE Std. 1547, namely, constant power factor, voltage–reactive power, active–reactive power, and constant reactive power. DERs are considered at the distribution network (DN) and within the MGs. The problem is formulated as a bi-level optimisation problem where the DN operator (DNO) is in the upper-level and each MG in the lower-level. The DNO and each MG are assumed to be players with their individual objective functions. Finally, they validate their formulation in two test systems: a 9-node system and a modified IEEE 33-node system. On average the proposed method can improve the efficiency of the grid by 4% compared to the economic operation scenario. The results of the study show that the different control modes of the DERs can have better performance depending on the objective of the VVO formulation. The findings of this study are compelling for the implementation of VVO in active distribution systems with networked MGs.

Inverter-based distributed energy resources (DERs) can supply high-quality ac power in a microgrid due to their fast dynamic response. To achieve high reliability in an islanded microgrid, they are normally operated as voltage-controlled sources. However, the net load supplied by voltage-controlled inverter-based DERs can exceed their rated capacity, particularly during their transition from the grid-connected operation mode. Therefore, a comprehensive analysis of the DER survivability for overload conditions is crucial. Several experimental tests were conducted at the Consortium for Electric Reliability Technology Solutions Microgrid Testbed on the prime-mover powered inverter-based DER for learning about its survivability during overload conditions. In this paper, a thorough investigation of the inverter-based DER's survivability is carried out based on the prime-mover stalling phenomenon. Analytical expressions are derived for key design parameters of load-shedding algorithms, such as time-to-threshold frequency, maximum time delay , and maximum survivability time . The theoretical estimates are validated with the results obtained from the experimental testing. Furthermore, the minimum load-shedding estimate is determined for any prime-mover powered inverter-based DER to survive a transient overload condition.

Converter-interfaced wind turbines (WTs) can contribute to inertial frequency regulation through appropriate control of the converter interface. The kinetic energy (KE) of the WT rotor blades is the transient power reserve for inertial frequency support. This work demonstrates that the partial loss of power extracted from the wind when the WT decelerates to release its KE into the network restricts the maximum deviation of the WT rotational speed from the Maximum Power Point (MPP). For higher amount of transient deviation from the MPP, the WT is found to be susceptible to instability. These insights are drawn from Lyapunov's theory for the robust stability of non-linear dynamic systems, applied to the converter-interfaced WT system. The state-space equations governing the operation of the system around the MPP, and modeling of the wind power output are presented. Further, this work quantifies the stability-constrained maximum allowable deviation from the MPP speed, and presents a formulation using Lyapunov's methods to compute this quantity. The robust stability limit provides insights for designing the inertial frequency support contribution of the WT. For this, a control method that uses a virtual synchronous generator (VSG) control loop in the converter interface is presented.

Inter-substation Generic Object Oriented Substation Events (GOOSE) communications that are used for critical protection functions have several cyber-security vulnerabilities. GOOSE messages are directly mapped to the Layer 2 Ethernet without network and transport layer headers that provide data encapsulation. The high-status-number attack is a malicious attack on GOOSE messages that allows hackers to completely take over intelligent electronic devices (IEDs) subscribing to GOOSE communications. The status-number parameter of GOOSE messages, stNum is tampered with in these attacks. Given the strict delivery time requirement of 3 ms for GOOSE messaging, it is infeasible to encrypt the GOOSE payload. This work proposes to secure the sensitive stNum parameter of the GOOSE payload using systematically encoded polynomial codes. Exploiting linear codes allows for the security features to be encoded in linear time, in contrast to complex hashing algorithms. At the subscribing IED, the security feature is used to verify that the stNum parameter has not been tampered with during transmission in the insecure medium. The decoding and verification using syndrome computation at the subscriber IED is also accomplished in linear time.

Battery energy storage (BES) has become very attractive to electric utilities due to its promising frequency response characteristics. Its fast response under disturbances is particularly appreciated, that is, the BES can take faster actions than traditional synchronous generators (SG) during abrupt load changes. This paper presents a dynamic analysis of an islanded mixed energy source microgrid, containing one BES and one synchronous generator based distributed energy resource. The dynamic model of voltage source converter (VSC) controller is developed, considering distributed droop control scheme. Besides, to track the dynamic behaviors of the system, an extended Kalman filter (EKF) algorithm is employed to derive dynamic state estimation (DSE). Case studies demonstrate the merit of BES in terms of absorbing the abrupt load changes. In addition, the effectiveness of proposed EKF based DSE strategy is validated, as the dynamic behaviors of system state are accurately tracked despite the existence of process and measurement noises.

The research on ship electrification is gaining renewed interest to take advantage of the numerous benefits offered by microgrids in the development of an all-electric ship (AES). A key aspect of the AES is in planning of cost effective and resilient shipboard power system (SPS). The integration of energy storage system (ESS) in SPS is found to help achieve this goal. An ESS can improve the fuel economy of diesel generators by regulating their load demand and provide emergency power promptly whenever necessary. This article proposes a planning strategy for sizing and siting of a special ESS integration configuration, distributed cloud ESS (DCESS), in the SPS. While the aim of DCESS sizing is minimizing the total cost of SPS, the objective of DCESS siting is to enhance the resilience of SPS. By stochastic programming, the optimal solution with respect to representative operating conditions and fault scenarios is obtained. The proposed DCESS configuration would facilitate easy power exchange among the electrical zones. A comparison with the conventional ESS configuration is presented and the benefit of DCESS configuration on resilience enhancement is demonstrated.

Power distribution infrastructure is undergoing a major transformation towards a more secure, flexible and resilience network, and microgrids comprising distributed energy resources are believed to facilitate this goal. In this paper, we explore and develop a market mechanism to enable a transactive energy framework among microgrids to provide an alternative market operation strategy. Specifically, the proposed market framework enables peer-to-peer power trading among microgrids to offer the microgrids an alternative channel to sell their surplus power. The major benefit of promoting the proposed framework is to facilitate mutual support among microgrids during the main grid outage, thus enhance the overall resilience of the system. An optimization model based on equilibrium problem with equilibrium constraints framework has been developed to formulate the gameplay among various microgrid participates in the transactive energy market. In addition, we adopt the data from a real-world distribution system located in Medellin, Colombia to demonstrate the merits of proposed framework. The numerical studies indicate that the unserved energy index during main grid outage reduces by 85.6% if the proposed strategy is applied, which validates the value of the strategy in enhancing system resilience.

Resilience of electricity grids to rare but severely disruptive events, such as natural disasters, has emerged in recent years as an important aspect in power system planning. Development of resilience-oriented techniques are needed due to the limitations of reliability-oriented methods in addressing large unexpected outages. This article presents a novel decision analysis approach to enhance the resilience of a power distribution system by leveraging the distributed nature of solar photovoltaic (PV) and battery energy storage system (BESS) resources. The proposed decision-making framework uses an analytic hierarchy process to evaluate different possible allocations of PV and BESS resources to load buses for multiple contingencies based on resilience enhancement and cost. Each allocation plan provides the size of PV arrays and BESS units to be installed at each bus within the distribution system. A deterministic formulation ranks line outage scenarios based on unserved load. The tradeoff between cost and resilience is modeled via cost-effectiveness analysis (CEA) that indicates the preferability of each allocation plan. The main contribution of this article is the development of an adaptable and computationally feasible decision support framework to determine cost-effective configurations of PV arrays and BESSs for mitigating the effects of power line outage contingencies. To evaluate the proposed framework, a case study is carried out on the IEEE 33-bus radial distribution system. The results show that the proposed method can offer effective guidance to the planner for making informed investment decisions and achieving cost-effective resilience enhancement.

This paper investigates the effect of uncertainty in the allocation of photovoltaic (PV) generation, solar irradiance, and its impact on the power flow in a distribution network. The solar irradiance available in the National Renewable Energy Laboratory Resource Data Center is clustered into two states: high and low irradiance defined by a threshold. The uncertainty is modeled based on Non-Gaussian distribution, obtained using kernel density estimation. This estimation aids in achieving the probability density function and cumulative distribution functions of the solar irradiance. Moreover, the load demand, wind speed, and generator location are modeled according to Gaussian, Weibull, and discrete uniform distribution functions, respectively. As a part of probabilistic power flow, the backward/forward sweep method is used to solve each scenario of the Monte Carlo simulation. The proposed framework is applied to the 33-node test system considering three different test cases. The first case considers deployment of PV systems in three microgrids of the electric grid, and the other two test cases analyze different levels of penetration of randomly allocated PV and wind power systems. At the end, the results indicate potential reverse power flow through certain branches of the grid, and the renewables have a major impact on the system.

A synchronous generator-based distributed energy resource (DER) is commonly employed in microgrids due to its low cost and simple controls. However, there are many challenges to the DER operation when it is sized for supplying the critical loads alone in a microgrid. In particular, the DER would experience an overload condition during the microgrid transition from grid-connection to islanded operation, when the noncritical loads are also supplied momentarily. Therefore, it is very important to have a clear understanding on the survivability of a synchronous generator-based DER for transient overload conditions. Recently, experimental tests on survivability of the DER were carried out in the Consortium for Electric Reliability Technology Solutions Microgrid Testbed at American Electric Power. In this paper, an in-depth analysis of the synchronous generator-based DER operation during transient overload conditions is presented. The key relationships governing the system dynamic behavior of synchronous generator-based DER are analyzed to design the load shedding scheme for its survivability. Several case studies are illustrated to demonstrate the validity of the proposed load shedding method.

Power electronic converter-interfaced distributed energy resources (DERs) are being increasingly deployed for achieving high energy efficiency, power quality, and flexibility of power system operation and controls. They facilitate access to a wide array of energy sources, including renewables, fuel cells, microturbines, variable speed engine-generator sets, etc. However, recent tests carried out at the Consortium for Electric Reliability Technology Solutions (CERTS) Microgrid have indicated that their deployment in the mixed source microgrid can cause a cascading collapse during extreme events. To investigate the problem, simulation models of two types of DERs are developed in PSCAD/EMTDC software and validated with the experimental test results. Furthermore, the validated models are used to study a cascading collapse problem in a large-scale mixed source microgrid on the benchmark IEEE 33-bus test system. In this paper, three alternative techniques are evaluated to prevent the cascading collapse in the large-scale microgrid caused by fast-acting inverter-based DERs.

The shipboard power system of an all-electric ship can be characterized as an isolated microgrid system. To achieve resilient, cost-effective and privacy-preserved operation of the shipboard power system, a novel energy management strategy is proposed in this paper. Currently, a master controller is required for energy management. However, such a centralized energy management strategy suffers from numerous disadvantages. Therefore, a modified nested energy management method is proposed to preserve privacy and run the microgrid system in a distributed manner for plug-and-play operation. Furthermore, the system resilience is enhanced against energy deficiency by reserving more in the energy storage system. This is achieved by a distributed algorithm, known as alternating direction method of multipliers (ADMM), to obtain the solution of an optimization problem with contradicting objectives. Simulation results are presented to demonstrate the benefits of proposed energy management system.

Power electronics for the utility interface of distributed energy resource (DER) offers many benefits in the electric grid operation through flexibility of the DER controls. Energy from various generation sources including renewables can be efficiently delivered to the consumers with high power quality and reliability. However, mixed source microgrids comprising both inverter- and synchronous generator-based DERs are susceptible to collapse, particularly when the system operates in the islanded mode. This paper presents robustness studies on microgrids from a qualitative point of view, borrowing features from ecological systems that are highly robust. The interrelationships between ecological species translate into the dynamic behavior of DERs, affected by their sizes and locations within the grid. The advantage of such qualitative analysis over traditional quantitative viewpoint is it explicitly identifies the nature of interactions and interconnections between the subsystems as beneficial or detrimental to stability. From the robustness studies, the best possible microgrid configurations are determined for IEEE 33-bus system having a mix of inverter-based DERs and synchronous generator-based DERs. Furthermore, all possible microgrid cluster formations are studied for finding the most robust microgrid islanding strategies.

Microgrids with distributed energy resources are being favored in various communities to lower the dependence on utility-supplied energy and cut the CO2 emissions from coal-based power plants. This paper presents a co-optimization strategy for distributed energy resource planning to minimize total annualized cost at the maximal fuel savings. Furthermore, the proposed scheme aids the community microgrids in satisfying the requirements of U.S. Department of Energy (DOE) and state renewable energy mandates. The method of Lagrange multipliers is employed to maximize fuel savings by satisfying Karush-Kuhn-Tucker conditions. With the Fourier transform and particle swarm optimization, the right mix of distributed energy resources is determined to decrease the annualized cost. A case study to test the proposed scheme for a community microgrid is presented. To validate its effectiveness, an economic justification of the solution and its comparison with HOMER Pro are also illustrated., 10 pages, 7 figures, 8 tables, journal

Microgrids with increased penetration of renewables experience serious challenges due to large frequency excursions under power system disturbances. An energy storage system can provide frequency regulation, but the effectiveness depends on whether it is configured for the grid-forming or grid-following mode of operation. For this purpose, two critical parameters are studied for frequency regulation in distribution systems; first, the initial rate-of-change-of-frequency (ROCOF), and second, the minimum value of frequency, also known as frequency nadir, following a load change. The aim of this paper is to identify analytical methods for accurately calculating the frequency parameters like ROCOF and frequency nadir. Reduced-order models are developed to determine the frequency deviation against power system disturbances. The results are verified against simulation models validated by testing at the Consortium for Electric Reliability Technology Solutions Microgrid test bed.

Microgrids are transforming the traditional way of meeting energy demands at several communities and establishments. They offer new avenues to achieve a carbon free, reliable, and resilient electric grid. With the advancements made in the power electronic converter technology, the DC microgrids are gaining popularity nowadays. This paper proposes a load dispatch model for energy management system (EMS) in a DC microgrid comprising solar (PV), wind power, diesel generator, and battery energy storage system. In the grid connected mode of operation, it facilitates a two way transaction of power between the microgrid and utility. The EMS with proposed model gave significant cost savings for the microgrid owner. In particular, application of the genetic algorithm based method resulted in optimal operation and maintenance costs as against the pattern search algorithm based method.

Faults in dc microgrids require quick interruption than in traditional ac power systems. This is due to the reduced stiffness of dc microgrids being powered by low inertia DERs interfaced to through power converters. For a high impedance fault, the limited magnitude of the fault current poses additional challenges in identification and locating the faults in the system, with difficulty in distinguishing the fault condition from the normal operating condition. This paper focuses on designing a cost-effective protection system for fast identification, selective isolation of high impedance faults and system restoration in such dc microgrids through proper coordination of source converters with sectionalizers, and with no solid state circuit breakers in action. The high impedance faults are identified through multi resolution analysis of the locally measured current signals with discrete wavelet transform and K-nearest neighbor based classifier at each source converter and contactor. The selectivity is achieved through adaptive resistance time curves set by the controllers installed at each contactor in the system.

This paper presents a novel modified Viterbi algorithm to identify the optimal distribution system restoration plan for improving the grid resiliency. In the proposed algorithm, the switching operations performed for system restoration are the states with the minimum bus voltage being seen as the cost metric for each state and the extent of load recovery as the observed event. When full load recovery is spotted, the dynamic programming algorithm stops, thereby giving the least number of switching pairs necessary for system restoration. Moreover, an improved flexible switching pair operation is employed to maintain the radial nature of distribution system. Several case studies are presented for verifying the performance of the proposed strategy. Multi-fault conditions are considered in testing the system restoration scheme on 33-bus and 69-bus distribution systems. Furthermore, the effects of integrating distributed energy resources and microgrid systems are analyzed., Comment: 10 pages, 11 figures, 7 tables, journal

Village or community microgrids are being encouraged to improve resiliency against unexpected events. They also improve energy efficiency and reliability of power delivery to critical loads. However, many protection challenges exist in making the shift away from conventional distribution systems. In this paper, a multilayered protection strategy is presented for developing a community microgrid in a village within the 69-bus distribution system. The proposed strategy is verified by simulation studies in MATLAB/Simulink against various fault conditions. A comparison between the proposed strategy and existing distribution protection schemes is also provided.

For a microgrid with a mix of distributed energy resources (DERs), major challenges on its survivability are found in the islanded condition. In particular, a sudden loss of generation or a large and fluctuating load could force the microgrid to operate near its capacity limits. Such a situation can cause a cascading collapse of the mixed-source microgrid, even when the load demand is within the system's power rating. This condition was observed during several tests carried out at the Consortium for Electric Reliability Technology Solutions Microgrid Test Bed. This paper analyzes the root causes behind the collapse. It highlights that the capacity of a low-inertia system to support load changes is contributed by faster responding DERs initially. Therefore, the microgrid is particularly susceptible if the faster responding DERs do not have adequate reserve margin. Two control methods are evaluated for providing safeguards to these DERs and prevent the system collapse.

Inverter-based distributed energy resources (DERs) facilitate flexible operation and control in a microgrid. To achieve high power quality, the inverter-based DERs are typically controlled as voltage sources. However, during changes in the load or microgrid operation mode, the DERs with regulated voltage can exceed their capacity. Therefore, it is crucial to analyze in-depth their survivability for overload conditions. Recently experimental testing of a prime-mover powered inverter-based DER was carried out at the Consortium for Electric Reliability Technology Solutions (CERTS) Microgrid Testbed. This paper presents the results obtained from experimental testing. A comprehensive analysis of the survivability of inverter-based DERs is carried out for transient overload conditions in a microgrid.

Industrial power systems in the mining and metal industries typically comprise several large and fluctuating loads, such as crushers, excavators, shovels, and steel mills. Flexible distribution of energy and storage resources (FDERS) is a proposed new framework for reliably regulating the quickly varying loads supplied by a network of multiple smaller-rated distributed energy resources (DERs), especially when power from the main grid is not available. It was inspired by the cooperative V-shape formation of flocks of birds and the peloton/echelon formation of cycling racing teams for extending their endurance limits. Similar ideas applied to integrating DERs can extend sustainability through increased resource lifetime, optimal energy storage deployment, enhanced controllability, and improved system robustness.

This paper presents protection strategies for a medium-voltage dc (MVDC) microgrid at a remote area mine site. The microgrid is operated to provide high power quality and reliability to sensitive loads and to improve the energy efficiency of the mining equipment. In the MVDC microgrid, various local distributed energy resources have been used, including photovoltaic arrays, wind turbines, a fuel-cell stack, an energy storage system, and mobile diesel generators. For the protection of transmission lines, a communication-based differential protection scheme with solid-state electronic relays is employed to isolate the faulted part of the MVDC microgrid. This is further reinforced by dc overcurrent protection as a backup. Earlier research work had neglected the backup protection for dc systems. In addition, communication-based dc directional overcurrent protective relays are used for both source protection and load protection to support a bidirectional power flow. MATLAB/Simulink modeling and simulation results are presented and discussed to illustrate the proposed system's dependability and security.

Industrial microgrids functioning under islanded mode of operation are often subjected to large and fluctuating demands from loads such as crushers, excavators, and steel rolling mills. This paper studies the supercapacitor (SC) cycle life when multiple small rated but distantly located distributed energy resources are supplying a cement plant crusher-conveyor load in the islanded operation of the microgrid. Each DER consists of a fuel cell (FC) supplemented with a SC. After having carried out extensive modeling, simulation, and analysis, this paper demonstrates that the SC cycle life can be equalized by employing the cooperative framework of flexible distribution of energy and storage resources.

Multiphase induction machine offers many advantages over the conventional three-phase machine, like lower harmonics, reduced torque pulsation amplitude while increasing its frequency, decreased phase current, and cutting down power loss. It is particularly useful in the emerging heavy-duty and off-road vehicle applications. In this paper, a control strategy for multifunction nine-phase induction machine is proposed to increase the maximum speed without sacrificing the maximum torque. Another advantage of this machine drive system is lower voltage and current requirements. With electric pole change, the induction machine can reduce mutual inductance at high speeds. Due to lower mutual inductance, the back EMF is lower and a large dc-link voltage is not necessary at high speeds. This helps in lowering the dc-dc power conversion requirements. Moreover, the conduction loss is also reduced with the decrease in phase current, thereby cutting the costs of cooling. The proposed park inverse transformation is elaborated for multiphase condition. Simulation results from MATLAB/Simulink are displayed first to illustrate the effectiveness of control strategy. The proposed nine-phase induction machine was tested on a Caterpillar off road vehicle and the brief performance evaluation of the system-level benefits is also presented in this paper.

This paper presents studies on improving the robustness of shipboard dc hybrid power systems. The shipboard power system can be regarded as an islanded microgrid. The objective, in particular, is to reduce the load curtailment when generator failures take place in the islanded microgrid. By applying the basic unit commitment (UC) operation model, the loads can be fully supplied during normal condition. However, a portion of the loads has to be shed if any generator fails. Two approaches are proposed to mitigate the loss of load during and after fault. They are developed by modifying the UC models. These approaches are evaluated for reducing load curtailment under loss of generation. Selected case studies indicate encouraging results that the loss of load can be reduced during and after generator failure. For carrying out the case studies, the optimization model is built on General Algebraic Modeling System (GAMS) platform.

Community microgrids offer many advantages for power distribution systems. When there is an extreme event happening, distribution systems can be seamlessly partitioned into several community microgrids for uninterrupted supply to the end-users. In order to guarantee the system reliability, distributed energy resources (DERs) should be sized for ensuring generation adequacy to cover unexpected events. This paper presents a comprehensive methodology for DERs selection in community microgrids, and an economic approach to meet the system reliability requirements. Algorithms of discrete time Fourier transform (DTFT) and particle swarm optimization (PSO) are employed to find the optimal solution. Uncertainties of load demand and renewable generation are taken into consideration. As part of the case study, a sensitivity analysis is carried out to show the renewable generation impact on DERs' capacity planning., Comment: 5 pages, 6 figures, 1 table, 2017 IEEE Power & Energy Society General Meeting. arXiv admin note: substantial text overlap with arXiv:1708.01025

The advent of microgrids paved the way for energy decentralization and self-sufficiency among consumers. Reciprocating engine-driven synchronous generators (also known as gensets) are one of the most commonly found distributed energy resources (DERs) installed in a microgrid. A key concern in microgrid operation is the frequency regulation, especially when it is islanded from the main grid. In recent years, the inverter-based DERs have witnessed huge growth. When fast-responding inverter-based DERs are working in parallel with the slow-acting gensets within the islanded mixed source microgrid, many challenges exist in coordinating their operation. In particular, an inverter-based DER is susceptible to collapse due to its large transient loading and this can bring down the entire system. This paper investigates load sharing and proposes new techniques for improved frequency regulation in an islanded mixed source microgrid. An improved coordination scheme between DERs is presented in this paper by accounting for their inertial and governor response characteristics. The unequal transient load sharing between gensets and inverter-based DERs is redistributed to prevent system collapse as well as achieve desired frequency regulation. For dealing with extreme scenarios, a smart load shedding scheme is integrated into the coordinated operation of DERs.

Careful design and planning is essential for successful integration of energy storage system (ESS) in a shipboard dc hybrid power system. An optimization model for resiliency enhancement and total cost reduction is proposed in this paper. The resilience of a shipboard power system with and without ESS are evaluated by means of resiliency index values under fault conditions. Furthermore, the influence of ESS on total cost is analyzed quantitatively. A detailed design of ESS is carried out, and optimal ESS configurations with different device combinations for various requirements are determined. Both single-node static and dynamic planning strategies are evaluated and the principles of planning strategy selection are discussed. Several key results are presented from the optimization model, built on General Algebraic Modeling System (GAMS) platform. Simulation results show significant improvement from the proposed design and planning of ESS on shipboard dc hybrid power system.

Reciprocating engine driven generator sets (or “gensets”) are a leading class of distributed energy resources (DERs) from the low kilowatt up to hundreds of kilowatt ratings. Natural-gas-based DERs are more likely to be favored by both industries and utilities in the near future because of their low cost due to the newly found shale deposits at many places in the world. The DERs such as gensets when operating under islanded conditions are susceptible to stalling and can bring down the entire industrial power system, particularly if they are loaded beyond 80% of the rated engine capacity. This paper presents graphical and analytical methods to determine the stalling conditions of the most common type of gensets that have a synchronous generator as the utility interface. A systematic approach is developed from the first principles of generator electromagnetic energy conversion. The engine fuel map limits have been integrated into the generator speed versus active power characteristics for this purpose. The stalling prevention by applying an underfrequency load relief (V/Hz) scheme is also discussed.

In this paper, a microgrid consisting of four fuel cell-battery hybrid Distributed Energy Resources (DERs) is devised for an industrial crusher–conveyor load. Each fuel cell was accompanied by a Li-ion battery to provide energy storage support under islanded condition of the microgrid since the fuel cells typically have poor transient response characteristics. After carrying out extensive modeling and analysis in MATLAB®, the battery utilization was found to vary significantly based on the DER's ‘electrical’ placement within the microgrid. This paper presents, under such conditions, a variety of battery life balancing solutions through the use of the new framework of Flexible Distribution of EneRgy and Storage Resources (FDERS). It is based on an in-situ reconfiguration approach through ‘virtual’ reactances that help in changing the ‘electrical’ position of each DER without physically displacing any component in the system. Several possible approaches toward balancing the battery utilization are compared in this paper taking advantage of the flexibility that FDERS offers. It was observed that the estimated battery life is dependent on factors such as cycling sequence, pattern, and occurrence.

The ever growing penetration of distributed generation (DG) in a distribution network has a profound impact on the network protection and stability. Traditional protection schemes and algorithms need to be extensively investigated as more and more DGs get introduced into the network. The current version of IEEE Std 1547 does not present a comprehensive solution for fault current detection in the presence of various kinds of DGs. Power electronic inverter-based DGs are of special concern in distribution network protection as they are often incapable of providing sufficient fault current and their controllers play a principal role in the DG behavior. In this paper, the effects of voltage and current controllers for inverter-based DGs on industrial and commercial power system distribution network protection schemes are investigated. It is shown that the type of controller and its design parameters during the fault have a direct impact on fault current levels and duration. A simplified distribution network model with inverter-based DG operating under voltage and current control modes was tested to verify the effects of these controllers. This paper also proposes an adaptive relaying algorithm to detect the faults in the presence of inverter-based DGs with various types of controllers.

Malfunctioning of distance relay third zone has been identified as one of the leading factors of power system blackouts in several nations. This inconsistency in operation happens when heavy loads start encroaching the zone 3 settings. In this paper, a novel multi-agent system based methodology for power system protection coordination is proposed. Various system agents are designed to collaborate and adaptively modify the setting of distance relay zone 3 via communication with neighboring substations. The proposed coordination scheme aids in preventing fault misjudgment and possible network breakdown because of load encroachment. Furthermore, it enhances the relay selectivity and loadability. It has been tested using MATLAB ® /Simulink™ with the agent programming in Java Agent DEvelopment Framework (JADE) platform. Analysis and test results demonstrate that the proposed method effectively mitigates distance relay malfunction under load encroachment.

Community microgrids are developed within existing power systems by integrating local distributed energy resources (DERs). So power distribution systems can be seamlessly partitioned into community microgrids and end-users could be largely supported when an extreme event happens. However, because of DERs low inertia, their power capacity should be well designed to cover unexpected events and guarantee system reliability. This paper presents a quantitative and qualitative combined methodology for DERs selection, and an economic approach to meet the system reliability requirements. Discrete time Fourier transform (DTFT) and particle swarm optimization (PSO) are employed to obtain the optimal solution, with consideration of load demand and renewable generation uncertainties. In addition, a sensitivity analysis is conducted to show how DERs' capacity design is impacted by counted portion of the forecasted renewable generation., Comment: 6 pages, 4 figures, 2 tables, 9th International Conference on Applied Energy, ICAE2017

Natural gas powered inverter-based distributed energy resources (DERs) are becoming increasingly popular. In such DERs, the output frequency is decoupled from the prime-mover speed. This is advantageous in terms of improved efficiency and reduced emissions for the internal combustion engine. However, under large load conditions the prime-mover can stall leading to a voltage collapse. This paper presents an analysis of prime-mover stalling in inverter-based DERs. Detailed studies are conducted on a mixed source microgrid comprising both inverter- and synchronous generator-based DERs. A modified active power-frequency droop control technique is proposed for the inverter-based DER to prevent its prime-mover from stalling in the mixed source microgrid.

For a microgrid with a mix of distributed energy resources (DERs), major challenges on its survivability are found in the islanded condition. In particular, a sudden loss of generation or a large and fluctuating load could force the microgrid to operate near its capacity limits. Such a situation can cause a cascading collapse of the system, even when the load demand is within the DER's kW rating — as observed during several tests at the Consortium for Electric Reliability Technology Solutions (CERTS) Microgrid Test Bed. This paper analyzes the prime-mover stalling phenomena behind the system collapse. It highlights how the reserve margin of the system is lowered during transient conditions. Furthermore, two control methods are evaluated to resolve the microgrid collapse problem.

A microgrid is capable of providing highly reliable power supply to sensitive loads like semiconductor fabrication or computer data processing equipment. This is especially required when the sensitive loads are located in distribution systems that also contain several single-phase and/or nonlinear loads. Voltage source inverter (VSI) based distributed energy resources can provide power quality conditioning support. They require filters to accurately detect unbalance and harmonics in the system. The state-of-the-art filtering techniques in three-phase power systems involve employing complex bandpass filters that pass frequencies within a band without much attenuation. Such methods however give good dynamic performance only when there is a wide separation between the desired and undesired frequencies. In power distribution systems containing imbalances and harmonic generating loads, the gap between the two frequencies may be very small, and therefore such methods don't offer good performance. This paper proposes improved methods of filtering signals in three-phase, three-wire power systems, especially when there is a narrow gap between the desired and undesired frequencies. The proposed techniques contain both complex bandpass and bandstop sections and are designed on three-phase space-vector quantities. Simulation and experimental results are presented to validate these novel filtering concepts.

This paper analyzes critical control issues associated with the deep field weakening operation of interior permanent magnet (IPM) synchronous machines. The singlecurrent-regulator control algorithm is reviewed, which controls the d-axis current actively and gives a fixed q-axis voltage command. To achieve better operational efficiency and performance, improvements are made to choose an optimal q -axis voltage for variable-speed and variable-load conditions. The control algorithm is implemented on a 50-kW IPM machine. Test results, including 7:1 constant power speed ratio operation, are presented to verify the theoretical analysis.

Distributed Generation, or DG, involves utilization of small generators that are distributed in a power network, to supply the electric power demands of utility customers. This paper presents the small signal analysis of droop based generation control schemes for pazallel connected DG inverters comprising of active power-frequency and reactive power-voltage controllers. Small-signal models aze developed for microgrids consisting of several DGs connected in a parallel configuration. Mathematical propositions that develop sufficiency conditions for stability of the system are developed.

Extension of electrical service to large rural populations in developing nations is a key requirement to realize human development goals set forth by international agencies. This paper presents the case for distributed generation in the form of microgrids, which should be the preferred path towards rural electrification in developing communities and a vital complement to expensive centralized grid expansion. The technical features of frequency and voltage control for distributed generation devices in a microgrid are discussed along with a presentation of their stability attributes. Computer simulation results and experimental results from a laboratory scale microgrid are also presented.

New measures for increasing energy efficiency and reducing CO2 emissions are being introduced by several nations to tackle the growing concerns on climate change. This paper presents optimal distributed energy resource (DER) planning for establishing microgrids. Such microgrid systems are devised for industrial sites and campus communities in the United States after evaluating location specific DER options. These are designed to maximize fuel consumption savings, besides meeting the U.S. Department of Energy (DOE) requirements and state renewable energy mandates. A qualitative evaluation of various types of DERs is presented cogitating factors like cost, environment, fuel consumption, controllability, longevity and government policy. Furthermore, the method of Lagrange Multipliers is used to determine the optimal allocation of DERs for microgrids. Due consideration is given to various factors such as climatic conditions, prevailing energy resources, and environmental regulations. The planning strategy presented in this paper can be extended to other conditions with minimal adjustments.

This paper analyzes the performance of a stone crushing facility powered by an islanded microgrid comprising two natural gas engine driven generator sets (also known as gensets). The goal is to achieve the microgrid performance in accordance with the ISO 8528-5 Standard. For improving the system frequency response, different approaches are evaluated including applying underfrequency load shedding and increasing generator inertia. However, it is shown that integration of energy storage system with fast frequency controls offers the best solution for satisfying the ISO 8528-5 Standard. Results from modeling and simulation using MATLAB/Simulink are presented to show the impact on microgrid performance.

Distributed energy resources (DERs) powered by natural gas engines are becoming more popular in several nations. This paper presents the modeling and analysis of engine fuel map limits on natural gas powered DERs installed at the CERTS Microgrid. A physics-based approach is used for correct modeling of the limiting conditions in DERs. The distinguishing characteristics of both inverter-based and synchronous generator-based DERs are established. Furthermore, the performance of CERTS Microgrid under is shown for different case studies of islanded operation.

This paper investigates the benefits of smart loads in an industrial microgrid. Such smart loads offer the microgrid greater flexibility to regulate frequency for large fluctuating load scenarios, commonly encountered in industrial plants. A case study of stone crushing facility is analyzed when it is fed by natural gas engine driven generator sets (also known as ‘gensets’). The problem of genset stalling is addressed in this work, and a solution of deploying smart loads is presented. Furthermore, smart load algorithms are proposed to restore the services at industrial sites in a timely manner.

The dynamic voltage restorer (DVR) as a means of series compensation for mitigating the effect of voltage sags has become established as a preferred approach for improving power quality at sensitive load locations. Meanwhile, the cascaded multilevel type of power converter topology has also become a workhorse topology in high power applications. This paper presents the detailed design of a closed loop regulator to maintain the load voltage within acceptable levels in a DVR using transformer coupled H-bridge converters. The paper presents system operation and controller design approaches, verified using computer simulations, and a laboratory scale experimental prototype.