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Plug-in electric vehicle (PEV) commercialization propels an extensive charging station deployment in a power distribution system to satisfy fast growing PEV charging demands. Considering the power distribution, some stations deployed at limited capacity feeders may undergo power overload at peak hours due to time-varying traffic and PEV demands. The potential power overload could lead to severe transformer degradation or even black-out on the aged power infrastructure. To avoid power overload without excessive expenditure on the infrastructure upgrade, proper energy compensation at limited capacity station is highly effective. In this paper, we investigate an energy compensation problem based on utility-owned mobile vehicular electric storage (MVES), aiming to mitigate the overload issues among a group of charging stations (GCS). First, a Markov Chain based energy capacity model is developed to estimate the energy statuses among GCS and a graph theory based GCS transportation model is developed to facilitate on-road MVES allocation. Then, a two-tier energy compensation framework is introduced to efficiently schedule MVESs to minimize the scheduling cost. Simulations are conducted based on real traffic data on California highway collected by California department of transportation, and the results validate the effectiveness of the introduced framework. [ABSTRACT FROM AUTHOR]

This paper presents a decision tree based high-speed intelligent scheme for series-compensated transmission line protection using differential phase angle of superimposed current (DPASC). The conventional distance relaying scheme undergoes many shortcomings in transmission line protection in the presence of series compensation devices. The proposed scheme calculates the differential phase angle of current signals using full cycle discrete Fourier transform. The DPASC for each phase is used as an input to the data mining model known as decision tree (DT). The DT is used to generate thresholds to detect and classify the faults since determination of robust thresholds is an important challenge in protective relay engineering. The proposed method has been tested for different operating modes of transmission line in SIMIULINK/MATLAB software. Simulation results indicate that the proposed method is able to detect and classify the faults with acceptable accuracy, in less than half cycle. [ABSTRACT FROM AUTHOR]

Identification of faulty feeders and sections during ground faults in compensated medium voltage systems is a complex task demanding development of new methods. Existing steady-state approaches, such as the watt-metric or the admittance based, can be compromised by various parameters of distribution lines or network configuration. Moreover, sensitivity might be threatened during high impedance faults. Transient methods (extensively studied in the recent literature) require thorough analysis before implementation due to their dependency on fault and system parameters. The current paper proposes a new approach for faulty feeder selection during ground faults. It has been tested in the laboratory utilizing electromagnetic transients program (EMTP) simulations. Performance of the developed algorithm has been compared with the conventional steady-state method implemented in a modern feeder relay. The results show improved selectivity and robustness of the new proposed algorithm. Moreover, its applicability for real systems has been demonstrated on fault records obtained from an actual distribution network. The proposed approach can be used as an additional criterion to increase selectivity of the ground fault protection in compensated networks. [ABSTRACT FROM AUTHOR]

Lightning electromagnetic fields can couple to overhead power transmission and distribution lines, causing serious effects to the power system. Lightning electromagnetic fields that couple to overhead lines have a nonuniform distribution along the line conductors. Therefore, to ensure the accuracy of the numerical calculation results, a large number of discretization points are needed along the line, which might dramatically increase the computation time since the evaluation of lightning electromagnetic fields in the presence of a lossy soil involves, in general,Sommerfeldintegrals, or, even in the case of a perfectly conducting ground, numerical integration along the channel. This paper proposes a new approach to address this problem. The proposed approach is based on the Agrawalet al. coupling model, in which the horizontal lightning electric field along the line is represented by the complex exponential functions in the frequency domain using the matrix pencil method. The method is highly efficient in terms of computation time since the lightning-induced response of the line can be solved semi-analytically. The proposed approach is validated by two different validation examples. [ABSTRACT FROM AUTHOR]

A novel scheme is proposed to monitor the operation of capacitors scattered in MV distribution systems. It first codes each capacitor with a distinctive switching character by setting a unique combination of a three-phase switching order and time interval. As a result, the transient of the three-phase reactive power during capacitor switching will appear in a unique way. Then, the reactive power disturbances monitored in the substation are decoded to identify which capacitor is being switchedonandoff. A detailed decoding method is developed to realize this identification without being impacted by the switching interference of loads and other reactive power compensation devices. Moreover, the implementation of the proposed scheme in the field is elaborated, and the resultant three-phase voltage unbalance is analyzed in this paper. Compared with existing methods, this scheme only requires one power quality monitor located at the substation to monitor the operations (energizing or de-energizing) of downstream distribution capacitors without extra communication devices. The operation information is valuable for tackling power quality problems caused by capacitor switching and optimizing the distribution grid operation. [ABSTRACT FROM AUTHOR]

In the framework of the more electric aircraft, the use of isolated dc–dc power conversion for the electrical power distribution system is one of the most investigated solutions. If the dc–dc converter produces a variable common-mode voltage, the leakage current can flow in the interwinding parasitic capacitance of the high-frequency transformer, leading to insulation deterioration and early failure. This paper proposes to use modified H-bridge structures, already employed in the photovoltaic system for dc–ac power converters, to enable a constant common-mode voltage for isolated dc–dc converters. The analysis shows that this solution can achieve the same efficiency as the conventional one, while simulations and experiments show a strong reduction of the common-mode current flowing through the transformer. A reliability analysis showed that the lifetime of the high-frequency transformer can be extended with the proposed solution. [ABSTRACT FROM AUTHOR]

This paper presents a new methodology based on multiobjective optimization techniques to perform an optimized, coordinated, and selective allocation of control and protection devices in distribution networks with distributed generation (DG). The proposed mathematical model consists of two objective functions that consider economic issues and the network continuity index. Physical and operational constraints are taken into account, with emphasis on the set of constraints based on practical rules of distribution companies and international technical standards, which require the specification, coordination, and selectivity of the protection devices installed in the network. The possibility of load transfer from neighboring feeders and islanded DG operation is also considered. The proposed model is a mixed integer nonlinear programming, and we use NSGA-II (Nondominated Sorting Genetic Algorithm) to solve it. The proposed methodology is applied in a real 135-bus system found in the literature. [ABSTRACT FROM AUTHOR]

This paper proposes a new analytical probabilistic power flow (PPF) approach for power systems with high penetration of distributed energy resources. The approach solves probability distributions of system variables about operating conditions. Unlike existing analytical PPF algorithms in literature, this new approach preserves nonlinearities of ac power flow equations and retain more accurate tail effects of the probability distributions. The approach first employs a multidimensional holomorphic embedding method to obtain an analytical nonlinear ac power flow solution for concerned outputs such as bus voltages and line flows. The embedded symbolic variables in the analytical solution are the inputs such as power injections. Then, the approach derives cumulants of the outputs by a generalized cumulant method, and recovers their distributions by Gram–Charlier expansions. This PPF approach can accept both parametric and nonparametric distributions of random inputs and their covariances. Case studies on the IEEE 30-bus system validate the effectiveness of the proposed approach. [ABSTRACT FROM AUTHOR]

In this paper, the coordinated investment in transmission and storage systems under uncertainty is addressed from the perspective of a central planner. The problem is formulated with the objective of achieving an effective expansion of both transmission and storage that minimizes the investment cost, while achieving an effective operation of a power system with high penetration of renewable power. The problem is stated within an adaptive robust optimization framework that incorporates stochastic modeling. Future available generation capacity and peak load in the target year (long-term uncertainty) are modeled using a robust set, while daily operating conditions (short-term uncertainty) are represented with a scenario set. The expansion tradeoff between transmission and storage systems is analyzed using the IEEE RTS 24-bus and IEEE 118-bus networks. [ABSTRACT FROM AUTHOR]

As the rapid development of natural-gas fired units (NGUs), power systems begin to rely more on a natural gas system to supply the primary fuel. On the other hand, natural gas system contingency might cause the nonavailability of NGUs and inevitably jeopardize power system security. To address this issue, this paper studies security-constrained joint expansion planning problems for this combined energy system. We develop a computationally efficient mixed-integer linear programming (MILP) approach that simultaneously considers N-1 contingency in both natural gas system and electricity power system. To reduce the combinatorial search space of MILP models, an extension of a reduced disjunctive model is proposed to decrease the numbers of binary and continuous variables as well as constraints. The involving nonlinear terms in N-1 constraints are exactly linearized without sacrificing any optimality. Numerical results on two typical integrated energy systems demonstrate the necessity of extending N-1 criterion to the whole network of a combined energy system. Experimental results also show that compared with the conventional approach, our proposed MILP approach achieves a great computational performance improvement in solving security-constrained co-optimization expansion planning problems. [ABSTRACT FROM AUTHOR]

A novel method is proposed to locate the source of events in power distribution systems by using distribution-level phasor measurement units, a.k.a., micro-PMUs. An event in this paper is defined rather broadly to include any major change in any component across the distribution feeder. The goal is to enhance situational awareness in distribution grid by keeping track of the operation (or misoperation) of various grid equipment, assets, distribution energy resources, loads, etc. The proposed method is built upon the compensation theorem in circuit theory to generate an equivalent circuit to represent the event by using voltage and current synchrophasors that are captured by micro-PMUs. Importantly, this method makes critical use of not only magnitude but also synchronized phase angle measurements, thus, it justifies the need to use micro-PMUs, as opposed to ordinary RMS-based voltage and current sensors. The proposed method can work with data from as a few as only two micro-PMUs. The effectiveness of the developed method is demonstrated through computer simulations on the IEEE 123-bus test system, and also on micro-PMUs measurements from a real-life 12.47 kV test feeder in Riverside, CA. The results verify that the proposed method is accurate and robust in locating the source of different types of events on power distribution systems. [ABSTRACT FROM AUTHOR]

Residential energy management (REM) systems facilitate the application of residential demand response programs to manage the increasing demand of electricity in power systems. The load curtailment at high price periods and the load shift from high-price to low-price periods are the main results of REM implementation, which may improve the technical and economical operation of the distribution systems. Customers’ satisfaction should be considered in the REM procedure to motivate the customers to respond to the received price signals. This paper proposes an optimization-based REM to minimize not only the customer's energy cost but also customer dissatisfaction, which is modeled as a function of load curtailment. In addition, the impact of broad application of REM in bus 6 of RBTS is studied on the reliability of a distribution system. To this end, two different methods for reliability evaluation are used to show the effect of load shift and load curtailment on the energy not supplied by the distribution system. The results verify the validity and effectiveness of the proposed REM approach and show the impact of application of REM programs with different penetration levels on the reliability of the distribution system. [ABSTRACT FROM AUTHOR]

Many modern industrial plants are equipped with local generation and are designed to operate as a microgrid. Under normal conditions, the plant is connected to and often mainly supplied by the utility's network. However, during a disturbance on the utility side, it may island from the grid and continue supplying its load using available on-site generation. When this generation is not sufficient to supply the entire load (which is often the case), some of the noncritical loads must be shed so as to ensure that the remaining loads receive the required quality of service. The decision to island and the amount of load to be curtailed are determined based on the values of the frequency/voltage. In this paper, we first propose a hybrid undervoltage/under frequency islanding scheme for an industrial park consisting of multiple substations (microgrids) each supplying one or more industrial plants. It is assumed that once the park is islanded from the grid, the substations are instantly formed into multiple islands where all noncritical loads are automatically disconnected. This is done to ensure that individual islands are not affected by potential instability of their neighboring networks. However, once the individual islands are stabilized, it is possible to share their available generation capacities to maximize the total load served. This would mean connecting one or more islands together to form bigger ones. We formulate this as a network reconfiguration problem that tries to maximize the amount of load served by reconfiguring the network topology and using backup energy resources. The problem is solved and analyzed for a simplified version of an industrial park, both at steady state and during transients. [ABSTRACT FROM AUTHOR]

This paper proposes an interactive bidding strategy for smart distribution networks with clustered aggregators to effectively coordinate the energy and profit of each entity. In the proposed one-leader $n$ -follower bidding model, there are two levels, where the upper level stands for the distribution operator (DO) to secure the operation quality and bid with energy aggregators (EAs), and the lower level represents each EA to bid for interactive energies with the DO and other EAs. The proposed interactive bidding mechanism takes advantages of both renewable generation and energy storage system into account, where the priority-based decision making is applied to the lower level to elaborately map the bidding mechanism and lead each EA's market interaction. Case studies on the IEEE 33-bus test feeder and a practical distribution grid in China demonstrate the effectiveness of the proposed methodology. [ABSTRACT FROM AUTHOR]

Inverse analysis is a known mathematical approach, which has been used to solve physical problems of a particular nature. Nevertheless, it has seldom been applied directly for loss reconstruction of electrical machines. This paper aims to verify the accuracy of an inverse methodology used in mapping power loss distribution in an induction motor. Conjugate gradient method is used to iteratively find the unique inverse solution when simulated temperature measurement data are available. Realistic measurement situations are considered and the measurement errors corresponding to thermographic measurements and temperature sensor measurements are used to generate simulated numerical measurement data. An accurate 2-D finite-element thermal model of a 37 kW cage induction motor serves as the forward solution. The inverse model’s objective is to map the power loss density in the motor accurately from noisy temperature measurements made on the motor housing’s outer surface. Furthermore, the sensitivity of the adopted inverse methodology to variations in the number of available measurements is also considered. Filtering the applied noise to acceptable ranges is shown to improve the inverse mapping results. [ABSTRACT FROM AUTHOR]

Power theories are advancing signal decomposition approaches used for electrical power signal analysis. Currently, they are key tools for designing reliable and efficient power electronic interface controllers. Due to the inherent uncertainty in the power generation within new technology of distributed generation units (such as renewable-based microgrids), most of these theories are not directly applicable in the era of new power engineering systems. Furthermore, the traditional formulations are not appropriate once we face the nonlinearity in the consumption along a weak grid that may not maintain steady voltage or frequency. Therefore, a new signal decomposition method with a higher level of selectivity must be developed to modify the traditional power theories and improve the control strategies from a design viewpoint. This paper describes a novel formulation of an instantaneous power theory, enhanced instantaneous power theory (EIPT), for unbalanced and nonlinear three-phase power systems. EIPT establishes a proper decomposition of current components for cases of balanced, unbalanced, and distorted voltage sources. In addition to mathematical analysis, this research provides comprehensive simulations under different loads and source conditions, which supports the performance of the EIPT in the active filtering methods. Moreover, the performance of the proposed method is compared with the state-of-the-art approach widely known as the conservative power theory. Our results indicate that this new comprehensive approach is helpful in optimizing control strategies for power electronic interfaces and power quality compensators. [ABSTRACT FROM AUTHOR]

Past performance of distribution networks against hurricanes has highlighted the high vulnerability of these systems in electric power networks and the need for their reliability assessment for risk-informed decision-making purposes. A network level reliability analysis would require the estimation of reliability of line segments between key switches in the network. Former reliability studies, however, are based on a number of limiting assumptions. These include assuming independent mechanistic behavior of spans in a line segment during strong winds and statistical independence of failure events of components in a line. Due to correlations in wind loadings on the poles, environmental conditions that affect the decay rate of the poles, and structural properties of the poles, failures of poles are expected to be correlated events. This paper investigates the effects of these factors on the hurricane reliability of power distribution lines. Couplings in the wind performance of adjacent spans are incorporated here properly through an equivalent boundary model. Moreover, a multiscale matrix-based method is adopted to efficiently assess system reliability of distribution lines considering correlations in the failure events of line components. Numerical results indicate that couplings and statistical correlations have a considerable impact on the reliability of distribution systems. [ABSTRACT FROM AUTHOR]

The industry of solar photovoltaic (PV) energy and its application is still booming to enhance the sustainability of the society. When PV systems are connected to the grid, challenging issues should be addressed. One of the challenges is related to interharmonics in PV systems, especially with a large-scale adoption of PV systems. However, the origins of interharmonics remain unclear, although the impact of interhamonics has been reported in the literature. Thus, this paper explores the generation mechanisms of interharmonics in PV systems and the characteristics. The exploration reveals that the perturbation from the maximum power point tracking (MPPT) algorithm is one of the origins of interharmonics appearing in the grid current. Accordingly, the MPPT controller parameters such as the perturbation step size and the sampling rate have an inevitable impact on the interharmonic characteristics. Furthermore, an approach to characterize the interharmonics in the grid current is proposed. With the proposed model, interharmonics can be predicted according to the designed controller parameters in terms of frequencies and amplitudes. Experimental tests are performed on a single-phase grid-connected PV system. The results are in a close agreement with the analysis and, thus, validate the effectiveness of the proposed model. [ABSTRACT FROM AUTHOR]

In power and energy applications, implementing a large number of phase-locked loops (PLLs) involves using transfer delays. These delays are employed for different control and filtering purposes, such as creating a fictitious orthogonal signal (which is required for the frame transformation in single-phase PLLs) and filtering harmonics, dc offset, and other disturbances. Depending on the application in hand and the expected variation range of the grid frequency, the length of these delays may be variable or fixed. Roughly speaking, the variable-length delays are often preferred for applications where large frequency drifts are anticipated and a high accuracy is required. To the best of authors’ knowledge, the small-signal modeling of a variable-length delay-based PLL has not yet been conducted. The main aim of this paper is to cover this gap. The tuning procedure and analysis of these PLLs are also presented. As design examples, some well-known single-phase and three-phase PLLs are considered. [ABSTRACT FROM AUTHOR]

Single-loop current control is an attractive scheme for the LCL-type grid-connected inverter due to its simplicity and low cost. However, conventional single-loop control schemes, which command either the inverter current or the grid current, are subject to the specific resonance frequency regions. The weighted average current control, which splits the filter capacitor into two parts (in form of an LCCL filter) and commands the current flowing between these two parts, is independent of the resonance frequency, but on the other hand, it is limited by the poor sensitivity to the grid impedance variation and weak stability in the grid current. These limitations are comprehensively explained in this paper and then addressed by identifying that the single-loop weighted average current control is equivalent to the dual-loop grid current control with an inherent capacitor current active damping. By tuning the capacitor split proportion as a second degree of freedom, an optimal damping performance that is robust to the grid impedance variation can be naturally achieved using only the inherent damping. Thus, no extra damping is required, and the single-loop structure with only one current sensing turns to be adequate. Moreover, for convenience of practical implementation, an improved LCCL filter configuration is proposed to allow the use of two equal nominal capacitances for the split capacitors. Finally, experiments are performed to verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

This paper presents a wide area control (WAC) method to coordinate the local controllers of generators and renewable energy sources (RESs), for robust power oscillation damping. The WAC signals are synthesized by a two-level hierarchical controller, which utilizes wide area measurements from all the installed synchronous generators and RESs for maximizing the performance of their corresponding local controllers. In the resulting WAC scheme, the generators are “aware” of the RES oscillations and vice versa, the RESs are “aware” of the generator oscillations. Further, the WAC signals intended for the RESs are adjusted in order to require only slight modifications on the RES local controllers. This study illustrates that the correct coordination of generators and RESs, through the WAC, improves the damping performance of the entire system even under high penetration of renewables. The performance of the proposed scheme has been tested and validated in the IEEE 9-bus and 39-bus test systems. [ABSTRACT FROM AUTHOR]

At Washington State University, a modern cyber–physical system testbed has been implemented based on an industry-grade distribution management system (DMS) that is integrated with remote terminal units, smart meters, and a solar photovoltaic array. In addition, the real model from the Avista Utilities distribution system in Pullman, WA, is modeled in DMS. The proposed testbed environment allows students and instructors to utilize these facilities for innovations in learning and teaching. For power engineering education, this testbed helps students understand the interaction between a cyber system and a physical distribution system through industrial level visualization. The testbed provides a distribution system monitoring and control environment for students. Compared with a simulation-based approach, the testbed brings the students’ learning environment a step closer to the real world. The educational modules allow students to learn the concepts of a cyber–physical system and an electricity market through an integrated testbed. Furthermore, the testbed provides a platform in the study mode for students to practice working on a real distribution system model. This paper describes the new educational modules based on the testbed environment. Three modules are described together with the underlying educational principles and associated projects. [ABSTRACT FROM AUTHOR]

The demand response provides an opportunity for load serving entities (LSEs) that operate retail electricity markets (REMs) to strategically purchase energy and provide reserves in wholesale electricity markets (WEMs). This paper concerns with the problem of simultaneously determining the optimal energy bids and reserve offers an LSE submits to the WEM as well as the optimal energy and reserve prices it sets in the REM so as to maximize its profit. To this end, we explicitly model the trilayer market structure that consists of a WEM, a REM, and a set of end user customers, so as to capture the coupling between the bidding problem and the pricing problem. Based on the trilayer market model, we then formulate the joint bidding and pricing problem as a bilevel programming problem and further transform it into a single-level mixed integer linear programming problem, which can be solved efficiently. Numerical studies using the IEEE test cases are presented to illustrate the application of the proposed methodology as well as to reveal several interesting characteristics of the LSE's profit-seeking behavior. [ABSTRACT FROM AUTHOR]

This paper proposes a stochastic control strategy, namely the unsynchronized Addictive Increase Multiplicative Decrease (AIMD) algorithm, to manage the power flow of interconnected microgrids (MGs). The proposed control aims at achieving a tradeoff between the individual utility function of each MG while ensuring the stability of the grid. Both centralized and decentralized AIMD approaches are considered and compared. Extensive Monte Carlo simulations are performed on the IEEE 39-bus system, and show that the proposed control strategy is able to provide the sought tradeoff. [ABSTRACT FROM AUTHOR]

In order to support an appropriate level of resource adequacy in the long term and also to achieve a reliable operation in the short term, a new pricing design and mechanism is needed as a key success factor of real-time energy-only market. This paper proposes optimization-based mathematical models to explore operating reserve demand curves (ORDCs) and two price adders in real-time energy-only market, including dispatch correction and extended security-constrained economic dispatch. The Lagrangian multipliers of the dispatch correction problem are used to construct the ORDCs. Then, the derivative of the ORDCs’ social welfare is formulated as real-time online reserve price adders such as the scarcity adder and the price-lift adder. In case studies, we justify the effectiveness of the proposed ORDCs and two price adders by a simple example with two aggregated units and the Electric Reliability Council of Texas data. [ABSTRACT FROM AUTHOR]

This paper proposes a generic steady-state modeling and power-flow analysis approach for droop- and isochronously controlled microgrids. The proposed framework adopts symmetrical sequence component models, rather than phase-coordinate models, of microgrid elements. Such approach immensely reduces the power-flow execution time, as it breaks down the system model into independent equation sets with considerably reduced sizes. To render the proposed approach practical and generic, it integrates different types and control schemes of distributed generation (DG), including synchronous generator-based DG (SGDG) and electronically interfaced DG units. Furthermore, it incorporates unbalanced loads and feeders, transformer connections, different load characteristics, and configurations, as well as microgrid droop features. A novel power-flow algorithm based on a modified Newton–Raphson method is proposed to solve for the microgrid steady-state voltage magnitudes, angles, and frequency. The accuracy of the models and algorithm is verified through comparison with detailed time-domain simulations in MATALB/Simulink. Additionally, the proposed approach is shown to outperform the reported Newton-Trust Region approach in generality, accuracy, and performance. Two case studies, incorporating IEEE 123-node test microgrid, are further performed to examine the effectiveness of the proposed approach in solving complicated droop-controlled microgrids, and to examine the behavior of droop-controlled DGs in isochronous microgrids. [ABSTRACT FROM AUTHOR]

The level of uncertainty, which the power system operators should account for, increases as more renewables are integrated in the system. Additional operating reserves needs to be scheduled within security constrained economic dispatch to ensure reliability. Existing practices rely on conventional generators for providing operational flexibility required to mitigate the uncertainty introduced by renewables. However, with the increased share of renewables in the generation mix, such intermittent resources would be expected to take part in the balancing tasks, too. Providing a reserve margin allows wind generators to hedge against uncertainty. This paper examines the market implications of wind reserve margin policies used to mitigate uncertainty from wind resources. The market implications of the recently proposed optimized reserve margin policy factors are studied. Analysis on the Reliability Test System 1996 shows that reserve margin policy factors along with the proposed compensation scheme help in allocating payments toward renewable resources that present a good quality of service. [ABSTRACT FROM AUTHOR]

The current transition towards smart distribution systems necessitates the development of educational curricula that have the interdisciplinary breadth together with the technical depth to furnish the present and future generation of engineers with a new set of skills and tools to address the challenges associated with emerging smart grid technologies. This work presents a newly designed smart distribution course that is intended to meet the needs of the power distribution industry. The paper gives a high-level overview of the broad range of topics related to developments and trends in smart distribution technologies including automatic restoration, data management, cybersecurity, interoperability and standards, and future vision. It stresses the multidisciplinary nature of the course and the importance of the strong collaboration between academia and key stakeholders, and the support from utilities, industry, government, and consultants. The course has been developed and taught by distribution system experts who are currently implementing smart grid technologies along with smart grid pioneers who are known worldwide. Moreover, to measure the effectiveness of the instructional approach of the course, students learning outcomes were assessed and discussed. The lessons learned from the implementation of the course are also summarized. [ABSTRACT FROM AUTHOR]

Demand Response (DR) is an important tool for Independent System Operators (ISO) for reliable operation of electricity markets, and there has been considerable interest from load-side market participants to offer their services for DR provisions. In this environment, the ISO needs to develop effective mathematical models for procurement of DR so as to maximize its benefits, such as reducing the peak demand, regulating electricity price shocks, and mitigating market power. In this paper, a new mathematical model for a Locational Marginal Price based, loss included, day-ahead, cooptimized, energy and spinning reserve market including DR provisions, is proposed. The proposed model includes a new proposition for load-side participants to submit price responsive demand (PRD) and load curtailment based DR bids simultaneously, in a unified market framework. Case studies considering DR providers participating in energy market only, in both energy and spinning reserve markets, and in spinning reserve market only, are presented, which examine the impact on system operation, market prices, and DR provider's benefits. The proposed model is tested on the IEEE Reliability Test System to demonstrate its functionalities and the results clearly justify the merits of simultaneous consideration of PRD bids and load curtailment based DR offers in a cooptimized energy and spinning reserve market. [ABSTRACT FROM AUTHOR]

The deployment of smart grids has facilitated the integration of a variety of investor assets into power distribution systems, giving rise to the consequent necessity for positive and active interaction between those investors and local distribution companies (LDCs). This paper proposes a novel incentive-based distribution system expansion planning model that enables an LDC and distributed generation (DG) investors to work in a collaborative way for their mutual benefit. Using the proposed model, the LDC would establish a bus-wise incentive program based on long-term contracts, which would encourage DG investors to integrate their projects at specific system buses that would benefit both parties. The model guarantees that the LDC will incur minimum expansion and operation costs while concurrently ensuring the feasibility of DG investors’ projects. To derive appropriate incentives for each project, the model enforces several economic metrics including internal rate of return, profit investment ratio, and discounted payback period. All investment plans committed to by the LDC and the DG investors for the full extent of the planning period are then coordinated accordingly. Several linearization approaches are applied to convert the proposed model into an MILP model. The intermittent nature of both system demand and wind- and PV-based DG output power is handled probabilistically, and a number of DG technologies are taken into account. Case study results have demonstrated the value of the proposed model. [ABSTRACT FROM AUTHOR]

The penetration of distributed renewable energy sources in the distribution grid is increasing considerably in the last years. This is one of the main causes that contributed to the growth of technical problems in both transmission and distribution systems. An effective solution to improve system security is to exploit the flexibility that can be provided by distributed energy resources (DER), which are mostly located at the distribution grids. Their location combined with the lack of power flow coordination at the system operators interface creates difficulties in taking advantage of these flexible resources. This paper presents a methodology based on the solution of a set of optimization problems that estimate the flexibility ranges at the distribution and transmission system operators (TSO-DSO) boundary nodes. The estimation is performed while considering the grid technical constraints and a maximum cost that the user is willing to pay. The novelty behind this approach comes from the development of flexibility cost maps, which allow the visualization of the impact of DER flexibility on the operating point at the TSO-DSO interface. The results are compared with a sampling method and suggest that a higher accuracy in the TSO-DSO information exchange process can be achieved through this approach. [ABSTRACT FROM AUTHOR]

Uncertainty in power system planning problems can be categorized into two types: exogenous and endogenous (or decision-dependent) uncertainty. In the latter case, uncertainty resolution depends on a choice (the value of some decision variables), as opposed to the former case in which the uncertainty resolves automatically with the passage of time. In this paper, a novel stochastic multistage planning model is proposed that considers endogenous uncertainty around consumer participation in demand-side response (DSR) schemes. This uncertainty can resolve following DSR deployment in two possible ways: locally (at a single bus) and globally (across the entire system). The original formulation is decomposed with the use of Benders decomposition to improve computational performance. Two versions of Benders decomposition are applied: the classic version involving sequential implementation of all operational subproblems and a novel version, specific to problems with endogenous uncertainty, which allows for the parallel execution of only those operational subproblems that are guaranteed to have a unique contribution to the solution. Case studies on 11-bus and 123-bus systems illustrate the process of endogenous uncertainty resolution and underline the strategic importance of deploying DSR ahead of time. [ABSTRACT FROM AUTHOR]

Rescheduling methods for mitigation of poorly damped power swings depend on a model-based evaluation of eigenvalue sensitivities and are slow to implement. This paper proposes an approach for an online model-free implementation of modulation-type control using Wide Area Measurement System (WAMS). Such a control measure can act as a primary line of defense before the slower rescheduling-type measures are taken. The proposed control measure utilizes special properties of swing modes derived analytically from a simplified system model to 1) synthesize a modal feedback signal as the input to the controller and 2) tune the controller parameters for adequate damping improvement, in a model-independent manner for certain FACTS devices and HVDC links. For a power system stabilizer (damping controller in a synchronous machine excitation system), the extent of model information required is limited to that of the well-known GEP $(s)$ transfer function and inertia constant of the concerned synchronous machine. Case studies with detailed system models provide the necessary proof-of-concept. [ABSTRACT FROM AUTHOR]

The increasing interdependencies between natural gas systems and power systems create new business opportunities in coupled energy distribution markets. This paper studies the marginal price based bilateral energy trading on the equilibrium of coupled natural gas and electricity distribution markets. Convex relaxation is employed to solve a multiperiod optimal power flow problem, which is used to clear the electricity market. A successive second-order cone programming approach is utilized to solve a multiperiod optimal gas flow problem, which is used to clear the gas market. In addition, the line pack effect in the gas network is considered, which can offer storage capacity and provide extra operation flexibility for both networks. In both problems, locational marginal energy prices are recovered from the Lagrangian multipliers associated with nodal balancing equations. Furthermore, a best-response decomposition algorithm is developed to identify the equilibrium of the coupled energy markets with bilateral gas and electricity trading, which leverages the computational superiority of SOCPs. Cases studies on two test systems validate the proposed methodology. [ABSTRACT FROM AUTHOR]

The aim of this paper is to define and develop an optimal hierarchical demand-side power-system primary-frequency control structure in order to provide a reliable complement to generator inertia and governor response while improving inter-area oscillation damping. This resilient optimal load control strategy utilizes both wide-area and local signals to guarantee that the system remains stable in the case of communication failures. In the device layer, we deal with demand-response and frequency regulation by minimizing the total disutility of consumers subject to power balance and frequency regulation over the network. In the supervisory layer, we handle the power system's electromechanical oscillations using an linear-quadratic regulator (LQR)-based state feedback scheme with sparsity promotion to achieve the necessary tradeoff between complexity and performance. Since the wide-area feedback loops are built on top of an existing decentralized load control strategy, this design approach creates a decentralized/hierarchical demand-side load-control structure with significant advantages in terms of reliability and operational flexibility. Our study clearly shows by simulation that a demand-side hierarchical load-control strategy has a significant potential for improving the dynamic performance of power systems, even when implemented with a limited number of measurement units and controlling less than $1\%$ of the total base load. [ABSTRACT FROM AUTHOR]

This paper proposes a zero-voltage ride-through (ZVRT) method and an LCL filter design method to meet the fault ride-through (FRT) requirements for a single-phase grid-connected inverter with a minimized LCL filter. A high inverter output current overshoot occurs at a grid voltage sag and a grid voltage recovery, when a low-inductance LCL filter design is employed in order to minimize the filter volume. In order to suppress the current overshoot, a high-speed gate-block operation and the design method of the minimized LCL filter are proposed. In particular, the filter design considers the delay time in the gate-block operation in order to clarify the reduction limitation of the inductance in the LCL filter. As a result, the maximum inverter output current overshoot is suppressed to 146% by the high-speed gate-block operation and the designed LCL filter, where the impedances of an interconnected inductor and a filter inductor are 1.0% and 0.78% of the inverter normalized impedance, respectively. Therefore, it is possible to meet the FRT requirements with the proposed ZVRT method even with the minimized LCL filter. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This paper investigates the injecting power stabilization of nonlinear dc microgrids (MGs) with constant power loads (CPLs). By considering a centralized controller scheme, the limitations of the communication utilities are considered. Therefore, limited information is transferred through the nonideal noisy communication network. Consequently, a cubature Kalman filter (CKF) with a third degree is proposed to mitigate the effect of the noisy measurement and the noisy network on the system's information. Moreover, an estimation-based robust feedback controller is developed to design an optimal value for the injecting power. The considered CKF algorithm is robust against the system uncertainty and noisy environments and has a low computational time for high-order dc MGs with a high number of sources and CPLs. In addition, a systematic procedure to compute the feedback gain of the controller is presented, which can be numerically solved by linear matrix inequality techniques. Hardware-in-the-loop real-time simulation results verify the simplicity of the controller implementation, enhanced performance for the case of limited information, and better robustness against the noisy measurements compared to the state-of-the-art methods. [ABSTRACT FROM AUTHOR]

The kinetic energy stored in the rotating mass of wind turbine generators can provide the effective power quality solution to the inertia-free stand-alone (IFSA) microgrid by improving its stability. In conventional power systems, the power released from the inertia of synchronous generators regulates the system frequency. However, the frequency does not vary much even when a large disturbance or a load change occurs in the IFSA microgrid with only converter-based generators. This paper proposes a new inertia control method for a type-4 permanent magnet synchronous generator wind turbine system in the IFSA microgrid by utilizing the measurement of the dc-link voltage of the converter and its derivatives, not by the system frequency. Several case studies are carried out to evaluate the performance of the proposed inertia control in the IFSA microgrid with electromagnetic transients program-based simulation. Also, its effectiveness is verified with the experimental results from the hardware-in-the-loop test implemented by the controller interface with the digital signal processor, which is connected to the real-time digital simulator. [ABSTRACT FROM AUTHOR]

Problem of the local damage detection is a crucial task in modern condition monitoring. However, most of the classical methods rely on being tested in laboratories in the isolated test stands. In case of the real world data, there are outer sources of the noise (for instance nearby machines). Such noise can affect shape of the signal and increase the level of difficulty in finding information about the fault. Thus, one can define problem of the fault detection as a finding cyclic impulses in the signal. In this paper, the authors propose a procedure for the local damage detection based on the time-frequency decomposition and distance between distributions. Local damage in bearings/gearbox provides specific response in the vibration signal. It can be further investigated via time-frequency decomposition where one can track energy distribution change in time. Applying measure of distances between distributions to absolute value of short time Fourier transform (STFT) matrix of the vibration signal, one can find deviation of subsequent samples from one used as a referential sample. Furthermore, thresholding of the absolute value of the STFT matrix, based on the log-variance of this matrix with respect to frequency allows for the enhancement of the results. In the extension of the proposed methods, we also use normalization of the spectrogram to omit additional step of the log-variance thresholding. Knowledge, which one needs to set appropriate threshold, can set this step to be difficult in the industrial application and thus, normalization of the spectrogram is proposed. Analyzed real signals were acquired from the belt conveyor driving unit in the mining facility. [ABSTRACT FROM AUTHOR]

Global environmental variations in the past two decades have contributed to a significant deviation of classic ecological patterns, leading to severe electricity outages triggered by extreme weather-driven phenomena. This has highlighted an urgent need for enhancing the resilience and robustness of the interconnected electricity grid against such high impact low probability (HILP) incidents. From the electrical safety point of view, it is essential to increase the operators’ awareness on a better understanding of such hazards and grid vulnerabilities, and enhance their preparedness on how to respond or mitigate the probable outages. This paper proposes a temporary, yet agile, restoration strategy in response to the forecasted HILP events, founded based on efficient utilization of the grid existing infrastructure, and aimed at improving its resilience against such extreme emergencies. The applied concept of reconfiguration is proactively planned to recover the electricity outages in a timely manner. In the meantime, two sets of metrics are proposed to quantify both the grid operational and infrastructure resilience. The presented framework aids the system operator to evaluate the outage recovery plans considering their impacts on system resilience and decide on the final implementation. The proposed approach is applied to the IEEE 118-bus test system facing an HILP event, where results reveal its applicability and efficiency. [ABSTRACT FROM AUTHOR]

Air circuit breaker (ACB) is widely used in power distribution system. The movable contact of ACB consists of multiple parallel contacts and the arc will be ignited between arcing contact and static contact when the short-circuit current appears. This paper focuses on the arc evolution process at various currents in multiple parallel contact systems. A 3-D magnetohydrodynamic model of a multiple parallel contact structures is developed. In this model, the anode consists to five parallel contacts, and they are separated by insulation material. The near-electrode layer with a nonlinear voltage–current density characteristic is modeled to describe the near-electrode voltage drop, and the difference between near-anode and near-cathode layers is considered. The magnetic vector potential approach is adopted to calculate the time-varying electromagnetic field produced by the current loop. The arc evolution processes at various currents are analyzed by current density and arc voltage. It is noted that the anode arc root appears on multiple contacts with the increase of current. The arc evolution process mainly depends on the arc resistance characteristic. [ABSTRACT FROM AUTHOR]

The inverter control plays a critical role in microgrid (MG) hierarchical control structure. In this paper, a dominant dynamic elimination control is studied for the voltage-controlled MG inverter. A compact control structure is designed to include separated static state feedback and feedforward terms. Benefitting from the designed control structure, the dominant dynamic can be canceled by the static feedforward control via the fundamental zero-pole cancelation principle. Thanks to the cancelation of the dominant dynamic, the load disturbance-rejection performance is improved, and the approximate unity gain from the reference to output is also achieved from the perspective of the application control layer, thereby the performance of power control for the upper application is improved. Furthermore, the strong robustness to parameter variations and low total harmonic distortion are also achieved. Comparative simulations and experiments are adopted to verify the effectiveness and superiority of the designed approach. [ABSTRACT FROM PUBLISHER]

In the hybrid ac–dc microgrid, the ac and dc subgrids are connected by bidirectional power converters (BPCs) that play an important role in the load power sharing and power interaction between the ac and dc subgrids. The coordination control and circulating current suppression for the parallel BPC system are very challenging. In this paper, a decentralized coordination control method is proposed for parallel three-phase BPCs, which can suppress the circulating currents, realize proper power interaction, and achieve overall load power sharing in both the grid-connected mode and the islanded mode. The performance of the proposed control methods is verified by the real-time hardware-in-loop tests. [ABSTRACT FROM PUBLISHER]

This paper presents a novel power distribution system (PDS) algorithm to be employed in a hybrid energy storage system (HESS). PDS is responsible for sharing the demand power between energy storage modules, which are battery and ultracapacitor (UC) in this study. The challenge in designing PDS is in assigning the power-share between these modules. A state of available power technique is proposed based on the prediction of the power limitations for a predefined time frame in the future. Another PDS based on the UC state of charge is developed. Various design variables are defined that affect the performance of the PDS. The genetic algorithm optimization technique is employed to determine the design variables. The proposed PDS techniques along with an energy storage system (ESS) consisting of a single battery and a basic PDS system is studied on a 12-kW electric motorcycle during the standard FTP and the New York City Cycle (NYCC) driving cycles. Battery lifetime, vehicle range, and regenerative braking energy recovery functions for the proposed methods compared with the ESS are improved by 2.6 times, 25%, and 29%, respectively. The results suggest that employing the proposed novel PDSs improves the performance of the HESS significantly. [ABSTRACT FROM PUBLISHER]

This paper investigates the optimal resource management in a microgrid under various operating conditions. A two-level optimization system is proposed for the distributed optimal resource management based on a multi-agent system framework. The proposed strategy generates a reference of the optimal power output at the top level through local communication. This strategy only requires the information among neighboring participants without a central control coordination, and simultaneously accomplishes resource optimization in a finite time while maintaining the supply–demand balance. The bottom-level control is responsible for the reference tracking of each corresponding participant in a microgrid. The convergent rate of the proposed algorithm is compared with other consensus-based algorithms through simulation studies. Simulation results in the IEEE 14-bus system and an actual islanded system are also presented to demonstrate the overall effectiveness of the proposed strategy. [ABSTRACT FROM PUBLISHER]

Energy storage systems (ESSs) are becoming indispensable components in electric power systems. They are used for energy scheduling, power/voltage smoothing, load shifting, as well as for emergency power supply. The most common control method for power/voltage smoothing is based on a high-pass-filter (HPF) structure. It generates the power reference according to the fluctuating power and provides a stabilization effect. The power and energy supplied by ESSs are majorly configured by the cutoff frequency and gain of the HPF. Considering the operational limits on ESS state-of-charge (SoC), this paper proposes an adaptive cutoff frequency design method to realize communication-less and autonomous operation of a system with multiple distributed ESSs. The experimental results demonstrate that the SoCs of all ESS units are kept within safe margins, while the SoC level and power of the paralleled units converge to the final state, providing a natural plug-and-play function. [ABSTRACT FROM PUBLISHER]

The recycled batteries can be assumed for the cost-effective grid energy storage (ES) applications, where the state of health (SOH) of recycled batteries are hard to make equal when reassembling them in one ES system. Therefore, when implementing the traditional state-of-charge balancing control methods, the batteries integrated into the same ES system will demonstrate the SOH deviation characteristics during the long-term operation due to the different degradation they suffered, which will reduce the mean time to repair, increase the maintenance duty, and shorten the life time of the ES system. Alternatively, this paper proposes an SOH balancing control method for the modular multilevel-converter-based battery energy storage system (MMC BESS) by fully using the unique modular configuration. The relationship among SOH, depth of discharge, and life cycles is analyzed in the theory, which builds the criteria for power distribution among battery packs in the MMC BESS. In addition, instead of estimating the specific SOH value, a relative SOH evaluation method is presented for easier practical implementation. And then, multiple control loops are designed for achieving the expected operational performance. MATLAB simulation and experimental results are presented to verify the proposed control method. [ABSTRACT FROM PUBLISHER]

This paper introduces a hybrid modular multilevel converter (MMC) with the full-bridge submodules (FBSMs) inserted in the ac side. It is intended for redistributing arm powers of the MMC system to reduce the submodule (SM) capacitor voltage fluctuation by injecting high-frequency powers in upper and lower arms without disturbing the output voltage. New power distribution of the hybrid MMC system can be realized by controlling the SMs and FBSMs working under the high-frequency powers. The proposed FBSMs in the hybrid MMC system also perform as the harmonic power generator to eliminate the common-mode voltages in the ac side. Since the FBSMs locate in the ac side of the hybrid MMC system, the traditional MMC control method can be directly applied in arm control of the hybrid MMC system. Meanwhile, relationship between the arm powers and SM capacitor voltage has been analyzed in detail to reduce the SM capacitor voltage ripples by redistributing the frequency spectrum of arm powers. Simulation and experimental results have also verified the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

The Sandia frequency-shift method, among all frequency-based active islanding detection methods (IDMs), is one of the most effective methods for inverter based distributed generators (DGs). The nondetection zone (NDZ) of the Sandia frequency shift (SFS) highly depends on its design parameters. If the design parameters are not properly tuned, they may result in failure of the method or deterioration of the system power quality (PQ) through injection of a high amount of harmonics. The main objective of this paper is to propose a new algorithm for SFS method parameter determination, which would add precision to the previous parameter design criterion. In this paper, also a new formula for multi-DG applications is proposed which results in optimally setting of all SFS parameters to eliminate NDZ. Using the new criterion, the negative impact of the conventional criterion on PQ is reduced, and the efficiency of the SFS IDM is increased. The simulation results show that the proposed algorithm results in more accurate detection of the islanding phenomenon in the shortest possible time. All of the simulations and NDZ analysis are carried out in the MATLAB environment. [ABSTRACT FROM PUBLISHER]