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The development of pulsed power supplies and switched-mode power supplies raises urgent need for medium-frequency high-power transformers. This paper proposes an optimal design method of medium-frequency Fe-based amorphous transformer based on multiobjective postdecision genetic algorithm. The optimization targets at transformer volume (expressed in terms of area product $A_{p}$) and its loss. Transformer operating frequency $f$ , operating magnetic flux density $B_{m}$ , and current density $J$ are taken as design variables, while temperature rise and efficiency are taken as constraints. This design method helps to solve the traditional transformer’s design problem of repetitive calculation. Moreover, it proposes to the designer a series of optimized transformers, rather than a single solution, so the designer can choose the best transformer according to the application needs. Finally, the simulation and experimental results are presented to validate the effectiveness and feasibility of the theoretical analysis. [ABSTRACT FROM AUTHOR]

Deployment of renewable energy sources in power grid causes an undesirable characteristic in the voltage profile due to its stochastic nature. Such electrical perturbations may impact the performance of equipment or machines connected to the grid, especially large rated machines (e.g., 250 MW). This paper investigates the electrical, thermal, and mechanical stresses on large rated doubly fed synchronous (fixed speed) and doubly fed asynchronous (variable speed) machines used in pumped storage power plants under voltage unbalance. Also, the lifespan of the drive train considering thermal stress is estimated. In this paper, considering the medium voltage distribution system (15.75 kV), the magnitude of voltage unbalance is opted as 2.5% and 5% to test the performance of doubly fed machines. With respect to these considerations, the impacts on machine parameters such as rotor current, stator current, input power, torque, and losses are comprehensively investigated. To observe the performance of large rated doubly fed machine drive system under voltage unbalances, the MATLAB/Simulink environment is adopted. Also, to realize the real-time impact on doubly fed machines, a prototype rig (with 2.2-kW synchronous and asynchronous machines) are experimented. The practical significance of this relative analysis is to minimize voltage collapse in the system and for developing the robust system with countermeasures. [ABSTRACT FROM AUTHOR]

This paper extends the dynamic coherency determination (DCD) method by including Type-3 wind power plants (WPPs) models in the coherency evaluation process and quantifies impacts of the high depth of wind power penetration on the coherency phenomena of interconnected power systems. The method is based on frequency-deviation signals, measured at nongenerator buses and terminal buses of WPPs and synchronous generators. Salient features of the presented method are its ability to account for the hybrid nature of enhanced generic models of Type-3 WPPs and expanding notion of the power system coherency beyond the classical definition by including models of Type-3 WPPs. This paper also investigates impacts of the high depth of wind power penetration; i.e., up to 30%, on the coherency structure of the 16-machine/68-bus NPCC equivalent system. The studies are based on time-domain simulations in PSS/E software. The investigations reveal that Type-3 WPPs can introduce new coherent areas, significantly change areas’ boundaries and number of areas, and alter frequencies/dampings of interarea modes. [ABSTRACT FROM AUTHOR]

Time delay is prejudicial to power system stability and generally worsens the performance of a control system. In this paper, the approaches for stability analysis and stabilization of a power system consisting of time-varying delay are established. The paper starts with the modeling of the power system according to time-delay differential algebraic equations. An integral quadratic constraints (IQC) method is constructed to guarantee the stability of the proposed feedback controller. The frequency-domain IQC and time-domain dissipation inequality are effectively combined to perform stability analysis and stabilization of the power system considering time delays, without complex numerical computation. A two-area four-machine system, an IEEE 10-machine 39-bus system, and a WECC 179-bus system are employed to support the stability criteria and the IQC method. The simulation results indicate that the combined methods effectively damp the oscillation and improve the performance. [ABSTRACT FROM AUTHOR]

Centralized electricity markets currently do not optimize reactive power and voltage in the market clearing software. Voltage and local reliability (VLR) commitment requirements are mostly identified through out of market operational procedures. Failure to maintain VLR may incur voltage collapse, generation, transformer loss, or even blackout. Midcontinent Independent System Operator (MISO) employs binary constraints, minimum/maximum generation constraints, interface constraints, and manual commitments to address VLR requirement in the market clearing process and ensure adequate commitment for reliability. This paper integrates binary VLR constraints in day-ahead security constrained unit commitment to improve market efficiency. However, VLR constraints may cause uplift cost, and sometimes the associated uplift cost can be significant. An uplift cost allocation method with the consideration of resources commitment reasons is developed in this paper. The proposed approach is considered for implementation in MISO market clearing process and a MISO test case is used to validate the effectiveness of the proposed approach. [ABSTRACT FROM AUTHOR]

This paper proposes a novel control method for an asymmetrical-cascaded-multilevel-converter-based hybrid energy storage system (HESS), which includes one battery and several electrical double-layer capacitors (EDLCs). Traditionally, it is challenging to control the power distribution between different cascaded H-bridges by using different energy storage components as dc sources. In this paper, a feedforward space-vector-modulation (FFSVM) technique is used to distribute the active power between the battery and EDLCs. With the proposed voltage feedforward mechanism, the HESS can flexibly operate in the normal operation mode, the high-power output mode, and the reverse power absorption mode. The principle and effectiveness of the improved FFSVM technique are analyzed. Meanwhile, the state-of-charge-balancing mechanisms are introduced. The simulation results obtained in MATLAB/Simulink as well as the experimental results of a hybrid energy storage test bed based on the proposed system are presented to verify its performance. [ABSTRACT FROM PUBLISHER]

Essential imbalance and fluctuation of the mobile train load draw some problems, e.g., three-phase unbalance, reactive power, voltage and load fluctuation, harmonics, etc. in both public and train supply networks (TSNs). Railway power flow controller (RPFC)'s good performance on dealing with those problems has been convinced in practice these years. However, as the primary task in commercialization, how to qualitatively determine RPFC's design capacity with high cost efficiency and how to comprehensively assess its performance in the design stage have perplexed engineers for many years. To solve those problems in both planning and real-time executing processes, this paper focuses on an RPFC design capacity optimization strategy for grid-connection compatibility and operating performance improvement in terms of both the utility and the TSN. The strategy not only makes a railway substation satisfy the grid-connection standards with high calculating efficiency, but also renders the RPFC to have the minimum design capacity, the excellent feeder voltage control ability, the good fixed capacitor installing prospect, and the high operating efficiency on the targets of reducing the investment and enhancing the transportation ability. The generic models, the industry-oriented design and the quantitative analysis, discussed in this paper give an insight for those concerned based on a balance transformer. Future RPFC projects on serviced railway power systems will benefit from the proposed methodology. [ABSTRACT FROM PUBLISHER]

This paper presents a uniform control strategy for the bidirectional ac/dc interlinking converter (BIC) in hierarchical controlled hybrid microgrid. The uniform control strategy unifies different control structures for multifunctional BIC in terms of power management, ac and dc voltage support. With the unified control structure, various triggering mechanisms for BIC mode-switch are not compulsory in response to the relevant scenario changes in the power network. Therefore, the negative consequences, such as unsmooth transition and system collapse due to the inaccurate or slower mode switch, can be avoided. Moreover, the uniform control strategy is also applicable for the hierarchical controlled hybrid microgrid, whose control architecture is typically comprised of the centralized and decentralized levels. This enables the communication fault ride-through capability and the impact from the communication failures can thus be mitigated. To sum up the above two features, the proposed control strategy is able to provide a smooth operation for the BIC without control mode switch in the event of unintentional scenario changes in power or communication network. To verify the validity of the proposed uniform control strategy, the controller hardware-in-the-loop experimental results have been provided in this paper. [ABSTRACT FROM PUBLISHER]

This paper proposes a new filter design method that can smooth the wind power generation output while keeping the energy capacity and power rating of the energy storage system (ESS) small. Wind power generation causes frequency fluctuations in power systems. Therefore, in many cases, the ESS is needed for smoothing the fluctuations of wind generator output. In order to improve the performance of the ESS controlled with the conventional low-pass filter (LPF), this paper investigates other types of filters. First, the relations between filter and energy capacity/power rating of the ESS are disclosed through the worst-case study. Then, the frequency fluctuation analysis of the power system with respect to the wind power generation is carried out in order to realize a pin-point smoothing. Finally, a metaheuristic optimization method is proposed for the multiobjective design of the filter based on these relations so as to achieve an optimal tradeoff between the output smoothing and energy capacity/power rating of the ESS. It is shown via simulation analysis with real wind data that the proposed method can suppress the frequency fluctuation of the power system effectively with the ESS having smaller energy capacity and power rating. [ABSTRACT FROM PUBLISHER]

This paper presents a new transformer, i.e., the custom power active transformer (CPAT) which integrates both series and shunt power conditioning through power electronics into a single transformer. This is achieved through a distinct design of the magnetic circuit and auxiliary windings of the transformer. In this paper, a single-phase CPAT is proposed as well as a preface into its extension to multiphase systems. Through its magnetic equivalent circuit model, several design considerations and control limitations are revealed in the paper. Analysis of the resulting CPAT structure shows some prospects in material saving as well as size and cost reduction when compared to the traditional multitransformer-based configuration. In this paper, the proposed single-phase CPAT is utilized in a distribution system application, where the control architecture is designed to attenuate voltage and current distortions at both the load and the grid side, respectively. Performance and effectiveness of the proposed CPAT are evaluated through simulation and experiments. [ABSTRACT FROM PUBLISHER]

Critical process loads need to be safeguarded against power system disturbances and erroneous operations caused by human factors. During such events, a fast synchronism-supervised transfer scheme is required to ensure continuous operation. This paper discusses the implementation of a fast motor bus transfer scheme using existing protective relays. The scheme is designed to respond to local and remote (upstream) events in the substation. This makes possible an attempt to initiate a fast transfer for events that are remote to the motor bus. On a failure to achieve a fast transfer, the scheme resorts to an in-phase transfer and, if that fails, finally a residual transfer. Real-time dynamic modeling was performed to simulate motor bus decay and reacceleration. This paper provides the results of the simulations and the response of the transfer scheme. [ABSTRACT FROM AUTHOR]

This paper proposes a fast and robust unscented Kalman filter based decentralized dynamic state estimator (DSE) for power system online monitoring and control. The proposed robust DSE is able to detect, identify, and suppress three types of outliers, namely the observation, innovation, and structural outliers. Observation outliers refer to the received PMU measurements providing unreliable metered values due to gross errors or cyber attacks; innovation outliers are typically caused by impulsive system process noise, whereas structural outliers are induced by incorrect parameters of the generators or its associated controllers, such as exciters and speed governors. To enable the fast estimation of generator states of large-scale power systems in a decentralized manner, two model decoupling approaches are presented and compared. It is shown that the generator decoupling approach presented in this paper achieves higher statistical efficiency than the ones proposed in the literature in the presence of both small and large measurement noise. To detect and distinguish three types of outliers, projection statistics based multiple hypothesis testing approach is proposed. Specifically, three hypotheses corresponding to the occurrence of three types of outliers are assumed by constructing three innovation matrices; these matrices are made up by time-correlated innovation vectors, and/or predicted states, and/or measurements; then projection statistics are applied to each of the innovation matrix and its calculated projection values are checked by a statistical test to validate the assumed hypothesis. The identified outliers are further suppressed by a generalized maximum-likelihood-type estimator. Numerical results carried out on the IEEE 39-bus system demonstrate the effectiveness and robustness of the proposed method. [ABSTRACT FROM AUTHOR]

Wide-area damping controller (WADC) is a very effective tool to damp out the low-frequency oscillation in wide-area power systems. However, the WADC needs communication networks to transmit remote signals; hence, the network-induced delay and packet dropout are inevitably introduced in the communication of wide-area measurement systems (WAMS). In order to effectively compensate delay and packet dropout, in this paper, a new wide-area dynamic damping controller (WADDC) is designed. Firstl the discrete-time model of power system with random delay, packet dropout, and external disturbance is established. Then, the WADDC based on robust H∞ control is designed and the sufficient condition about stability of the closed-loop system is given. Finally, the controller designed in this paper is tested on the two-area four-machine power system and the 16-machine 68-bus system. Simulation results demonstrate the effectiveness the proposed methods for damping out the low-frequency oscillation and compensating the network-induced delay and packet dropout. [ABSTRACT FROM AUTHOR]

As the power system evolves to better address environmental and reliability concerns, its overall dynamics changes and consequently challenges the adequacy of established operating procedures. This evolution brings a significant increase in the number of integrated renewable energy sources (RES) and HVDC connections. RES are normally connected to the grid through power electronic converters, which reduces or completely eliminates their electrical coupling to the power grid. As a result, such units are unable to contribute to the inertia of the system, posing a potential threat to the grid's physical security. More specifically, postfault frequency characteristics, such as rate of change of frequency (RoCoF), frequency nadir, and quasi-steady-state frequency, depend on the system inertia and their respective limits may potentially be violated. One way to address this problem is adding constraints to the unit commitment formulation so that operations maintain their frequency characteristics within acceptable limits. This paper studies how such changes affect the system frequency deviation from its rated value. The power system is modeled as an enterprise control that combines multiple layers of control operations into one package. Such integration allows capturing how the effects of wind integration and the addition of unit commitment inertia constraints propagate through control layers to impact the system frequency. [ABSTRACT FROM AUTHOR]

The ability to identify electric shock in the human body is a crucial consideration in the design of touch/leakage protective devices. In this paper, the $\alpha$ -dispersion characteristics of electrical impedance in the human body are investigated based on the Cole–Cole model. An improved electric shock identification method is proposed accordingly. The effects of various factors (e.g., transition resistance and feeder reactance) on the accuracy and reliability are analyzed. Feasibility and effectiveness of the method are verified via numerical simulation. The results indicate that 1) $\alpha$-dispersion is an effective feature for distinguishing living or nonliving organisms; 2) the proposed method is robust and unaffected by transition resistance; and 3) the computational cost is low to satisfy standard leakage current protective device requirements. This paper provides a solution to the dead-zone problem as well as a set of workable guidelines for protective device design. [ABSTRACT FROM AUTHOR]

Analyzing the harmonic distortions at the point of common coupling is thoroughly addressed in this two-part paper. The main aim of such an analysis is to identify which of the utility and customer sides is significantly responsible for the harmonic distortions at the point of common coupling. In Part I, the meaning of the dominant side is challenged fundamentally. Here, two different definitions for the dominant side are discussed: The side with the larger equivalent harmonic “voltage” or “current” source. It is shown that these definitions are not identical. Subsequently, common methods are categorized in three general concepts based on: the direction of active power flow, the reactive power, and the voltage-current ratio. These three categories as well as their validity are analytically reviewed for both the definitions. The concept based on the voltage–current ratio has been explicitly presented in the original work for identifying the dominant equivalent harmonic voltage source. This concept is developed in this paper for identifying the dominant equivalent harmonic current source as well. In Part II, the application of the methods is illustrated using some common calculation examples. In addition, these methods are described verbally to provide a physical interpretation. Some practical aspects regarding the implementation of the methods are discussed as well. [ABSTRACT FROM AUTHOR]

In hydroelectric power plants, which are characterized by particularly high short-circuit current levels and high time constants, conventional current transformer specifications can result in increased equipment dimensions, thus complicating their installation, especially during refurbishment projects. This paper presents a study to assess the potential of various low-power instrument transformers (LPITs) for generator protection applications. Two types of LPITs were evaluated: the optical current transformer (OCT) and the stand alone merging unit (SAMU). To test the OCT, a 65-kA-peak test source was developed using a real-time simulator. This source was used to inject symmetrical and asymmetrical currents into LPITs for the assessment of protection accuracy class. Low-current tests were also performed to assess their metering classes. This paper presents the design of a high-current test bench, measurement uncertainty analysis, and analysis algorithms used for device evaluation. Analysis results are then presented and discussed in terms of their applicability to generator differential protection using SAMUs and OCTs. [ABSTRACT FROM AUTHOR]

This paper studies the vulnerability of flow networks against adversarial attacks. In particular, consider a power system (or, any system carrying a physical flow) consisting of $N$ transmission lines with initial loads $L_{1}, \ldots , L_{N}$ and capacities $C_{1}, \ldots , C_{N}$ , respectively; the capacity $C_{i}$ defines the maximum flow allowed on line $i$. Under an equal load redistribution model, where load of failed lines is redistributed equally among all remaining lines, we study the optimization problem of finding the best $k$ lines to attack so as to minimize the number of alive lines at the steady-state (i.e., when cascades stop). This is done to reveal the worst-case attack vulnerability of the system as well as to reveal its most vulnerable lines. We derive optimal attack strategies in several special cases of load-capacity distributions that are practically relevant. We then consider a modified optimization problem where the adversary is also constrained by the total load (in addition to the number) of the initial attack set, and prove that this problem is NP-hard. Finally, we develop heuristic algorithms for selecting the attack set for both the original and modified problems. Through extensive simulations, we show that these heuristics outperform benchmark algorithms under a wide range of settings. [ABSTRACT FROM AUTHOR]

This paper presents a nonintrusive load monitoring (NILM) algorithm based on mixed-integer linear programming. The formulation deals with the problem of multiple switching that arises when disaggregating individual appliance’s consumptions from a compound power measurement. Mixed-integer linear constraints are used to efficiently represent the load signatures of each appliance. Also, a window-based strategy is used to enhance the computational performance of the proposed NILM algorithm. The disaggregation can be made using only active power measurements at a low sampling rate, which is available in most energy meters. Moreover, if available, other signatures can be added to the model to improve its accuracy, such as reactive power signatures or harmonics. The performance of the algorithm is evaluated using three test cases from the almanac of minutely power dataset. The proposed method is also compared with a disaggregation method called aided linear integer programming. Results demonstrate the ability of the proposed method to accurately identify and allocate individual energy signatures in a computationally efficient manner, which makes it suitable for inexpensive home energy management. [ABSTRACT FROM AUTHOR]

The uncertainties of renewable energy may bring impacts to power system reliability. This paper proposes a novel generation rescheduling algorithm, which adjusts generation outputs to mitigate the variations of branch power flows and relieve the overload probability. This algorithm helps prevent power congestion and balance the aggregate renewable generations and loads in power systems. Besides, the paper also proposes a probabilistic method evaluating the system uncertainty issue in the power system considering generation rescheduling operation. The proposed generation rescheduling algorithm has been tested on the Arizona transmission system. The generation rescheduling method enhances power system reliability analysis with a high penetration of renewable energy resources. [ABSTRACT FROM PUBLISHER]

Power system operation will encounter numerous variabilities as the proliferation of renewable energy continues. Such random events will require the evaluation of corresponding variables and the assessment of their impacts on the monitoring and the control of stochastic power systems. In this paper, a global sensitivity analysis (GSA) method is proposed to perform a priority ranking of renewable energy variabilities that will affect the voltage stability of power systems. First, a probabilistic model for the load margin calculation is presented considering the renewable power generation. Then, GSA is applied to models with correlated random input variables and the importance index is designed for evaluating the impacts of such variables. Next, the stochastic response surface method is adopted in GSA to improve the computation efficiency of the proposed evaluation method. Finally, the overall procedure is presented to identify critical variables that can affect the variability of load margins in voltage stability analyses. The proposed method is applied to power systems with a large penetration of renewable power and the influences of critical variabilities on voltage stability are analyzed. In this paper, the proposed method is tested using the IEEE 9-bus and the IEEE 118-bus systems, and its accuracy is compared with those of the local sensitivity analysis method and the commonly used GSA methods. [ABSTRACT FROM PUBLISHER]

In this paper, we model topology control through transmission switching as a recourse action in the day-ahead operation of power systems with large-scale renewable generation resources. We prove that transmission switching could only reduce the linear objective value of direct current optimal power flow when congestion exists. However, we also show, through a simple example, that unit commitment cost could be reduced by transmission switching even in the absence of congestion. To solve the stochastic unit commitment with topology control within reasonable computational time, we proposed a heuristic that first decomposes a practical system into zones and then solves the problem for each zone in parallel. The benefit of topology control recourse is demonstrated on a network representing the Central European System. We compare the costs of the network with different loading and renewable generation conditions. The cost reduction of the test system can reach 3.34% with heavy load and large-scale renewable generation while in a single zone the cost reduction can be above 7%. [ABSTRACT FROM PUBLISHER]

This paper examines the impact of dynamic interactions between the voltage source converters (VSCs) on the small-signal stability of an AC/MTDC (multiterminal dc) power system. The examination is carried out based on a closed-loop interconnected model consisted of an open-loop VSC subsystem and an open-loop subsystem of the rest of MTDC network (RDCN). Open-loop modal coupling is the modal condition that an oscillation mode of open-loop VSC subsystem is close to an oscillation mode of open-loop subsystem of the RDCN on the complex plane. Analysis indicates that the open-loop modal coupling may very likely degrade the small-signal stability of the AC/MTDC power system. If a VSC uses the active power control, the open-loop VSC subsystem is of no oscillation mode. Hence, open-loop modal coupling between the VSCs cannot occur in the MTDC network implementing the master–slave control. Whilst the open-loop modal coupling may introduce instability risk to the MTDC network using the dc voltage droop control. Therefore, the paper reveals the mechanism about how and why the dynamic interactions between the VSCs may degrade the small-signal stability of the AC/MTDC power system from the perspective of the system modal condition—the open-loop modal coupling. [ABSTRACT FROM PUBLISHER]

This paper applies finite control set model predictive control (FCS-MPC) for dynamic reactive power compensation using a hybrid active power filter (HAPF). The FCS-MPC uses a model based on LCL-filter equations to predict the system behavior and optimize the control action. In fact, the application of FCS-MPC in grid-connected converters with LCL-Filter is quite recent. This algorithm is a very promising control technique for power electronics converters and its use for reactive power control of hybrid filter has not been reported in the literature yet. This paper uses the FCS-MPC in a multivariable structure along with an adaptive notch filter to damp resonance. The main purpose is to improve the dynamic response of the HAPF. Simulation as well as practical results prove the feasibility of FCS-MPC application in HAPF reactive power control. The dynamic response of the equipment was significantly improved and represents the main contribution of this paper. As a result, the FCS-MPC allows tracking fluctuations and abrupt changes in load reactive power. [ABSTRACT FROM PUBLISHER]

This paper jointly addresses two major challenges in power system operations: 1) dealing with non-convexity in the power flow equations, and 2) systematically capturing uncertainty in renewable power availability and in active and reactive power consumption at load buses. To overcome these challenges, this paper proposes a two-stage adaptive robust optimization model for the multi-period AC optimal power flow problem (AC-OPF) with detailed modeling considerations, such as reactive capability curves of conventional and renewable generators and transmission constraints. This paper then applies strong second-order cone programming (SOCP)-based convex relaxations of AC-OPF combined with the use of an alternating direction method to identify worst-case uncertainty realizations, and also presents a speed-up technique based on screening transmission line constraints. Extensive computational experiments show that the solution method is efficient and that the robust AC OPF model has significant advantages both from the economic and reliability standpoints as compared to a deterministic AC-OPF model. [ABSTRACT FROM PUBLISHER]

Clustered unit commitment (CUC) formulations have been proposed to provide accurate and fast approximations to the unit commitment (UC) problem. In these formulations, identical or similar plants are grouped into clusters. This way, the binary commitment variables of all the plants within a cluster can be replaced by a single integer variable. This approach has recently been mainly used for tractably integrating flexibility constraints in generation expansion planning problems. However, a thorough general validation is still missing. In addition, these formulations do not provide commitment schedules on a plant-by-plant level and hence cannot be used directly for operating actual systems or markets. A first contribution of this paper is to show that errors can be introduced both due to the problem formulation and the grouping of nonidentical units. A case study is presented in which these errors are quantified under different conditions. Overall, the error in approximating the total cost does not exceed 0.06%. A second contribution of this paper is the development of a hybrid approach, which sequentially uses a CUC and a traditional UC model. This approach allows to reduce the computational cost of solving the UC problem while providing a guaranteed feasible and near-optimal solution. [ABSTRACT FROM AUTHOR]

This paper deals with an innovative design strategy of building power systems by introducing criteria based on both the “installation approach” and the “operating approach” applying plan–do–check–act (PDCA) cycle. The In-Op design of the electrical power systems takes care of the worst cases of configurations, adequate gaps on load in selecting the rating of components, the actual mean losses to evaluate their energetic operation, and to avoid excessive gaps on the lifetime of components. With this aim, the authors suggest consideration of the thermal aging model of Arrhenius to review the actual gap on load in selecting the rating of components. In reference to IEC standards, this paper underlines in the circuits design the cable steady and transient current densities, the load current torque density as “natural” parameters that allow applying a thumb rule in the classic sizing of the cross-sectional area of circuit conductors. Microsystem criteria in power systems design allow structuring their configuration with components of smaller size to reduce radically the volume of circuit conductors with more sensitive results in the branch distribution. The authors suggest why not reconsider the series of commercial cross section areas of power cables. [ABSTRACT FROM PUBLISHER]

As electric power system operators shift from conventional energy to renewable energy sources, power distribution systems will experience increasing fluctuations in supply. These fluctuations present the need to not only design online decentralized power allocation algorithms, but also characterize how effective they are given fast-changing consumer demand and generation. In this paper, we present an online decentralized dual descent (OD3) power allocation algorithm and determine (in the worst case) how much of observed social welfare can be explained by fluctuations in generation capacity and consumer demand. Convergence properties and performance guarantees of the OD3 algorithm are analyzed by characterizing the difference between the online decision and the optimal decision. We demonstrate validity and accuracy of the theoretical results in the paper through numerical experiments using real power generation data. [ABSTRACT FROM PUBLISHER]

Today the dq0 reference frame is mainly used for modeling and control of traditional electric machines and small power sources. A current challenge is to merge various dq0-based models appearing in recent literature to obtain a complete model of a large power system. To this end, in this paper we propose a model describing the dynamics of large transmission networks based on dq0 quantities. The proposed model is based on a standard network topology, uses sparse system matrices, and is of minimal order. We also demonstrate how this model may be used to construct a small-signal description of a complete system that includes the transmission network, generators, and loads. Results are illustrated on the basis of a long transmission line, and using the 118-bus test case network. This paper is accompanied by a free software package. [ABSTRACT FROM PUBLISHER]

Many power systems applications such as power flow and short-circuit analysis require very large sparse matrix computations. With the increase in reliance on our electric infrastructure, power systems are continually growing in size, creating greater computational complexity in solving these large linear systems within reasonable time. For sparse matrix applications, it is desirable to have an algorithm with low runtime complexity in terms of the number of nonzeros in the matrix. There have been several recent advances in computational methods in other fields that, if applied to power system, could make real-time dynamic simulation a reality. Much work has been done for specific types of these problems where the system is symmetric and diagonally dominant, similar to the form of power system matrices. This paper details an expansion on the current work in fast linear solvers to develop power system specific methods that show potential for accurate solutions in $O(m \log ^2 n)$ run times, where $n$ represents the number of nodes and $m$ represents the number of nonzeros in the power system matrix. This paper presents the simulation validation of a recently developed recursively solved iterative chain method for sparse matrices using a low stretch spanning tree preconditioner. [ABSTRACT FROM PUBLISHER]

This paper presents a distributionally robust planning model to determine the optimal allocation of wind farms in a multi-area power system, so that the expected energy not served (EENS) is minimized under uncertain wind power and generator forced outages. Unlike conventional stochastic programming approaches that rely on detailed information of the exact probability distribution, the proposed method attempts to minimize the expectation term over a collection of distributions characterized by accessible statistical measures, so it is more practical in cases where the detailed distribution data is unavailable. This planning model is formulated as a two-stage problem, where the wind power capacity allocation decisions are determined in the first stage, before the observation of uncertainty outcomes, and operation decisions are made in the second stage under specific uncertainty realizations. In this paper, the second-stage decisions are approximated by linear decision rule functions, so that the distributionally robust model can be reformulated into a tractable second-order cone programming problem. Case studies based on a five-area system are conducted to demonstrate the effectiveness of the proposed method [ABSTRACT FROM PUBLISHER]

This paper proposes a model to carry out analysis of storage facilities operation including a transmission network. The model represents a short-term storage operation in an approximated way that reduces computational requirements, which makes it suitable for medium- and long-term operational planning in power systems with a high level of renewable energy penetration. In the proposed model, we cluster hourly data using the so-called system-states framework developed in previous work. Within this framework, nonconsecutive similar time periods are grouped, while chronological information is represented by a transition matrix among states. We extend the system-state framework from a single-bus system to a transmission network. We define and analyze two alternative sets of representative variables for clustering hours to obtain system states when the transmission network is considered. This extension of the system states framework allows us to evaluate the impact of transmission congestions in medium- and long-term planning models in a reasonable computation time. A case study shows that the proposed model is 235 times faster than an hourly approach, used as benchmark, whereas the overall system cost is approximated with less than 2% error. The overall charging/discharging trends are similar enough to those of the hourly model, being hydro storage better approximated than fast-ramping batteries. Besides, for the analyzed case study, it is shown how congestion in the transmission network in fact improves the accuracy of the proposed approach. [ABSTRACT FROM PUBLISHER]

The increasing penetration of variable energy resources has led to more uncertainties in power systems. Flexible Ramping Products (FRP) have been adopted by several electricity markets to manage the uncertainties. We reveal that neglected line congestion for FRP may not only cause infeasibility, but also result in a failure of cost recovery. To address the deliverability issues on FRP, this paper proposes a new concept, Deliverable Robust Ramping Products (DRRP), in real-time markets. The DRRP includes generation ramping reserve and generation capacity reserve. The DRRP is deliverable and immunized against any predefined uncertainty. It also fully addresses the bid cost recovery issue caused by the line congestion in existing FRPs. The prices of DRRP are derived within the Affine Adjustable Robust Optimization (AARO) framework. These prices can be used to identify valuable reserves among available reserves and quantify the values of flexible resources that provide reserves. This paper also proposes a general approach to obtaining the time-decoupled prices for DRRP and generation, which can be used for the market settlement of the first interval only in real-time markets. Simulations on a 3-bus system and the IEEE 118-bus system are performed to illustrate the concept of DRRP and the advantages of DRRP compared to existing FRP. [ABSTRACT FROM PUBLISHER]

In this paper we address some shortcomings in existing nonlinear dynamic models of power system experiencing symmetrical and unsymmetrical faults in their transmission/distribution networks. The shortcomings relate to: 1) approximations relating to stator dynamics, internal voltage of the positive sequence network and the dynamics of the negative and zero sequence networks, and 2) existing models are time -variant, which may not be suitable for system studies such as stability and fault detection studies that require time invariant model. The approximations outlined in 1) adversely affect the modeling accuracy, especially that of the system response during the period immediately after the occurrence of faults. We present in this paper a full fault-dependent time-invariant dynamical model of power systems experiencing symmetrical and unsymmetrical faults in their transmission/distribution networks and verify it through simulation studies mimicking real life scenarios. IEEE 30 bus power system is considered as the study case. The simulation results are compared to Matlab's “SimPower” and PSCAD/EMTDC software packages. [ABSTRACT FROM AUTHOR]

The proper modeling of the transient thermal behavior of mutual heating effects between underground power cables is very important for the rating of transmission and distribution cables. The IEC standards proposed an accurate model based on exponential integrals that it can be difficult to implement in basic electrical software. The model is not consistent with the layered modeling of the cable thermal resistances. In this paper, a simple and easy-to-use alternative model is presented. It consists of injecting the correct current at the right position of the RC circuit representing the soil. The new model can accurately reproduce the full physics of the transient phenomenon and is consistent with the modeling of the cable used in the IEC standards themselves. The new model is tested and validated against numerous finite-element simulations for realistic cable installations. [ABSTRACT FROM AUTHOR]

Neatly represented and properly classified load profiles are fundamental to many control optimization techniques of modern power systems, especially in a distribution area. This paper presents a novel load profile management software framework for boosting the efficiency of power systems operation. The proposed framework encodes and classifies load profiles in real-time. Imperfections as well as time-shifts in the input (measured power consumption levels) are tolerated by the suggested system, thus always providing accurate, fast and reliable output. The framework’s fully component based structure allows easy customizations of the encoding as well as the classification engines. The default encoding engine is based on an artificial neural network, a variant known as a deep learning auto-encoder comprised from stacked sparse auto-encoders. The default classifier engine is based on an implementation of a locality sensitive hashing algorithm. The developed methodology was tested on the real case of a set of anonymous customers supplied by a power distribution company. The paper also contains an elaboration about the experiences gained during the design, implementation and testing phase of this system as well as a detailed engineering use case of the framework’s applicability. [ABSTRACT FROM PUBLISHER]

In this paper, a new concept for analyzing the dielectric severity supported along transformer windings when a transformer is submitted to a nonstandardized transient voltage waveform induced by switching operation of a vacuum circuit breaker (VCB) is examined. There are two new factors considered for evaluating the severity supported by the insulation windings in factory and in service. One factor is based on the methodology suggested by the authors called time-domain severity factor and another one is the frequency-domain severity factor. Both methodologies are here applied to two case studies in order to show and compare their capabilities and sensibilities to detect the risk of dielectric failures. The analyzed case studies, performed as practical applications, consist of: 1) a power transformer submitted to damped oscillatory waves at the resonant frequency and 2) a power system consisting of a power transformer connected to a VCB. [ABSTRACT FROM AUTHOR]

Shipboard control systems equip an expert operator with the ability to safely open and close breakers to facilitate electric plant operations. In more advanced systems, ship integrated power systems are equipped with automatic control systems that provide power management by automatically connecting and disconnecting power generation sources based on plant's present load and online generation capacity. What is generally lacking, however, is an effective manner to provide autonomous reconfiguration of the power system in response to electric plant casualties and ship's mission changes when the ship's electric plant is in a degraded condition. This paper explores the use of graph theory principles as they apply to developing automation control system algorithms to provide electric plant operations full autonomous control in the event of electric plant casualties and/or ship's mission changes. [ABSTRACT FROM AUTHOR]

This paper proposes a generalized approach of the per unit normalization, named complex per unit normalization (cpu), to improve the performance of fast decoupled power flow methods applied to emerging distribution networks. The proposed approach takes into account the changes envisaged and also already faced by distribution systems, such as high penetration of generation sources and more interconnection between feeders, while considering the typical characteristics of distribution systems, as the high R/X ratios. These characteristics impose difficulties on the performance of both backward-forward sweep and decoupled-based power flow methods. The cpu concept is centred on the use of a complex volt-ampere base, which overcomes the numerical problems raised by the high R/X ratios of distribution feeders. As a consequence, decoupled power flow methods can be efficiently applied to distribution system analysis. The performance of the proposed technique and the simplicity of adapting it to existing power flow programs are addressed in the paper. Different distribution network configurations and load conditions have been used to illustrate and evaluate the use of cpu. [ABSTRACT FROM PUBLISHER]

Integrating wind power into power systems contributes to existing variability in system operations. Current methods to mitigate this variability and uncertainty focus on using conventional generator ramping capability. There is also the option of using wind power itself to mitigate the variability and uncertainty that it introduces into the system. This paper introduces the concept of a flexible dispatch margin as a means for wind to participate in mitigating net variability and net uncertainty. In providing a flexible dispatch margin, wind generators under-schedule in the hour-ahead energy market in order to have additional expected flexibility available for the real-time market. The implementation of the flexible dispatch margin is analyzed in a two-stage optimization model with recourse to the flexible dispatch margin, flexible demand and generator ramping. This modeling framework combines Monte Carlo simulations with AC OPF analysis, using the IEEE 39-bus test system. Results show that use of the flexible dispatch margin decreases the reliance on peaking generators to mitigate net variability and uncertainty, and also decreases the frequency of price spike events, particularly as wind penetration increases from 10% to 30%. The analysis emphasizes the importance of increasing flexible resource capability as power system variability and uncertainty increase. [ABSTRACT FROM PUBLISHER]

All-electric ship power systems include less generation capacity and smaller rotating inertia compared with large power systems. The systems include large portions of nonlinear loads and dynamic loads, which may reduce the stability margin. Moreover, various operational constraints, such as system frequency constraint, motor voltage constraint and dynamic cable constraint, need to be satisfied in operational real time. Further, pulse loads draw very high short-time power in an intermittent way, which may significantly deteriorate the power quality of the system. In this paper, a novel multi-agent system cooperative controller for a medium voltage AC (MVAC) system of all-electric ship power systems is developed to balance load and generation in real time while satisfying system's operational constraints and considering load priorities. The new method coordinates the pulse load and the propulsion load to reduce the impact of pulse load changes on the power quality of all-electric ship power systems. The dynamic behavior of the new method is evaluated using case studies in PSCAD software. [ABSTRACT FROM PUBLISHER]

This paper studies the optimal control problem for large-scale systems with unknown parameters and dynamics. By using robust adaptive dynamic programming (RADP) method, a decentralized optimal control design is given for large-scale systems with unmatched uncertainties. The convergence of the proposed RADP algorithm and the asymptotic stability of the closed-loop large-scale system are studied rigorously. Finally, a numerical example of a large-scale power system is adopted to illustrate the effectiveness of the obtained algorithm. [ABSTRACT FROM PUBLISHER]

Phasor measurement units (PMUs) are becoming an important component in the power grid. The PMUs provide time-synchronized measurements of multiple remote measurement points, enabling more accurate and real-time monitoring of the system state. Heuristically, it is difficult to tell how the placement of a PMU at a specific location in the power system would affect the state estimation error, not to say the effect of the PMU synchronization and measurement accuracy. In this paper, we derive the posterior Cramér-Rao bound (PCRB) on the state estimation error based on a measurement model which considers the phase-angle mismatch from PMU measurements. We then propose a PMU placement strategy using the derived PCRB. The greedy algorithm is used to solve the optimization problem. The results are then compared with other heuristics, with the optimal solution through an exhaustive search (for small systems), and with a lower bound on the optimal placement obtained through convex relaxation. For some design criteria, the objective functions are submodular, which guarantees a performance bound on the greedy solution. For other design criteria where the objective functions are not submodular, numerical examples demonstrate the effectiveness of the greedy algorithms. [ABSTRACT FROM AUTHOR]

Power system loads are one of the crucial elements of modern power systems and, as such, must be properly modelled in stability studies. However, the static and dynamic characteristics of a load are commonly unknown, extremely nonlinear, and are usually time varying. Consequently, a measurement-based approach for determining the load characteristics would offer a significant advantage since it could update the parameters of load models directly from the available system measurements. For this purpose and in order to accurately determine load model parameters, a suitable parameter estimation method must be applied. The conventional approach to this problem favors the use of standard nonlinear estimators or artificial intelligence (AI)-based methods. In this paper, a new solution for determining the unknown load model parameters is proposed—an improved particle swarm optimization (IPSO) method. The proposed method is an AI-type technique similar to the commonly used genetic algorithms (GAs) and is shown to provide a promising alternative. This paper presents a performance comparison of IPSO and GA using computer simulations and measured data obtained from realistic laboratory experiments. [ABSTRACT FROM AUTHOR]

This paper discusses the design criteria for the electrical systems of roadway tunnels with particular regard to the safety in the daily operation and in the case of fire events. It proposes a fit distribution system and an adaptive criterion for the support lighting system in order to minimize costs and energy impact. Electric systems of roadway tunnels need sophisticated architecture to allow the presence of extensively distributed loads and more stringent installation requirements due to the presence of fire hazard. Mechanical and electrical design criteria must be based on equipment qualification categories (EQCs), which are characterized by thermal inherent resistance and environmental parameters. Design criteria must include variable configurations to simplify installation, allow flexible operation, and optimize the cost–benefit ratio. A special power distribution, herein defined as “brush distribution,” and a temperature zone classification are proposed for road tunnels with a higher risk in the case of a fire event. Therefore, this paper suggests as design parameters the temperature exposure levels characterizing the thermal demand in each zones and the EQCs in order to choose the equipment with adequate thermal resistance. [ABSTRACT FROM PUBLISHER]

A hierarchical decentralized network reconfiguration approach to minimize power losses for smart distribution systems was presented in Part I. In this paper, the proposed approach is applied to four test distribution systems to examine its performance. A demonstration system consisting of the test system and distributed intelligent agents is built using MATLAB/Simulink to illustrate how the decentralized approach is implemented. Simulation results of the proposed approach are then compared with results of a centralized implementation and the harmony search method. It is shown that the decentralized approach can achieve similar results as other methods with significantly reduced computation time. The impacts of time-varying loads and faults are also studied through dynamic network reconfiguration on the 118-bus test system. Simulation results illustrate that dynamic network reconfiguration with time-ahead planning can determine the optimal configuration for each operating period to significantly reduce system energy losses. The enhanced performance of the hierarchical decentralized approach is clearly established. [ABSTRACT FROM PUBLISHER]

Magnetic-valve controllable reactor (MCR) has been widely applied in many kinds of industries, such as power systems and ferrous metallurgy. As electrical equipment, MCR can adjust its reactance smoothly and continuously, which has advantages like low dissipation and maintenance costs, high reliability. In this paper, a precise 2-D field-circuit coupling model of MCR is established by the finite element analysis software-ANSYS, and then the analysis of the harmonic characteristics of this model is presented in detail. Compared with the conventional numeric method, the proposed method could obtain more practical and accurate results and also has the ability to analyze electromagnetic field. Meanwhile, an experimental platform of a 2200 VA/380 V MCR is built. This paper provides detailed harmonic characteristics analysis of simulation and experiment. The simulation and experimental results verify that the proposed method is more accurate than using conventional ways. [ABSTRACT FROM PUBLISHER]

Short-term load forecasting has been playing an increasingly important role in electric power systems. Effective forecasting of the future electricity demand, however, is difficult in view of the complicated effects on load by a variety of factors. A hybrid method based support vector regression (SVR) with meteorological factors and electricity price is proposed to address such problem. First, the input used in this paper, are specific ratio value combinations of each characteristic parameter affecting the hourly electricity load. Second, SVR is used to analyze and develop a load forecasting model. Third, an improved adaptive genetic algorithm (IAGA) is utilized to optimize the specific ratio value combinations of each characteristic parameter, penalty factor C and Gaussian kernel function σ to accurately establish a forecasting model. The experimental results show that the proposed method can obtain better forecasting performance in comparison with other standard and state-of-the-art methods. [ABSTRACT FROM AUTHOR]

This paper presents a sufficient and necessary condition for transient stability of multimachine power systems based on the passivity formalism. The condition derived using the extended classical model (ECM) with zero transfer conductance (TC). The ECM of power systems relaxes slightly the assumption of “voltage-behind-transient-reactance” from “constant”, which is used in the conventional classical model to “positive, bounded and independent of machine rotor angles”. The results of time domain simulation of a full model of Western Interconnection used for regular operation planning study are presented for verifying the model assumptions and the storage functions of the system in four different scenarios (well stable, marginally stable, marginally unstable and very unstable), thus illustrating the sufficiency and necessity of stability criterion based on passivity. [ABSTRACT FROM AUTHOR]

Solar energy is one of the most important and widely utilized renewable energy resource. Despite the many attractive features of solar-based renewables, the wide scale integration of solar generation into electric power systems presents significant challenges to network planners and operators, mainly due to the intermittent nature of solar energy. Most published work in this area is, however, focused on short-term forecasting studies used for unit commitment and energy market decisions with very little attention paid to solar irradiance probability density estimation needed for network planning and design studies. In this paper, a reliable nonparametric model of solar irradiance probability density is proposed based on the application of local linear regression in tandem with a root transformation method, introduced here for the first time. The performance of the proposed estimator is assessed via comparisons with the parametric Beta distribution (conventionally employed to model solar irradiance probability density) and two nonparametric kernel density estimation models; using the Kolmogorov–Smirnov (K–S) goodness-of-fit test, coefficient of determination ($R^2$), and a number of error metrics. Results confirm the suitability and accuracy of the proposed method for solar irradiance probability density estimation. [ABSTRACT FROM AUTHOR]