Search

Dynamic voltage support is a type of critical ancillary service in electric power networks. With the increasing penetration of inverter-based renewable energy resources, utilizing their idle capacity to provide dynamic voltage support is becoming essential. However, the performance of traditional control methods is ofter limited due to the frequently changing operating point and network parameters, which are tuned only in a specific condition and suffer performance deterioration in others. This article presents a model-free dynamic voltage control method for inverter-based energy resources to supply dynamic voltage support. This method can dynamically estimate the system with pseudo gradients, in which a continuous parameter function is proposed to adaptively approximate the optimal intermediate parameters. It guarantees the performance when the host system operating states vary without tuning the controller's parameters, while in comparison the PID controllers require the parameters being tuned repeatedly. Both numerical simulation and field tests demonstrate that the proposed method significantly outperforms the classic PI and adaptive PI controllers, especially in the case when the host system varies over time. [ABSTRACT FROM AUTHOR]

Phasor measurement units (PMUs) are being widely installed in the transmission grid. Many power system applications based on PMUs have been developed or are under development in academia and industry. For those applications, data latency is often a critical factor that affects their performance thus making the topology of the communication network that exchanges real-time data between the control center (CC) and substations (SS) of vital importance. This paper introduces a method to conceptualize and analyze possible communication topologies by simulating them in Network Simulator 3 (NS3). Moreover, a new algorithm is developed to optimize the clustering of substations in such a way that the data latency performance of the decentralized communication topology can meet the requirements for PMU based applications. To validate the proposed methodology, the IEEE 118-bus system is used as the test case. A PMU based wide-area controller for transient stability is simulated in the MATLAB Simulink to validate the proposed communication topologies. It is concluded from the simulation results that the decentralized communication topology at a lower cost designed by optimizing the substation cluster boundaries can be an alternative choice and can help PMU based applications achieve good performance by limiting data latency to an acceptable level. Also, this paper can provide a technical guidance for power utilities choosing the most appropriate communication network for the PMU based real-time applications. [ABSTRACT FROM AUTHOR]

It is of growing concern to ensure the resilience in electricity infrastructure systems to extreme weather events with the help of appropriate hardening measures and new operational procedures. An effective mitigation strategy requires a quantitative metric for resilience that can not only model the impacts of the unseen catastrophic events for complex electric power distribution networks, but also evaluate the potential improvements offered by different planning measures. In this article, we propose probabilistic metrics to quantify the operational resilience of the electric power distribution systems to high-impact low-probability (HILP) events. Specifically, we define two risk-based measures: value-at-risk ($VaR_\alpha$) and conditional value-at-risk ($CVaR_\alpha$) that measure resilience as the maximum loss of energy and conditional expectation of a loss of energy, respectively, for the events beyond a prespecified risk threshold, $\alpha$. Next, we present a simulation-based framework to evaluate the proposed resilience metrics for different weather scenarios with the help of modified IEEE 37-bus and IEEE 123-bus system. The simulation approach is also extended to evaluate the impacts of different planning measures on the proposed resilience metrics. [ABSTRACT FROM AUTHOR]

The development and deployment of advanced distribution management systems (ADMSs) is imperative to address the increasingly complex operational challenges faced by aging electric power distribution systems, while ensuring reliable and resilient operations. Along with integrating the processes across multiple systems that are typically isolated, an ADMS allows for the development of applications that can readily access information from various subsystems, apply advanced analytics, and effectively control and coordinate traditionally segmented systems. This article presents an overview of ADMS applications for emerging electric power distribution systems and identifies future research directions. [ABSTRACT FROM AUTHOR]

Substation asset health has always been one of the utmost concerns for utilities. The substation secondary assets such as current transformers, potential transformers, and coupling capacitor voltage transformers play vital roles for system situational awareness and grid operations. This paper proposes a novel on-line substation instrument transformer health monitoring system (SITHMS), which merely uses time-synchronized and high-resolution phasor measurement unit (PMU) data. The SITHMS can provide early warning and alert utility personnel to diagnose the equipment malfunction and take proactive actions for asset management to prevent equipment failure. The core component of the SITHMS is a model-based three-phase substation-level linear state estimator, which features a built-in largest normalized residual (LNR) module that can detect anomalies in PMU data by using substation model and configuration, so as to probe if there is malfunction or potential failure of these secondary equipment. In addition, we present the system's implementation architecture and testing environment setup. Case studies with the PSCAD simulated data and field PMU data from actual substations at American Electric Power (AEP) demonstrate the effectiveness of the proposed system. [ABSTRACT FROM AUTHOR]

The continuing rollout of phasor measurement units enables wide area monitoring and control (WAMS/WACS), but the difficulty of sharing data in a secure, scalable, cost-effective, low-latency manner limits exploitation of this new capability by bulk electric power grid operators. GridCloud is an open-source platform for real-time data acquisition and sharing across the jurisdictions that control a bulk interconnected grid. It leverages commercial cloud tools to reduce costs, employing cryptographic methods to protect sensitive data, and software-mediated redundancy to overcome failures. The system has been tested by ISO New England and the results reported here demonstrate a level of responsiveness, availability, and security easily adequate for regional WAMS/WACS, with the capacity for nation-wide scalability in the future. [ABSTRACT FROM AUTHOR]

Conventional loss of excitation (LOE) detection methods for synchronous generators may misoperate during power swings. In this paper, a novel method based on measured slip frequency at the terminal of synchronous generators is proposed to differentiate power swing conditions from LOE conditions. To enhance performance of the proposed method for noisy measured signals, a modified Prony method based on a combination of generalized total least-squares method and conventional Prony method is implemented to estimate slip frequency and an energy sorting technique is applied to distinguish the dominant frequency components of measured signals. Performance of the proposed method is evaluated under various operating conditions of a test system that is simulated in a co-simulation platform by linking CAPE and PSS/E software. Case study results illustrate that the proposed method can accurately differentiate power swing conditions from LOE conditions. [ABSTRACT FROM AUTHOR]

With the increasing applications of VSC-HVDC technologies in power grids, the importance of incorporating DC grids and converter stations into the optimal power flow (OPF) problem is increasing. The modeling of a converter station involves highly nonlinear operational constraints and integer variables representing the tap settings of LTC transformers. In this paper, an efficient OPF algorithm for hybrid AC–DC grids with discrete control devices is presented. A successive linear approximation method for the power flow equations in both AC and DC grids is introduced. The operational constraints of the converter station are thoroughly investigated. The proposed linearization of the power flow equations facilitates the convexity of the VSC modeling. A fictitious branch is added to the AC grid to handle the highly nonlinear converter losses. The discrete nature of the LTC transformer in the converter station is accurately modeled. An iterative solving algorithm is proposed for the OPF model. The strict satisfaction of the power flow equations is enabled through the application of an AC feasibility recovery process based on the power flow calculation in hybrid AC–DC grids. Case studies demonstrate that the proposed algorithm outperforms several selected commercial solvers. [ABSTRACT FROM PUBLISHER]

From the study of dispatcher power flow in a distributed energy management system (DEMS) among multiple control centers, a fixed-point iteration scheme for boundary bus states is constructed to modify the exterior network equivalent through data exchange. Implementation details such as determination of combination parameters, independent choice of reference bus, and distribution of unbalanced power are analyzed. Using this method, each subsystem involved in distributed computing can maintain its method of modeling the exterior network. Adverse effects of communication interference on computing can also be eliminated. Results consistent with integrated power flow are obtained with little loss of accuracy. Thus, the proposed algorithm is especially suitable for application in DEMS, in which control centers can only communicate by WAN. Tests are conducted on the IEEE 118-bus system partitioned into five subsystems, the IEEE 300-bus system, and an actual power system, which verifies the favorable convergence and effectiveness of the method. [ABSTRACT FROM PUBLISHER]

In this study, a linearized and convergence-guaranteed optimal power flow (OPF) model with reactive power (Q ) and voltage magnitude (v) is proposed. Based on a linearized network model, a fully linearly-constrained OPF model is formulated with constraints on Q and v and limits on the apparent branch flow. Compared with the commonly used DC OPF method, the proposed method narrows the deviation from the AC OPF solution without requiring any additional information of the power grid. The locational marginal price (LMP) of the proposed method is closer to the AC OPF solution than the DC OPF method. The marginal price of the reactive power (Q-LMP) is provided, which offers the opportunity to price the reactive power. Case studies on several IEEE and Polish benchmark systems show that the proposed OPF method substantially enhances the performance of the prevalent DC OPF method. In addition, it is shown that if the accuracy of the linearized network model needs to be further improved, such as that during the iterative quasi-optimization process that reconstitutes the AC feasibility, a solution that is notably close to the optimum of the AC OPF model can be obtained by taking only one more iteration. [ABSTRACT FROM AUTHOR]

In this tutorial we present the state-of-the-art as well as new methods for simulating various planning, operation, stability, reliability, and economic models of electric power systems. The discussion is driven by both first-principle models and empirical models. First-principle models result from the fundamental physics and engineering principles that govern the behavior of various components of a grid. Empirical models, on the other hand, are models that result from statistics and data analysis. We overview a wide spectrum of applications starting from planning models with a time-scale of simulation in years to real-time models where the time-scale can be in the order of milliseconds. We present a list of simulation software popularly used by the power engineering research community across the world. The increasingly important roles of power electronics, communication and computing, model aggregation, hybrid simulation, faster-than-real-time simulation, and co-simulation in emulating the daily operation of a grid are enumerated. The importance of research testbeds for testing, verification and validation of complex grid models at various temporal and spatial scales is also highlighted. The overall goal is to provide a vision on how simulations and their supporting implementation methods can help us in understanding the evolving behavior of tomorrow’s power networks as a truly intelligent cyber-physical system. [ABSTRACT FROM PUBLISHER]

In this paper, the concept of locational marginal price (LMP) is revisited by analyzing the Karush–Kuhn–Tucker (KKT) condition of a general optimal power flow (OPF) problem. The impact of losses on LMP is investigated. Several well-known properties and formulations of the LMP are illustrated from a novel perspective. In particular, the special case of the lossless DC OPF model is discussed. Based on this theoretical analysis, a linear model for the loss-embedded LMP is proposed. The influence of losses on the LMP is recovered by solving a system of linear equations. The proposed method does not rely on strong subjective assumptions, such as the selection of reference buses or the determination of the “loss factor.” Case studies show that the proposed method has distinct advantages compared with the method currently practiced in major electricity markets. [ABSTRACT FROM PUBLISHER]

As more phasor measurement units (PMUs) are installed, portions of the power grid become observable with just phasor measurements, making feasible the estimation of the state of these observable portions at much faster rates than the traditional state estimator. Although such a linear state estimator (LSE) was proposed over a decade ago, the first field implementation was completed at Dominion Virginia Power in 2013. Although this LSE is a stand-alone function not integrated to their energy management system (EMS), it demonstrated the feasibility of the LSE. In this paper, we present the design, development, and implementation of an LSE that is fully integrated with the existing EMS and can estimate the state of the extra high voltage portion of a power system at 30 times per second. Integration of the LSE to the existing EMS environment and some of the issues in the design and testing are presented in this paper. The work paved way for LSE to supply cleansed PMU data to other synchrophasor applications that are sensitive to data quality. [ABSTRACT FROM PUBLISHER]

In this paper, a novel solution to the optimal reactive power dispatch (ORPD) problem is proposed. The nonlinearity of the power flow equations is handled by a new successive linear approximation approach. For the voltage magnitude terms, a mathematical transformation that improves the accuracy and facilitates the linear modeling of shunt capacitors is used. Without loss of accuracy, the load tap changers and shunt capacitors are both modeled by linear constraints using discrete variables, which facilitates the linearly constrained mixed-integer formulation of the proposed ORPD model. An efficient iterative solving algorithm is introduced. The obtained solution strictly satisfies the power flow equations. Case studies on several IEEE benchmark systems show that the proposed algorithm can efficiently provide near-optimal solutions with the error of the objective functions of less than 0.1%. Compared with several commercial solvers, the proposed method shows distinct advantages in terms of both robustness and efficiency. Moreover, based on the round-off results, a heuristic method that reduces the optimization ranges of the discrete control variables is proposed. This method can further improve the computational efficiency with small losses in accuracy. [ABSTRACT FROM AUTHOR]

As the power demand becomes higher all over the world, transmission lines are often carrying electric power near their limits, which can cause power systems to be operated under serious stress. Voltage collapse is one of the more critical problems that impacts power system operational security and many of the recent major blackouts were caused, at least partially, by voltage collapse. Therefore, a fast and accurate voltage stability monitor is necessary for the modern system, together with a fast calculation of possible remedial actions. The development and application of wide-area measurement systems established the foundation of online assessment of voltage stability in large-scale power systems. In this paper, a voltage stability (QV) index based on phasor measurements is used to identify the weak buses and a new parallel optimization method that increases this voltage stability margin is introduced. Results on the IEEE standard systems show the accuracy and efficiency of the methods. [ABSTRACT FROM PUBLISHER]

Smart grid technologies are expected to increase system efficiency and reliability using advancement in automation, communication, computation, and optimization. Several control algorithms have been developed or enhanced for operation and control of smart distribution grid. In recent years, volt/var control (VVC) algorithms have been proposed for energy saving in distribution systems due to advancement provided by smart grid automation and control. VVC helps to lower distribution feeder voltage to decrease energy consumption. However, quantification of this impact is hard due to several external factors such as weather and end users' behavior. On the other hand, existing evaluation methods of VVC algorithms are either not suitable for long-term study or intrusive. This paper addresses these issues by proposing a new technique to estimate “distribution system demand without smart grid implementation” utilizing “data measured from system with smart grid implementation.” Interdependence of voltage and load is considered based on estimated load characteristic. Our key contribution is developing a method for quantifying the real-time energy saving of smart grid automation and control focused on VVC and implementing in an electric utility in eastern Washington, USA. The algorithm is developed using both commercial and open-source software. [ABSTRACT FROM AUTHOR]

With the spotlight on smart grid development around the world, it is critical to recognize the key factors contributing to changing power-system characteristics. This is more apparent in distribution systems with the integration of renewable energy sources, energy storage, and microgrid development. Source and load control at the distribution level is a key requirement of the evolving system. These activities require distribution automation (DA) strategies that take advantage of available technologies, while promoting newer solutions. It is necessary to create a roadmap for holistic DA strategies in a smarter grid. Sustainable and resilient grid development is a paradigm shift requiring a new line of thinking in the engineering, operation, and maintenance of the power system. Distributed control architectures based on dynamic load and source data should be explored as a possible solution. This paper discusses a novel approach that integrates protection, control, and monitoring using high-performance computing at the primary distribution substation level. The business case for infrastructure investment in the distribution systems is also discussed. This paper concludes with a discussion on emerging and future technologies for DA to improve the resiliency of a sustainable grid. [ABSTRACT FROM PUBLISHER]

With the spotlight on smart grid development around the world, it is critical to recognize the key factors contributing to changing power system characteristics. This is more apparent in distribution systems with the integration of renewable energy sources, energy storage, and microgrid development. Utilities are also focusing on the reliability and resiliency of the grid. These activities require distribution automation (DA) strategies that take advantage of available technologies while promoting newer solutions. It is necessary to create a roadmap for holistic DA strategies in a smarter grid. Sustainable and resilient grid development is a paradigm shift requiring a new line of thinking in the engineering, operation, and maintenance of the power system. International perspectives on DA are also addressed, with the understanding that one solution will not fit all. Integrating technical, business, and policy decisions into the challenges will generate the development of technologies, standards, and implementation of the overall solution. The challenges in the development of industry standards are also discussed. This paper explores the challenges and opportunities in the changing landscape of the distribution systems. Evolution of technologies and the business case for infrastructure investment in distribution systems are covered in another paper by the same authors. [ABSTRACT FROM PUBLISHER]

Due to the rapid deployment of phasor measurement units (PMUs) on large power grids, the system operators now have access to high speed high resolution data. A new class of monitoring and control applications are made possible with the PMUs. Although PMU based monitoring systems have been well developed, implementations of PMU based fast acting closed loop wide area control systems are relatively rare. To meet the stringent latency requirements of a wide area controller the communication and power infrastructures have to collaborate strongly. In this paper, a combined process for design and simulation of both communication network and power network has been presented with the objective of damping interarea oscillations. A method to determine the optimal location of data routing hubs so as to minimize the volume of communications is also proposed. The IEEE 118 bus system is used to study the performance of communication system and the wide area power damping control system on both centralized and decentralized topologies, and the results are discussed. One of the conclusions of the paper is that the decentralized communication architectures involving data routing hubs are better suited for control applications requiring fast control actions. [ABSTRACT FROM PUBLISHER]