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The recent transformation of the energy sector brings new challenges in areas such as supply security, efficiency, and reliability. Especially the increase of decentralized power plants leads to a more complex energy system and an increasing complexity. This requires expansion and digitization of the power grid as well as an initiative-taking operation of the grid operator. To investigate such complex systems and its phenomena, modern development methods such as real-time simulation or digital twins (DT) can be used. In this approach a digital replica of the real-world system, a grid section, is developed, which can represent or predict the behavior of the real distribution grid. For this, a model of the real-world system is derived and implemented in a co-simulation environment, in which it receives data via an analyzer or measurement system from the grid model. This paper focuses on the development of the digital twin of a testing grid and a grid analyzer for the measurement. With the digital twin of the testing grid, a first approach is achieved in a real-time capable environment showing the functionalities and interactions of a digital twin. Subsequently the development of the digital twin model is explained, and the results are discussed.

This research addresses a significant gap in power system protection methodologies by developing a dedicated simulation environment that supports the communication of protection relays via the IEC 61850 protocol. Current studies have focused on hardware-in-the-loop approaches, but there is a lack of research in the software-in-the-loop domain. This limitation means that manufacturer-independent simulations cannot be performed, restricting testing to the capabilities provided by the manufacturer. By introducing a relay capable of communicating within a Simulink-modeled power system through socket programming, this study harnesses the capabilities of the IEC 61850 GOOSE protocol and sampled values. This work aims to eliminate the manufacturer dependencies present in hardware-in-the-loop approaches, thereby enabling the independent development of new protection and control strategies in an academic context. Furthermore, by facilitating advanced communication strategies through a detailed simulation framework, this research contributes to the broader field of electrical engineering by offering a robust tool for developing, testing, and validating new relay communication techniques and protection schemes. This approach not only fills a critical gap in simulation capabilities but also paves the way for future advancements in power system protection and management regarding the IEC 61850 protocol.

As both the generation resources and load types have changed and grown over the past few decades, there is a growing need for analysis that spans traditional simulation boundaries; for example, evaluating the impact of distribution-level assets (e.g. rooftop solar, EV chargers) on bulk-power system operation. Co-simulation is a technique that allows simulators to trade information during run-time, effectively creating larger and more complex models. HELICS is a co-simulation platform that has been developed to enable these kinds of power system analysis, incorporating tools from a variety of domains including the electrical power grid, natural gas, transportation, and communications. This paper summarizes the technical design of HELICS, describes how tools can be integrated into the platform, and reviews a number of analyses that have been performed using HELICS. A short video summary of this paper can be found at https://youtu.be/BIUiR_K87Wc.

The proliferation of Power Electronic Converters (PECs) has had a pervasive affect in a variety of industries including the power generation, automotive and aerospace sectors, where their use brings reliability to the forefront, especially in applications where safety critical and harsh environments are experienced. Continuous improvements in the power density and efficiency through extensive research into new semiconductor technologies, passive components, circuit topologies and control methodologies has seen the performance of PECs improve indubitably. However, the manifestation of stresses occurring from significant heating due to high currents and switching frequencies; which over time can cause degradation in the performance of PEC components is still a real concern. This paper outlines a methodology for monitoring the degradation of PECs over the operational lifetime by utilizing a component level, physics based Digital Twin (DT). As well as providing a methodology for the real time comparison of parameters to realize the onset of faults subjected to operational stresses, the DT also provides a novel method of training a classifier by simulating the faults within the PEC, a process that in reality, would be difficult to achieve from a physical device. Feature extraction is via Wavelet Scattering and classification is provided using a Support Vector Machine (SVM) approach. The overall approach is one that is novel and expandable to a wide range of PEC topologies and will be beneficial to the optimization and maintenance of PECs in a variety of platforms.

For parallel-in-time simulation of large-scale power systems, this paper proposes a differential transformation based adaptive Parareal method for significantly improved convergence and time performance compared to a traditional Parareal method, which iterates a sequential, numerical coarse solution over extended time steps to connect parallel fine solutions within respective time steps. The new method employs the differential transformation to derive a semi-analytical coarse solution of power system differential-algebraic equations, by which the order and time step, as well as the window length with a multi-window solution strategy, can adaptively vary with the response of the system. Thus, the new method can reduce divergences and also speed up the overall simulation. Extensive tests on the IEEE 39-bus system and the Polish 2383-bus system have verified the performance of the proposed method.

The trend toward higher switching frequency and larger scale of power electronic systems poses challenges for real-time simulation. This article presents an event-driven hardware-in-the-loop (ED-HIL) simulation framework that does not rely on the small fixed simulation step-size related to the switching frequency. ED-HIL framework can improve the calculation efficiency by positioning switch events and using variable simulation step-size. Further, a parallel acceleration and circuit partitioning (PACP) solver is proposed based on this framework. The PACP solver partitions the circuit with energy storage elements and ensures that the partitioning does not introduce simulation distortion by using the higher order derivatives of the energy storage elements. Meanwhile, it achieves a process-level paralleling through a shared memory architecture in order to accelerate the simulation. As a result, the proposed PACP solver based on the ED-HIL framework can achieve about three times the simulation scale of a commercial FPGA-based real-time simulator at 1/16 the hardware cost under the same conditions. An accurate real-time HIL example of a power electronic transformer with 32 switches at a switching frequency of 20 kHz has been implemented on a personal computer. The simulation results are analyzed by comparing with experiment, offline software, and commercial real-time simulator. [ABSTRACT FROM AUTHOR]

The OPA (ORNL-PSERC-Alaska) model has been widely used in cascading failure simulations to predict likely and plausible sequences of cascading failures. This letter focuses on an algorithmic approach to enhance the OPA model whose main engine is based on quasi-steady-state models without considering the impact of collective transient dynamics of the entire system on the sequence of cascading failures. In particular, the enhanced OPA model incorporates dynamically induced cascading failures in fast time scales, which allows it to capture more realistic and detailed cascading scenarios. In this work, we outline the enhanced OPA model and provide simulation results to illustrate its feasibility with the realistic test network. [ABSTRACT FROM AUTHOR]

The integration of uncertain photovoltaics (PVs) and flexible loads leads to uncertainties in the power system dynamic simulation results. Furthermore, geographically close PV farms are correlated and may exhibit nonlinear correlations. This article proposes a copula-based sparse polynomial chaos expansion (PCE) framework for quantifying the impacts of uncertain dynamic PVs and loads on power system dynamic simulations and stability. The dynamics include both PV and load stochasticity and those governed by differential and algebraic equations. The copula statistics are utilized to accurately characterize the dependence structure of PVs and further used to develop the copula-PCE for quantifying the impacts of uncertain PVs and loads. A probabilistic TSI is also developed to assess the uncertainties from PVs and loads on the system stability. To address the cases, where both stable and unstable conditions coexist, a preprocessing step via sample classification is proposed. The effects of different dependence structures of PVs and different numbers of uncertain sources are investigated. Comparison results with other methods on the modified IEEE 39- and 118-bus systems, including the Monte Carlo method, Latin hypercube sampling, and traditional PCE without consideration of uncertain input correlations show that the proposed method is able to accurately quantify the uncertain dynamic simulations and transient system stability while being computationally efficient. [ABSTRACT FROM AUTHOR]

Voltage source converter (VSC) is fundamental and critical in renewable energy integration and transmission and has become ubiquitous in power systems. For the design and operation of power systems with VSCs, electromagnetic transient (EMT) simulation is indispensable. However, a large number of VSCs in power systems cause a high time-consuming issue in EMT simulation. This article proposes a fast EMT simulation model for VSCs with arbitrary topology based on switch-state prediction. The accurate switch-state prediction has two steps: Preliminary switch-state prediction and simultaneous switching prediction. It avoids the iterative computation required to obtain a feasible switch-state combination in the traditional EMT simulators. Extensive tests on different types of VSCs and a dc microgrid demonstrate that the proposed fast model significantly improves the EMT simulation efficiency of power systems with VSCs. [ABSTRACT FROM AUTHOR]

Accurate calculation of semiconductor losses and temperature is the foundation of any design methodology for a power electronic converter. Computation accuracy and speed play a vital role if a large set of parameters needs to be considered. Averaged loss models often neglect the temperature dependence of transistors, leading to fast, but inaccurate results. In contrast, iterative methods and simulation tools, which can include temperature dependence, take significantly longer to compute, but yield more precise results. This paper presents a best of both worlds approach, by using the harmonic balance method to obtain the steady-state solution for any inverter topology including temperature dependent conduction and switching losses. The proposed method solves for the discrete Fourier series of the device temperature, by expressing the temperature dependence and operating parameters in the frequency domain. The set of equations for each coefficient is solved by a single matrix inversion, resulting in very fast computation for steady-state temperature cycles. The steady-state operation of over one thousand possible inverter designs is calculated within less than one minute, matching iterative simulation in device temperature, conduction and switching losses, at a fraction of the computation time. In addition, the method shows good agreement with temperature measurements of a three-phase silicon-carbide inverter.

The electric power system is currently undergoing a major transition due to growing numbers of distributed energy resources (DERs) and increased distribution automation. If optimally managed and operated, DERs could provide flexibility and highly valuable grid services such as restoration, peak shaving, voltage regulation, and frequency support to maintain grid reliability. Different applications and enterprises, such as distributed energy resources management systems (DERMS), are being developed for coordinated and optimal operation of DERs. However, to attract sufficient DER participation and achieve the coordinated operation of DERs, systems and components must be interoperable and information exchange must be secure. Along this line, the Portland State University power engineering group is developing Energy Grid of Things (EGoT) DERMS prototype. The proposed application requires the coordinated dispatch of large numbers of DERs and testing such a system presents a challenge; it is not practical to test system prototypes using thousands of real DERs. Hence, the modeling environment (ME) is designed as a co-simulation tool to model interactions between a DERMS and a mass of simulated DERs. The ME is expected to address the scalability issue inherent to hardware-in-the-loop DERMS simulation; many assets are needed to observe effects on the grid from deployment and dispatch of DERs. To enable the development and testing of such advanced applications for power distribution system planning and operations, the U.S Department of Energy developed GridAPPS-D™, an open-source, standards-based platform at Pacific Northwest National Laboratory. This paper introduces the proposed ME for testing a DERMS application. The architecture of the ME is presented, and the GridAPPS-D features for a such simulation environment are discussed. Additionally, the procedure for developing the ME within the GridAPPS-D platform and use of different APIs for efficient and timely integration are discussed in detail.

Current trends in power system development and the issues they pose have increased the urgency of automatic and emergency control alongside transient electromechanical processes. Such control devices place high demands on mode-parameter estimation algorithms in terms of their speed, accuracy, and transient sensitivity. This paper proposes a rapid estimation algorithm for power system parameters to investigate its optimal settings and applicability in both static and dynamic states. The proposed algorithm is based on signal approximation on sliding window using a multiparameter model, which is highly stable and reliable. The signals modeled in MATLAB/Simulink were used as initial data. From the experimental results, it became clear that the rapid estimation algorithm of the power system parameters showed high accuracy in steady-state mode as well as during transients, and its optimal parameters were identified. The developed algorithm can be used in relay protection, automatic and emergency control devices, and synchronous machine state-monitoring systems.

Power distribution systems are experiencing large deployment of behind-the-meter distributed generation and storage along with electrified transport and heat, requiring fundamental changes in planning and operation. There are increasing efforts to directly model real large-scale networks and conduct detailed analysis beyond conventional practices. Utilizing optimization methods to leverage distributed generation to the benefit of the distribution system and all customers is the ideal. However, progress towards adoption of such controls by system operators are impeded by concerns over privacy, regulatory and market issues in many jurisdictions. While these issues are being addressed, there may be opportunity to exploit the synergistic effect of mixing low carbon technologies (LCT). This paper presents a large-scale medium voltage (MV)-low voltage (LV) integrated system model building, scenario determination and analysis approach for distribution systems. Data with different formats from several databases are used in model building. In collaboration with the national distribution system operator (DSO) in Ireland (ESB Networks), a pilot study is conducted for a rural system in the Southwest of Ireland, highlighting the challenges of directly modelling real distribution systems and investigating the potential synergies between multiple low carbon technologies.

In this work we present a novel technique, based on a trust-region optimization algorithm and second-order trajectory sensitivities, to compute the extreme trajectories of power system dynamic simulations given a bounded set that represents parametric uncertainty. We show how this method, while remaining computationally efficient compared with sampling-based techniques, overcomes the limitations of previous sensitivity-based techniques to approximate the bounds of the trajectories when the local approximation loses validity because of the nonlinearity. We present several numerical experiments that showcase the accuracy and scalability of the technique, including a demonstration on the IEEE New England test system. [ABSTRACT FROM AUTHOR]

The fast development of renewable energies leads to an increase in the power electronics penetration in transmission systems. This is particularly true if one considers a 100% renewable energies power system, where wind and solar photovoltaic energies, which make most of the renewable energies connections today, are connected to the grid through power electronics converters. Because power electronics-based generators and synchronous machines-based generators have very different dynamic behaviours, some approximations usually used to run transient simulations of transmission systems might not be optimal for future grids. The systematic use of the phasor approximation applied to the power lines, implemented in most of the Transient Simulation Programs, is indeed not relevant any more. To avoid the use of Electromagnetic Transient simulations, that are resource-demanding and time-consuming, this paper presents a novel Model Order Reduction technique for large grids with a high penetration of power electronic devices. Compared to the classical phasor approximation, this event-based state residualization approximation allows accurate transient simulations and at the same time an optimal reduction of the number of the system’s state variables depending on the observed variables, the considered events and the tolerated approximation error. [ABSTRACT FROM AUTHOR]

Power system planning is essential for ensuring development of a safe and stable power system. Articles on power system planning have been published in recent decades. In this paper, bibliometric analysis is applied to power system planning to identify its basic characteristics, and to summarize the research hotspots and trends. A total of 4562 publications were obtained from the Web of Science during 1971–2020. The 4562 publications cover 8136 keywords, 1526 journals, 107 countries/territories, and 2519 institutions. IEEE Transactions on Power Systems is the key journal in power system planning; USA, China, and England are the countries that dominate publication production. Research hotspots and trends were analyzed using author-keyword co-occurrence analysis and keyword burst detection. Four clusters were identified and topics from Cluster I (central nodes as power system stability and transient stability) and Cluster IV (central nodes as power system simulation and economics) are important for power system planning research. However, their relative popularities have declined over the past two decades. This indicates that Cluster II (central nodes as renewable energy, wind power, and energy storage) and Cluster III (central nodes as distributed generation and smart grids) will be the focus of future research. [ABSTRACT FROM AUTHOR]

Accurate evaluating the lightning induced voltages of distributed networks has been the subject for several decades. The technique on the interface between the field-to-line coupling model and power system simulators are of particular interest. In this article, a solution of the Agrawal's field-to-line coupling model is derived and an easy-to-implement macro-model is developed. Combining with the “Frequency Dependent (Phase) Model” component included in PSCAD, the proposed macro-model can be directly integrated into PSCAD to evaluate the lightning induced voltages on the overhead lines. The validity and efficiency of the proposed method is demonstrated by several examples. Finally, a 1-km 35 kV overhead line above an imperfectly conducting ground is studied, and the influences of the metal-oxide arrester to the lightning induced voltages are discussed. [ABSTRACT FROM AUTHOR]

Trends in power system simulation that demand computationally-intensive, physics-based models may impede the acquisition of useful results for applications like condition-based maintenance, electrical plant load analysis (EPLA), and the scheduling and tasking of finite generation and distribution resources. A tool that can quickly evaluate many scenarios, as opposed to intense, high fidelity modeling of a single operating scenario, may best serve these applications. This paper presents a behavioral simulator that can quickly emulate the operation of a relatively large collection of electrical loads, providing “what-if” evaluations of various operating scenarios and conditions for more complete exploration of a design or plant operating envelope. The presented simulator can provide time-series data of power system operation under loading conditions and usage assumptions of interest. Comparisons to field data collected from a microgrid on-board a 270-foot (82 meter) US Coast Guard medium-endurance cutter demonstrate the utility of this tool and approach.

With the development of dc renewable power generation and dc power consumption, more and more attention has been paid to residential low-voltage dc (RLVDC) power systems in recent years because of their advantages in conversion efficiency and control flexibility. Meanwhile, there are still some obstacles and challenges in the practical application of RLVdc due to the lack of standardization. One of the most important issues in RLVdc standardization progress is the voltage level standard. In this article, a comparative study on the performance of different RLVdc system voltage levels is presented. The main purpose of the article is to provide a voltage level selection guidance for energy prosumers and equipment manufacturers interested in RLVdc systems. The voltage levels commonly used in academia and industry, from 220 to 750 V, are compared and analyzed considering their influence on compatibility, topology, power supply capability, and safety. The article contains a research surveys, market statistics, power system simulations, and calculations with simplified models. The results of the comparative study show that ±375 V is optimal for the RLVdc system in cases with large power ratings and voltage levels below 240 V are suitable for RLVdc systems with special safety requirements. [ABSTRACT FROM AUTHOR]

Hydrogen-integrated transportation and power systems (HTPS) will become an important way to achieve the goal of carbon neutrality. As an important coupling unit of HTPS, the business mechanism of hydrogen fueling stations (HFS) is an important starting point for improving system economy and promotion value. This article proposed an interaction mechanism between HFS and HTPS and hydrogen and fuel cell EVs (HFEVs) in smart cities for HFS pricing strategies. First, we construct the framework of the HTPS interaction mechanism based on the basic combination of HTPS. Then, the interactive model of HTPS is constructed, including the scheduling model of HTPS, the pricing model of HFS and the response model of HFEVs. Finally, an HTPS system is constructed based on the improved IEEE 33-node power distribution system for simulation and analysis. The results show that the interaction mechanism and pricing strategy can improve the economics of HTPS and HFS, the operating cost of HTPS has been reduced by approximately 5.57%, the operating income of HFS has increased by approximately 4.17%. [ABSTRACT FROM AUTHOR]

This paper presents a novel approach to dynamic phasor-based transient stability simulation. The proposed method is based on the modified nodal analysis (MNA) approach to circuit simulation, which is used to construct continuous differential-algebraic equations (DAEs). The proposed method makes use of the stamp technique, which makes it possible to construct a general purpose MNA-based simulator. Stamp-based models for common power system components are derived in this work. A new MNA-based synchronous machine model is presented, which represents machines as nonlinear inductances instead of subtransient equivalents. The resultant continuous DAEs are numerically solved using the general purpose variable step and variable order library IDA. Simulation results from the IEEE 68 bus test system, a real 400 bus power system, and the IEEE 39 bus test system with an embedded HVdc transmission system demonstrate that the proposed method is suitable for large ac networks with power electronic devices. The results demonstrate good agreement between the proposed method and electromagnetic transient (EMT) simulation. The results also demonstrate that the proposed method is fast and scalable with CPU times that are up to 200 times faster than EMT simulation. [ABSTRACT FROM AUTHOR]

The power grid is transforming with large amounts of distributed energy resource (DER) integration that is impacting the bulk power system planning and operations. Grid regulators have identified that traditional power system analysis techniques are challenged under the changing grid conditions. Transmission and distribution (T&D) co-simulation is an effective methodology to accurately account for the changing power-grid. A scalable multitimescale T&D (SMTD) co-simulation framework is developed with commercial transmission system solver that can handle large-scale system models, and distribution system solver that can model the distribution systems in detail with dynamic models of load and DER. In this article, PSS/E and GridLAB-D are combined using a Python interface with Hierarchical Engine for Large-scale Infrastructure Co-Simulation software to enable T&D co-simulation. This framework is scalable and parallel computing compatible that enables large-scale system simulation and adoption of T&D co-simulation by the industry and utilities. The SMTD cosimulator is designed to integrate with existing system models and new ones. The article also highlights functional specifications for the T&D co-simulation solvers and models along with providing the algorithms for the steady state, quasi-steady state, and dynamic T&D co-simulation. In context of changing power grid, future power grid planning, validation of controls under critical contingencies and validation of various wide area monitoring and controls can effectively utilize the proposed framework that can capture the T&D interactions accurately. The SMTD cosimulator can also be used to generate realistic synthetic measurement-data with noise and packet drop for uncommon grid events enabling development and validation of power system data analytics and controls. [ABSTRACT FROM AUTHOR]

Resilient distributed coordination control is studied on multiarea power systems with low inertia under hybrid attacks, including denial-of-service (DoS) attack and deception attack. The communication among various areas under the DoS attack is deteriorated to switching residual topologies whose time characteristic is modeled by model-dependent average dwell time (MDADT). Deception attack with malicious strategy targeting at negative feedback control is modeled by a sign function. To obtain resilience performance of the power system under low inertia and hybrid attacks, resilient distributed scheme combining load-frequency control (LFC) with virtual inertia control (VIC) is proposed. Then, resilient frequency control problem of the studied power system is converted to $H_{\infty }$ control of the switched nonlinear system. By employing the Lyapunov stability theory and switched system method, the resilient conditions are given by the lower bound of the average dwell time of each residual topology and the upper bound of deception attacks. Furthermore, a linear matrix inequality (LMI) technique is used to design the distributed resilient control gains of the LFC-VIC scheme. Finally, a simulation of four-area power systems is carried out to verify the validness of our theory. [ABSTRACT FROM AUTHOR]

Modeling grounding systems is necessary for the calculation of ground potential rise (GPR), power system simulations and insulation coordination studies. In this work, a methodology for estimating equivalent circuit parameters through the optimization of the time-domain impulse response was developed. It allows to obtain equivalent circuits with positive parameters that accurately represent grounding systems considering both effects related to frequency and soil ionization. Additionally, linear and nonlinear equivalent circuits for calculating the impulse response of typical grounding systems were proposed. The Nelder-Mead optimization method was applied to adjust the circuit parameters. For evaluating the methodology developed and the proposed models, data from impulse current tests was used. It was found that the use of nonlinear circuits increases the accuracy of the simulated response, resulting in errors of less than 4% in the estimation of GPR. The proposed methodology allows obtaining representative circuits of typical grounding systems used in the electrical system. The circuits can be used for systemic studies and calculation of GPR considering short-circuit or lightning currents. [ABSTRACT FROM AUTHOR]

This paper outlines a novel loss of excitation (LOE) protection scheme for synchronous generators (SGs) based on reactive power increment (RPI) strategy and tracking the variation of SG output voltage (VSG). When variation of the VSG exceeds lesser than a specified threshold value, the proposed RPI strategy is triggered and VSG deviation is analyzed. For RPI execution, generated reactive power by SG (QSG) is shifted in increment direction. Following the applying RPI strategy, the VSG does not have any increasing changes during LOE events due to lack of excitation system to provide the required field current; while for Non-LOE (NLOE) events, VSG will be increased. Therefore, this provided feature by RPI strategy can properly and immediately cluster all LOE/NLOE events even under worst-scenarios. Due to power quality issues, the value of the shifted reactive power (ΔQSG) is considered small as much as possible. Meanwhile, it does not require any extra devices for execution. The exhaustive simulation studies on the power system prove that, the proposed scheme is quite reliable for clustering all LOE/NLOE events, and is much faster than other available methods. [ABSTRACT FROM AUTHOR]

With continuing advances in high-performance parallel computing platforms, parallel algorithms have become powerful tools for development of faster than real-time power system dynamic simulations. In particular, it has been demonstrated in recent years that parallel-in-time (Parareal) algorithms have the potential to achieve such an ambitious goal. The selection of a fast and reasonably accurate coarse operator of the Parareal algorithm is crucial for its effective utilization and performance. This paper examines semi-analytical solution (SAS) methods as the coarse operators of the Parareal algorithm and explores performance of the SAS methods to the standard numerical time integration methods. Two promising time-power series-based SAS methods were considered; Adomian decomposition method and Homotopy analysis method with a windowing approach for improving the convergence. Numerical performance case studies on 10-generator 39-bus system and 327-generator 2383-bus system were performed for these coarse operators over different disturbances, evaluating the number of Parareal iterations, computational time, and stability of convergence. All the coarse operators tested with different scenarios have converged to the same corresponding true solution (if they are convergent) and the SAS methods provide comparable computational speed, while having more stable convergence to the true solution in many cases. [ABSTRACT FROM AUTHOR]

This article introduces a novel multirate cosimulation architecture that overcomes previous challenges integrating faster real-time, microseconds-scale, power-hardware-in-the-loop (PHIL) with larger scale but slower, real-time, seconds-scale, quasi-static time-series (QSTS) simulation. Specifically, an intermediate reduced-equivalent electromagnetic transient (EMT) model duplicates the key power system topology to capture high-speed dynamics and converge hardware-power system interactions between QSTS updates. Exchanging multidimensional parameter vectors (loads, control status, etc.) between the QSTS and EMT models enables capturing the interactions of the rich, high-node-count (thousands of electrical nodes) QSTS model with the hardware. This architecture offers full spatial resolution from QSTS, including individual load dynamics, actual distribution management system controls, and nodal voltages. Simultaneously, the intermediate EMT model provides more detailed high-speed transients of key distributed energy resource hardware interactions. In addition, we use careful PHIL interface design and the exchange of complex power data, rather than current, to further improve performance. This cosimulation architecture is demonstrated by testing a simulated distribution system with an interconnected 500-kVA advanced photovoltaic (PV) inverter in PHIL. The architecture successfully captured PV local volt–volt ampere reactive (volt-VAR) control interactions with the larger network under time-varying electrical and weather conditions. [ABSTRACT FROM AUTHOR]

The modern power grid is being used under operating conditions of increasing stress, giving rise to grid stability issues. One of these stability issues is the phenomenon of inter-area oscillations. Simulations have demonstrated the advantages of Wide-area Measurement Signals (WAMS)-based Oscillation Damping Controls in achieving improved electromechanical mode damping compared to traditional, local signal-based Power System Stabilizers (PSS). This work takes an existing Phasor-based oscillation damping (POD) algorithm and uses it to implement a proof-of-concept, wide-area, real-time controller on National Instruments hardware. The developed prototype is tested in a real-time Hardware-in-the-loop setup (RT-HIL) using OPAL-RT's eMEGASIM real-time simulation platform and synchrophasor data from actual Phasor Measurement Units (PMUs). The prototype and experiments provide insight into the feasibility and real-world limitations of wide-area controls. Further, it is demonstrated how the proposed control architecture has applications independent of the controlled power system device. Challenges faced, the solutions implemented together with the present prototype's limitations are also discussed.

Assessing the transient behavior of electric power transmission/distribution systems, when they are subjected to major disturbances such as lightning discharges, is an essential procedure to ensure the operational security of these systems, in order to supply good quality power to all consumers. Electromagnetic transient studies are routinely performed in the planning and operation phases of these systems, by using world widely known computer programs, among which stands out the Alternative Transient Program (ATP), via its graphical interface ATPDraw. However, preparing files for running case studies by using ATPDraw can become a time-consuming and human error-prone task. To overcome this drawback, this paper presents a toolbox for automatic generation and execution of Alternative Transient Program input files based on information directly obtained from technical databases of distribution utilities. This toolbox aims to reduce modeling time and susceptibility to human errors in the process of describing the grid in the software input file, which constitute the biggest obstacles to the extensive use of this program in real electric transmission/distribution networks. For the toolbox validation, a comparison was made between the input file generated by the ATPDraw auxiliary graphic interface and the file generated by the proposed toolbox by using the IEEE 13-bus and IEEE 34-bus test feeders. Besides that, the simulation results of both feeders for both softwares were compared, so that the correct operation of the Alternative Transient Program automatic case creator and executor proposed in this article were proved. In addition, the automatic generation of ATP cases for larger grids is exemplified with the IEEE 123-bus test feeder.

Reliability and survivability of electric power systems (EPS) depend on transient stability assessment (TSA). One of the most effective way to TSA is time-domain simulation. However, large-scale EPS mathematical model contains a stiff nonlinear system of high-order differential equations. Such system cannot be solved analytically. At the same time, numerical methods are imperfectly applied for such system due to limitation conditions. To make it appropriate, the EPS mathematical model is simplified and additional limitations are used. These simplifications and limitations reduce reliability of simulation results. Consequently, their validation is needed. The most reliable approach to provide it is to compare the simulation results with the field data. However, in practice, there are not enough data for such validation. This paper proposes an alternative approach for validation - the application of a reference model instead of field data. A hardware-software system HRTSim was used as a reference model. This power system simulator has all the necessary properties and capabilities to obtain reliable information required for comprehensive validation of transient stability calculations in EPSs. Main disturbances leading to instability in EPSs are investigated to conduct the validation (processes in cases of faults, single-phase auto-reclosing operation and power system interconnection). Fragments of corresponding experimental studies illustrate the efficiency of the proposed approach. Obtained results confirmed the possibility of the developed approach to identify the causes of numerical calculation errors and to determine disturbances calculated with the significant error. In addition, experimental studies have revealed that numerical calculations error depends on disturbances intensity.

Moving towards low-carbon electricity systems through the massive deployment of renewable energy sources (RES) presents a unique opportunity to combat climate change, but it also poses enormous technical challenges, especially from a frequency viewpoint. To ensure a secure RES integration in terms of frequency stability, system operators worldwide have adopted new grid codes requiring RES to provide fast frequency response (FFR). However, if not properly justified, stringent requirements may pose an unnecessary barrier to further RES development and slow their network integration. In this context, this paper presents a methodological framework for systematically defining FFR requirements for RES to ensure system frequency stability. The proposal comprises: i) a model for simulating the dynamic response of system frequency following a contingency with reduced computational effort, ii) a model for reallocating contingency reserves with economic criteria to avoid loss of load following a contingency, and iii) novel indices for characterizing the dynamic performance of system frequency in terms of key operational characteristics, which are then used for defining frequency related grid codes. The benefits and practicability of our proposal are demonstrated in a case study on the Northern Interconnected System in Chile. We show how our proposal can be used to i) identify system operating conditions in which the contribution of RES with FFR is necessary to avoid loss of load and ii) to propose a technically and economically justified grid code that allows both to foster further RES integration while ensuring power system security.

Parallel-in-time methods are emerging to accelerate the solution of time-consuming problems in different research fields. However, the complexity of power system component models brings challenges to realize the parallel-in-time power system electromagnetic transient (EMT) simulation, including the traveling wave transmission lines. This paper proposes a system-level parallel-in-time EMT simulation method based on traditional nodal analysis and the Parareal algorithm. A new interpretation scheme is proposed to solve the transmission line convergence problem. To integrate different kinds of traditional EMT models, a component-based EMT system solver architecture is proposed to address the increasing model complexity. An object-oriented C++ implementation is proposed to realize the parallel-in-time Parareal algorithm based on the proposed architecture. The results on the IEEE-118 test system show 2.30x speed-up compared to the sequential algorithm under the same accuracy with 6 CPU threads, and a high parallel efficiency around 40%. The performance comparison of various IEEE test cases shows that the system's time-domain characteristics determine the speed-up of Parareal algorithm, and the delays in transmission lines significantly affect the performance of parallel-in-time power system EMT simulations.

The transience and unpredictability of processes in electric power systems (EPS) determine complexity of its control. This problem is especially relevant for EPS with renewable energy sources and flexible alternating current transmission systems technologies. Automatic control systems simplify the solution of this problem. Despite this, many issues related to EPS state control are solved by power system operators. Decision support systems (DSS) are applying to increase efficiency of operators work. However, existing algorithms in practice are inoperable in some cases: unrealizable decisions are formed, or decision cannot be found at all, etc. Another important problem is impossibility to preliminarily verify the proposed solution. In this regard, operators can additionally use EPS simulators, which are usually limited either by the size of simulated scheme or by the details of equipment mathematical models. The limitations are a consequence of numerical methods using, which are badly applicable for large-scale power systems simulation. In this article, a novel DSS has been developed based on a hybrid approach to EPS modeling combining properties and capabilities of several simulation techniques: analog, physical and digital. The implicit integration of differential equations in analog way makes possible modeling faster than real time. Such opportunity allows operator to verify more decisions and select the most effective ones. The algorithm for DSS application has been developed and described in the article. The properties and capabilities of the developed DSS are confirmed by experimental studies and tests in a real EPS. [ABSTRACT FROM AUTHOR]

In transient stability simulators such as PSS/E, the bus frequency is estimated using a window of (positive-sequence) phasor angle measurements. A digital filter is often used to account for the filtering effect in actual measurement devices and to eliminate sudden changes during frequency computations. Although transient stability simulators label the filtered angle derivative as the “frequency,” the frequency provided by such programs does not match actual measurements reported by phasor measurement units (PMUs), which makes it difficult to gauge the validity of studies (e.g., wide-area event detection and control applications) that are based on such simulations. In this paper, we implement a frequency computation method directly using positive phasor angles provided by simulators. The proposed method is tested on two systems extensively and validated against the measurements of an actual PMU. The improved frequency measurements closely match PMU responses. Cross-validation results also suggest the method may be used for other systems without conducting full time-domain simulations. [ABSTRACT FROM AUTHOR]

The paper presents accurate and simple dynamic model of a supercapacitor bank system for power system dynamics studies. The proposed model is derived from a detailed RC circuit representation. Furthermore, a complete control system of the supercapacitor bank is also presented. The proposed model is easy to integrate in any power system simulation software and consists of only up to four standard datasheet parameters. The performance of the proposed model in grid frequency control and low-voltage ride through is illustrated on IEEE 14-bus test system in DIgSILENT PowerFactory. It is shown that in case of transient stability simulations the ideal (simplified) model of the supercapacitor can be used while in case of frequency control the ideal representation may not always be appropriate. [ABSTRACT FROM AUTHOR]

Safe and effective exploitation of lithium ion (Li-ion) batteries requires advanced battery management systems. This article proposes a computationally efficient, control-oriented model of a Li-ion cell. The model describes the spatial nature of both the chemical species and temperature dynamics in a computationally efficient way. The method takes advantage of the algebraic structure that arises from the distributed nature of the model. We show that, by discretizing the model partial differential equations with a finite difference method, the coupling equations take a semiseparable structure for which an efficient algebra exists. This approach yields an efficient modeling tool that can be employed to design model-based estimation and control algorithms. The proposed model is validated against a high order computational fluid dynamics model showing accuracy and efficiency. [ABSTRACT FROM AUTHOR]

As the importance of renewable energy increases, the capacity of dispersed generations (DGs) has increased worldwide. However, the connection of DGs in the power distribution system can cause the fault current to increase as well as malfunction of the overcurrent relay (OCR) due to the reverse directional fault current. As the countermeasure to limit the fault current in the power distribution system with DG, though the superconducting fault current limiter (SFCL) is reported to be more effective, the research on the protection algorithm of the protective relay considering the application of SFCL is preferentially required. In this paper, the correction method of the OCR using voltage components for application of SFCL in a power distribution system with DG was suggested. To verify the effectiveness of the suggested method, the fault simulation for the power distribution system with DG including the OCR and the SFCL was performed. By applying the proposed correction method in the OCR, the protection coordination of OCRs for the application of SFCL in power distribution system with DG was confirmed to be improved through the suppression of the malfunction of the OCR. [ABSTRACT FROM AUTHOR]

Switching processes of voltage source converters can emit significant high-frequency distortions of frequencies between 5 to 20 kHz. Furthermore, the distortions can partly propagate from the place of their origin into a medium voltage system via capacitive coupling of power transformers. The origin, parameters, and propagation process of distortions were clarified by a numerical simulation of a 1-MW photovoltaic power plant connected to the medium voltage distribution grid. The determined results provided input data for the following accelerated aging test setup. The main idea behind the accelerated aging tests was to confirm the effect of the high-frequency distortions on the degradation rate of cable insulation systems. The tests were performed on cable samples, with terminations mounted on each end, which were split into three groups. The first sample group was stressed by increased power frequency voltage and by maximum operating temperature. The second group was stressed similarly, but with superposed high-frequency distortions present. The last group was not stressed to provide reference values for the other groups. Partial discharge, dissipation factor, and breakdown voltage measurements were carried out on both aged groups. The results indicate that cable insulation degradation progresses faster under power frequency voltage with superposed high-frequency distortions. [ABSTRACT FROM AUTHOR]

Geomagnetic Disturbance (GMD) impacts a power system by causing the circulation of quasi-dc Geomagnetically-induced Currents (GICs) in transmission lines and high-voltage transformer windings leading to transformer saturation, increased reactive power losses, and voltage regulation problems. Utility planners use various analysis methods and simulation tools to analyze GMD system impacts. These techniques can be broadly categorized into load-flow-based (LF), transient stability type (TS), and electromagnetic transient type (EMT) methods. These methods are based on different modeling assumptions and solution techniques. There is a need for evaluation of these assumptions and cross-examination of results to ensure their accuracy. Such an evaluation is essential to ensure that planners performing required GMD vulnerability assessments have confidence in the results. This paper evaluates the LF, TS, and EMT methods through cross-examination of their results. The objective is to identify their limitations, assess the consistency of their results, and provide assumptions on their use for analysis of GMD system impacts. The study is conducted in consistence with the North American Electric Reliability Corporation (NERC) GMD guidelines and standards. [ABSTRACT FROM AUTHOR]

This paper analyses the frequency stability of ac grids in the presence of non-dispatchable generation and stochastic loads. Its main goal is to evaluate conditions in which the system is robust to large, persistent active power disturbances without recurring to time-domain simulations. Considering the ongoing energy transition to more renewable sources, defining robustness boundaries is a key topic for power system planning and operation. However, much of the research on long-term studies has not dealt with robust dynamic constraints, while short-term analyses usually depend on time-consuming simulations to evaluate nonlinearities. To bridge this gap, the authors derive an algebraic equation that provides sufficient conditions for robust frequency stability in ac power systems and a relationship among four key quantities: the maximum active power perturbation, the minimum system damping, the steady-state and the transient frequency limits. To achieve this goal, it uses a nonlinear average-model of the ac grid and Lyapunov's direct method extended by perturbation analysis requiring only limited knowledge of the system parameters. The algebraic calculations are validated using time-domain simulations of the IEEE 39-bus test system and results are compared to the traditional Swing Equation model. [ABSTRACT FROM AUTHOR]

Computer-aided analysis is playing an important role in the design and control of power electronic systems. A discrete-state event-driven (DSED) framework with state-space modeling has been proposed recently for accurate and efficient off-line simulation. Nevertheless, automated equation formulation for arbitrary circuits is also required to develop the DSED framework toward general simulation software. However, the traditional state equation generation method is very time-consuming, especially for large-scale systems due to the variable topologies brought by switching events. In this article, an automated semi–symbolic state equation generation method is proposed. Based on the switching function modeling of basic switching legs, an explicit function from switching states to state equation matrices is given, which reduces the computational cost without sacrificing any accuracy. The operating and topological characteristics of power electronics systems are utilized for further optimization. The proposed method greatly increases the simulation efficiency of power electronic systems, especially for large-scale systems. Two cases of the 2 MW 4-port solid-state transformers with different system scales are simulated with the proposed method under the DSED framework. About 700-fold and 1200-fold acceleration is achieved compared with one fast-speed commercial software, where the proposed method contributes 50-fold and 110-fold acceleration in the two cases, respectively. [ABSTRACT FROM AUTHOR]

Traditional energy management strategies of wireless sensor network (WSN) nodes with hybrid energy storage do not adequately combine the merits of supercapacitors (SCs) and batteries, and thus, battery degradation remains a problem that restricts the lifetime of the WSN nodes. In this paper, an adaptive rule-based energy management strategy is proposed to extend the battery lifetime of a solar-powered wireless sensor node. The energy models are constructed with the consideration of the battery degradation, and Poisson distribution is utilized to simulate the power consumption variation of the node. A rule-based energy management strategy that is adaptive with the SC capacity and load conditions is designed. Traditional energy management strategies of the WSN nodes are compared with the proposed one. The simulation results indicate that the proposed strategy can improve the node lifetime from several tens of days to more than ten years. Meanwhile, the strategy ensures the continuous availability of the solar-powered WSN nodes even at night throughout the long lifetime. The robustness of the strategy is also tested. It is revealed that the strategy is adaptive with the SC capacity and workload conditions. The proposed strategy is broadly applicable and promising to resolve the problem of limited battery lifetime for the solar-powered WSN nodes.

Smart grid technologies are deepening the interdependence of electric power and communication systems, but that interdependence is difficult to quantify. In the case of microgrids, communication systems can be essential to maintaining stability during islanded operations. Though many power system studies assume the presence of perfect communication networks, detailed modeling of power and communication systems for dynamic studies of microgrids is rare. This article develops a framework, for power and communication system co-simulation, to study the effects of communication systems on microgrid stability. An operational use case is examined, in which a battery energy storage system operates to offset the loss of generation in an islanded microgrid. The framework is evaluated for different communication technologies, network structures, and communication media. [ABSTRACT FROM AUTHOR]

This article presents the innovative control scheme of renewable ancillary services to support the system operation of a bulk power system with high penetration of renewable energy. The smart inverters of PV systems can be controlled to adjust the renewable generation of real and reactive power according to the variation of system voltage and frequency. The dispatch control of renewable ancillary services is integrated with the energy management system to achieve the coordination control of renewable energy and synchronous generators. The sensitivity factors of renewable system was applied to determine the generation curtailment for the mitigation of line overloading. The ancillary service of reactive power compensation by renewable energy was considered to improve the system voltage quality. The emergency generation control of renewable systems with fast ramping up capability was applied to illustrate the effectiveness of renewable ancillary service to improve the system frequency response after sudden generator tripping. Based on the computer simulation of an actual power system with large renewable energy to be integrated, the functions of virtual synchronous generators by the photovoltaic systems and wind farms have to be applied to ensure the successful steady-state operation and to improve the system transient stability for severe disturbance contingency. [ABSTRACT FROM AUTHOR]

This paper proposes a data-driven cooperative method for load frequency control (LFC) of the multi-area power system based on multi-agent deep reinforcement learning (MA-DRL) in continuous action domain. The proposed method can nonlinearly and adaptively derive the optimal coordinated control strategies for multiple LFC controllers through centralized learning and decentralized implementation. The centralized learning is achieved by MA-DRL based on a global action-value function to quantify overall LFC performance of the power system. To solve the MA-DRL problem, multi-agent deep deterministic policy gradient (DDPG) is derived to adjust control agents’ parameters considering the nonlinear generator behaviors. For implementation, each individual controller only needs local information in its control area to deliver optimal control signals. Numerical simulations on a three-area power system and the fully-modeled New-England 39-bus system demonstrate that the proposed method can effectively minimize control errors against stochastic frequency variations caused by load and renewable power fluctuations. [ABSTRACT FROM AUTHOR]

The reliability of power systems with high penetration of renewables, a fast response mechanism, and precise decision-making scheme is more important than ever. This study presented a novel scheme that utilizes the predicted frequency nadir after a generation trip event to initiate necessary ancillary services such as fast spinning reserve units, energy storage units, and demand responses to restore the frequency back to the secure operating range. The proposed scheme coordinates Under-Frequency Load Shedding (UFLS) with ancillary services in the sense that the unnecessary load shedding can be avoided. By using the proposed scheme, the system becomes more resilient against disturbances, and the actions of load shedding are minimized. In this scheme, the frequency data is captured by phasor measurement units (PMUs), and a frequency nadir prediction algorithm is proposed. We demonstrate the effectiveness of the proposed scheme by using 1700-bus power system simulations and realistic frequency data from real generation trip events captured by a laboratory micro-phasor measurement unit (μPMU). [ABSTRACT FROM AUTHOR]

The inclusion of distributed renewable energy sources, new goals of efficiency and reliability, and the technological advancement of the power grid has led to a significant increase in the complexity of distribution systems. Although multiple devices can be controlled to achieve these objectives during smart grid operation, many proposed algorithms are based on ideal scenarios where the complex distribution system is assumed to be fully observable or measurable. As this condition obstructs many advanced applications, it is necessary to implement novel alternatives that provide support and validation in the field. In this paper, we show that embedded simulation is capable of providing accurate results of the system real-time condition. The designed platform exploits the technological development of mobile devices, a specific purpose solver, and concurrent processing to embed the power systems simulation into small, flexible, and affordable devices. Simulation results demonstrate the accuracy and timeliness of the proposed realtime simulation based on the IEEE 37 bus test feeder emulation and other large-scale scenarios such as the IEEE 8500 node test feeder. We anticipate that this simulation approach will be useful for applications covering advanced protection relaying, volt-var control, topological reconfiguration, distributed generation management, storage control, and cyber security assessment among others.

This paper proposes a co-simulation platform using field-programmable gate array (FPGA) and real-time digital simulator (RTDS) for the simulation of large power systems. It combines the advantages of high computational power from FPGA and better modelling flexibility from RTDS together. The FPGA therefore acts as an efficient and economical extension to RTDS especially when simulating large ac systems. One of the significant advantages of the proposed co-simulator is that it avoids the potential interface error existing in the conventional approach of interfacing transient stability program with electromagnetic transient programs. Two key aspects of the proposed co-simulator are discussed: 1) the interface design between FPGA and RTDS and 2) the hardware implementation and expandability of the platform. Two case studies are presented to verify the simulation accuracy and capability of the proposed co-simulator. The first case simulates a two-area four-machine power system with one area simulated in FPGA and the other area in RTDS. Comparisons are made with the case where the complete system is simulated in RTDS. The second case simulates a system of 141 buses in FPGA to demonstrate the simulator's capability in simulating large power systems.

The field-programmable gate array (FPGA) based hardware-in-the-loop (HiL) test, which minimizes the time-step of the real-time simulation below 500 ns, is an enabling technology for the development of the control unit of high-power electronic systems (HPE). In order to improve the time performance of FPGA-based HiL, this article proposes a novel parallel structure using the predictive behavior of the power electronic system. With this structure, we design an improved system-level solver applied to HPE. A piecewise insulated-gate bipolar transistor (IGBT) model is used to determine the state of the switch, offering a quasi-realistic model of the power converter. A parallel integration method is also implemented to solve the status of the circuit elements. Moreover, the proposed parallel structural can execute both the IGBT model and circuit element model at the same time, thus, reducing the simulation time-step significantly. The numerical accuracy of the solution, the architecture design, and the issue of the parallel computation are discussed in detail. An ac–dc–ac topology is presented as a case study. At last, a 25 ns time step in the National Instruments FlexRIO platform is achieved. Results comparison with the reference model is also identified and discussed. [ABSTRACT FROM AUTHOR]