The electromagnetic transient (EMT) simulation is an essential tool for studying power grids dominated by inverterbased resources (IBRs).However, due to small simulation time steps and increasing problem sizes, performing EMT simulations for large-scale power grids becomes computational-intensive, and often impractical.To address this challenge, we developed Pa-raEMT, an open-source Python-based EMT simulator that is parallelizable and compatible with high-performance computing (HPC) systems for simulating large-scale power grids with a significant presence of IBRs.Its key features include: 1) utilizing parallel computation for network solution by decomposing the network conductance matrix into the bordered block diagonal form; 2) enabling parallel updates of device states and network historical currents; 3) leveraging HPC to further accelerate simulation through a developed generic interface.The accuracy of ParaEMT has been validated on the reduced 240-bus (720-node) Western Electricity Coordinating Council system by benchmarking the EMT dynamics against PSCAD.Furthermore, ParaEMT achieves a notable speedup of approximately 25 to 36 times on a synthetic 10,080-bus (30240-node) system by leveraging the HPC resource named Eagle at the National Renewable Energy Laboratory.A regional 100% renewable case of the reduced 240-bus system has been developed for simulating system-wide IBRs' interactions in large-scale power grids using ParaEMT.

Improving the resilience of Cyber-Physical Systems (CPS) against extreme events is vital. Current research, overly focused on power system restoration, often misses the complex interplay between the physical and cyber aspects of these systems, leading to potential vulnerabilities. This paper first proposes a framework for CPS considering interdependence. The framework accounts for cyber-physical collaborative recovery and the connectivity between cyber nodes and control center in the cyber system. The model is built considering factors such as repair crew, repair time, and network reconstruction, aimed at rapidly restoring the structural and functional resilience of CPS in the shortest possible time. Next, it integrates complex network theory to propose different repair strategies based on structural and functional indicators. Finally, the repair efficiency of the proposed strategies is comprehensively evaluated using structural and functional metrics. Simulation results show that the repair efficiency of CPS is superior to traditional power grids, and moderate reduction in the repair time of cyber nodes and a decrease in network size both contribute to enhancing repair efficiency.

Evaluating the robustness of cyber-physical system (CPS) under multi-stage attacks is fundamental to enhancing CPS resilience. Currently, many models inadequately consider information flow, which is not aligned with reality. The initial focus of this paper is on introducing a weakly coupled interdependent model for CPS. This model considers probabilistic line outage rules, cyber flow transmission characteristics, and the probabilities of inter-system coupling failures. Subsequently, the multi-stage attack strategies are presented and employed by the proposed model during disaster scenarios, along with the proposed robustness assessment indicators. The numerical results illustrate the robustness of the weakly-coupled CPS model under multi-stage attacks. This lays a modeling and simulation foundation for repair crew to enhance the CPS resilience.

Forced oscillation source location (FOSL) plays a significant role in mitigating forced oscillations (FOs), which threaten the power system stability. This paper proposes a data-driven approach for FOSL in power systems using synchrosqueezing wavelet transform (SWT). The proposed approach conducts SWT on the measured system responses to obtain the SWT matrix. Then, the SWT-based dissipating energy flow (DEF) model in time-frequency domain and dissipating energy spectrum (DES) model in frequency domain are derived from the traditional DEF model. Further, the characteristics of SWT-based DEF and DES are revealed by referring to the traditional DEF, and the FOSL criteria of the SWT-based DEF and DES can be hereby obtained. Using the obtained FOSL criteria, the FO source can be located from the measured responses. The performance of the proposed FOSL method is evaluated by simulation data of the WECC 179-bus test system and field-measurement PMU data of the ISO New England. The results confirm the accuracy and efficiency of the proposed method in the FOSL.

Transmission line is an important component of power transmission in electrical power system (EPS), and its security and stability directly affect the reliability of EPS. With the continuous growth of various industries, the demand for energy is increasing, and the demand for power supply reliability is gradually increasing. At present, the power grid company has accumulated a large amount of data related to power equipment, which includes the basic account data of the equipment, the running state of the equipment, the fault records of the equipment, the micro-topography data where the equipment is located and the meteorological data. How to use these data to ensure the safe and reliable transmission of transmission lines is of great significance to improve the stability and security of EPS. In order to quickly and accurately identify the fault lines in the power grid and maintain the safe and stable operation of the power grid, it is of great significance to identify the fault types of transmission lines. In this article, a transmission line fault pre-alarm model based on the big data classification algorithm of support vector machine (SVM) is proposed, which can diagnose the faults of transmission lines based on big data analysis, so as to realize the optimal design of transmission lines.

This paper proposes a data-driven approach for estimating participation factors for a power system using only simulation results on selected disturbances. The approach is purely response-based and does not need a linearized system model for eigen-analysis, which makes it applicable to systems whose detailed, complete mathematical models are not available. Considering the unavoidable nonlinearity as exhibited in the transient period of a system response, the Synchrosqueezed Wavelet Transform is applied to simulated responses for modal analysis to obtain participation factors. Based on simulations of Kundur’s two-area system using both the electromagnetic transient model and phasor model, the participation factors estimated by the proposed approach are compared with two other signal processing tools, the Prony analysis and continuous wavelet transform, and are also benchmarked with conventional model-based participation factors.

Synchrophasor data have a range of applications, from planning, market operation to reliability operation. Oscillation source location (OSL) is among the most successful synchrophasor applications in today's control rooms, which identifies the equipment destabilizing the system. Having such equipment identified in a timely manner offers real-time, actionable information to grid operators, which is critical for mitigating such dynamic risks and improving system reliability. In the past two decades, many OSL methods have been proposed based on different principles. Synchrophasor data have captured many real-life oscillation events and helped approach a more comprehensive explanation of the oscillation phenomenon in power systems: from natural mode oscillations to forced oscillations, from non-resonance conditions to resonance conditions, from model-based analysis methods to data-driven analysis methods or hybrid methods using both model and data. In addition to the significant progress in both theory and application of OSL, it cannot be denied that all the existing OSL theories are not complete, yet, and there are still rooms to improve the engineering practice of OSL.This chapter starts with a literature review of existing OSL methods, and then focuses on a promising OSL method, named dissipating energy flow (DEF) method , and its latest applications. Specifically, detailed studies on longitudinal power systems are presented to reveal more insights into DEF's practical effectiveness and capability. Subsequently, DEF analysis results on multiple cases from the 2021 IEEE-NASPI Oscillation Source Contest are presented and discussed.

In this paper, we demonstrate the distribution of real-valued power flow solutions and its application to the long-term voltage stability. It is the first time in power engineering we realize that even a small-scale IEEE standard power system can admit a humongous number of real-valued solutions for a single load and generation profile. For example, the IEEE 30-bus system can achieve 25686 many different real-valued solutions at a light loading condition. Furthermore, a mysterious class of false power flow solutions is reported and analyzed rigorously as legitimate numerical solutions. All solution sets investigated in this paper are posted online associated with this paper to support potential future applications [1]. Based on these extensive solved power flow solutions, we exhibit their occurrence patterns and distributions at different loading levels, and propose a long-term voltage stability margin index to quantify the long-term voltage stability of a given power flow condition. Numerical studies on a 5-bus system and a 57-bus system show the feasibility and effectiveness of the proposed index in assessing power system long-term voltage stability margin.

This letter discusses the 18-20 Hz oscillation event at 05:30 am on November 21, 2021, in Kaua`i's power system following the trip of an oil power plant. As far as the authors are aware, this is the first report of a transmission system-wide subsynchronous oscillation driven by inverter-based resources (though the system in question is relatively small). In this letter, we leverage two data-based methods-the dissipating energy flow method and the sub/super-synchronous power flow method-to locate the sources of the oscillation. Also, we build an electromagnetic transient model of the Kaua`i power system and replay the 18-20 Hz oscillation. Finally, we propose two mitigation methods and validate their effectiveness via numerical simulation.

An increasing penetration level of inverter-based renewable energy resources changes the inertia of power systems, posing challenges for maintaining the desired system frequency stability. An accurate frequency nadir estimation is crucial for power system operators to prepare preventive actions against large frequency excursions. In this paper, five machine learning methods—linear regression, gradient boosting, support vector regression, an artificial neural network, and XGBoost—are applied to two different datasets, i.e., 1) the unit generation dataset and 2) the system total inertia and headroom dataset, for the prediction of the frequency nadir. The training and testing datasets are generated through extensive generation scheduling simulations using Multi-timescale Integrated Dynamic and Scheduling (MI-DAS) toolbox on the Western Electricity Coordinating Council 240-bus system with high renewable penetration levels. Numerical results show that all five machine learning methods perform well in predicting the nadir frequency of the system. Among them, the gradient boosting and the XGBoost are clear winners yielding the best prediction accuracy in terms of four evaluation metrics.

Accurate measurement of grid frequency is a critical component of reliable grid control. Traditionally, inverters and phasor measurement units (PMUs) have used methods such as phase locked loops (PLLs) and discrete Fourier transforms (DFTs) to measure frequency. However, as inverter-based resources (IBRs) such as solar and wind have increased, these conventional frequency measurement methods have yielded incorrect frequency measurements leading to unreliable control in some cases. One challenge is measuring frequency during transient events. During these events, measured frequency may contain significant spikes due to the disrupted waveform, much more rapid and significant than any expected physical frequency dynamics. New methods must balance between suppressing spikes in frequency during faults, and providing fast, accurate, measurements in all other grid operation conditions, especially during events with a high rate-of-change-of frequency (ROCOF), which are more prevalent in high-IBR power systems. This paper first surveys frequency measurement methods that have been proposed to reduce measurement errors during transient events in low-inertia grids. Then, both conventional and more novel frequency measurement methods are tested against an IEEE standard and industry recommendations, and their performance is evaluated for events simulated in PSCAD. Results quantify trade-offs in performance during different grid conditions and lead to suggestions for the most appropriate frequency and ROCOF measurement methods for low-inertia grids.

This paper describes in detail the design process and creation of 13 oscillatory test cases for the IEEE and NASPI cohosted Oscillation Source Locating Contest conducted in 2021. The challenges behind the 13 cases are fully explained. Based on the philosophy, implementation considerations, and techniques used for the case design presented in this paper, interested readers can create additional interesting cases for testing the efficiency of their oscillation source location methods.

As power systems become increasingly dependent on inverter-based resources (IBRs), the dominant physical and control interactions that determine system stability might no longer be accurately captured in positive sequence dynamic simulation tools; electromagnetic transient (EMT) simulations may be needed. This paper describes the process of creating and validating an EMT model of the entire Maui island transmission system in PSCAD software. The model is verified against the utility PSSE model and validated against field data for an event that consisted of a single-phase fault followed by a generation trip. The methodology and lessons learned are summarized.

针对交直流混联系统交流输电线路故障后盲目重合于故障引发直流换相失败的问题,提出一种利用故障相等值阻抗相位特征识别故障性质的单相自适应重合闸方案.瞬时性故障时故障相线路侧等值阻抗主要由对地电容组成,阻抗呈容性且熄弧瞬间阻抗相位变化显著;永久性故障时故障相线路侧的等值阻抗主要由线路自阻抗、对地电容和过渡电阻组成,阻抗呈阻容或阻感特性.因此,以瞬时性故障等效模型为基准模型,采用工频相量快速提取算法计算等值阻抗,利用等值阻抗相位特征差异区分瞬时性故障和永久性故障.大量仿真分析表明,该判别方法适用于带并联电抗器输电线路,可快速识别单相故障性质并确认故障熄弧时刻,减小盲目重合于故障引发换相失败的可能,具有较好的耐过渡电阻能力.

This paper proposes a novel approach to estimate the steady-state angle stability limit (SSASL) by using the nonlinear power system dynamic model in the modal space. Through two linear changes of coordinates and a simplification introduced by the steady-state condition, the nonlinear power system dynamic model is transformed into a number of single-machine-like power systems whose power-angle curves can be derived and used for estimating the SSASL. The proposed approach estimates the SSASL of angles at all machines and all buses without the need for manually specifying the scenario, i.e. setting sink and source areas, and also without the need for solving multiple nonlinear power flows. Case studies on 9-bus and 39-bus power systems demonstrate that the proposed approach is always able to capture the aperiodic instability in an online environment, showing promising performance in the online monitoring of the steady-state angle stability over the traditional power flow-based analysis.

A fundamental challenge in computer analysis of power flow is the rigorous understanding of the impact of different loading levels on the solutions of the power flow equation. This letter presents a comprehensive study of possible numerical solutions that may arise as the loading level varies. In particular, a type of "false" load flow solutions is reported for the first time as a legitimate numerical solutions but with no engineering justification. The existence and the mechanism of why this category of solutions exist are rigorously analyzed. The probability mass function of voltage solution is shown to be less dependent on loading levels. Furthermore, numbers of all actual solutions and those solutions within engineering limits are summarized. This letter presents a first attempt to compute such huge numbers of solutions to the tested systems, and analyze their distribution patterns. All solution sets investigated in this letter are posted online associated with this letter to support any further research purposes.

太阳帆板驱动机构(solar array drive mechanism,SADM)是长寿命、大功率航天器上负责能源传输的关键部件,对空间充放电效应非常敏感.为检验SADM导电环绝缘介质聚酰亚胺的深层充放电对功率传输性能的影响,提出材料掺杂改性和几何结构优化的方案并进行试验研究.利用电子加速器产生2 MeV高能电子束,对以聚酰亚胺为基体的不同成分掺杂和不同几何构型的试样进行辐照试验,顺次监测试样金属环片接地、恒压和悬浮3种工况下聚酰亚胺挡边的表面充电电位.结果表明,聚酰亚胺挡边高度越高充电越严重,挡边宽度对不同成分掺杂的试样表现出不同的影响规律.对充电影响最显著的是聚酰亚胺掺杂改性后产生的非线性电导特性,通过合理掺杂可以显著缓解深层充电风险并达到抗辐射加固的效果.

Deploying charging stations (CSs) catering to the demand from electric vehicles plays an important role in modernizing energy infrastructures. In this paper, a bi-level optimal allocation model for allocating fast CSs is proposed aiming to maximize the CS investor benefit (upper layer sub-problem) by optimally allocating CSs with the coordinated determination of the expected efficiency of charging service supply (lower layer sub-problem). The efficiency is formulated as a charging performance index in terms of user satisfaction degree, which mathematically couples the upper level and lower level subproblems. The proposed nonlinear bi-level model is reduced to a single-layer optimization model under the Karush-Kuhn-Tucker optimality conditions. An improved dynamic differential evolution algorithm with an adaptive update strategy is proposed to solve this single-layer optimization model. The proposed method is validated using a realistic case. The test results show that the proposed methodology is able to co-ordinate both objectives of interest, i.e., allocating CSs network with the maximized benefits and optimizing the fast charging service efficiency at the same time.

Based on the LI(Longitudinal Impedance) characteristic of single-phase model, an accurate decoupling algorithm of LI for three-phase model is proposed, which ensures its theoretical reliability. An improved pilot protection applying the LI of fault component is thus proposed for transmission line. When external fault occurs, its LI is equal to the positive-sequence impedance of line; when internal fault occurs, it is equal to the negative phasor sum of the positive-sequence impedances of equivalent system. The proposed protection scheme has sensitive operation and reliable performance, avoiding the synchronous sampling of electrical variables at each terminal of line. The composite influence of system impedance and line capacitance on LI is analyzed and an auxiliary criterion is added, which makes the proposed protection scheme suitable for various operational environments. Simulative results show its correctness.