This paper summarizes the technical activities of the Task Force on Power System Dynamic State and Parameter Estimation. This Task Force was established by the IEEE Working Group on State Estimation ...Algorithms to investigate the added benefits of dynamic state and parameter estimation for the enhancement of the reliability, security, and resilience of electric power systems. The motivations and engineering values of dynamic state estimation (DSE) are discussed in detail. Then, a set of potential applications that will rely on DSE is presented and discussed. Furthermore, a unified framework is proposed to clarify the important concepts related to DSE, forecasting-aided state estimation, tracking state estimation, and static state estimation. An overview of the current progress in DSE and dynamic parameter estimation is provided. The paper also provides future research needs and directions for the power engineering community.
Inverter-based resources (IBRs) possess dynamics that are significantly different from those of synchronous-generator-based sources and as IBR penetrations grow the dynamics of power systems are ...changing. This article discusses the characteristics of the new dynamics and examines how they can be accommodated into the long-standing categorizations of power system stability in terms of angle, frequency, and voltage stability. It is argued that inverters are causing the frequency range over which angle, frequency, and voltage dynamics act to extend such that the previously partitioned categories are now coupled and further coupled to new electromagnetic modes. While grid-forming (GFM) inverters share many characteristics with generators, grid-following (GFL) inverters are different. This is explored in terms of similarities and differences in synchronization, inertia, and voltage control. The concept of duality is used to unify the synchronization principles of GFM and GFL inverters and, thus, established the generalized angle dynamics. This enables the analytical study of GFM-GFL interaction, which is particularly important to guide the placement of GFM apparatuses and is even more important if GFM inverters are allowed to fall back to the GFL mode during faults to avoid oversizing to support short-term overload. Both GFL and GFM inverters contribute to voltage strength but with marked differences, which implies new features of voltage stability. Several directions for further research are identified, including: 1) extensions of nonlinear stability analysis to accommodate new inverter behaviors with cross-coupled time frames; 2) establishment of spatial-temporal indices of system strength and stability margin to guide the provision of new stability services; and 3) data-driven approaches to combat increased system complexity and confidentiality of inverter models.
This document is a summary of a report prepared by the IEEE PES Task Force (TF) on Microgrid Stability Definitions, Analysis, and Modeling, IEEE Power and Energy Society, Piscataway, NJ, USA, Tech. ...Rep. PES-TR66, Apr. 2018, which defines concepts and identifies relevant issues related to stability in microgrids. In this paper, definitions and classification of microgrid stability are presented and discussed, considering pertinent microgrid features such as voltage-frequency dependence, unbalancing, low inertia, and generation intermittency. A few examples are also presented, highlighting some of the stability classes defined in this paper. Further examples, along with discussions on microgrid components modeling and stability analysis tools can be found in the TF report.
The restoration of stability is major problem in power transmission system after the disturbance. Flexible AC transmission system (FACTS) devices have the ability to restore the stability of the ...system by manipulating the transmission parameters. The combination of FACTS devices is more effective than single device used alone. This paper investigates a coordinated control strategy involving static var compensator (SVC) and static synchronous series compensator (SSSC). The SSSC is used to lower the line's equivalent impedance and improve its active power transfer capabilities. To maintain bus voltage magnitude, a SVC is used for shunt compensation. Utilizing identical signal input tracking enables the operation of a device depending on the compensation provided by the other device. The efficacy of the proposed scheme is demonstrated by applying it to a tie line of two area 4-machine 11-bus Kundur test system and observing the system variables after a major fault is created on another tie line. The improvement achieved is highlighted by comparing the behavior with that of the uncompensated and conventionally compensated system. The simulation study is carried out in MTALAB Simulink which further supported by the real time simulation in Opal RT digital simulator. Also, cost function analysis shows that the proposed scheme is cost effective compared to other conventional schemes.
As the penetration of variable renewable generation increases in power systems, issues, such as grid stiffness, larger frequency deviations, and grid stability, are becoming more relevant, ...particularly in view of 100% renewable energy networks, which is the future of smart grids. In this context, energy storage systems (ESSs) are proving to be indispensable for facilitating the integration of renewable energy sources (RESs), are being widely deployed in both microgrids and bulk power systems, and thus will be the hallmark of the clean electrical grids of the future. Hence, this article reviews several energy storage technologies that are rapidly evolving to address the RES integration challenge, particularly compressed air energy storage (CAES), flywheels, batteries, and thermal ESSs, and their modeling and applications in power grids. An overview of these ESSs is provided, focusing on new models and applications in microgrids and distribution and transmission grids for grid operation, markets, stability, and control.
Differing from synchronous generators, there are lack of physical laws governing the synchronization dynamics of voltage-source converters (VSCs). The widely used phase-locked loop (PLL) plays a ...critical role in maintaining the synchronism of current-controlled VSCs, whose dynamics are highly affected by the power exchange between VSCs and the grid. This article presents a design-oriented analysis on the transient stability of PLL-synchronized VSCs, i.e., the synchronization stability of VSCs under large disturbances, by employing the phase portrait approach. Insights into the stabilizing effects of the first- and second-order PLLs are provided with the quantitative analysis. It is revealed that simply increasing the damping ratio of the second-order PLL may fail to stabilize VSCs during severe grid faults, whereas the first-order PLL can always guarantee the transient stability of VSCs when equilibrium operation points exist. An adaptive PLL that switches between the second-order and the first-order PLL during the fault-occurring/-clearing transient is proposed for preserving both the transient stability and the phase-tracking accuracy. Time-domain simulations and experimental tests, considering both the grid fault and the fault recovery, are performed, and the obtained results validate the theoretical findings.
Grid-connected converters exposed to weak grid conditions and severe fault events are at risk of losing synchronism with the external grid and neighboring converters. This predicament has led to a ...growing interest in analyzing the synchronization mechanism and developing models and tools for predicting the transient stability of grid-connected converters. This paper presents a thorough review of the developed methods that describe the phenomena of synchronization instability of grid-connected converters under severe symmetrical grid faults. These methods are compared where the advantages and disadvantages of each method are carefully mapped. The analytical derivations and a detailed simulation model are verified through experimental tests of three case studies. Steady-state and quasi-static analysis can determine whether a given fault condition results in a stable or unstable operating point. However, without considering the dynamics of the synchronization unit, transient stability cannot be guaranteed. By comparing the synchronization unit to a synchronous machine, the damping of the phase-locked loop is identified. For accurate stability assessment, either nonlinear phase portraits or time-domain simulations must be performed. Until this point, no direct stability assessment method is available which consider the damping effect of the synchronization unit. Therefore, additional work is needed on this field in future research.
Communication infrastructure (CI) in microgrids (MGs) allows for the application of different control architectures for the secondary control (SC) layer. The use of new SC architectures involving CI ...is motivated by the need to increase MG resilience and handle the intermittent nature of distributed generation units. The structure of SC is classified into three main categories, including centralized SC (CSC) with a CI, distributed SC (DISC) generally with a low-data-rate CI, and decentralized SC (DESC) with communication-free infrastructure. To meet the MGs' operational constraints and optimize performance, control and communication must be utilized simultaneously in different control layers. In this survey, we review and classify all types of SC policies from CI-based methods to communication-free policies, including CSC, averaging-based DISC, consensus-based DISC methods, containment pinning consensus, event-triggered DISC, washout-filter-based DESC, and state-estimation-based DESC. Each structure is scrutinized from the viewpoint of the relevant literature. Challenges such as clock drifts, cyber-security threats, and the advantage of event-triggered approaches are presented. Fully decentralized approaches based on state-estimation and observation methods are also addressed. Although these approaches eliminate the need of any CI for the voltage and frequency restoration, during black start process or other functionalities related to the tertiary layer, a CI is required. Power hardware-in-the-loop experimental tests are carried out to compare the merits and applicability of different SC structures.
This work presents a novel concept and formulation of the "Phasor Area Criterion" (PAC), which assesses the qualitative and quantitative aspects of a power system's transient stability using time ...synchronized measurements. Unlike most existing techniques, the PAC method is computationally inexpensive and free from state estimation of rotor angles. It utilizes direct synchrophasor measurements from a phasor data concentrator to assess the system's post disturbance transient stability status and identify the out-of-step generators. The PAC extracts the area of the convex hull from the trajectory of positive sequence voltage phasors within the phasor domain; therefore, the criterion outputs a monotonically increasing parameter that can assess the transient stability of the system. Thus, it is robust to false triggers due to multiple crossovers with the thresholds. The PAC algorithm is validated on Kundur's two area system, IEEE 39 bus system with different operating conditions, and also for the <inline-formula><tex-math notation="LaTeX">8^{th}</tex-math></inline-formula> January 2021 system split event for the European grid. Compared to the transient stability index, PAC delivers high situational awareness with accurate and early alerts of transient stability assessment.
Since the publication of the original paper on power system stability definitions in 2004, the dynamic behavior of power systems has gradually changed due to the increasing penetration of converter ...interfaced generation technologies, loads, and transmission devices. In recognition of this change, a Task Force was established in 2016 to re-examine and extend, where appropriate, the classic definitions and classifications of the basic stability terms to incorporate the effects of fast-response power electronic devices. This paper based on an IEEE PES report summarizes the major results of the work of the Task Force and presents extended definitions and classification of power system stability.
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