یک شاخص غیرخطی ارزیابی پایداری ولتاژ مبتنی بر روش آنالیز برداری و اندازه‌گیری‌ از توان‌های اکتیو و راکتیو سیستم قدرت

این مقاله به ارائۀ یک شاخص جدید سنجش پایداری ولتاژ مبتنی بر روش آنالیز برداری می‌پردازد. اساس استخراج شاخص پیشنهادی، اندازه‌گیری به‌هنگام از توان‌های اکتیو و راکتیو ورودی و خروجی شینه‌های متصل به شینه‌های ژنراتوری است. در این راستا با توجه به قضیۀ حداکثر توان انتقالی از یک ژنراتور به بار متصل به آن، حدی برای شروع فروپاشی ولتاژ تعیین می‌شود. از طرفی در مواردی که سیستم قدرت نیازمند حذف‌ بار است، یک‌ حذف‌‌ بار جدید ولتاژی/ فرکانسی ارائه شده است. ساختار این حذف ‌‌بار به‌گونه‌ای است که با تقسیم‌بندی بارهای شبکه به‌عنوان بارهای مجاز و غیرمجاز جهت خروج و اولویت‌بندی خروج بارهای مجاز، پایداری ولتاژ و فرکانس شبکه تضمین خواهد شد. شبیه‌سازی‌ها در محیط نرم‌افزار دیگسایلنت بر روی شبکۀ استاندارد 39 شینۀ ieee، صحت و کاربرد بسیار مناسب روش پیشنهادی را نسبت به سایر روش‌ها نشان می‌دهد.

A Nonlinear Voltage Stability Index Based on Vector Analysis Method and Measurements of Active and Reactive Powers of Power System

Introduction: Voltage stability generally acts as a main role in power system operation and control. During recent years, voltage instability has led systems to plenty of large blackouts. Voltage stability is well known as the ability of the system to be stable in cases of changes in voltages.Voltage instability usually starts from a non predictable point of the system, and if it would not to be predicted and prevented, its effects may lead the whole system into a nonrecoverable voltage collapse. Recently, financial limitations have forced power systems to work nearing their load limitations in cases of large increases in power demands; that means that power systems are disposed for fast large voltage collapses. Indeed, keeping voltage stability is crucial in modern power systems, and it has been an attractive concern for researchers. During the last decades, researchers have proposed variety of impressive methods and indices to deal with the matter. Sensitivity analysis, Modal analysis, Artificial Neural Networks (ANNs) and Deep Learning, optimal power flow equations, metaheuristic algorithms, the use of threshold limits index, conversion of power system to The venin equivalent circuit, Curve stability, and so on have previously been proposed for voltage stability. These methods can be categorized in local and remote methods. In the local methods, detection and prevention methods wok based on the local data, but in remote ones data are synchronized using Global Positioning System (GPS) in Phasor Measurement Units (PMUs) and transmitted to a Wide Area Monitoring, Protection, and Control (WAMPAC) center for implementing voltage stability. Previously studied methods usually confront problems such as high memory requirements, the dependence on power system structure, the lack of optimal solution, inaccurate estimation, long and timeconsuming calculations, and solving equations statically.Materials and Methods: This paper introduces a nonlinear voltage stability evaluation index based on active and reactive powers of buses connected to generator buses. This index works by using online measurements of injectable powers in the system based on the WAMPAC roles; based on the rule of maximum power transfer ability of the system, and the lossless consumption of the transmission system. In cases of disturbances and loss of power generation sources, if total generation are equal to the total amount of the load, the maximum power will be transmitted to the load. Using the proposed index, the maximum injected power to the load will be calculated from the maximum load capacity of the line. In this case, the transmitted active and reactive power has a threshold in comparison with one another. It can be seen that in cases where line current reaches its limits and cannot pass higher values of power, voltage collapse will ensue. In this method, all the disturbances in the power system are defined and divided into the categories of ldquo;internal part rdquo; for disturbances at the generator buses and their adjacent buses and ldquo;external part rdquo; for disturbances caused in other places. During any disturbance, in case of equality of active and reactive power, maximum injected power has been injected through the line to the connected load. If this condition remains, Voltage Collapse is predictable. Buses those use for determining index will evaluate voltage stability of the system even in cases of inobservability of the system; that means that the power system has interwoven dynamics, and the other buses in observed parts of the system will contribute in checking the others. The name of this method is vector analysis.Results: This approach will be implemented in a dynamic format, and the analysis is, thus, more realistic than that of a static method. Also, independency from the system structure makes the method evaluate voltage stability without performing complex calculations. This means that the proposed method requires less calculation and less memory than the others. Voltage stability assessment helps identify and evaluate the stability status. In real power systems, voltage collapse may cause wide area blackouts and a loss of a large amount of generation and loads; therefore, preventing voltage collapse is so important and demands appropriate control and protection operations. In this paper, after evaluating the voltage stability status and voltage collapse prediction, the new load shedding index is presented. This index for load shedding is stabilized based on the combination of voltage and frequency. Voltage collapse is usually accompanied by frequency collapse. Therefore, the common load shedding based on combination of two aspects gives a better preventing effect on wide area blackouts. The basis of the index is to rank the system loads based on the amount of their power and load priorities. Unlike many existing methods, the proposed index does not shed the loads as a common percentage for all the loads. In contrast, the proposed index determines the allowable load shedding priority based on online measurements of voltage and frequency in the load buses. Increasing the load shedding speed leads to system stability and to less load outage than the other methods. Therefore, it can be considered that the proposed method for load shedding will prevent the instability during and after the disturbances in power systems.Discussion and Conclusion: In this paper a new method for voltage collapse identification was presented. The basic point of the method is the measurement of active and reactive power of buses connected to generator bus. One of the advantages of the index is its high accuracy, independent on timeconsuming and complicated calculation with soaring accuracy. Additionally, in this paper, a new index has been introduced in the model of smart load shedding. Subsequently, when load shedding is required in the power system, excessive load of the system will not have been eliminated, which results in system efficiency. Simulation results in DIGSILENT Power Factory and MTLAB software on IEEE39 bus (New England) dynamic test system demonstrate the efficiency of the proposed approach with respect to the other methods.