An intelligence technique-based control model for power system stabiliser

Gerilim kararlılığı, güç sistemlerinde incelenmesi gereken önemli bir konudur. Sürekli artan elektrik enerjisi talebi, artan talebi karşılamak için yeni elektrik üretim santrallerinin kurulumu ve güç sistem arızaları gerilim kararlılığını olumsuz yönde etkilemektedir. Günümüzde gerilim kararlılığını iyileştirmek için güç sistemlerinde Esnek Alternatif Akım İletim Sistemleri (FACTS cihazları) kullanılmakta olup, ayrıca enerji talebini karşılamak ve gerilim kararlılığını iyileştirmek için güç sistemlerine Dağıtık Üretim Kaynakları (DGs) entegre edilmektedir. Bu çalışmada, IEEE 30 baralı güç sistemi ile Kuzeybatı Anadolu (KBA) güç sistemi, gerilim kararlılığı bakımından temel (nominal), aşırı yüklenme ve hat kopması durumlarında incelenmiştir. İncelenen güç sistemlerine FACTS cihazlarından Statik Var Kompanzatör (SVC) ve Tristör Kontrollü Seri Kapasitör (TCSC), DGs’lerden ise Yakıt Hücresi (YH), Güneş Enerji Santrali (GES) ve Rüzgâr Enerji Santrali (RES) ayrı ayrı ve birlikte bağlanmıştır. Güç sistemlerinin bara gerilim değerlerinde ve yüklenme parametresinde meydana gelen değişimler analiz edilmiştir.

An innovative technique to evaluate network equivalent for voltage stability assessment in a widespread sub-grid system

This paper investigates on-load tap changer OLTC effect on voltage stability. Chaos theory used in this analysis is via the calculation of the maximum power transmission. Resulted chaotic behavior is exhibited by singular induced bifurcation which clearly shows the voltage stability of the power system with OLTC from a singular induced bifurcation point of view. The paper is organized as follows: 1) increasing in the maximum reactive power via increasing the ratio of OLTC and the possibility of voltage collapse decrease under the same load command. 2) Noting that the voltage instability is directly affected by the load characteristics, shown via the effect of OLTC on the voltage instability under different static load models. 3) Studying voltage stability in state space and the effects of the generator excitation current limit, the OLTC and load dynamics on voltage collapse. In addition, a small-disturbance voltage stability region of a power system is constructed. The voltage stability of the system is determined by the dynamic characteristics of both the OLTC and the load.

Integrating large-capacity wind power into a power system has a great impact on the voltage stability of a power system. Especially, a fault in such a system can result in the tripping of a large amount of wind power generation or system collapse. This article studies the effect of large-capacity wind power generation on power system voltage stability under a fault condition. The adopted wind power model consists mainly of a wind turbine, drive device, asynchronous generator, and control system. The proposed analysis approach is applied to a practical power system with wind power, which is located in Gansu province in China. Through simulation and analysis, the characteristic and stability principle of an asynchronous wind generator group are recognized. A speed increase in a wind generator group is closely related to voltage drop after fault, which may cause voltage instability if they both impact each other after fault. The detailed results are presented in the article.

Voltage Stability Improvement In Multi-bus System Using Static Synchronous Series Compensator

ABSTRACTThis paper reveals the impact of an ultra-capacitor (UC) and thyristor control phase shifter (TCPS) on frequency stability of large hybrid interconnected power system. The impact of UC and TCPS has been studied for general purpose hybrid generated multi areas power system. Further to this, an adaptive neuro fuzzy inference system (ANFIS) is is proposed for automatic load frequency control (ALFC). Thermal and reheat thermal plants are connected in Area-1 and area-2, whereas area-3 has hydro plant and area-4, 5, 6 consists of nuclear power plant, diesel power and gas turbine plant, respectively. A micro grid based on Solar Photovoltaic (PV) system and fleet of electric vehicle (EV) system is developed and integrated with load side of area-1 for load management in interconnected grid. Effect of Small load change and large load change are discussed in separate cases. The controllers are tuned by adding sliding surface to enhance the performance. A comparison between ANFIS and PI-based control approaches with and without UC and TCPS exhibits the superiority of ANFIS controller by integrating UC and TCPS. The results of the proposed control technique are compared with already published results.

With large wind energy integration into power systems, wind farms begin to influence power systems in a much more significant manner. As wind energy systems utilize different generator technologies from the one utilized in the conventional power plants, the steady-state, transient and small-signal dynamics, as well as, power system stability will thus be significantly affected. The impact of wind energy systems on the power system dynamics and stability is thus of practical importance. As there is a significant increase in installation of wind turbines equipped with doubly-fed induction generator (DFIG) in recent years, a dynamic model of the DFIG wind turbine is firstly developed in this thesis. The model is validated against field measurement data, and the validation gives confidence about the accuracy and applicability of the developed model. DFIG wind farms consist of tens to hundreds of identical DFIG wind turbines increasing the complexity of the wind farm model and simulation time. A novel aggregation technique is developed in this thesis that incorporates a multiplication factor, namely mechanical torque compensation factor (MTCF), to the mechanical torque of the full aggregated wind farm model. The MTCF is initially constructed to approximate a Gaussian function by using fuzzy logic method. By optimizing the MTCF on a trial and error basis, less than 10 percent discrepancy is then achieved between the proposed aggregated model and the complete model. The proposed aggregation technique is then applied to a 120 MVA offshore wind farm comprising of 72 DFIG wind turbines and shows higher accuracy in approximating the wind farm dynamics as it appears at the point of common coupling (PCC) as compared to the full aggregated model. The proposed aggregated model computes faster than the complete wind farm model by 90.3 percent during normal operations and 87 percent during grid disturbances. To overcome the adverse effects due to the fluctuating nature of wind, two wind power smoothing methods are proposed using a fuzzy logic pitch angle controller for a smooth performance with a minimum drop in output power. One method performs partial smoothing with only 4.74 percent drop in the output power while the other method offers complete smoothing with a 8.28 percent drop in output power. The impact of wind energy integration on power system transient stability (PSTS) is studied quantitatively with the transient energy margin (TEM), which is calculated through the evaluation of the transient energy function (TEF). This study is carried out in two ways in the thesis. One is to analyse the impact of transient fault on the DFIG wind turbine as compared to SGs for different factors, like the fault clearing time, the grid coupling, the inertia constant and the voltage sag. The study reveals that transient stability of the DFIG wind turbine is hardly affected by the grid coupling, the inertia constant and the generator terminal voltage sag variations indicating its consistent transient performance within a wide range of these factors. The fault clearing time should be almost 11 percent faster for the system with the DFIG than the synchronous generator (SG). The other is to investigate the impact of the DFIG wind farm on the PSTS with the variation of different factors, which are the voltage sag, the fault clearing time, the load and the wind power penetration level. The study reveals that power systems integrated with DFIG wind farms are sensitive to transient events with high voltage sag, high fault clearing time, low load operation and high wind power penetration level. Machines at different locations individually possess distinct fault response and suffer from a large-scale power imbalance. As a result, reliable operation of DFIG wind farm integrated power systems demands upgraded equipment, such as advanced switchgear, fast breakers/isolators, efficient power reserve systems and advanced reactive power compensating device, etc.

This paper presents voltage stability in power systems when connected by wind farm generators. Two models of wind generator, namely squirrel cage induction generator and doubly fed induction generator are used and based on steady-state model. P-V curve is used to express maximum loading factor in power system when wind farm was installed. The test IEEE 14 bus system is selected to show proposed performance. The results of this paper can be shown that maximum loading factor before install wind farm generator is 0.70398 p.u. The weakest bus is bus no.14. Therefore, loading factor of system that connects two types of wind turbine with 7 m/s wind speed are 0.8688 p.u and 0.7997 p.u respectively. To improve the voltage stability, FACTS device is selected. The results show that STATCOM can improve maximum loading factor better SVC for both types of wind farm generator. Maximum loading factor increased when setting STATCOM up to 56.33% and 53.28% in systems that connected squirrel cage induction generator and doubly fed induction generator wind turbine respectively. Therefore, this methodology can give direct advantage for organization that are responsible to built convincing of power system in study the respond of setting wind turbine generator on voltage stability.

With the recent growing interest in renewable energy integrated power systems across the globe for the various economic and environmental benefits, it is also significant to consider their influence on voltage stability in power systems. Therefore, this paper reports the static voltage stability impact of solar photovoltaic generation on power networks using PowerWorld simulator power-voltage (P–V)- and voltage-reactive power (V–Q)-curves to investigate the renewable energy generator model performance suitability. The impact of varying power factor control and static voltage droop control of a photovoltaic plant on the maximum generated power, threshold voltage profile and reactive power marginal loading has been examined. Besides, the concept of percentage change in voltage-power sensitivity has been systematically utilized to determine the optimal location for the solar photovoltaic generator on the power grid and the feasible penetrations have been defined for selected system buses. From the simulation results it can be concluded that in a steady-state analysis of the grid integrated power system the effects of power factor (pf) control and voltage droop control should be considered by power grid engineers for effective system operation and, equally, the application of percentage change in voltage-power sensitivity should be extended to real networks to determine the best positions for multiple installations of renewable energy resources.

This article is aimed at justifying the need to modernize the existing systems that ensure voltage stability in the Unified Power System of Russia under the conditions of its permanent development, structural complication and active implementation of distributed generation. To this end, an analysis of the existing systems of emergency control used in the Unified Power System of Russia was conducted by considering their efficiency during major system accidents, including those in 2005 and 2017. In addition, specific features of operating power system facilities in the northern part of the Irkutsk Oblast were investigated from the standpoint of voltage stability. The conducted analysis of the operation of emergency control systems in the context of system accidents, including possible incorrect actions, identified their following disadvantages: insufficient fault tolerance, weak adaptability to emergency disturbances (including abnormal situations), as well as a lack of coordination between local devices and the discreteness of regulation. These shortcomings can be eliminated by introducing intelligent automation systems based on artificial neural networks and machine learning, as well as high-performance multi-agent systems into the structure of the emergency management of the Unified Power System of Russia. The results obtained indicate the need to modernize the existing voltage stability systems operated in the Unified Power System of Russia, both their software and hardware components. The proposed implementation of intelligent systems is expected to improve the existing systems at the same time as maintaining the current effective hierarchical principles of emergency management.

This paper presents an application of Artificial Neural Network (ANN) algorithm for improving power system voltage stability. The training data is obtained by solving several normal and abnormal conditions using the Linear Programming technique. The selected objective function gives minimum deviation of the reactive power control variables, which leads to the maximization of minimum Eigen value of load flow Jacobian. The considered reactive power control variables are switchable VAR compensators, OLTC transformers and excitation of generators. The method has been implemented on a modified IEEE 30-bus test system. The results obtain from the test clearly show that the trained neural network is capable of improving the voltage stability in power system with a high level of precision and speed.

Voltage stability of power systems reflects challenges to the power system operators due to its effect on the power systems components performances. Therefore, many solutions were invented in order to keep the systems within the voltage stability accepted limits. Because of the huge expansion of the power grids and the different loads natures on the grids, many techniques and solutions are used. The On Load Tap Changing Transformer (OLTC) was one of those techniques. In this paper, a review of past works that deal with the voltage stability limits, voltage stability improvement ways, OLTC types, the OLTC reverse action, and OLTC effect on voltage stability, in addition to several ways that make the OLTC work better. are discussed. The paper also sheds the light on the possible ways that may be employed to prevent the OLTC reverse action.

Voltage stability analysis is the major concern in order to operate any power system safely. In this context considerable research work has been carried out to improve the voltage stability. FACTS devices can used for controlling power flow, transmission voltage, improving voltage profile, and reducing reactive losses. In this paper two different FACTS devices have been selected to place in suitable location to improve voltage stability in power system. The mathematical model of the power system equipped with a Static VAR Compensator (SVC) and Static synchronous compensator (STATCOM) separately is systematically derived and the parameters of the shunt FACTS are modeled into the power flow equations and used in the control strategy. The two models of FACTS are developed for the IEEE 30-bus system and implemented in Newton-Raphson load flow algorithm in order to control the voltage of the bus to which the shunt FACTS is connected. In this study a MATLAB written program is used for the solution of power flow problems and calculate voltages, active and reactive power at each bus of IEEE 30-bus system.

Automatic generation control plays an important role in power system to maintain frequency and voltage stability in power system. Frequency of the electrical supply system should be maintained at a constant standard value inorder to maintain the proper working of different machinery and different components connected with the power system. Both real and reactive power control can be achieved through frequency and voltage control in the power system respectively. Today, power system complexity increases day by day due to integration of power electronic components and renewable energy generation units. This will lead to some issues in stability of the entire power system and power quality from utility side may be become a challenging one. This paper discusses a solution for this challenges by introducing AC DC parallel tie line with coordinated operation of super conducting magnetic energy storage(SMES) and thyristor controlled series compensator(TCSC). This type of method is analysed with taking thermal thermal two area power system and thermal hydro power system in MATLAB platform. Simulation results clearly validates that this methodology in AGC improve system performance.

Improvement of power system stability in wind connected generator by using PSAT