Power System Stability Studies Research Articles

New Approach for Optimal Location and Parameters Setting of UPFC for Enhancing Power Systems Stability under Contingency Analysis

Operation of power system within specified limits of voltage and frequency are the major concerns in power system stability studies. As power system is always prone to disturbances, which consequently affect the voltage instability and optimal power flow, and therefore risks the power systems stability and security. In this paper, a novel technique based on the “Artificial Algae Algorithm” (AAA) is introduced, to identify the optimal location and the parameters setting of Unified Power Flow Controller (UPFC) under N-1 contingency criterion. In the first part, we have carried out a contingency operation and ranking process for the most parlous lines outage contingencies while taking the transmission lines overloading (NOLL) and voltage violation of buses (NVVB) as a performance parameter (PP = NOLL + NVVB). As UPFC possesses too much prohibitive cost and larger size, its optimal location and size must be identified before the actual deployment. In the second part, we have applied a novel AAA technique to identify the optimal location and parameters setting of UPFC under the discovered contingencies. The simulations have been executed on IEEE 14 bus and 30 bus networks. The results reveals that the location of UPFC is significantly optimized using AAA technique, which has improved the stability and security of the power system by curtailing the overloaded transmission lines and limiting the voltage violations of buses.

Probabilistic stability analysis: the way forward for stability analysis of sustainable power systems.

Future power systems will be significantly different compared with their present states. They will be characterized by an unprecedented mix of a wide range of electricity generation and transmission technologies, as well as responsive and highly flexible demand and storage devices with significant temporal and spatial uncertainty. The importance of probabilistic approaches towards power system stability analysis, as a subsection of power system studies routinely carried out by power system operators, has been highlighted in previous research. However, it may not be feasible (or even possible) to accurately model all of the uncertainties that exist within a power system. This paper describes for the first time an integral approach to probabilistic stability analysis of power systems, including small and large angular stability and frequency stability. It provides guidance for handling uncertainties in power system stability studies and some illustrative examples of the most recent results of probabilistic stability analysis of uncertain power systems.This article is part of the themed issue 'Energy management: flexibility, risk and optimization'.

MODELING OF POWER SYSTEMS AND TESTING OF RELAY PROTECTION DEVICES IN REAL AND MODEL TIME

The methods of modelling of power system modes and of testing of relay protection devices with the aid the simulation complexes in real time and with the help of computer software systems that enables the simulation of virtual time scale are considered. Information input protection signals in the simulation of the virtual model time are being obtained in the computational experiment, whereas the tests of protective devices are carried out with the help of hardware and software test systems with the use of estimated input signals. Study of power system stability when modes of generating and consuming electrical equipment and conditions of devices of relay protection are being changed requires testing with the use of digital simulators in a mode of a closed loop. Herewith feedbacks between a model of the power system operating in a real time and external devices or their models must be determined (modelled). Modelling in real time and the analysis of international experience in the use of digital simulation power systems for real-time simulation (RTDS simulator) have been fulfilled. Examples are given of the use of RTDS systems by foreign energy companies to test relay protection systems and control, to test the equipment and devices of automatic control, analysis of cyber security and evaluation of the operation of energy systems under different scenarios of occurrence of emergency situations. Some quantitative data on the distribution of RTDS in different countries and Russia are presented. It is noted that the leading energy universities of Russia use the real-time simulation not only to solve scientific and technical problems, but also to conduct training and laboratory classes on modelling of electric networks and anti-emergency automatic equipment with the students. In order to check serviceability of devices of relay protection without taking into account the reaction of the power system tests can be performed in an open loop mode with the use of hardware and software test systems. Testing methods for relay protection and their models in open-loop mode have been proposed.

Algebraic Topology Approach to Stability Studies of Electrical Power Systems

In this paper we study geometric structure of stability regions of a fairly broad class of dynamical systems, including gradient systems. The lower bounds obtained via an algebraic topology approach can be used to estimate the structure of the boundary of this region and in many cases give the exact number of equilibria corresponding to the bounding surfaces. The results have numerous applications to electrical power systems and to electronic circuits. The methods we use in this study belong in the area of Morse Theory, Algebraic topology and geometric dynamical systems.

Dynamic equivalent of wind farm model for power system stability studies

ABSTRACTA new dynamic equivalencing method for stability assessment of a grid-integrated wind farm is proposed in this article. The accuracy of the method is validated for a 34-bus system with 28-unit wind farm connected to Indian utility system. This wind farm consists of several wind turbines of two different ratings. The electrical parameters of the equivalent generator are derived from the mathematical model of the squirrel-cage induction generator. The parameters of the equivalent wind-turbine generator are optimized to yield minimum deviation from the detailed system response using genetic algorithm. The small-signal and transient stability responses of the study system with detail wind farm and equivalent model are simulated using MATLAB. Equivalent model eigenvalues are compared to the centre of inertia based detailed system eigenvalue. In addition, the computed eigenvalues and time-domain responses of the proposed equivalent model, detailed wind farm are compared against weighted model proposed earlier. In most of the investigated cases, the average error of dynamic responses between the proposed equivalent and detailed models are less when compared to weighted model. Thus, the large-signal responses of the proposed equivalent model show superior agreement with detailed system response.

Transient Stability Study of Power System with Large-Scale Wind Farm Integration

Large-scale wind power integration has become the current development trend of the power system. Large-scale wind power integration can change the original structure and characteristics of the system. Thus, it’s necessary to analyse the transient stability of power system which contains wind power, and to study the controlling strategy for improving the transient stability of power system. Based on EEAC, this paper studies the transient stability of the power system which contains wind power system theoretically, proposes the calculation method for accelerating area, decelerating area and margin, and illustrates the impact of wind power integration on the transient stability with power angle curve. Furthermore, this paper studies the modeling and simulation, and the experimental results prove the correctness of the theories.

Approach in the modeling of wind turbines for power system stability studies and evaluation of their impact on electric power systems

Wind power - one the fastest evolving in renewable energy industry. From year to year the share of wind energy in power systems are increasing as well as increasing the size of wind farms. A large-scale wind farms that produce hundreds of megawatts of electricity have a serious impact on the power grid. This paper discusses proposed approaches to modeling wind farms using the Hybrid Real-Time Power System Simulator (HRTSim), to study stability and transient processes in electric power systems.

Validation of Generic Models for Variable Speed Operation Wind Turbines Following the Recent Guidelines Issued by IEC 61400-27

Considerable efforts are currently being made by several international working groups focused on the development of generic, also known as simplified or standard, wind turbine models for power system stability studies. In this sense, the first edition of International Electrotechnical Commission (IEC) 61400-27-1, which defines generic dynamic simulation models for wind turbines, was published in February 2015. Nevertheless, the correlations of the IEC generic models with respect to specific wind turbine manufacturer models are required by the wind power industry to validate the accuracy and corresponding usability of these standard models. The present work conducts the validation of the two topologies of variable speed wind turbines that present not only the largest market share, but also the most technological advances. Specifically, the doubly-fed induction machine and the full-scale converter (FSC) topology are modeled based on the IEC 61400-27-1 guidelines. The models are simulated for a wide range of voltage dips with different characteristics and wind turbine operating conditions. The simulated response of the IEC generic model is compared to the corresponding simplified model of a wind turbine manufacturer, showing a good correlation in most cases. Validation error sources are analyzed in detail, as well. In addition, this paper reviews in detail the previous work done in this field. Results suggest that wind turbine manufacturers are able to adjust the IEC generic models to represent the behavior of their specific wind turbines for power system stability analysis.

Dynamic Voltage Stability Studies using a Modified IEEE 30-Bus System

Power System stability is an essential study in the planning and operation of an efficient, economic, reliable and secure electric power system because it encompasses all the facet of power systems operations, from planning, to conceptual design stages of the project as well as during the systems operating life span. This paper presents different scenario of power system stability studies on a modified IEEE 30-bus system which is subjected to different faults conditions. A scenario whereby the longest high voltage alternating current (HVAC) line is replaced with a high voltage direct current (HVDC) line was implemented. The results obtained show that the HVDC line enhances system stability more compared to the contemporary HVAC line. Dynamic analysis using RMS simulation tool was used on DigSILENT PowerFactory.

Field Validation of IEC 61400-27-1 Wind Generation Type 3 Model With Plant Power Factor Controller

Generic electrical simulation models of wind power generation have been developed as standards, such as the IEC 61400-27-1, to be used by wind industry, system operators, and academia for power system stability studies. In this paper, the IEC type 3 wind turbine model with wind turbine level voltage controller and with wind power plant level power factor controller is validated based on field measurements from a 52-MW wind power plant. In addition to the validation of the IEC type 3 wind turbine and wind power plant controller models, a comparison of the validation approaches, which are the full grid and play-back simulation, is provided together with a survey of the existing validation studies and recommendations for future modeling and validation tasks. The implemented IEC models are tuned to match the measurements accurately and the validated values for the control parameters of the reference wind power plant model are given.

Modeling approaches for considering active distribution grids in power system stability studies

This paper analyzes two different modeling approaches for the dynamic representation of active distribution grids regarding their applicability in power system stability studies. The first one is derived from a coherency-based aggregation method. It represents the distributed generation (DG) by equivalent generators in combination with a static load. The second modeling approach uses a linearized model for representing distribution grids and is named state-space model highlighting its inheriting nature. This approach is expanded by a new strategy considering explicit state limitations. It is shown that this limitation strategy significantly increases the accuracy of the state-space model. Both models are benchmarked against a detailed distribution grid model, and model accuracies are evaluated. The state-space model shows a higher accuracy for voltage dips smaller than 50 %, since all characteristic modes are preserved, and state limitations are represented in detail. For voltage dips above 50 %, the aggregated model may be applied to achieve higher accuracy.

Development of a WAMS based test platform for power system real time transient stability detection and control

The real-time transient stability detection and emergency control technology based on wide area response has become a hot research area in power system stability studies. Several different technologies have been proposed, but lots of problems remain to be solved before they can be applied in practice. A wide area measurement system (WAMS) based test platform is developed for transient stability detection and control. The design as well as main function modules of the platform are introduced. In addition, three generator power angle prediction methods and six response based transient instability detection technologies are given. Results of engineering application demonstrate that the developed test platform can provide a real-time operation environment, which can effectively compare and analyze the validity and practicability of these transient stability detection technologies. Based on the measured perturbed trajectories from actual power systems or the Real-Time Digital Simulators (RTDS), the platform can realize the assessment and visual result presentation of various responses from different transient instability detection technologies. The test platform can be applied to different power systems and it is convenient to embed new transient instability detection modules. Meanwhile some deficiencies and shortcomings in engineering application are pointed out and corresponding suggestions are given. In conclusion, the hardware and software structure, function modulus and engineering applications are presented. The application in actual power systems shows that it has a good application perspective.

Assessing the Applicability of Uncertainty Importance Measures for Power System Studies

This paper critically evaluates a number of uncertainty importance measures for use in power system stability studies. Sensitivity analysis of uncertain system parameters is vital as new technologies proliferate and the total level of system uncertainty grows. Accurate assessment of the importance of different uncertainties can guide power system operators towards parameters which will require the greatest levels of mitigation or increased monitoring in order to reduce the uncertainty and its subsequent impact. Local and global sensitivity analysis techniques are described and evaluated within this paper, including nonparametric methods, variance-based approaches, and distribution-based techniques. The techniques are illustrated using a large 295-bus realistic network model of a generic distribution system. Numerical experiments on dynamic models are used in order to assess the impact of uncertainties on the mitigation of system frequency excursions using single-site and distributed energy storage devices.

Measurement-based investigation of inter- and intra-area effects of wind power plant integration

This paper has a two pronged objective: the first objective is to analyze the general effects of wind power plant (WPP) integration and the resulting displacement of conventional power plant (CPP) inertia on power system stability and the second is to demonstrate the efficacy of PMU data in power system stability analyses, specifically when knowledge of the network is incomplete. Traditionally modal analysis applies small signal stability analysis based on Eigenvalues and the assumption of complete knowledge of the network and all of its components. The analysis presented here differs because it is a measurement-based investigation and employs simulated measurement data. Even if knowledge of the network were incomplete, this methodology would allow for monitoring and analysis of modes. This allows non-utility entities and study of power system stability. To generate inter- and intra-area modes, Kundur’s well-known two-area four-generator system is modeled in PSCAD/EMTDC. A doubly-fed induction generator based WPP model, based on the Western Electricity Coordination Council (WECC) standard model, is included to analyze the effects of wind power on system modes. The two-area system and WPP are connected in various configurations with respect to WPP placement, CPP inertia and WPP penetration level. Analysis is performed on the data generated by the simulations. For each simulation run, a different configuration is chosen and a large disturbance is applied. The sampling frequency is set to resemble the sampling frequency at which data is available from phasor measurement units (PMUs). The estimate of power spectral density of these signals is made using the Yule–Walker algorithm. The resulting analysis shows that the presence of a WPP does not, of itself, lead to the introduction of new modes. The analysis also shows however that displacement of inertia may lead to introduction of new modes. The effects of location of inertia displacement (i.e. the effects on modes if WPP integration leads to displacement of inertia in its own region or in another region) and of WPP controls such as droop control and synthetic inertia are also examined. In future work, the methods presented here will be applied to real-world phasor data to examine the effects of integration of variable generation and displacement of CPP inertia on inter- and intra-area modes.

Frequency‐dependent cable modelling for small‐signal stability analysis of VSC‐HVDC systems

State-of-the-art time-domain models of power cables account for the frequency dependency of physical parameters to enable accurate transient simulations of high-voltage transmission schemes. Owing to their formulation, these models cannot be directly converted into a state-space form as required for small-signal eigenvalue analysis. Thus, dc cables are commonly represented in high-voltage direct current (HVDC) power system stability studies by cascaded pi-section equivalents that neglect the frequency-dependent effects. This study demonstrates how the conventional cascaded pi-section model is unable to accurately represent the damping characteristic of the cable and how this can lead to incorrect stability assessments. Furthermore, an alternative model consisting of cascaded pi-sections with multiple parallel branches is explored, which allows for a state-space representation while accounting for the frequency dependency of the cable parameters. The performance of the proposed model is benchmarked against state-of-the-art cable models both in the frequency domain and in the time domain. Finally, the study provides a comparative example of the impact of the cable modelling on the small-signal dynamics of a point-to-point voltage-source converter (VSC) HVDC transmission scheme.

Analysis of simultaneous unbalanced short circuit and open conductor faults in power systems with untransposed lines and six-phase sections

The paper introduces a generalized method for analysis of multiple, simultaneous short circuit, open circuit, and open circuit falling conductor faults in mixed three-phase and six-phase power systems with untransposed lines. The method is systematic and suitable for all types of faults, any number of simultaneous faults, and any number of phases. Calculation of all network unbalanced voltages and currents during faults is done in one straightforward step. Coupling among sequence networks in untransposed transmission lines is accounted for. Coupling between the three-sequence networks of the three-phase part and the six-sequence networks of six-phase part is also derived. The method is applied also for transient stability study of mixed three-phase and six-phase power systems during any type of faults. Detailed derivation of the governing equations in each part is presented. Simulation results on the IEEE 300-bus system and the IEEE 30-bus system are given to validate the proposed method.

Stability and nonlinear controller analysis of wind energy conversion system with random wind speed

In the recent years, globally wind energy has played a vital role in renewable sources in order to minimize the environmental consequence on power generation, As a result of this, computer models of wind turbines for power system stability studies have been developed and supplied to the consumer. Therefore, the development of such models is of particular consequence for stability of power system, which has been studied and can be structured and integrated into network simulation software are needed. However, in this contribution a nonlinear control design modeling is required to stabilize and analyze wind energy conversion system (WECS) by regulating the electrical frequency and stator voltage amplitude of the squirrel-cage induction generator (SCIG) at random wind speed approach is presented. A design scheme consists of dynamic wind turbine system and 3-phase SCIG unit. In this research study, we employ a unique technique based on feedback linearization technique through field oriented control concepts. The controllers were designed in simulated software Matlab in order to regulate the SCIG constraints. The validation of the developing system models will be appropriate to provide for large system stability and control.

Simplified variable frequency induction-motor drive model for power system stability studies and control

Abstract: Powerful variable frequency drives (VFD) are becoming more widely used in power systems. However, there are only a few works addressed to VFD motor dynamics that are suitable for large-scale power system stability studies. The paper proposes a fundamental frequency simplified model of the VFD, which provides an adequate modeling for the study of electromechanical transients in large-scale power systems. Its implementation was carried out in Power System Toolbox (PST), an open source software available for both scientific and commercial purposes. The model was complemented by a number of protection and control strategies that allow to perform adequate modeling for severe disturbances.

Dynamic Modeling and Control of Wind Turbine Scheme Based on Cage Generator for Power System Stability Studies

Among renewable sources, wind source is the more sympathetic and favorable source because it is free from pollution and no carbon die emissions as it appraised in conventional energy sources. Based on existing literature, the development of wind-generator dynamic model is of great interest nowadays. In this paper, a complete dynamic wind-generator mathematically modeling approaches for wind energy system is carried out. Moreover, due to uncertain wind speed circumstances, it is desirable to evaluate the state of the art stability and controller performance analysis for wind-generator unit through feedback control techniques based on field oriented control concept, which plays a significant role in power system stability and control. The proposed dynamic wind-generator system model consists of three phase cage rotor induction machine unit, and it is intended in Matlab software tool for the simulation purpose. The dynamic wind-generator system stability and control design has broadened prospectus for the applications and developments. Among renewable sources, wind source is the more sympathetic and favorable source because it is free from pollution and no carbon die emissions as it appraised in conventional energy sources. Based on existing literature, the development of wind-generator dynamic model is of great interest nowadays. In this paper, a complete dynamic wind-generator mathematically modeling approaches for wind energy system is carried out. Moreover, due to uncertain wind speed circumstances, it is desirable to evaluate the state of the art stability and controller performance analysis for wind-generator unit through feedback control techniques based on field oriented control concept, which plays a significant role in power system stability and control. The proposed dynamic wind-generator system model consists of three phase cage rotor induction machine unit, and it is intended in Matlab software tool for the simulation purpose. The dynamic wind-generator system stability and control design has broadened prospectus for the applications and developments.

STEADY STATE STABILITY ANALYSIS AND ENHANCEMENT OF THREE MACHINE NINE BUS POWER SYSTEM USING TCPS FACTS DEVICE

Power System stability study is the important parameter of economic, reliable and secure system planning and operation. Studies are important during the planning and conceptual design stages of the project as well as during the operating life of the plant periodically. This paper presents the power system steady state stability analysis for IEEE9 bus test system and examines influence of TCPS FACTS device based controller on test system. It is assumed that system under study has been perturbed from a steady state equilibrium that prevailed prior to the application of the disturbance. If system is stable, we would expect that for temporary or permanent disturbance, system will acquire initial or new operating state after a transient period. The stability study is accessed using Lyapunov’s first method. The effectiveness of damping controller in enhancing the steady state stability is investigated by incorporating available constraints. For analysis MATLAB software is employed. The conclusions have been drawn here, based on theoretical and mathematical analysis so as to provide an insight and better understanding of steady state stability of considered multi machine power system.