Power System Analysis Applications Research Articles

Experiences about calculating ZIP and exponential load model parameters

Abstract To reduce greenhouse emission and achieve sustainability in the electric power industry, improved efficiency and energy conservation are key to finding a sound solution. Energy conservation through voltage reduction (CVR) is one such program. To implement effective CVR programs, load models are of utmost importance in determining proper feeders and methods to implement the CVR programs. Exponential and polynomial load models stand out as the most widely adopted models. The polynomial load model, often referred to as the ZIP (constant impedance, current and power) model, is especially notable for its ability to represent the relationship between the applied voltage and power consumption. This paper sheds light on the limitations of commonly used ZIP load model estimation methods and highlights the significance of using ap-propriate measurement samples and understanding the true nature of the load. Two distinct ZIP load models, i.e., the regular ZIP (RegZIP) and the Non-traditional ZIP (NTZIP) models, have been used for ZIP parameter estimation. The RegZIP load model consumes equal or more power when voltage increases, while the NTZIP model consumes equal or less power when voltage increases. It is emphasized that the RegZIP is an existing load model and the NTZIP is an artificial load model this research created for comparison purposes. The intention of this paper is not to propose any new load model, but to investigate the implications of choosing the wrong model and the impacts of measurement errors of voltage and power data. The research has shown that the two different models can fit the same measurement data equally well for some measured data. The results have demonstrated that simply using certain methods such as the optimization method for estimating load model parameters using unfiltered real time measurements may yield misleading and unreliable results. Wrong load models will inevitably lead to wrong CVR assessment. Identifying the correct measurement samples, obtained during natural or staged events causing substantial voltage variations, is critically important in calculating load parameters and ensure the soundness of the obtained results. The accurate load parameters will be important in the assessment of CVR program effectiveness and will ensure that power system analysis applications that utilize the load models will provide reliable results.

Robust Framework for Online Parameter Estimation of Dynamic Equivalent Models Using Measurements

The ever-increasing demand for electricity, the advent of microgrids and the increasing penetration of distributed generators has renewed the interest in dynamic equivalencing, due to to its importance on power system analysis and control applications. This paper introduces a robust measurement-based framework for the online derivation of dynamic equivalent models. First, events/disturbances suitable for the derivation of dynamic equivalent models are automatically detected. Next, signal processing techniques are applied to recover missing samples and to remove noisy components from measured data. To exclude unnecessary post-disturbance data, a fine-tuning technique of the signal window length is also proposed as a supplementary offline process. Finally, model parameters are estimated using nonlinear least-squares optimization. The performance of the proposed methodology is tested using artificially created signals, simulation results obtained from a modified benchmark distribution grid and measurements acquired from a laboratory-scale active distribution network.

불량데이터의 고속 검출을 위한 PMU 데이터 활용 2단계 상태추정 연구

As the dependence on electrical energy increases, the power system is becoming lager. Since the size of power system is gradually increasing, the calculation of various power system analysis applications used to check the current state of the power system is complicated and may consume a lot of calculation time. In addition, due to the aging of the power system, it is difficult to maintain the precision of the measuring instrument, and when a large number of bad data are included in the measurement set, a lot of time may be spent detecting and identifying them. The factor that determines the computation time of state estimation is related to the size of the system. When the measurement includes a number of bad data, most of the computation time in state estimation is consumed to process the bad data. If the power system can be divided into small scales to reduce the size of the system, the calculation time and the bad data detection of state estimation can be improved. When the state estimation is performed on the partitioned system, the estimated voltage magnitudes are same as the result of the original whole system. When the state estimation is performed on the partitioned small-scale systems, the voltage angles are calculated as angle differences with respect to the slack buses for each small-scale systems. If PMUs are installed for each small-scale systems, it is possible to recognize the difference in phase angle for each partitioned system. It is possible to perform a two-step state estimation, which consists of performing the state estimation of a partitioned system and correcting the phase angle of partitioned system using PMU measurement. In this paper, we propose a method to perform state estimation in two steps on a partitioned system using PMU measurement to shorten the calculation time of the state estimation and the detection time of the bad data for the large-scaled system.

Three-Phase Unbalanced Power Flow Using a <formula formulatype="inline"> <tex Notation="TeX">$\pi$</tex> </formula>-Model of Controllable AC-DC Converters

Microgrids are unique in that they can combine unbalanced three-phase systems with other AC and DC network sections, which may include a range of renewable energy sources, energy storage elements, and controllable AC-DC converters. Existing unbalanced power flow techniques such as the Ladder Iterative Technique and the three-phase Newton-Raphson (NR) method can analyze microgrids in sections but lack a complete system representation. Hence, there is a need for a power flow algorithm that considers the complete system model and solves it. A novel $\pi$ -model of a controllable AC-DC converter and a single set of power balance equations for modeling a grid comprising multiple three-phase AC and DC sections is proposed. The $\pi$ -model of a controllable AC-DC converter enables its inclusion into the network bus admittance matrix (YBUS) along with three-phase AC and DC network sections. Verification of the $\pi$ -model is also described in the paper. The results of power flow studies with three-phase balanced and unbalanced AC and DC network sections are presented. The outcome of the $\pi$ -model verification study and power flow study show that the proposed $\pi$ -model is consistent and accurate. While the proposed model was developed for microgrids, it is applicable for all power system analysis applications.

A probabilistic security assessment approach to power systems with integrated wind resources

Renewable energy sources, such as wind and photovoltaic solar, have added additional uncertainty to power systems. These sources, further to the conventional sources of uncertainty due to stochastic nature of both the load and the availability of generation resources and transmission assets, make clear the limitations of the conventional deterministic power flow in power system analysis and security assessment applications. In order to manage uncertainties, probabilistic approaches can provide a valuable contribution.In this paper, we propose a new scheme for probabilistic security assessment. The model can deal with various types of probability distributions modeling power injections and can explicitly represent the effects on system security of correlation among nodal power injections (such as wind power) and of contingencies due to branch and generating unit outages. In addition, the steady-state behavior of the frequency regulation is explicitly included in the model. A new approach to deal with current limits is also proposed.Extensive testing on both the modified IEEE-14 bus test system and the Sicilian power system indicates good performance of the proposed approach in comparison with the result obtained by the computationally more demanding Monte Carlo approach.

Parameter Estimation for Series Compensated Transmission Line

Transmission line parameters are essential inputs to various power system analysis programs and applications such as protective relaying algorithms, and precision of line parameters is thus significant in ensuring the analysis accuracy and algorithm reliability. This paper proposes methods for estimating positive sequence parameters of a series compensated transmission line. The methods are based on distributed parameter line model and utilize voltages and currents from both terminals of the line during normal operations. In particular, based on nonlinear estimation theory, an optimal estimator is designed for deriving positive sequence line parameters. The algorithm is capable of detecting and identifying bad measurement data, and thus improving the estimation accuracy. The proposed method is independent of the operation status of the compensation device.

Translating CIM XML Power System Data to a Proprietary Format for System Simulation

The problem of exchanging data between two or more organizations in a format that is accessible and understandable by each is a universal problem. Furthermore, the problem of translating or accessing data in the correct format for applications using proprietary data formats is challenging. Legacy software applications may endure, for some time given, regulatory expenditure pressures on electricity system operators and these require data translators (importer/exporter) and access facilities. The basis of this paper is that the Electric Power Research Institute (EPRI) common information model (CIM) in eXtensible Markup Language (XML) represents the first stage in a revolution of data exchange and manipulation for power systems. This paper explores the problem of translating data in the CIM XML format to the required format for such legacy power system analysis applications. This paper discusses solutions to some of the challenges in data translation, and illustrates how these solutions can be implemented.

Enhancement of Data Handling in Integrated Power System Analysis Package, Named Impact, Using Information Technologies

This paper describes a new method to enhance data handling and reduce effort in power system analysis. The power system is very large and incorporates many pieces of equipment. To reduce effort in power system analysis, it is necessary to increase data handling efficiency. However, conventional power system analysis applications incur a complicated data format requiring experienced operators and/or planners. On the other hand, many useful data-handling methods are provided by information technology (IT). In this paper, a graphical user interface and database function are applied to data handling and are installed in an integrated power system analysis package, named IMPACT.

Design of Generic Direct Sparse Linear System Solver in C++ for Power System Analysis

This article presents the design of the generic linear system solver (LSS) for a class of large sparse symmetric matrices over real and complex numbers. These matrices correspond to one of the following: (1) symmetric positive definite (SPD) matrices, (2) complex Hermitian matrices, or (3) complex matrices with SPD real and imaginary matrices. Such matrices arise in various power system analysis applications like load flow analysis and short circuit analysis. A template facility of C++ is used to write a generic program on float, double, and complex data types. The design of the algorithm guarantees numerical stability and efficient sparsity implementation. A reusable class SET is defined to cater to graph theoretic computations. LSS problems with matrices up to 20,000 nodes have been tested. Another feature of the proposed LSS is the implementation of associative array, which allows subscripting an array with character strings, such as bus names. This helps in making the four power system analysis software user friendly. The proposed LSS reflects an important development towards a truly object-oriented four power system analysis software.

Object-oriented software engineering for transmission planning in open access schemes

The object oriented approach has gained wide spread importance and acceptance in software development due to the advantages it offers concerning flexibility, expandability, maintainability, and data integrity. For the purpose of determining a dynamic planning of a transmission system in a deregulated open access environment, an object-oriented market simulation model of power systems is proposed. Traditional power system analysis applications are realised with object-oriented programming methods. The presented concept makes use of these object-oriented applications, and its applicability to a real system is shown with the Chilean business structure.

Solving for three phase conductively isolated busbar voltages using phase component analysis

Three-phase busbar voltage solutions, derived from the Y-bus network model and unbalanced current injections, are used in a variety of three-phase power system analysis applications, such as Z-bus power flow and short circuit studies. When phase coordinate analysis is used to solve these problems, existing techniques can result in divide-by-zero errors. These errors occur when the network contains one or more islands conductively isolated from the ground. This paper combines the limit processes of calculus and linear circuit analysis to derive an algorithm which can perform a LDL/sup T/ factorization of the phase coordinate Y-bus model of such networks. This factorization can then be used to solve for voltages in islands conductively isolated from ground, yet energized through magnetic coupling to one or more islands with a ground reference. >

An integrated personal computer graphics environment for power system education, analysis and design

An integrated graphics environment for power system analysis and design (PSADE) is presented. The environment runs on a personal computer with standard memory and graphics hardware requirements (VGA or EGA). PSADE is based on a general purpose graphics development software which provides numerous tools to facilitate the creation and modification of particular power system analysis applications. The integrated environment contains extensive color graphics representations of power systems, interface with external power system simulation programs, dynamic display of the results on the graphical representation of the network, and straightforward communication among the external and the internal databases. The use of this environment is illustrated by several particular applications. PSADE is specially useful to universities and industry for teaching and training purposes, as well as being a valid research tool for preliminary study of planning or operational schemes. >