Power System Studies Research Articles

On-Line Thévenin Impedance Estimation Based on PMU Data and Phase Drift Correction

In this paper, a new approach based on synchronized phasor measurements is developed to estimate the online Thévenin impedance of the power system seen at the generator terminal. The method uses two consecutive synchronized measurements reported by phasor measurement unit located at the generator terminal. An innovative algorithm based on rate of change of frequency is also introduced to correct the phase drift and synchronize the two consecutive measurements. The algorithm is tested on the standard 39-Bus New England network for different scenarios consisting of steady-state, progressive load variation, during fault, post fault, and noisy data. The proposed method is further verified using real phasors data obtained from the PDC center in Iran Grid Management Company. The obtained results verify that the algorithm is able to estimate the online Thévenin impedance and can be efficiently used in online power system studies in particular when the power system frequency changes considerably from its nominal value under abnormal conditions.

Incomplete information based multi-port two-layer active network equivalent for electromagnetic transient states studies in large power systems

In this study, an approach is presented for external network modeling of power systems in the absence of required data involving all of transmission lines and equipment in all of the substations. In the proposed approach which is based on multi-port networks, the studied power system is divided into two parts of surface layer and deep region. The surface layer should be modeled high accuracy, thorough details and frequency dependent. The deep region should be modeled by a multi-port equivalent network. This multi-port equivalent network is achievable using a steady state model of the power system which is under the study. In order to investigate the performance of the proposed approach, numerical studies are performed for a typical network. Results show the high precision of the modeled network in comparison to the complete network. Effectiveness of the presented approach in electromagnetic transient studies of large-scale power systems has been indicated in this paper.

Global value chain assessment based on retrospectively induced economic costs associated with technology application: A case study of photovoltaic power system in Japan

Abstract Global warming is a worldwide problem that requires an international strategy to ensure compatibility of economic growth and overcoming climate change. Although global use of low-carbon technology is a solution, consideration of economic consequences is important to promote future technology development and use. Photovoltaic (PV) solar power system is a promising renewable technology that carries climate mitigation expectations. We conducted a value chain analysis to evaluate the economic effect of the manufacture and use of silicon PV solar power system worldwide. We quantitatively reviewed the flow of manufacturing and installation for cells, modules, and facilities (e.g., inverters) related to Japan, and estimated the retrospectively induced economic costs for Japan and other developed and developing countries. Material, equipment, labor, utility, transportation, and business operation costs were studied in detail at different manufacturing and installation stages. This unique evaluation methodology quantified economic costs from an international perspective. The retrospectively induced economic effect of 2014 PV solar power system sales in Japan (induced by cell module and system production by Japanese companies and increased domestic use) was 1.6 trillion Japanese yen worldwide, of which 63% was attributable to Japan, 10% to other developed countries, and 27% to developing countries. The economic effect in Japan in terms of equipment cost and installation stage was 37% and 71% of the total effect, which was particularly high. Further technical improvement, cost reduction, and improvement in inverter and manufacturing equipment reliability are important to capitalize Japan's strengths. Currently, Japan's involvement in the manufacturing of cells and modules is small. Therefore, both technical innovation and cost reduction are necessary. We present new methodology to obtain inputs into policy development for further research, development, and technology diffusion.

Modelling and detection of live tree‐related high impedance fault in distribution systems

Despite the importance of high-impedance fault (HIF) modelling as a key issue in numerous power system studies, there is no single model accurately representing the behaviour of each type of HIFs. Tree-related HIF (THIF) is a complex type that occurs when a power line comes in contact with a live tree. Given that available models for HIF cannot represent the expected behaviour of a live THIF, the need for a more accurate model seems obvious. So, in this study, based on experimental data obtained from measurements, the effective factors in HIF caused by live trees are studied and a new mathematical model of THIF provided in order to present the effects of both environmental conditions and biological classification. This model represents low and high frequency behaviours of THIFs, which are, respectively, derived in block-oriented feed-forward form and sinusoidal functions. Moreover, this study proposes a hybrid technique based on the combination of kernel density estimation and wavelet analysis to perform a feature extraction from THIF signals.

Application of soft computing neural network tools to line congestion study of electrical power systems

Application of soft computing neural network tools to line congestion study of electrical power systems

Effects of Front-End Converter and DC-Link of a Utility-Scale PV Energy System on Dynamic Stability of a Power System

This paper presents a method for small-signal dynamic studies of power systems including utility-scale PV energy systems considering the effects of dc-side components. Existing methods commonly model a PV energy system as a dc source connected to a grid-tied inverter. This paper shows that the dc components of a PV energy system can also contribute in the dynamics of the power system in the range of small-signal studies. The paper first develops the model of a PV energy system by merging the submodels of dc- and ac-side components. Then, a method to obtain the augmented model of the power system including a PV energy system will be explained using a study system. The study system consists of a PV energy system in parallel with a synchronous generator connected to a grid. Then, based on eigenvalue analysis, verified by time-domain simulations, it is shown that the dc-link capacitor, front-end converter, and its controller can introduce oscillatory modes in subsynchronous range of frequencies. Furthermore, it is shown that the damping of the sensitive modes can significantly vary with respect to the parameters of the dc-side components.

Análisis de transitorios electromagnéticos en el Sistema Nacional Interconectado (S.N.I.) a nivel de 230 kV y 500 kV usando el simulador digital en tiempo real HYPERsim

El presente trabajo utiliza el Simulador Digital en Tiempo Real HYPERsim para poder modelar los componentes del Sistema Nacional Interconectado (S.N.I.), en los niveles de voltaje de 230 kV y 500 kV, y realizar simulaciones en valores instantáneos para transitorios electromagnéticos (EMT) de maniobra. De esta forma, se analizan sobrevoltajes de frente lento originados por maniobras de energización de líneas de transmisión y transformadores. Para esto, se plantea una metodología que permite modelar los elementos del SNI en HYPERsim, sobre la base de un apropiado despliegue conceptual de los modelos de cada componente. El desarrollo del presente trabajo constituye un insumo fundamental para realizar estudios eléctricos en HYPERsim que permitan analizar el comportamiento de transitorios del SNI. Este aspecto es aún más significativo, considerando que el aplicativo HYPERsim no ha sido usado en el país de forma previa. De esta forma, se realizan simulaciones en tiempo real completamente digitales, lo cual permite exaltar las potencialidades del trabajo desarrollado, y permitirá a CENACE realizar estudios especializados futuros de sistemas de potencia, por ejemplo, calibración de relés, diseño de esquemas de protección, pruebas de controladores, etc.

Estimación de los Parámetros Eléctricos de un Generador Sincrónico basada en Mediciones de Laboratorio usando Métodos de Optimización No Lineal

Este artículo presenta los resultados de la implementación de una metodología para la estimación de los parámetros eléctricos de un generador sincrónico basada en mediciones de laboratorio y utilizando métodos de optimización no lineal, con la finalidad de mejorar la representación de la máquina sincrónica que podría ser utilizada en estudios de sistemas eléctricos de potencia. Para ello se realizaron pruebas bajo la Norma IEEE 115 en el Laboratorio de Máquinas Eléctricas de la Escuela Politécnica Nacional. Estos parámetros obtenidos constituyen el punto de partida para la herramienta de estimación de parámetros que ayudará a sintonizar la respuesta de la máquina. Luego, se aplica una perturbación eléctrica a la máquina para obtener una respuesta experimental en forma de oscilograma. La perturbación se replica en MATLAB-Simulink para obtener la respuesta simulada de la máquina en la forma de un oscilograma. La etapa final utiliza como recurso la herramienta de identificación de parámetros de MATLAB-Simulink para sintonizar los parámetros eléctricos al modelo de la máquina sincrónica. Con la aplicación de esta metodología se encuentra que la respuesta simulada del generador sincrónico mejora y reproduce adecuadamente los valores medidos.

Multi-Domain Semantic Information and Physical Behavior Modeling of Power Systems and Gas Turbines Expanding the Common Information Model

Due to the rapid increase of intermittent energy resources (IERs), there is a need to have dispatchable production available to ensure secure operation and increase opportunity for energy system flexibility. Gas turbine-based power plants offer flexible operation that is being improved with new technology advancements. Those plants provide, in general, quick start together with significant ramping capability, which can be exploited to balance IERs. Consequently, to understand the potential source of flexibility, better models for gas turbines are required for power system studies and analysis. In this paper, both the required semantic information and physical behavior models of such multi-domain systems are considered. First, UML class diagrams and RDF schemas based on the common information model standards are used to describe the semantic information of the electrical power grid. An extension that exploits the ISO 15926 standard is proposed herein to derive the multi-domain semantics required by integrated electrical power grid with detailed gas turbine dynamic models. Second, the Modelica language is employed to create the equation-based models, which represent the behavior of a multi-domain physical system. A comparative simulation analysis between the power system domain model and the multi-domain model has been performed. Some differences between the turbine dynamics representation of the commonly used GGOV1 standard model and a more detailed gas turbine model are shown.

Design of a Droop Control Scheme for Programmable Sources in a Microgrid Testbed

Abstract The Clean Energy Research Lab (CERL) in Nanyang Technological University, Singapore has a three-phase, 400V, 50Hz microgrid (MG) testbed to perform power system studies. The MG testbed comprises a 13.5kVA synchronous generator, 18kVA programmable source, 6kvar capacitor bank, 5kW solar photovoltaic (PV) system, 13.5kW wind simulator, 5kW battery energy storage system (BESS), 5kW fuel cell, 13.5kW programmable load as well as a 10kW simulated industrial load. The MG can operate either in islanded mode or in grid-connected mode. In the islanded mode, distributed generators such as the synchronous generator and the programmable source determine the frequency and voltage of the MG. A major difference between the synchronous generator and the programmable source is that the synchronous generator has inertia while the programmable source is inertialess. This means that the former has an inherent power-frequency droop associated with it whereby the synchronous generator frequency changes according to its power generated. Conversely, the programmable source does not have a power-frequency droop characteristic since it has no rotating parts. This paper demonstrates how the programmable source can be programmed to contain the power-frequency droop characteristics inherent to the synchronous generator. The experimental results presented in this paper are obtained from the CERL MG testbed. The results demonstrate the utility and performance of the developed droop scheme.

Models of synchronous generators with excitation system, for transient power system studies

Design and operating criteria for power system stability largely depend on a synchronous generator’s capability to remain in synchronism. In the field of mathematical modeling of the dynamics of synchronous generator’s with excitation systems, there is a need for more practical studies investigating the impact of Fault Ride Through criteria from system operators on actual cases. This paper describes a practical method which illustrates the different aspects of how this type of modeling and simulation can be carried out on a case study. Results show that the type of excitation system, time of fault, and the generators rotating mass have large impact on the system stability.

The increasing impact of weather on electricity supply and demand

Wind and solar power have experienced rapid cost declines and are being deployed at scale. However, their output variability remains a key problem for managing electricity systems, and the implications of multi-day to multi-year variability are still poorly understood. As other energy-using sectors are electrified, the shape and variability of electricity demand will also change. We develop an open framework for quantifying the impacts of weather on electricity supply and demand using the Renewables.ninja and DESSTINEE models. We demonstrate this using a case study of Britain using National Grid's Two Degrees scenario forwards to 2030.We find the British electricity system is rapidly moving into unprecedented territory, with peak demand rising above 70 GW due to electric heating, and intermittent renewable output exceeding demand as early as 2021. Hourly ramp-rates widen by 50% and year-to-year variability increases by 80%, showing why future power system studies must consider multiple years of data, and the influence of weather on both supply and demand. Our framework is globally applicable, and allows detailed scenarios of hourly electricity supply and demand to be explored using only limited input data such as annual quantities from government scenarios or broader energy systems models.

Cross-border reserve markets: network constraints in cross-border reserve procurement

Cross-border reserve markets—the procurement and activation of reserves in one control area to maintain system balance in another control area—can lead to increased cost-efficiency and reliability. However, network constraints impose limits on cross-border reserve coordination. Transmission capacity allocation in the reserve market is a complex problem, as it happens under uncertainty and interferes with transmission capacity allocation in energy markets. This paper studies network constraints in the reserve procurement phase, by means of a simulation model and scenario analysis. Three different approaches are proposed and evaluated based on a case study of the Central Western European electricity system. Towards this aim, a dedicated model is developed to simulate the day-ahead energy market, the day-ahead reserve procurement and the real-time reserve activation. In a case study of the Central Western European power system, we show that the best reserve market outcome—weighing cost-efficiency and system reliability—is obtained when reserve activation scenarios are considered in the procurement phase. Policy makers should design, in close cooperation with regulators and system operators, efficient and robust transmission capacity allocation procedures for cross-border reserve markets. This paper can help them to do so as it demonstrates the impact of transmission capacity allocation on cross-border reserve markets.

The Stochastic Response Surface Method for Small-Signal Stability Study of Power System With Probabilistic Uncertainties in Correlated Photovoltaic and Loads

This paper explores applications of stochastic response surface method (SRSM) in the small-signal stability analysis of the power system with probabilistic uncertainties in correlated photovoltaic and loads. A detailed model is provided to simulate the dynamics in the PV system. SRSM is presented to approximate the critical damping ratio as a function of independent standard random variables, which are transformed from correlated loads and irradiance by Nataf transformation. Two applications of SRSM are explored, namely, estimating the probability of power system small-signal instability, and providing the emergency control when the system damping is reduced suddenly. The modified two-area four-machine system and IEEE 39-bus 10-machine standard system are used to test SRSM and its applications.

Whale optimization algorithm based optimal reactive power dispatch: A case study of the Algerian power system

Optimal reactive power dispatch (ORPD) is a particular case of the optimal power flow. ORPD was usually considered as the minimization of an objective function representing the total active power losses in the electrical networks. The constraints involved are the generator voltages, tap regulating transformers ratios and the amount of reactive shunt compensators. The goal of this study is to find the best vector of control variables, so that the power loss decreasing can be realized. In this paper, a new metaheuristic technique inspired from the bubble-net hunting technique of humpback whales, namely whale optimization algorithm (WOA), has been applied to solve the ORPD problem. The WOA method has been examined and confirmed on the IEEE 14-bus, IEEE 30-bus, in addition to a practical and large scale Algerian electric 114-bus test system. The obtained outcomes have been compared with two own developed methods, namely, particle swarm optimization (PSO) and particle swarm optimization with time varying acceleration coefficients (PSO-TVAC). Afterwards, an analysis of variance (One-way ANOVA test) has been implemented in order to verify the performance of our proposed algorithm in solving the ORPD problem. In summary, the comparison study shows the potential of this recent optimization method, and proves its robustness and effectiveness in solving the ORPD problem.

Modelling and dynamic performance of inverter based generation in power system studies: an international questionnaire survey

Owing to the increasing penetration level of Inverter Based Generation (IBG) over the last years, there has been much effort on the development of IBG models for power system dynamic studies. Therefore, CIGRE and CIRED have established a joint working group CIGRE C4/C6.35/CIRED: ‘Modelling and dynamic performance of inverter based generation in power system transmission and distribution studies’ with the aim of collecting the present best practices in the industry on modelling of IBG for power system dynamic studies, with the focus on PhotoVoltaic (PV) systems. For this purpose, a questionnaire was developed and distributed to utilities and system operators around the world. This paper summarises some of the key findings and observations and identifies prevalent information about: (i) the type of IBG technology that is modelled (e.g. wind, PV etc.); (ii) the used IBG models (individual or aggregated models); and (iii) the type of the power system dynamic study performed. This survey supports utilities and system operators as well as research institutes and academia to benchmark their approach against the prevailing international industry practice.

PLL-Induced Modal Resonance of Grid-Connected PMSGs With the Power System Electromechanical Oscillation Modes

This study investigates the impact of a grid-connected permanent magnet synchronous generator (PMSG) for wind power generation on the power system electromechanical oscillation modes (EOMs) caused by a phase-locked loop (PLL). A closed-loop interconnected model of a power system with the PMSG is established, where the PLL and rest of the power system are modeled as two separate open-loop interconnected subsystems. Analysis based on the established model indicates that, when an open-loop PLL oscillation mode (POM) is close to an open-loop EOM of concern on the complex plane, the dynamic interactions between the PMSG and the power system may become strong. It is very likely that the modal resonance due to the closeness of the open-loop POM and EOM may degrade the small-signal stability of the power system. In this paper, case studies of an example power system with PMSGs are presented. It is demonstrated that open-loop modal resonance occurs when power system operating conditions change and the PLL parameters are tuned. Strong dynamic interactions between the PMSGs and power system are caused by the open-loop modal resonance, resulting in considerable damping degradation of the low-frequency electromechanical oscillations.

Publicly accessible online power quality monitoring databases

While performing power system studies, it can be difficult to find real-world data to supplement and/or reinforce experimental data. This study provides information on how four databases can be obtained through a new online power quality (PQ) monitoring system accessible via the Internet and how the data in these databases can be used. The available data includes National Oceanic and Atmospheric Administration Space Weather, National Renewable Energy Laboratory Wind, the Department of Energy (DOE)/Electric Power Research Institute Disturbance Library, and the PQSoft PQ Waveform Library. The cloud-based databases are available at no cost to educational institutions worldwide for the purpose of training electric power engineering students.

A stochastic MILP energy planning model incorporating power market dynamics

This paper presents an optimization-based methodological approach to address the problem of the optimal planning of a power system at an annual level in competitive and uncertain power markets. More specifically, a stochastic mixed integer linear programming model (MILP) has been developed, combining advanced optimization techniques with Monte Carlo method in order to deal with uncertainty issues. The main focus of the proposed framework is the dynamic formulation of the strategy followed by all market participants in volatile market conditions, as well as detailed economic assessment of the power system’s operation. The applicability of the proposed approach has been tested on a real case study of the interconnected Greek power system, quantifying in detail all the relevant technical and economic aspects of the system’s operation. The proposed work identifies in the form of probability distributions the optimal power generation mix, electricity trade at a regional level, carbon footprint, as well as detailed total supply cost composition, according to the assumed market structure. The paper demonstrates that the proposed optimization approach is able to provide important insights into the appropriate energy strategies designed by market participants, as well as on the strategic long-term decisions to be made by investors and/or policy makers at a national and/or regional level, underscoring potential risks and providing appropriate price signals on critical energy projects under real market operating conditions.

Techno-economic analysis of a hybrid system to power a mine in an off-grid area in Ghana

In spite of the abundance of renewable energy and its potential application to mining industries, Ghana has not seen much investment in this area. The provision of electricity for mining activities in Ghana is cost intensive, especially in remote areas that are not connected to utility-grids. In this study, a technical and economic analysis of a hybrid electric power system for an off-grid mine company was conducted. Three different hybrid systems, together with a “Generator only” system as base case were analysed using HOMER software, to select the optimum energy system. The selected system consists of 50MW of Solar PV, 15MW of fuel cell system, 600 batteries, 20.5MW of converter and 20MW of diesel generator. The system produces 152.99GWh of electric energy annually. The PV array produces 44%, the fuel cell produces 40% and the diesel produces 14%. At the current cost of system components, and based on assumptions adopted in this study, the optimal system yields a cost of energy of US$0.25/kW and a least cost of energy of US$0.22/kWh, at a diesel price of US$0.80/litre and 30% reduction in both PV module and fuel cell system costs.