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Linear active-power-only power flow approximations are pervasive in the planning and control of power systems. However, AC power systems are governed by a system of nonlinear nonconvex power flow equations. [...]

This paper presents an overview on available tools and methods for the simulation of electromagnetic transients in power systems. Both off-line and real-time simulation tools are presented and discussed. The first objective is to give the reader an overview on the modeling and simulation capabilities in currently available state-of-the-art tools. The second objective is to provide perspectives on research topics and needed enhancements. Index Terms--Electromagnetic transients, EMTP, power system models, real-time digital simulation.

The harnessing of the electric power associated with space weather storms is discussed. A simple system based on a large-scale coil located at high latitudes is devised and the power output of the system for a sample storm is calculated. It is shown that independently of the resistances of the conductors used in the coil and the number of turns in the system the maximum output of the system is restricted to the 1-10 MW range, which is comparable to the maximum output of a single large wind turbine. [DOI: 10.1119/1.3119172]

A novel procedure to extract and analyze the power losses, mainly due to mismatch effects, in a photovoltaic (PV) system is presented. The developed model allows the extraction of the main PV module and PV array parameters from I-V characteristics, as well as in dynamic behavior under real conditions of work. The method allows a good estimation of the mismatch effect on the total PV system power losses. [DOI: 10.1115/1.3097275] Keywords: power losses, mismatch effects, PV modules

A nonlinear model, called TOOCS-off, (1) has been developed in this paper for optimal operation of combined heating, cooling, and power systems. The system includes combined heating power (CHP) module, auxiliary boiler, absorption chiller, heat storage unit, utility grid and electrical, thermal, and cooling loads. In fact, by solving this offline model, we will determine t optimal energy flow regarding both the amounts of electric, thermal, and cooling loads in each time interval and prices of electricity sold to costumers or purchased from utility, and prices of heating and cooling. In the cost function of this model, the total economic benefit of this system is maximized during total daily operation time. The results of an optimal operation model have been discussed techno-economically and a case study has been investigated. Index Terms--Combined heating, Cooling and power (CHCP), optimal operation, techno-economic optimal operation of cogeneration systems (TOOCS)-off.

This research presents an accurate comprehensive cost function for the problem of optimal location of subtransmission substations. Technical constraints and economical parameters are investigated in the modeling. Genetic algorithm is used to optimize the cost function. Coding of decision variables is done in a way that finding the correct solutions is achieved faster. For the first time in this study, free capacity of medium voltage distribution feeders is used for optimal location of subtransmission substations. Also cost of coupling to upward grid in candidate substations with considering different levels of subtransmission voltage is presented. Efficiency of the proposed algorithm is evaluated via several case studies. Key words: Optimization, genetic algorithm, power system planning, medium voltage feeder, INTRODUCTION The main target of power system planning and developing in each part of generation, transmission and distribution is response to consumption growth through confident method with maximum reliability and [...]

This paper presents a comprehensive and detailed study of an optimization-based approach to identify and analyze saddle-node bifurcations (SNBs) and limit-induced bifurcations (LIBs) of a power system model, which are known to be directly associated with voltage stability problems in these systems. Theoretical studies are presented, formally demonstrating that solution points obtained from an optimization model, which is based on complementarity constraints used to properly represent generators' voltage controls, correspond to either SNB or LIB points of this model. These studies are accomplished by proving that optimality conditions of these solution points yield the transversality conditions of the corresponding bifurcation points. A simple but realistic test system is used to numerically illustrate the theoretical discussions. Index Terms--Limit-induced bifurcations (LIBs), maximum loadability, optimization methods, saddle-node bifurcations (SNBs), transversality conditions, voltage stability (VS).

In electricity markets, a pool trading model with a power exchange pool is a typical market organization that attracts much more attention than a bilateral trading model. To date, quite a few papers have focused on bilateral trading models, particularly those under network constraints. This trend is due to the model's complexity in terms of the various trading patterns, reflecting the self-interested behavior of the market participants striving to find potentially profitable transactions. In this paper, we propose a new approach based on complex networks suitable for assessing different aspects of bilateral market. This work strives to analyze the bilateral trading patterns in the electricity markets where physical network constraints need to be considered for the feasible and secure operation of the power systems. The goal of the work is to find the stable network structures that can be used to anticipate possible bilateral transactions in the real market place and to provide a novel and applicable approach to studying the bilateral model in electricity markets. The proposed approach has been tested on several test systems in which the transmission network structure of the market that accommodates the transactions is considered. The proposed model is illustrated with examples using a four-bus test system, the IEEE 30-bus, and the IEEE 118-bus test systems. Index Terms--Bilateral model, complex network, electricity markets, network constraints.

This paper describes the estimation of the electric load composition on a consumer side of a distributed power system. That is to say, the purpose of estimation is to determine the amount of each load class with respect to the total electric current waveform from instrument reading. To carry out this work, the reduced multivariate-polynomial model is applied when the distributed power system has the electric loads supplied from the different voltage level through a nonideal transformer. The estimation problem in this paper is also considered with relation to the power-quality issue. Index Terms--Distributed power system, electric load composition, nonideal-transformer modeling, power quality, reduced multivariate-polynomial (RMP) model.

This study presents transient stability assessment of electrical power system using Probabilistic Neural Network (PNN) and principle component analysis. Transient stability of a power system is first determined based on the generator relative rotor angles obtained from time domain simulation outputs. Simulations were carried out on the IEEE 9-bus test system considering three phase faults on the system. The data collected from the time domain simulations are then used as inputs to the PNN in which PNN is used as a classifier to determine whether the power system is stable or unstable. Principle component analysis is applied to extract useful input features to the PNN so that training time of the PNN can be reduced. To verify the effectiveness of the proposed PNN method, it is compared with the multi layer perceptron neural network. Results show that the PNN gives faster and more accurate transient stability assessment compared to the multi layer perceptron neural network in terms of classification results. Key words: Transient stability assessment, dynamic security assessment, probabilistic neural network, INTRODUCTION Recent blackouts in the USA, some European and Asian countries have illustrated the importance and need of more frequent and thorough power system stability study. Nowadays, power systems have [...]

This paper presents the application of hybrid particle swarm optimization technique to find optimal location of unified power flow controller to achieve optimal power flow. Objective function in the OPF, that is to be minimized, are the overall cost functions, which include the total active and reactive production cost function of the generators and installation cost of UPFCs. The OPF constraints are generators, transmission lines and UPFCs limits. We propose HPSO algorithm to consider the objective function and all equality and inequality constraints. Simulations are performed on 4 bus test system and modified IEEE 14 bus system for optimal location of UPFC and the results obtained are encouraging and will be useful in electrical restructuring. Keywords: Deregulated Power System, Hybrid Particle Swarm Optimization, Optimal Location, Optimal Power Flow, Unified Power Flow Controller, INTRODUCTION Nowadays, actual power systems are facing new challenges due to deregulation and restructuring of the electricity markets. Hence, in order to be able to obtain a high operational efficiency [...]

A substantial increase of photovoltaic (PV) power generators installations has taken place in recent years, due to the increasing efficiency of solar cells as well as the improvements of manufacturing technology of solar panels. These generators are both grid-connected and stand-alone applications. We present an overview of the essential research results. The paper concentrates on the operation and modeling of stand-alone power systems with PV power generators. Systems with PV array-inverter assemblies, operating in the slave-and-master modes, are discussed, and the simulation results obtained using a renewable energy power system modular simulator are presented. These results demonstrate that simulation is an essential step in the system development process and that PV power generators constitute a valuable energy source. They have the ability to balance the energy and supply good power quality. It is demonstrated that when PV array-inverters are operating in the master mode in stand-alone applications, they well perform the task of controlling the voltage and frequency of the power system. The mechanism of switching the master function between the diesel generator and the PV array-inverter assembly in a stand-alone power system is also proposed and analyzed. Finally, some experimental results on a practical system are compared to the simulation results and confirm the usefulness of the proposed approach to the development of renewable energy systems with PV power generators. Index Terms--Autonomous power systems, master/slave inverter operation, photovoltaic (PV) systems, power system modeling and simulation.

In evaluating the energy-generation potential of a photovoltaic (PV) energy system, the system is usually assumed to work without interruptions over its entire life. PV energy systems are fairly reliable, but as any complex system, they may fail. In PV systems, the inverter is responsible for the majority of failures, and most inverter failures are blamed on the aluminum electrolytic capacitors typically used in the dc bus. This paper investigates the effects of common failure modes on the reliability of PV inverters and suggests a model framework for decomposing the inverter into subsystems for more detailed study. The challenges of statistical analysis based on small data sets are discussed, and simulations are performed to illustrate the proposed model using a simple decomposition into subsystems of the inverter used in the 342-kW PV system at the Georgia Tech Aquatic Center. Index Terms--Photovoltaic (PV) power systems, power-system reliability, power-system simulation, reliability modeling, simulation.

The fourth-order converter known as superbuck is often used to interface the solar arrays into the rest of the power system due to the continuous input current it provides. Peak-current-mode (PCM) control is applied. The small-signal models of such a converter do not exist in public domain literature and its dynamical features are not known. The paper introduces the dynamical modeling based on consistent methods. The characterization shows that the PCM-controlled superbuck converter may have similar features characteristic to the conventional buck converter such as high input-voltage-noise attenuation, effectively first-order output dynamics, and high insensitivity to source interactions, when the inductor-current feedback is properly compensated. The converter is, however, more susceptible to the input-filter instability due the shape of the ideal input impedance than the conventional buck converter. Experimental evidence is provided based on a 440-kHz converter. Index Terms--Internal dynamics, peak-current-mode control, superbuck converter.

Rotors supported by active magnetic bearings (AMBs) can spin at high surface speeds with relatively low power losses. This makes them particularly attractive for use in flywheels for energy storage in applications such as electric vehicles and uninterruptible power supplies. In order to optimize efficiency in these and other applications, the loss mechanisms associated with magnetic bearings and rotating machinery must be well understood. The primary parasitic loss mechanisms in an AMB include complex magnetic losses, due to eddy currents and hysteresis, and windage losses along the entire rotor in nonvacuum environments. In low-loss magnetic bearing designs, the windage loss component along the rotor can become dominant at high speeds, and the need for accurate windage models becomes even more critical. This study extends previous AMB power loss work by evaluating five different windage loss models using the experimental rundown data from the previous work. Each of the five windage models, along with standard models of eddy current and hysteresis losses, are used to reduce the rundown data into the associated power loss components. A comparison is then completed comparing the windage power loss component extracted through the rundown data reduction scheme to the associated analytical windage prediction in order to identify the most accurate model for calculating windage losses along a smooth rotor. Five empirical flat-plate drag coefficient models are implemented, four turbulent and one laminar. An empirical flat-plate turbulent boundary layer formula (referred to here as 'Model 2') developed by Prandtl and Schlichting displayed the best agreement between experimentally extracted and analytically predicted windage loss values. The most accurate model formula (Model 2) dictates that the frequency dependency of windage loss is both logarithmic and power based and represents the minimum error between experimentally extracted and analytically predicted losses of all models in the study of high-speed power losses in a smooth rotor supported in AMBs. Keywords: magnetic bearing, windage, power loss, drag coefficient, rotating machinery, flywheel

System power reliability under varying weather conditions and the corresponding system cost are the two main concerns for designing hybrid solar-wind power generation systems. This paper recommends an optimal sizing method to optimize the configurations of a hybrid solar wind system employing battery banks. Based on a genetic algorithm (GA), which has the ability to attain the global optimum with relative computational simplicity, one optimal sizing method was developed to calculate the optimum system configuration that can achieve the customers required loss of power supply probability (LPSP) with a minimum annualized cost of system (ACS). The decision variables included in the optimization process are the PV module number, wind turbine number, battery number, PV module slope angle and wind turbine installation height. The proposed method has been applied to the analysis of a hybrid system which supplies power for a telecommunication relay station, and good optimization performance has been found. Furthermore, the relationships between system power reliability and system configurations were also given. Keywords: Hybrid solar--wind system; Optimization; LPSP; Annualized cost of system; Genetic algorithm

Experiment and electromagnetic-topology (EMT)-based simulation are performed to study the effects of wideband EM pulses on large electrical systems. The EMT simulation relies on the topological modular junction concept with the simultaneous use of a number of analytical and computational methods, including the transmission-line-matrix compaction method, the finite-difference time-domain method, and the reciprocity theorem, to come up with a final result. The EMT simulation approach that uses the topological modular concept is an effective way to perform tradeoff analysis of different wideband pulse excitations without having to repeat the simulations of the entire system. As part of validating the EMT simulation approach, we performed the experiment to measure the current induced by a wideband EM pulse on a cable behind a slot aperture. The simulated current and the measured current resulted in good agreement with each other, thus demonstrating the validity of the proposed simulation scheme. Index Terms--Aperture-cable coupling, electromagnetic topology (EMT), wideband pulse interaction.

This paper presents the computer simulation of the Multistage Model for Distribution Expansion Planning with Distributed Generation, as described in Part I. The simulations deal with the planning of an electrical power distribution network in three stages, in five different situations: 1) each of the three stages planned independently; 2) multistage planning; 3) multistage planning with distributed generation; 4) multistage planning with distributed generation and constraints on investment; and 5) multistage planning with distributed generation considering three load levels. The influence of additional constraints is analyzed in terms of the computational effort required to find the optimum solution to the problem. Index Terms--Distributed generation (DG), power distribution, power distribution economics, power distribution planning.

The most critical attribute of a power control strategy for a fuel cell (FC) and ultracapacitor (UC) based hybrid vehicular power system is the sharing of load demand between available power sources. Transients and rapid changes of the power demand may cause drying of the FC membrane resulting in degradation of FC lifetime. The load demand profile of a hybrid electric vehicle (HEV) is a nonstationary fluctuating signal and consists of transients. Wavelet transforms are suitable for analyzing and evaluating such signals for dynamic systems. This paper focuses on the integration of a developed novel-wavelet-based load sharing algorithm and dynamic model of the FC/UC hybrid vehicular power system in order to ensure efficient power flow control strategy. Index Terms--Fuel cell (FC), hybrid system, power management, ultracapacitor (UC), vehicular application, wavelet.

In this paper, the primal-dual nonlinear interior point method has been used as a basis for the derivation of a novel supply function equilibrium (SFE) algorithm for modeling the strategic interactions in the electricity market, using the ac network model, which incorporates modeling of the transformer tap-ratio control. The algorithm is used to investigate the impact of transformer tap-ratio control on the electricity market equilibrium and the effect of the interactions between network constraints and transformer tap-ratio control. The interior point social welfare optimization problem is combined with the optimization problem for maximizing the profit of each strategic generating firm in the market. The final combined single-level SFE problem is solved iteratively based on solution techniques of the interior point method. Numerical examples illustrate the effect of network constraints and especially the impact of transformer tap-ratio control on market equilibrium. Index Terms--AC network modeling, electricity market equilibrium, interior point algorithm, market power, power generation economics, power system economics, power system modeling, power systems, power transformers, power transmission economics, supply function equilibrium, transformer control.

An equivalent current injection (ECI)-based hybrid current-power optimal power flow (OPF) model is proposed in this paper, and the predictor-corrector interior point algorithm (PCIPA) is tailored to fit the OPF for solving nonlinear programming (NLP) problems. The proposed method can further decompose into two subproblems. The computational results of IEEE 9 to 300 buses have shown that the proposed algorithms can enhance the performance in terms of the number of iterations, memory storages, and CPU times. Index Terms--Equivalent current injection, nonlinear programming, optimal power flow, predictor-corrector interior point algorithm.

Following several governmental policies trying to reduce C[O.sub.2] emissions, renewable energies have been largely promoted during the last decade. Among the green energies that have been developed, wind can actually be seen as one of the most promising solution if we refer to its past and predicted evolutions. However and, even though wind can be considered as an interesting alternative to fossil fuels, it is imperious to emphasize on problematic situations that could be due to the intermittent behavior of wind generation. Indeed, actually, most of the electric utilities do not consider wind power in the classical units management; consequently involving, in the case of increased wind powder penetration, untimely stopping of big thermal (or nuclear) units. It is, therefore, necessary to calculate wind equivalent capacities in order to introduce a coherent evaluation of wind production in the management of the centralized production park. In this paper, wind equivalent capacities are calculated using a Non Sequential Monte Carlo Simulation. Moreover, in order to evaluate the importance of the wind correlation level between parks located in the same geographical region, two cases are investigated, respectively considering entirely correlated wind parks and, on the opposite, totally independent wind sites. Finally, simulation results show that durations of simultaneous zero wind power production for each considered wind parks stay, in both cases, very low involving quasi-identical calculated equivalent capacities; what tends to demonstrate the minor importance of the wind parks correlation level for wind power estimation in reliability studies. Note that, here, the proposed conclusions are obtained using the Belgian production park data and that the objective is not to dynamically estimate wind production on the short-term (by the use of an autocorrelation function) but rather to give a simplified way to introduce an hourly evaluation of wind production in the day by day management of the classical thermal (nuclear) units. Index Terms--Power system modeling, Weibull distributions, wind energy.

A modeling framework based on normal form theory and singular perturbation techniques is proposed for analyzing the nonlinear behavior of power system models described by nonlinear differential-algebraic equations (DAEs). The method exploits the time scale separation of power system dynamic processes, to avoid reduction of the original DAE model and may therefore be used to assess control effects and network characteristics on system behavior. This approach allows the full potential of the normal form formulation to be reached, and is applicable to a wide variety of nonlinear phenomena described by DAEs. Using a control theory framework, a constructive approach is outlined for transforming a system of DAEs to a state space approximation that is suitable for normal form analysis. By casting the problem in the context of singular perturbation theory, a structure-preserving nonlinear mathematical model of the power system is then established for the study of nonlinear behavior. Criteria for this representation are derived and implementation issues are discussed. The developed procedures are tested on a four-machine, two-area test system. The accuracy of the model is quantified by comparing normal form simulations with those from a commercial stability software. Index Terms--Nonlinear power system behavior, normal form theory, singular perturbation analysis.

Real-time digital simulation of large power systems requires not only significant computational power but also simpler and accurate models. This paper proposes a new approach for transient simulation of power systems using a robust two-layer network equivalent model and an advanced PC-Cluster based parallel real-time simulator. Using a combination of well established fitting and optimization methods, the generated low-order model is of high accuracy compared to its full model over a wide frequency bandwidth. The merits of this method are its robustness in terms of stability and positive-realness, its accuracy at not only transient frequencies but also at dc and power frequency, and its optimal order determination feature. To validate the new method, a realistic large-scale power system--the Alberta Interconnected Electric System--is simulated in real-time. The real-time electromagnetic transient program is implemented in C++ language using object-oriented programming techniques on the PC-Cluster. A time-step of 20 [micro]s has been used for the real-time simulation. The captured oscilloscope results demonstrate excellent accuracy and efficiency of the proposed model in comparison to a full-scale off-line simulation of the original system in the ATP version of EMTP. Index Terms--Electromagnetic analysis, frequency domain analysis, object oriented programming, power system transients, real-time systems, transmission lines.

This paper demonstrates that transfer function zeros are equal to the poles of a new inverse system, which is valid even for the strictly proper case. This is a new finding, which is important from practical as well as theoretical viewpoints. Hence, the dominant zeros can be computed as the dominant poles of the inverse transfer function by the recent efficient SADPA and SAMDP algorithms, which are applicable to large-scale systems as well. The importance of computing dominant zeros and the performance of the algorithms are illustrated by examples from large practical power system models. These examples constitute new practical uses for single-input single-output (SISO) and multi-input multi-output (MIMO) zeros, which may be of benefit to power system simulation studies and field tests related to oscillation damping control. Index Terms--Inverse systems, large-scale systems, modal analysis, model reduction, multivariable systems, pole-zero map, power system dynamics, small-signal stability, sparse eigenanalysis, system oscillations, transfer function, transfer function residues, transfer function zeros.