Sharif Digital Repository

In this paper, a simple and efficient method for fast dynamic stability assessment of power systems is presented. The proposed approach determines the dynamic stability of a power system without the full dynamic formulation and eigenvalue analysis. This method could be applied as a valuable aid for monitoring dynamic stability in a new system control centers. Application of the singularity of standard load-flow Jacobian has already been presented for evaluation of dynamic stability under certain conditions, but the result is optimistic for any type of dynamic analysis. This deviation is misleading for system control operators and is not recommended. The modification proposed here can... 

To study the dynamic stability of a power system, suitable models of the network and dynamic devices, with different levels of accuracy, are needed. In this paper, a modular method is introduced for modelling power systems. The method is perfectly suited for systems containing FACTS devices. Due to the modularity of the method, which is based on augmentation of state equations of the network and dynamic devices, the introduction of new devices is straightforward. The method presented here can cover both high and low frequency ranges of dynamic phenomena in power systems  

This paper first proposes a competitive market structure for reactive power procurement and then develops a methodology for incorporating voltage stability problems into the model. The owners of electric transactions should participate in this competitive framework and submit their own firmness bids in ($/MW) to the Independent/System/Market Operator (ISOIMO). ISO clears the market for reactive energy regarding the value of each transaction and utilization cost of reactive power on one hand, and the impact of transaction amount on the voltage security of the power system on the other hand. Here, the voltage stability margin is incorporated into the power flow equations so that the security... 

Power quality has become an increasing concern to utilities and customers. The increased concern has resulted in measuring power quality variations and characteristic disturbances for different distribution companies. This paper explains the results of power quality indexes for 50 customer loads at two voltage levels 20kV and 400v. The measurement period is 7 days with 10 minutes intervals. Also this survey has been presented according to IEC61000 and Iranian Power Quality Standard (IPQS). IPQS has some differences from IEC61000, EN50160 and IEEE standards in power quality indexes, which are investigated in this paper. At the end of paper, individual and global power indicators for all... 

This paper discusses the application of unified power quality conditioner (UPQC) for improving power quality of a system supplying an electric arc furnace (EAF). The UPQC comprises a combined series and shunt active filters sharing a common DC link. It is used to mitigate voltage disturbances and compensate for reactive power, harmonics and interharmonics. A novel control strategy of the UPQC is presented. Since voltages at the point of common coupling (PCC) contain low frequency interharmonics, conventional methods can not be used for extracting voltage reference signals. In the proposed method, voltage references are extracted using active power processing to generate sinusoidal waveforms.... 

This paper presents several techniques for the processing of power system signals in a power system setup. The techniques exhibit a desirable performance against signal pollutions such as noise and distortions, signal unbalance (in three-phase applications), and Variations in the signal attributes (mainly its frequency). These features render them a promising set of options for modern power systems in which all or some of these undesired factors may be amplified depending on the case. Single-phase and three-phase applications are both examined and appropriate techniques are suggested for different scenarios. © 2007 IEEE  

This paper presents a power flow controller for a matrix converter as the power electronic interface between a high-speed micro-turbine generator and a utility distribution system. The matrix converter converts the high-frequency of a micro-turbine generator to a conventional frequency of the utility system, based on a novel switching strategy. The controller regulates magnitude and phase-angle of the converter output voltage to accommodate real and reactive power flow requirements of the utility system. Performance of the matrix converter based microturbine generation system including the power flow controller is evaluated based on digital time-domain simulation studies in the PSCAD/EMTDC... 

Nowadays, application of renewable energies has taken a rapid trend. Wind energy is among those mostly used for this purpose. Doubly Fed Induction Generators (DFIG) are widely used in wind power plants due to several advantages such as partial rating converter, capability of decoupled active and reactive power control, etc. Application of a suitable control strategy is of great importance in wind power plants. In this paper, the parameters of a hybrid controller are calculated using Particle Swarm Optimization (PSO) subjected to satisfying the required criteria in output active and reactive powers of a DFIG. In the proposed system Direct Power Controller (DPC), Variable Structure Controller... 

This chapter describes performance of the power system stabilizer (PSS) of a large thermal power plant as tuned by the manufacturer. The stabilizer was redesigned based on extended phase compensation of the exciter input-the electrical torque transfer function and root locus analysis; and its effect on local, interplant, and interarea electromechanical oscillations was thoroughly analyzed. Participation factors and mode shapes were effectively employed to identify local, interplant, and interarea modes, as well as their characteristics. The PSS designed with extended phase compensation improves the damping of local and interplant oscillation modes considerably, and has some positive damping... 

This paper presents the results of a thorough power quality analysis in order to determine the cause of failure in a Compressed Natural Gas (CNG) distribution transformer. The paper presents the field data and determines power quality indices of such loads based on IEEE/IEC standards. It provides steady state time-series parameters as well as transient waveforms. Different signatures of the voltage and current signals are extracted, and consequences of the distortions are described. The analysis is clarified by presenting both time domain captured waveforms and statistical power quality indices. Optimum solution for improving power quality and prevent component failure is also proposed. ©... 

The paper presents a new approach that assists power system restoration planning with regards to control of temporary overvoltages (TOVs) due to transformer energization. The frequency-domain analysis in combination with analytical calculations is applied to find an optimum resonance condition. The analytical equations are based on sensitivity analysis for single frequencies and are extended to total sensitivity calculation. After an introduction of the phenomenon of overvoltages during power system restoration and harmonic resonance overvoltages, basic principles of their control are explained. Also, an algorithm is introduced for the results evaluation of harmonic resonance studies where... 

The paper presents a new approach that assists power system restoration planning with regard to control of temporary over-voltages (TOV) due to transformer energization. The frequency domain analysis in combination with analytical calculations is applied to find an optimum resonance condition. The analytical equations are based on sensitivity analysis for single frequencies and are extended to total sensitivity calculation. After an introduction to the phenomenon of overvoltages during power system restoration and harmonic resonance overvoltages, basic principles of their control are explained. An algorithm is introduced for the results evaluation of harmonic resonance studies where it is... 

In this paper, a novel fast straightforward method for thermal generating units scheduling is presented. The new method decomposes the solution of the unit commitment (UC) problem into three subproblems. In the first subproblem, the quadratic cost functions of units are linearized and hourly optimum solution of UC is obtained considering all constraints except the minimum up/down time constraints. In the second subproblem, the minimum up/down times are enforced through a novel optimization process by modifying the schedule obtained in the first step. Finally, in the third subproblem, the extra reserve is minimized using a new decommitment algorithm. For testing the proposed method, the... 

This paper presents a reactive power valuation method with regard to its effect on realization of MW transactions. The security constraint optimization model in which the objective function is maximization of transactions is solved by the genetic algorithm approach. The proposed scheme allocates a specific amount of MW transactions to each dynamic reactive power source. An index is introduced to derive VAr value from the calculated optimal parameters of power network. This index represents the system-wide effect of MVAr sources on MW transactions implementations. Application of proposed method has been illustrated using IEEE 30 and 14 bus test systems. Results are discussed and compared in... 

This paper presents an investigation of power quality problems arising from electric arc furnace (EAF) operation, and the required compensating system capabilities. It also proposes a compensation system using a shunt active filter and a series inductor. A shunt active filter compensates for the reactive power and the current harmonics of the highly varying load. Reference signals for the compensation logic are obtained from the instantaneous current vector components on a rotating reference frame. Due to noninteger harmonics on voltages at the point of common coupling, conventional methods for the inverter dc bus voltage regulation fail to perform properly. Hence, a new method is introduced... 

This paper presents a dynamic programming methodology for finding the optimum preventive maintenance schedule of generating units of a GENCO in open power systems. The objective function for the GENCO is to sell electricity as much as possible, according to the market price forecast. Various constraints such as generation capacity, duration of maintenance and maintenance crew are taken into account. In a case study, introducing a GENCO with six generating units, and implementing dynamic programming, we obtain the optimal maintenance schedule over the planning period. © 2002 IEEE  

This paper describes a new capacitor sharing technique for pipeline ADCs. It enables power reduction of the first and second MDACs simultaneously. The presented noise and power analysis shows that the proposed method is about 30% more efficient than the conventional one in terms of the first and second MDACs power dissipation. A 10-bit 40MS/s pipeline ADC employing the proposed technique was designed in 90-nm CMOS technology achieving a power consumption of 4.2 mW  

This paper presents a novel flexible control strategy for Unified Power Quality Conditioner (UPQC), which achieves more flexibility in compensation of power quality disturbances as compared to the existing methods. The proposed control strategy provides priority-based compensation as well as full and standard-based compensation considering the rating of series and shunt parts of a UPQC. The priority-based compensation is done based on the compensation priority among different power quality disturbances. In this control strategy, an on-line estimation of different voltage and current disturbances is required. For this purpose, a Unified Adaptive Power Quality Estimator (UAPQE) has been... 

This paper establishes a simple and topological approach to track real and reactive power flow in electric transmission systems. The presented method utilizes the well-known Proportional Sharing Theorem in order to evaluate the contribution of each power source to grid elements' supplied input power. We have also put forward an approximate power tracing method for upgraded grids, using its own previously surveyed results. The main advantages of the proposed procedure, compared with conventional methods, are discussed extensively. The effectiveness of this approach has been studied and ascertained for small-scale power systems, showing prominent speed and accuracy  

This paper presents the results of a thorough analysis of applying power quality standards to a granite factory. It explains the procedure of determining power quality indices in a power system. The paper presents the field data and provides the results of statistical analysis in order to extract power quality indices. A comparison against standard limits is also given. The case study gives an overview of power quality in such customers and brings up some practical limitations when applying power quality standards. ©2006 IEEE