Method Of Symmetrical Components Research Articles

Asymmetrical Fault Ride through based on Predictive Current Control in Wind Power Generation System

In order to improve the asymmetric fault ride-through capability of wind power generation system, asymmetric voltage and current can be decomposed into positive sequence, negative sequence and zero sequence components respectively via symmetrical component method. The mathematical models of grid side converter in static coordinate system and synchronous rotating coordinate system were given; predictive current control strategy proposed can achieve no static error tracking of current in each switching cycle, can eliminate the negative sequence current in asymmetric fault and wipe off the secondary ripple of the dc side capacitor voltage. The dc side super-capacitor circuit can prevent the dc side from over-voltage. The methods introduced in this study can improve the large grid asymmetric fault ride through capability of wind power generation system. Effectiveness of the proposed methods is verified by the numerical simulations.

Three-phase power flow in distribution networks using Fortescue transformation

Analysis of power systems is typically made using the method of either phase coordinates or symmetrical components depending on the type of network (un/symmetrical). The use of the symmetrical components method, a three-phase specific application of the Fortescue transformation, has been limited to pure three-phase symmetrical networks. Therefore phase coordinates has been the method used most for the analysis of distribution networks. This paper is extending the use of the symmetrical components method to distribution networks combining one-phase, two-phase, and three-phase symmetrical network parts. This paper derives a new integrated approach for the description of such networks based on Fortescue transformation. This approach is demonstrated using the forward-backward sweeping algorithm (FBS).

Influence of Longitudinal End-Effects on Electromagnetic Performance of a Permanent Magnet Slotless Linear Launcher

Longitudinal end-effects seriously affect the electromagnetic performance of linear motor especially for large volume devices such as electromagnetic launchers. So, the purpose of this paper is to study longitudinal end-effects in a permanent magnet (PM) slotless linear launcher and proposes some measures for improvement. The longitudinal end-effects induced by finite length of PM mover can give rise to two mechanisms, uneven airgap magnetic field and partial saturation. The splitting edge magnets method is used to improve the uniformity of flux distribution, and it is also beneficial for enhancing thrust. In addition, we focus on asymmetrical phase characteristics stemming from finite stator part with distributed windings. Its influence on thrust and thrust ripple are investigated based on symmetrical component and energy method. The comprehensive analyses are established to aid initial design and assessment of performance for PM slotless linear launcher.

Approaching the Processes in the Generator Circuit Breaker at Disconnection through Sustainability Concepts

Nowadays, the electric connection circuits of power plants (based on fossil fuels as well as renewable sources) entail generator circuit-breakers (GCBs) at the generator terminals, since the presence of that electric equipment offers many advantages related to the sustainability of a power plant. In an alternating current (a.c.) circuit the interruption of a short circuit is performed by the circuit-breaker at the natural passing through zero of the short-circuit current. During the current interruption, an electric arc is generated between the opened contacts of the circuit-breaker. This arc must be cooled and extinguished in a controlled way. Since the synchronous generator stator can flow via highly asymmetrical short-circuit currents, the phenomena which occur in the case of short-circuit currents interruption determine the main stresses of the generator circuit-breaker; the current interruption requirements of a GCB are significantly higher than for the distribution network circuit breakers. For shedding light on the proper moment when the generator circuit-breaker must operate, using the space phasor of the short-circuit currents, the time expression to the first zero passing of the short-circuit current is determined. Here, the manner is investigated in which various factors influence the delay of the zero passing of the short-circuit current. It is shown that the delay time is influenced by the synchronous machine parameters and by the load conditions which precede the short-circuit. Numerical simulations were conducted of the asymmetrical currents in the case of the sudden three-phase short circuit at the terminals of synchronous generators. Further in this study it is emphasized that although the phenomena produced in the electric arc at the terminals of the circuit-breaker are complicated and not completely explained, the concept of exergy is useful in understanding the physical phenomena. The article points out that just after the short-circuit current interruption by the generator the circuit-breaker (when the GCB has been subjected at the metal contact terminals to the high temperature of a plasma arc, up to 50,000 K) between its opened contacts, there arises the transient recovery voltage (TRV) which constitutes the most important dielectric stress after the electric arc extinction. Since the magnitude and shape of the TRV occurring across the generator circuit-breaker are critical parameters in the recovering gap after the current zero, in this paper, we model, for the case of the faults fed by the main step-up transformer, the equivalent configurations, with operational impedances, for the TRV calculation, taking into account the main transformer parameters, on the basis of the symmetrical components method.

Double-Loop Control of Inverter with LCL Filter in Electrical Power System Based on Improved Instantaneous Symmetrical Component

An improved instantaneous symmetrical component method is adopted to improve the performance of inverter with LCL filter under asymmetric voltage conditions in electrical power system. Positive and negative sequence components in voltage and current in electrical power system are calculated with fewer calculation time,which is suitable for pratical application.In addition,this paper analyses active and reactive power in the system.A double-loop control strategy is proposed to eliminate the influence of double frequency components in power and negative sequence current.The simulation results verify its feasibility and effectiveness.

Performance analysis of a new configuration of three-phase self-excited induction generator feeding a single-phase load

This paper presents a steady-state performance analysis for a new configuration of self-regulated self-excited three-phase squirrel cage induction generator feeding single phase loads. The proposed scheme provides the required reactive power for excitation, small voltage regulation, acceptable phase balance and large output power. Using an equivalent circuit model incorporated with the method of symmetrical components, the total impedance equation of the generator’s model is derived. This non-linear equation is minimised to obtain the operating frequency and magnetising reactance. Based on the derived circuit model, the performance of the generator under different operating conditions is predicted. To confirm the validity of the proposed scheme, simulation results are compared with their corresponding test results.

Capacitor Optimization of the Single-Phase Capacitor-Run Induction Motor

Capacitor matching in single-phase capacitor-run induction motor (SPCRIM) is investigated in this paper. Combining symmetrical components method with resultant current method, capacitor value is calculated. Relationship between turn ratio of main winding and auxiliary winding, main winding current, auxiliary winding current and capacitor value is analyzed by simulation. SPCRIM is optimized on the ground of the theoretically calculated capacitor value and turn ratio of the main and auxiliary windings with FEA (Finite Element Analysis). Results show that calculated capacitor value contributes to the determination of turn ratio of the main winding and auxiliary winding, and with appropriately calculated capacitor value and turn ratio, small winding current can be got.

Simulation Research on the Single-Phase Operation of a Line Start Permanent Magnet Synchronous Motor

In this paper, the single-phase operation of a line start permanent magnet synchronous motor (LSPMSM) has been analyzed in detail. At first, based on symmetrical component method, the condition for balanced operation is derived. Secondly, steady state performances are analyzed by computer programming. Thirdly, the transient performances are studied on the basis of MTLAB/Simulink. The results demonstrated that the LSPMSM running on a single-phase supply has lower efficiency but higher power factor than three-phase balanced operation, besides good starting and operating performances can be achieved.

Concept of Symmetrical Component as a Technique for analysis of fault and Improvement of Over current Protection Scheme

Electrical energy is one of the fundamental resources of the modern industrial society. Electrical power is available to the user instantly, at the correct voltage and frequency, at exactly the amount needed. The power system maintains its steady state mainly because of the correct and quick remedial action taken by the protective relaying equipment. The response of the protection system must be automatic, quick, and should cause a minimum amount of disruption to the power system. Concept of Symmetrical component for an enhancing protection scheme shows an outstanding feature. The method of symmetrical components provides a practical technology for understanding and analyzing power system operation during unbalanced conditions. Such as those caused by faults between phases and/or ground, open phases, unbalance impedances, and so on. Also, many protective relays operate from the symmetrical component quantities. Thus a good understanding of this subject is of great value and very important tool in protection. In this paper how the concept of symmetrical components helps for improvement of different protection schemes.

First-Zone Distance Relaying Algorithm of Parallel Transmission Lines for Cross-Country Grounded Faults

A novel distance protection algorithm for the first-zone distance relay of parallel transmission lines is proposed for cross-country grounded faults. The algorithm calculates the fault impedance using one-end sampling voltages and currents from a single line. The theoretical basis of the proposed algorithm is described in this paper, which is based on the symmetrical component method for parallel lines. And an attempt is made to express the zero-sequence current of the adjacent parallel line at the relay location by the zero-sequence current of the concerned line in combination with the fault characteristics of the system model, by which the impact of the mutual coupling between the lines can be eliminated. And, thus, the distance algorithm for cross-country grounded faults is presented. The simulations show that the proposed algorithm can obtain the accurate fault reactance when cross-country bolted faults occur, which is superior to the existing distance protection algorithm based on one-end data from a single line.

Method of Parallel Active Power Filter Compensation on 3-Phase 3-Wire Nonlinear Unbalanced Load System

The parallel active power filter has been accepted by users because of its’ installing and removing without disturbing other users and so its’ detecting and controlling algorithms have been studied with large efforts .A method about direction of active power flow (DAPF ) was raised in present paper under condition of the 3-phase asymmetrical voltage and 3-wire nonlinear unbalanced load. It’s means that detected currents on the point of common coupling can be put into two parts according the active power flow direction ,one of which is called positive direction current and another is called negative direction current .then decompose the asymmetrical voltage and positive directional current with Symmetrical Component Method. We can obtain the reference current components with clear physical meaning for the paralleled active power filter .The method shows there are several harmful power components could not be eliminated with parallel active power filter.

On the application of wavelet transform for symmetrical components computations in the presence of stationary and non-stationary power quality disturbances

Symmetrical components method allows systematic analysis of unbalanced three-phase systems. This method represents the backbone for many applications in an electric power system (EPS) such as fault analysis, power system protection, power and energy measurements. Moreover, with the increased penetration of plug-in hybrid electric vehicles (PHEVs), studying and evaluating the distribution system unbalance considering power quality disturbance pronounced by fleet of these vehicles, becomes a necessity. In time-invariant polluted environment, the measurements of the symmetrical components for the fundamental and harmonic components could be performed using Fourier basics. However Fourier-based techniques are unsuitable in the presence of any time-variant power quality disturbance which is typically the case when considering PHEVs and other nonlinear industrial process such as computer numerical control (CNC) machines. In this paper, time-frequency expressions for the symmetrical components are developed using different wavelet transforms: Discrete Wavelet Transform (DWT), Wavelet Packet Transform (WPT) and Stationary Wavelet Transform (SWT). The paper also includes a comparative study of the results obtained when applying the developed approach using different wavelet basis functions, such as Daubechies, Coiflets and Symlets into three case studies (two synthetic and one real) including unbalanced three-phase system under different operating conditions while considering different kind of disturbances. The results are analyzed and conclusions are presented. The outcomes of this study lay the ground for further studies in unbalanced distribution system with high penetration of PHEVs, two-way protection devices for smart grid and power quality evaluation.

Advanced symmetrical components method

The article deals with symmetrical components method applied for the calculation of (a)symmetrical steady states of three-phase (un)balanced networks. When one considers these states, they are faced with the choice between two undesirable things: (i) to stay in the phase domain and cope with huge number of inductive and capacitive couplings inside network elements or (ii) to enter into the symmetrical components (sequence) domain and cope with complex-valued transformation ratios (non-zero phase shifts) of transformers. To resolve this issue, the article proposes an advancement of the symmetrical components method. The advancement results in the reduction of sequence domain non-zero phase shifts of network's transformers to zero.

New Unbalance Factor for Estimating Performance of a Three-Phase Induction Motor With Under- and Overvoltage Unbalance

This paper evaluates the influence of the unbalance factors in calculating total copper losses, efficiency, power factor, input power, output torque, peak currents, and derating factor of the motor operating under unbalanced voltage system. The complete definition for the voltage unbalance is using complex voltage-unbalance factor that consists of its magnitude and angle. A coefficient to determine either under- or over-unbalance conditions is inserted. The analysis of the motor is performed using the method of symmetrical component, and MATLAB software is used to investigate the performance of the induction motor. The simulation results show that the International Electrotechnical Commission definition of the voltage unbalance combined with the coefficient of unbalance condition can be applied to evaluate total copper losses, input power, power factor, and total output torque precisely. However, the phase angle of the unbalance factor must be included for accurate prediction of peak current and peak copper losses of the phase windings and derating factor of the motor.

A QUANTITIES METHOD OF INDUCTION MOTOR UNDER UNBALANCED VOLTAGE CONDITIONS

The most complete definition for the voltage unbalance is using complex voltage unbalance factor (CVUF) that consists of its magnitude and angle. Unfortunately, the definition did not distinguish between undervoltage and overvoltage unbalance conditions. In this paper, t he analysis of the motor is performed using the method of symmetrical component and MATLAB software is used to investigate the performance of induction motor. The simulation results show that the International Electrotechnical Commission (IEC) definition of the voltage unbalance can be applied to evaluate total copper losses precisely. However, the phase angle of unbalance factor must be included for accurate predicting of peak currents and peak copper losses of the phase windings of the motor.The unbalanced conditions which distinguish between under and over voltage unbalance must also be taken into consideration for assessing all the quatities.

Study of a Novel Energy Efficient Single-Phase Induction Motor With Three Series-Connected Windings and Two Capacitors

This paper presents a novel energy efficient single-phase induction motor with three series-connected windings and two capacitors. By suitable selection of capacitors, the currents in three windings are approximately symmetrical, and thus, the motor can operate approximately symmetrically from single-phase supply. Based on the symmetrical components method, the condition for balanced operation is studied, and the method for determining capacitances is proposed. The performance analysis method is put forward to calculate the steady performances. Performance tests are performed on the proposed motor and three-phase induction motor. It is proved that their rated efficiency is approximately the same, while the power factor of the former is higher than that of the latter. In comparison with the ordinary single-phase induction motor, it has the advantages of higher efficiency and smaller volume, thus can take the place of the latter in some applications.

Design of New Load Balancers for Modern High Speed Railway Systems

Traditional electric trains have a low power factor, high loading variation change and inefficiency, generating both negative sequence current and the imaginary part of positive sequence current. Delta type Load Balancer associated with specially connected transformers is generally adopted to correct power factor and voltage imbalance. However, the modern trains used in High Speed Railway (HSR) have a power factor approximately close to unity, and therefore only need voltage imbalance correction. This study presents novel Load Balancer schemes, which are a modification of the Delta-type Load Balancer, with various connected transformers to correct imbalance. The symmetric component method is also adopted to determine the installation capacity of the proposed Load Balancer schemes.

DESIGN AND IMPLEMENTATION OF DSTATCOM FOR FAST LOAD COMPENSATION OF UNBALANCED LOADS

This paper proposes a distribution level static synchronous compensator (DSTATCOM) for fast load compensation of unbalanced loads in electric power distribution systems. For fast response requirement, a new feedforward compensation scheme is derived and employed in the paper. First, the compensation scheme of the DSTATCOM is derived with the symmetrical components method. Then, computer simulation with the program Matlab/Simulink preliminarily verifies the effectiveness of the proposed DSTATCOM. Accordingly, a hardware prototype is built with a floating-point DSP TMS320C6711-based system. Use of a current-regulated PWM (CRPWM) inverter as the power stage of the DSTATCOM generates needed compensation currents for real-time load compensation. Finally, experimental results confirm the effectiveness of the proposed DSTATCOM.

Voltage unbalance numerical evaluation and minimization

Among a series of parameters, power quality studies are concerned with voltage unbalances, which represent the voltage magnitude and phase deviation from nominal values. In order to determine the influence of the network's parameters on voltage unbalances, and to provide exact solutions to reduce or even eliminate them, the present study develops and presents two methods. First, a sensitivity analysis is used to determine the influence of each parameter, and then analytical solutions are developed in order to provide the changes needed for correction. The quantification index considered is the symmetrical components method.

ADVANCED CHARACTERIZATION OF VOLTAGE SAGS AND ASSESSMENT OF EQUIPMENT SENSITIVITY

The paper proposes a new approach for characterization and classification of voltage sags and for the assessment of sag influence on sensitive equipment. The existing classifications of voltage sags mainly use the method of symmetrical components and describe voltage sags in terms of magnitude and duration. It has been recognized though, that the other sag characteristic may influence sensitive equipment operation. In this paper, the approach based on Odq-components method (Park's transformation) is used for sag description and equipment sensitivity assessment. This approach enables to represent voltage sags as a function of time, magnitude, instant of fault initiation and phase-angle jump at the same time or as a function of more than two characteristics simultaneously. Furthermore, this new representation of voltage sags facilitates the investigation of equipment sensitivity to phase-angle jump, moment of fault initiation and to any combination of these and other sag characteristics.