New Publications are available for Asynchronous machines
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New Publications are available now online for this publication.
Please follow the links to view the publication.Grid code interrelation, wind generation evolution and reactive compensation, special topics inside a grid code
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0788
By all appearances, the evolution of wind generation has been orientated to satisfy the requirements, every time inside narrower limits, imposed by the grid codes, standing out among all the determining ones, the administration of the reactive power. In the age of induction generator's fixed speed, the requirements to access to the network were lax, considering the lack, for any practical, end of the capability's curves. The advent of the DFIG's and the electronic switch (IGBT's) evolution, have allowed that a wind farm, in the first instance, can handle the reactive power by means of the availability of a capability curve and comply, this way, with the most restricted codes. The update has been given in very recent date, with a wind farm's activation of an integrated by DFIG's and full converter generators, whose capability's curve are similar to that of a conventional plant. Seeing to the future, probably let's be able attend the elimination of the gear's box. Nowadays the wind generators operate better with high speeds and, therefore, they need gear's box to reduce it. Considering all gear train's issues: cost, vibrations, noise, fatigue, lubrication and maintenance, eliminating the box would have big advantages. The recent versions of the grid code, authorizes the operator to treat the wind farm just like a conventional plant, using the capacity of reactive power inside the extended range of the capability curve. This is not just for reducing the limits inside which one must move the tension and the power factor; now the wind farms must satisfy polygon's critical points of operation, impossible to satisfy with the first generation machines. Under this new operation criterion, the good administration of reactive power is the result from a combination of machines contributions, switched capacitor banks and the reactive dynamic compensation get it using switch electronic devices. The grid code tacitly, yields the owner of the wind farm, the responsibility of solving extraordinary problems or out of the normal catalogue, like a subsynchronous resonance or torsional effects. Give an idea of the entail of all these factors is the purpose of this paper. (4 pages)A simple capacitor voltage balancing scheme for the cascaded five-level inverter fed AC machine drive
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0234
This paper proposes a simple scheme for balancing the series capacitor voltages at the three-phase cascaded five-level inverter fed an induction motor by using the logic circuits. Using switching patterns based on the multi-carrier technique, two series-capacitor voltages can be only balanced during one cycle. However, they have a ripple voltage, which may cause the induction motor drive to be unstable. The proposed scheme for balancing capacitor voltages can be implemented by simple logic circuits. It can be verified that the series capacitor voltages are maintained constant at wide frequency range through experimental results with 32-bit DSP and Cyclone-III FPGA. (5 pages)Intermittent duty of induction machine: investigations of energy efficiency for environmental impact minimization
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0295
This paper presents an approach for estimating the efficiency of an induction motor operating in periodic intermittent service. The theoretical approach is based on a space vector model. This model yields the electrical behaviour of the motor during transients and, by extension, losses and instantaneous powers. Energy efficiency is calculated for the considered intermittent service. The accuracy of the theoretical model and its associated hypothesis are discussed considering experimental data recorded on a testing bench for periodic starting from zero speed. The differences between the efficiency for an intermittent service and the classical permanent operating point may be significant. This model gives extra information for the design of motorized systems working in intermittent services, in order to minimize their global environmental impact determined for their whole life. (7 pages)Overall differential protection for pump storage power plant with tapped-delta design of the unit transformer
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0018
Every pump storage hydro power plant has at least three different operating modes of the synchronous machine which can cause possible challenges during the design of the plant protection scheme. These three operating modes are generating mode, pumping mode and machine starting into pumping mode. The main differences between the generating and pumping operating modes are changes in direction of the synchronous machine rotation and change of direction (i.e. sign) of the active power flow. This rotation direction change is achieved by so-called phase reversal disconnect switches. These disconnect switches simply swap two phases in pumping mode in order to reverse the phase sequence to the synchronous machine. However, the physical location of the phase reversal disconnect switches can be crucial for proper design of some protection functions (e.g. overall differential protection 87O) for the generator/motor-transformer unit. For this particular installation, phase reversal disconnect switches 89G and 89P are located in-between the low-voltage bushings of the unit transformer and the synchronous machine (see Figure 1 for more details), thus within the protection zones of the overall differential relay 87O. Machine starting into pumping mode of operation is specific for every pump storage power plant. In this particular station, machine is started as an asynchronous motor by using direct on line starting method with reduced voltage. Voltage reduction is obtained by a special design of the unit transformer. So-called tapped-delta design, of the unit transformer secondary delta winding, is used (see Figure 2). (6 pages)Structural comparison of permanent magnet direct drive generator topologies for 5MW wind turbines
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0286
Direct drive electrical generators offer a reliable alternative to conventional induction machines since they omit the gearbox from the drivetrain. Their large structural mass though makes them difficult to manufacture, transfer and assembly. Topologies other than the conventional iron-cored have been suggested in literature to minimise this attribute. This paper will investigate the structural stiffness of three different permanent magnet direct drive generator topologies against static forces that apply to such wind turbine generators. Finite element analysis (FEA) models of all tested generators were developed. Results from the structural analysis will be used to draw valuable conclusions. (6 pages)Inverter control of medium and high speed linear induction motors
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0361
This paper suggests a unique configuration of certain standard inverters to give better performance from medium and high speed Linear Induction Motors (LIMs). It extends the control method suggested for low speed LIMs [1] and allows a given system parameter to be optimised. (4 pages)Motion control for short primary linear drive using induction or synchronous operation in different sections for material handling applications
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0299
The moderate thrust force and high accuracy make the short primary linear motor a good selection for material handling application with very long track and closed paths. This paper deals with the motion control of a linear drive which operates at some sections of the track as synchronous machine and for other sections as induction machine. Unlike applications with long primary linear motors, the costs can be considerably reduced by using an active vehicle on a passive track. In sections where no fast speed changes are necessary, a sensorless speed control method is used. A suitable vehicle motion control strategy is necessary especially during the transition between synchronous to induction motor operation and between sensor based to sensorless region operations. The classic MRAS (Model Reference Adaptive System) speed and flux estimators are activated in the sensorless induction motor operation mode. The transition control strategies are experimentally verified, discussed and presented. (6 pages)Research on a novel online condition monitoring technique for induction machinery
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0143
Condition monitoring of induction machinery is traditionally implemented by conducting spectral analysis of either vibration or stator current signals, because it is believed that once a fault occurs, it will produce a unique characteristic frequency in the signals. Hence, the fault and its further growth can be detected and traced through observing the variation tendency of the amplitude at this fault-related frequency. Such a condition monitoring approach requires significant pre-knowledge about the machine and its components, however does not always work very well in practice, in particular when the fault is in its infancy. In addition, to date there has not been convincing proof demonstrating that electrical faults can be readily detected by the means of vibration analysis, although much effort has been done to prove the validity of stator current analysis in detecting the mechanical faults occurring in induction machinery. In view of this, a new online condition monitoring technique is developed in this paper dedicated for induction machinery, which is based on detecting the phase angle of the stator current with respect to the corresponding voltage. In the paper, the proposed technique is verified through both simulated and practical experiments. It is shown that the proposed technique is not only valid in detecting electrical and mechanical faults occurring in the induction machine, but is also able to distinguish stator winding faults from rotor winding faults without requiring any pre-knowledge about the machine. Moreover, the proposed technique uses relatively simple calculations and is therefore ideally suited for performing the condition monitoring task online. (5 pages)Finite element analysis of winding fault effects in a wound-rotor induction machine with experimental validation
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0291
Effective condition monitoring of remote wind turbine power plant induction generators is significantly gaining importance in modern wind industry. This paper uses a finite element time stepping transient model to investigate the influence of winding faults on the air-gap field distribution of a wound-rotor induction generator. The analysis shows that winding faults cause a severe air-gap field distortion, giving rise to field harmonic orders that would not otherwise be present in the air-gap, and links these to observed winding fault specific changes in the predicted and measured machine current spectrum. (6 pages)Short circuit current calculation of doubly fed induction generator
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0121
Based on the basic voltage and flux equations of the Doubly Fed Induction Generator, this paper derived expressions of short-circuit current of wind turbines-which are expressed by transient equations of stator and rotor flux. The transient equations of stator and rotor flux were functions of initial values of stator and rotor flux and transient time constants of stator and rotor windings. The initial value of stator flux was calculated, considering the influence of stator resistance, and the rotor flux equation under steady state condition was used to calculate the initial value of rotor flux. Transient behaviors of the stator and rotor flux were analyzed when three-phase faults occurred at terminals of generators, then the transient equations of stator and rotor flux and detailed equations of the short-circuit current of DFIG could be obtained. DIgSILENT/PowerFactory program was used to execute electromagnetic transient simulations when three-phase faults occurred at terminals of generators and at the power system respectively. Simulation results show that it is efficiently to use the equations of short-circuit current proposed by this paper to calculate the short-circuit current of DFIG. As the stator and rotor resistances are considered in the equations of the short-circuit current, calculation results are closer to simulation results, and all differences are less than 4%. (6 pages)Wind turbine condition monitoring using generator control loop signals
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0292
This paper presents an advanced monitoring and diagnosis method for detecting of incipient electrical and mechanical faults in a wind-turbine-driven doubly-fed induction generator (DFIG). In this application, the stator windings are directly connected to the grid, whereas a converter controls the rotor currents by means of a Field Oriented Control (FOC) scheme. A new diagnostic method, based upon frequency analysis of the dq rotor current error signals inside the machine-side converter controller, is proposed. Simulation results confirm that the spectra of these signals have features that are suitable for an effective diagnostic procedure. The proposed system could be embedded in a wind turbine at very low cost. (6 pages)Modelling and analysis of DFIG wind turbine system in PSCAD/EMTDC
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0321
Wind turbine technology is currently driven by offshore development, which requires more reliable, multi-megawatts turbines. Models with different levels of detail have been continuously explored for years. This paper presents a 4.5MW doubly-fed induction generator wind turbine model established in PSCAD/EMTDC with two control levels, the wind turbine control and the DFIG control. Two converter models, a detailed and a simplified model are discussed. Mathematical representations of the closed-loop control systems are developed and verified against the PSCAD/EMTDC model. Simulation studies show good correspondence between the two results. In addition, the dynamic response of a 2-mass shaft model to a wind step is also simulated to examine the effect of torsional oscillations. This model can be employed to evaluate the control scheme, mechanical and electrical dynamics and the fault ride-through capability. (6 pages)Brushless doubly fed induction machine as a variable frequency transformer
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0179
Variable frequency transformer (VFT) has been recently used as an alternative to HVDC to control power flow between asynchronous networks. VFT consumes less reactive power than a back-to-back HVDC system, provides faster initial transient recovery, and has better natural damping capability. VFT is simply a doubly-fed induction machine (DFIM) where the machine torque controls the power flow from stator to rotor and vice versa. The main disadvantage of this VFT is the slip rings and brushes required for the rotor circuit, especially in bulk power transmission. The brushless doubly fed machine (BDFM) with nested cage rotor machine is proved to be a comparable alternative to conventional DFIM in many applications with the advantage that all windings being in the stator frame with fixed output terminals. In this paper, the BDFM is used as a variable frequency transformer (BVFT). A prototype machine is designed and simulated to verify the system validity. (7 pages)Impact of airflow impingment on heat transfer from induction generators in oscillating water columns
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0185
Computational Fluid Dynamics models based on the LIMPET OWC turbo generation section were created to investigate how airflow impingement created by a rotating turbine directly upstream increased the heat transfer away from electrical generators as compared to purely axial airflow. Finned and smooth generator casings were compared for the two cooling methods. The CFD results of average heat flux and total heat transfer were compared with results obtained through theoretical and empirical equations applicable to axial airflow acting on smooth and finned surfaces with defined temperatures. During axial flow, the CFD and analytical results for heat flux and heat transfer correlated very well over a range of velocities with a maximum deviation of 4.94%. The highest heat transfer, and thus highest potential power output, was obtained by the finned generator when cooled via airflow impingement. (6 pages)STATCOM and UPQC: options to enhance fault-ride-through capability of a fixed speed wind generator
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0191
The enhancement of fault-ride through (FRT) capability of a Fixed Speed Induction Generator (FSIG) with the help of a Unified Power Quality Conditioner (UPQC) and STATCOM are examined in this paper. The FRT performance of these equipments are evaluated and compared in accordance with Irish Grid Code requirement. A simulation study carried out on a 2 MW wind turbine with varying power system parameters has shown that the application of a STATCOM can be economical for a stronger networks where as a UPQC seems to be the economical option when the FSIG is connected to a weaker network. (6 pages)Effect of fault resistance and grid short circuit MVA on impedance seen by distance relays on lines fed from wind turbine generating units (WTGU)
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0027
This paper deals with line protection challenges experienced in system having substantial wind generation penetration. Two types of WTGU: Doubly Fed (DFIG) and Squirrel Cage (SCIG) Induction Generators are simulated and connected to grid with single circuit transmission line. The paper summarizes analytical investigations carried out on the impedance seen by distance relays by varying fault resistances and grid short circuit MVA, for the protection of such transmission lines during faults. The results are also compared with systems having conventional synchronous machine connected to the grid. (6 pages)Design and testing of a 250 kW medium-speed brushless DFIG
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0320
This paper presents the design and testing of a 250 kW medium-speed Brushless Doubly-Fed Induction Generator (Brushless DFIG), and its associated power electronics and control systems. The experimental tests confirm the design, and show the system's steady-state and dynamic performance. The medium-speed Brushless DFIG in combination with a simplified two-stage gearbox promises a low-cost low-maintenance and reliable drive train for wind turbine applications. (6 pages)Implementation of a PI phase angle controller for finite element analysis of the BDFM
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0293
Time-stepping finite element analysis of the BDFM for a specific load condition is shown to be a challenging problem because the excitation required cannot be predetermined and the BDFM is not open loops stable for all operating conditions. A simulation approach using feedback control to set the torque and stabilise the BDFM is presented together with implementation details. The performance of the simulation approach is demonstrated with an example and computed results are compared with measurements. (6 pages)Comprehensive and quantitative analysis of protection problems associated with increasing penetration of inverter-interfaced DG
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0091
In the last two decades there has been a continuous increase in the amount of Distributed Generation (DG) connected to the power network. This has resulted in a number of technical challenges for network protection including: sympathetic tripping of DG interface protection; blinding of feeder over-current (OC) protection; and deterioration of feeder OC protection grading. While the available literature typically analyses the impact of synchronous and induction DG (which is characterised by a high fault current contribution), this paper focuses on the impact of inverter-interfaced distributed generators (which are characterised by low fault current contributions). This paper quantifies the `tipping points' at which protection problems occur by modelling a series of fault scenarios on a typical UK distribution network with inverter-interfaced DG, all simulations have been modelled in PSCAD. The results of this paper suggest that the occurrence of sympathetic tripping is highly dependent on the grid infeed fault level and the inverter-interfaced DGs fault location; protection blinding is unlikely to be a problem on UK power networks as it was not observed in any of the scenarios simulated in this paper; in all cases of protection grading deterioration the grading margin between the protection devices was found to increase meaning the protection devices never operated in an uncoordinated fashion. The tipping point at which these protection issues occurred was evaluated on a typical UK network. The conclusions drawn from these simulations may not be equally valid on future power networks that could employ novel network architectures and higher penetrations of DG. (6 pages)Control of doubly-fed induction machine storage system for constant charging/discharging grid power using artificial neural network
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0177
A large-capacity low-speed flywheel energy storage system based on a doubly-fed induction machine (DFIM) basically consists of a wound-rotor induction machine, and a back-to back converter for rotor excitation. It has been promoted as a challenging storage system for power system applications such as grid frequency support/control, power conditioning, and voltage sag mitigation. This paper presents a power control strategy to charge/discharge a flywheel doubly-fed induction machine storage system (FW-DFIM) to obtain a constant power delivered to the grid. The proposed controller is based on conventional vector control, where an artificial neural network (ANN) is used to develop the required rotor current component based on the required grid power level and the flywheel instantaneous speed. This technique is proposed for power levelling and frequency support to improve the quality of the electric power delivered by wind generators, where a constant power level can be delivered to the grid for a predetermined time depending on the required power level and the storage system inertia. The controller is designed to avoid overloading stator as well as rotor circuits while the flywheel charges/discharges. The validity of the developed concept in this paper, along with the effectiveness and viability of the control strategy, is confirmed by computer simulation using Matlab/Simulink for a medium voltage 10MJ/1000hp FW-DFIM example. (6 pages)Symmetrical low voltage ride-through of a 250 kW Brushless DFIG
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0322
The Brushless Doubly-Fed Induction Generator (Brushless DFIG) shows commercial promise for wind power generation due to its lower cost and higher reliability when compared with the conventional Doubly-Fed Induction Generator (DFIG). In the most recent grid codes, wind generators are required to be able to ride through a low voltage fault and meet the reactive current demand from the grid. Hence, a Low-Voltage Ride-Through (LVRT) capability is important for wind generators which are integrated into the grid. In this paper the authors propose a control strategy enabling the Brushless DFIG to successfully ride through a symmetrical voltage dip. The control strategy has been implemented on a 250 kW Brushless DFIG and the experimental results indicate that LVRT is possible without a crowbar. (6 pages)Wind turbine induction generator fault frequency tracking by reference frame transformation
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0323
Wound rotor induction machines in wind turbine drives operate in predominantly transient conditions resulting in constant changes of current fault frequencies of interest with operating speed. Classical frequency domain techniques aimed at stationary signals are therefore not adequate for development of fault frequency tracking algorithms. To overcome this limitation this work proposes a simple and effective fault frequency tracking algorithm based on reference frame transformation of stator currents. The potential of the proposed technique to be used for tracking the rotor electrical unbalance fault specific frequencies and obtaining an indication of fault severity is verified in this research by analysis of numerical simulation and experimental data. (6 pages)Selective harmonics elimination PWM with sel-balancing capacitors in three-level inverter
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0157
This paper deals the DC-link voltage balancing problem in 3- level rectifier-3-level inverter-Induction Motor (IM) cascade In order to improve the performance cascade, we have proposed the use of the redundant states with the selective harmonics elimination PWM instead of space vector PWM to control the DC-link voltages and the inverter switches in the same time. The make use of the proposed algorithm is based on the matrix representation on the NPC 3-level inverter. (6 pages)Computations of electromagnetic forces and fields in double sided linear induction motor (DLIM) using finite element method
http://dl-live.theiet.org/content/conferences/10.1049/ic.2011.0058
This paper aims to present the material aspects of Linear Motion Induction Motor. The Electromagnetic Characteristics of Linear Induction Motor (LIM) are more complex than other rotating type induction motors[1]. It is very significant to evaluate Magnetic Field parameters for the design of an optimized model for various applications. In this present work. Double Sided Linear Induction Motor (DLIM) has been analyzed to compute Magnetic Field Density, Magnetic Vector Potential and other force components by using one of the latest Finite Element Method (FEM) software i.e. Maxwell The simulation results of DLIM are also validated with experimental setup of DLIM.Simulation of an induction motor including eddy-current effects in core laminations
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0034
The purpose of this paper is to investigate the common mode ground current induced in an induction machine controlled by Pulse Width Modulation(PWM)at high frequencies. Using the transmission line approach the parameters are extracted from both two-dimensional (2D) and three-dimensional (3D) field simulations. 2D finite element (FE) analysis is an efficient tool for simulating the entire motor cross section. However, eddy currents in the lamination cannot be modeled explicitly and have to be approximated by a semi-analytical formulation. The pa per investigates the accuracy of this model for a wide frequency range (100 Hz...100 kHz). The results show the necessity of fully 3D simulations taking into account the detailed distribution of eddy currents in the laminations. A specialized 3D simulation tool for induction motors with laminated cores is being developed and will be presented in the full paper.Cost optimal design of micro hydel systems
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0355
Micro hydel systems are turning out to be an important choice for power generation as a renewable energy source, considering the hydel resource available in India. Reports from Ministry for New Renewable Energy (MNRE) states that the estimated potential for power generation in India from hydel plants is about 15,000 MW from 5718 identified sites. Researchers are trying to develop hydel systems with induction generators, operating both in grid-tied and stand-alone modes. This paper describes an optimization model which gives a cost optimized design for micro hydel systems. The model is applied to obtain an optimal design at a typical site in Kerala.Modelling and power quality enhancement of induction motor with soft starter using synchronous reference frame theory
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0333
An This paper presents a method for obtaining the desired reference current for Voltage Source Inverter (VSI) of Shunt Active Filter fed Induction motor using Synchronous Reference Frame (SRF) theory. The modeling is based on the a-b-c stationary frame to 0-d-q rotating frame transformation of the ac system variables. The cur rents injected by the active filter are controlled in the synchronous orthogonal 0-d-q frame using a decoupled nonlinear control strategy. The reference harmonic components are extracted from the sensed nonlinear load currents by applying the synchronous reference frame method, where an AC voltage controller fed three-phase Induction motor is taken as the nonlinear load. To improve the performance of the PI controller, the feedback path to the integral term is introduced to compensate the winding up phenomenon due to integrator. The Phase Locked Loop (PLL) with PI filter is used for Synchronization, with much emphasis on minimizing delays. The results confirm the performances considered theoretically for the shunt active filter topology and to comply with IEEE 519 recommended harmonic standards.A three level neutral point clamped Inverter with buck-boost capability for renewable energy sources
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0361
As demand for renewable energy generation increases, the demand for power inverters with voltage buck-boost capability is also expected to rise. This is because the output of renewable energy sources such as solar panel, wind turbines etc are not constant due to varying climatic as well as geographic conditions. So in order to obtain an ac supply with adjustable voltage and frequency, a multi level inverter with buck boost capability is proposed. Multi-level converters are power-conversion systems composed by an array of power semiconductors and capacitive voltage sources that, when properly connected and controlled, can generate a multiple step voltage waveform with variable and controllable frequency, phase, and amplitude. In this a three level neutral point clamped inverter topology is used. Normally a neutral point clamped (NPC) inverter has a disadvantage of input capacitor voltage unbalancing. This can also be avoided by a special arrangement of input capacitors. Alternate Phase Opposition Disposition (APOD) modulation scheme is used for the modulation of NPC bridge. This inverter is used to drive a three phase induction motor. Simulation works are carried out in MATLAB/SIMULINK.Performance analysis of self-regulated and self-excited six-phase induction generator
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0410
This paper presents a simple method to determine the performance of a Self-regulated, Self-Excited Six-Phase Induction Generator. The problem is formulated as multivariable unconstrained non linear optimization problem. The admittance of the equivalent circuit of the Six-Phase Self-Excited Induction Generator (SPSEIG) is taken as an objective function. Attention is focused on the influence of the different capacitor connections on the generator overload and output power capabilities. The generator voltage with simple shunt excitation connection collapses when it is overloaded. With short shunt excitation connection, the generator is able to sustain the load but at lower operating voltage and larger load current. The frequency and magnetic reactance or speed and magnetic reactance or frequency and capacitive reactance are selected as an independent variables depending upon the operational condition of the machine. The optimization problem is solved using Fmincon method. The developed mathematical model is quite simple and can be implemented for any type of load such as resistive or reactive with capacitor connected either across single three-phase winding set or both the winding sets. The computed results are found to be in good agreement with the experimental results.Effects of external yoke and end-bells on AC motor external field
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0047
This paper focuses on the external flux in the vicinity of AC electrical rotating machines. The influence of the external housing, the external yoke and the end-bells, is studied with a Finite Element modelling, an analytical model and an induction machine equipped of flux sensors.A novel adaptation approach for electromagnetic device optimization
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0073
In order to carry out a successful case adaptation in our case-based reasoning system for EM device design, we make use of semantic networks to organize related domain knowledge, and then construct a rule system as an inference engine which is based on the network. Based on the rule system, a novel adaptation algorithm is proposed to derive a new device case from an induction motor case-base with high dimensionality.Simplified SVPWM based hybrid PWM for induction motor drives for the reduction of torque ripples
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0416
A voltage source inverter-fed induction motor produces a pulsating torque due the application of no sinusoidal voltages. Torque pulsation is strongly influenced by switching fashion employed. This paper presents the simplified hybrid pulse width modulating technique for the reduction of torque ripples in an induction mo tor. In conventional space vector pulse width modulating (CSVPWM) technique (0127-7210) the zero states are divided equally and give rise to continuous modulating technique. The hybrid PWM is a combination of both continuous and discontinuous PWM techniques. To modulate the required voltage vector calculation of magnitude and angle are required which is complex. In this paper a simplified algorithm based on the concept of imaginary switching times is implemented. To validate this method simulation has been carried out in MATLAB 7.8 on v/f control of induction motor.Finite element analysis of transient electromagnetic-thermal phenomena in a squirrel cage motor working at cryogenic temperature
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0075
The paper presents an algorithm for transient FE analysis of coupled electromagnetic-thermal phenomena in a squirrel cage submerged motor working at cryogenic temperature. The non-linearity of the magnetic circuit, the movement of the rotor, skewed slots, and the influence of temperature on electric and thermal properties of the materials has been taken into account. The results of the simulations and measurements are presented.Modelling of a linear induction motor for automated material
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0445
Linear Induction Motor, due to its linear motion is finding wide range of applications mainly in the process industries. For an automated material handling application the performance of the motor need to be analysed using a mathematical model. Due to the complexity of the LIM's electromagnetic field theory an analysis of the LIM equivalent electrical circuit is used here. This paper mentions the dynamic model of a LIM with d-q model of the equivalent circuit considering the end effects.Realization of grid fault on grid connected wind energy conversion system using real time simulator
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0351
DFIG is the most common rotatory machine which is used on the grid connected wind energy conversion system for the fulfilment of the system requirement such as grid stability, fault ride through (FRT), power quality improvement, and grid synchronization and power control etc. Though the requirements are not fulfilled directly by the machine rather the control strategy is used in both the stator as well as rotor side along with converters to fulfil the requirements stated above. In this paper the performance of the DFIG system is analysed under the symmetrical grid fault and the theoretical results are obtained from the MATLAB/SIMULINK environment and the proposed work is validated experimentally using RT-LAB.Decoupled control of real and reactive power by limiting the DC-link fluctuation for a doubly fed induction generator
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0390
This paper brings out an enhanced control technique for reactive power control of a Wind Generator using a grid-side converter control. The dynamic model of DFIG is developed through d-q reference frame. The back-to-back converter are modulated with SPWM and SVM techniques and hence compared. The converters allow four-quadrant operation in the P-Q plane by adjusting its switching pattern, thereby paving way for several drive applications. The role of the grid-side converter is to keep the DC-link voltage constant with less fluctuation regardless of the magnitude and direction of the rotor power flow.Experimental based capacitance calculation of induction motor: as wind power generator
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0350
This paper describes the review of capacitance determination of an induction motor working as generators. An experimental based capacitance value calculation has been propose and implemented successfully in laboratory model of induction generator. A 5Hp, 220V, 15A separately excited d.c motor coupled (mechanically) with a2.2kW, 415V, 4.7A, Y-connected, 1440-rpm induction motor emulates the induction generator characteristics with a 50 microfarad capacitor bank (calculated capacitance) connected across the stator windings. For validation of the proposed method, experimentation has been rig-up and tested in the laboratory. The result has a good agreement with this method and extends to use of this method, to calculate the additional capacitance required to reduce the reactive power burden in grid connected induction generator, used in wind power( variable speed) generation.Improvement of power factor and reduction of harmonics in three-phase induction motor by PWM techniques: A literature survey
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0419
In this paper presents a literature survey on improvement of power factor and reduction of harmonics in three phase induction motor by Pulse Width Modulation (PWM) techniques. Also presents the current status of the improvement of power factor and reduction of harmonics in three phase induction motor by PWM techniques. Authors strongly believe that this survey article will be very much useful to the researchers for finding out the relevant references in the field of improvement of power factor and reduction of harmonics in three phase induction motor by PWM-techniques.Determination of performance parameters of a small-size high-speed induction motor using the field-circuit method
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0041
Core losses generated in small size high-speed induction motors constitute a significant part of total losses in the motor, in particular at higher frequencies. Precise determination of these losses is vital to assure the proper functioning of the motor. Core losses in electrical machines depend on the power loss density of the electrical sheets used, which in turn depends strongly on frequency, magnitude and form of the applied magnetic field. The specific losses are usually only given for the 50 Hz alternating flux. Consequently, various estimations are applied for higher frequencies. To avoid errors associated with such an approach a direct use of specific losses measured on ring samples has been proposed. The no-load and load losses in the core have been calculated using a field-circuit and a circuit method. The machine parameters and load characteristics have also been determined at supply frequencies from 50 to 200 Hz. The computational results have been verified against measurements.Comparative analysis of variable speed wind energy conversion systems
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0353
The modelling of PWM Doubly Fed Induction Generator (DFIG) for wind turbine application is used for improving the power quality of the grid and it is more attractive in comparison to the PWM Synchronous and PWM-Induction generator with a variety of reasons. While the technology of PWM-Synchronous (PWM-SYN) and PWM-induction (PWM-IND) generator is used for constant speed of wind velocity, more recently, the variable wind speed induction generator was introduced. Doubly Fed Induction Generator is used for wind energy conversion . This allows the operation of the turbine at variable wind speed enhancing the conversion system. This paper gives an overview of the simulation results for comparing the DFIG with the PWM based induction and synchronous machine. Doubly Fed Induction machines uses AC-AC converter in the rotor circuit which is the best option for high power applications with limited speed ranges. The power converter rated only to handle the rotor power. It allows the power output in both stator winding and rotor winding of an induction machine with a wound rotor winding to yield good power factor even the machine is running at speed different from synchronous speed.Indirect vector control of induction motor using sliding-mode controller
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0415
The paper presents a sliding-mode speed control system for an indirect vector controlled induction motor drive for high performance. The analysis, design and simulation of the sliding-mode controller for indirect vector control induction motor are carried out. The proposed sliding-mode controller is compared with PI controller with no load and various load condition. The result demonstrates the robustness and effectiveness of the proposed sliding-mode control for high performance of induction motor drive system.Impact of grid connected distributed generation on voltage sag
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0341
Distributed Generation (DG) has impacts on the performance when connected to distribution system. The term "distribution generation (DG)" refers to small-scale generation located near the source of the load it serves. Distributed Generation from renewable sources is more and more widely used due to the growing concern on environmental protection. DG can also provide power supply to customers in the event of an outage or during scheduled interruption. DG had impacts on the performance of connected distributed network. Application of distributed generation in distribution system is expected to increase in near future due to its positive impacts such as voltage support, improved reliability, small size and loss reduction. However, DGs may have negative impacts on power quality such as voltage regulation, harmonic distortion, voltage sag, islanding and confliction with relaying and reclosing. A comparative analysis is done on the impact of different types of DGs on voltage profile and voltage sag in distribution system. The analysis shows that voltage profile is improved with DG, with highest voltage for synchronous generator with power factor controller. Synchronous generators with excitation control have less impact on voltage sag compared to other types of generators. Simulation results also shows that volt age sag magnitude is highest for induction generator followed by synchronous generator with power factor control.Non-linear FE-based modeling of induction machine for integrataed drives
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0031
The linear and non-linear FE-based model of a three phase wound rotor induction machine is presented. The effect of stator and rotor currents on the self and mutual inductance is considered. The mathematical representation of the machine in presence of saturation is developed. The calculated model is compared with a simple d-q model, full FE-model, and a linear FE-based phase variable model. The calculated result shows a good match in accuracy with full-finite element model and in run-time with the d-q model.Implementation of variable structure DTC-SVM based VWF for an induction motor drive using FPGA-SPARTEN III
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0413
This paper proposes a novel torque control scheme for induction motors. Compared with field orient control (FOC), direct torque control (DTC) is known to provide fast and robust response for induction motors. However, while offering high dynamic performance, classical DTC produces notable torque, flux, and current ripples, and operates with a variable inverter switching frequency. The proposed direct torque scheme is combined with simplified Space Vector Pulse Width Modulation (SVPWM) technique to control the inverter output voltage. The desired voltage vector for the inverter for controlling the torque is given by the proposed DTC SVM scheme. The direct torque control is based on the relation ship between instantaneous slip angular frequency and rotor angular frequency in adjustment of the reference stator flux angle. The amplitude of the reference stator flux is always kept constant at rated value. The proposed scheme therefore provides smooth, fast and robust regulations of the electrical torque and the stator flux. Simulation results are provided to evaluate the performance of the proposed scheme. The proposed scheme has been implemented in FPGA. Experimental results have been provided to evaluate the motor performance.Impact of fixed and variable speed wind turbine systems on power system voltage stability enhancement
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0199
This paper investigates the effect of fixed speed and variable speed grid-connected wind generators on the voltage stability of a power system network. The wind generators considered are the squirrel cage induction generator (SCIG), which is fixed speed, the doubly-fed induction generator (DFIG) and the direct driven synchronous generator (DDSG) which are variable speed. Studies were conducted on a standard five machine, 14-bus system augmented by a radially connected wind power plant (WPP), which contains 215 wind turbine generators (WTG).The studies include examining the voltage magnitude, loading margin and voltage collapse of the system. These studies are conducted for the normal state as well as for line contingencies. It is found that large scale integration of WTG (direct drive synchronous generator) at the transmission level has the potential to improve the long term voltage stability of the grid by injecting reactive power. (9 pages)State modeling based prediction of torsional resonances for horizontal-axis drive train wind turbine
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0179
This paper focuses on the state space modeling approach and output torques prediction of torsional vibrations for variable speed wind turbines. The multi-body system model under study is mainly comprised of a wind turbine, a three stage planetary gear box and an induction generator. The masses-springs approach of shaft system differential equations are developed from Newton's law and Lagrange formulas. For an easy comprehension for electrical engineers and tutorial purpose, an electrical equivalent circuit of the system is proposed using mechanical and electrical components similarities. Extensive numerical simulations are performed to investigate system mechanical resonances and impacts of damping factors on the system dynamic and stability. (9 pages)Reducing bearing wear in induction generators for wave and tidal current energy devices
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0220
Marine energy devices such as wave energy converters and tidal current turbines are set to play a significant role in contributing to electricity generating by renewable means. The offshore location where these devices operate demands high reliability and robust fault tolerance. Bearing failure is a key issue for renewable energy devices and is a cause of significant downtime in wind turbines. Bearing wear is accelerated due to unbalanced magnetic pull in the rotor of an electrical generator. This paper presents a review and assessment of methods to reduce bearing wear through both machine design and active control through power electronics. (6 pages)Second-order sliding-mode controller design and tuning for grid synchronization and power control of a wind turbine-driven DFIG
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0181
This paper presents a second-order sliding-mode control (2-SMC) scheme for a wind turbine-driven doubly-fed induction generator (DFIG). The tasks of grid synchronization and power control are undertaken by two different algorithms, designed to command the rotor-side converter (RSC) at fixed switching frequency. Effective tuning equations for the parameters of both controllers are derived. A procedure is also provided that guarantees bumpless transition between the two controllers at the instant of connecting the DFIG to the grid. The resulting 2-SMC scheme is evaluated via real-time hardware-in-the-loop (HIL) emulation over the virtual prototype of a 660-kW DFIG. HIL results evidence both the high dynamic performance and the superior robustness achieved with the proposed control scheme. (6 pages)Investigation of grid-support capabilities of doubly fed induction generators during grid faults
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0234
Doubly-Fed Induction Generators (DFIGs) are utilized nowadays in wind farms due to their advantages as compared with other corresponding ones. Control complexities and their unique dynamic characteristics may, however, raise different problems during abnormal or faulty operating conditions considering grid-supporting purposes. This results mainly from their fast control mechanisms, tight thermal limits of their IGBT inverters as well as the reaction of the associated rotor protection mechanisms. Accordingly, DFIGs show different grid-support profile as compared with either single fed induction generators or conventional synchronous ones. In this paper, the performance of DFIG units for grid faults is investigated. Detailed dynamic modeling of the DFIG units is utilized considering rotor protection circuitry with either crowbar or DC choppers. Scenarios for grid-supporting are explored. This facilitates realizing a better understanding of the real behavior of such generators and highlighting their features well in order to get a better utilization of wind energy resources in the future. (7 pages)Low voltage ride-through control strategy of a large capacity DFIG with grid-side thyristor controlled voltage regulator
http://dl-live.theiet.org/content/conferences/10.1049/cp.2011.0215
With the rapidly increasing capacity of grid-connected wind power and the development of offshore wind power, the operating characteristics of wind turbine during the fault have drawn more concern. This paper adopts a relatively simple method to achieve low voltage ride-through (LVRT) of doubly-fed induction generator (DFIG) based wind turbine. A thyristor controlled voltage regulator (TCVR) is installed in the low-voltage side of the wind farm substation. When voltage dip occurs, the grid-side voltage is reasonably compensated according to the degree it drops to improve the stator voltage of DFIG, thereby reducing the flux changes in amplitude, so that the rotor current is restricted under the limit and at the same time the over-voltage of DC bus during the fault is suppressed. A 5MW DFIG wind power system model with the proposed control strategy is established in PSCAD/EMTDC to simulate the operating characteristics of the wind turbine under severe symmetrical fault to verify the validity of the proposed method. (6 pages)