Calculation of torque and speed of induction machines under rotor winding faults

Based on the multi-loop method, the rotating torque and speed of theinduction machine are analyzed. The fluctuating components of the torque and speed caused by rotorwinding faults are studied. The models for calculating the fluctuating components are put forward.Simulation and computation results show that the rotor winding faults will cause electromagnetictorque and rotating speed to fluctuate; and fluctuating frequencies are the same and their magnitudewill increase with the rise of the severity of the faults. The load inertia affects the torque andspeed fluctuation, with the increase of inertia, the fluctuation of the torque will rise, while thecorresponding speed fluctuation will obviously decline.

Optimization of linear induction machines based on a novel adaptive genetic algorithm

In order to improve the thrust-power ratio index of the linear induction motor（LIM）, a novel adaptive genetic algorithm （NAGA） is proposed for the design optimization of the LIM. A good-point set theory that helps to produce a uniform initial population is used to enhance the optimization efficiency of the genetic algorithm. The crossover and mutation probabilities are improved by using the function of sigmoid and they can be adjusted nonlinearly between average fitness and maximal fitness with individual fitness. Based on the analyses of different structures between the LIM and the rotary induction motor （RIM） and referring to the analysis method of the RIM, the steady-state characteristics of the LIM that considers the end effects of the LIM is calculated and the optimal design model of the thrust-power ratio index is also presented. Through the comparison between the optimal scheme and the old scheme, the thrust-power ratio index of the LIM is obviously increased and the validity of the NAGA is proved.

A Novel Fuzzy Direct Torque Control System for Three-level Inverter-fed Induction Machine

Diode clamped multi-level inverter （DCMLI） has a wide application prospect in high-voltage and adjustable speed drive systems due to its low stress on switching devices, low harmonic output, and simple structure. However, the problem of complexity of selecting vectors and capacitor voltage unbalance needs to be solved when the algorithm of direct torque control （DTC） is implemented on DCMLI. In this paper, a fuzzy DTC system of an induction machine fed by a three-level neutral-point-clamped （NPC） inverter is proposed. After introducing fuzzy logic, optimal selecting switching state is realized by applying various strategies which can distinguish the grade of the errors of stator flux linkage, torque, the neutral-point potential, and the position of stator flux linkage. Consequently, the neutral-point potential unbalance, the dr/dr of output voltage and the switching loss are restrained effectively, and desirable dynamic and steady-state performances of induction machines can be obtained for the DTC scheme. A design method of the fuzzy controller is introduced in detail, and the relevant simulation and experimental results have verified the feasibility of the proposed control algorithm.

NOVEL SENSORLESS VECTOR CONTROL SYSTEM OF INDUCTION MACHINE BASED ON FLUX OBSERVER IN FIELD WEAKENING

A speed-sensorless vector control system for induction machines （IMs）is presented, According to the vector control theory of IMs, the rotor flux is estimated based on a flux observer,and the speed is estimated through the method of q-axis rotor flux converging on zero with proportional integral regulator, A 0.75 kW,50 Hz,two-pole induction machine was used in the simulation and experimental verification, The simulation model was constructed in Matlab. A series of tests were performed in the field weakening region, for both no-load and loaded operation. The estimated speed tracks the actual speed well in the based speed region and field weakening region （ 1 per unit value to 4 per unit value）. The small estimation error of residual speed is due to the existence of slip.

Parameter Deviation Effect Study of the Power Generation Unit on a Doubly-Fed Induction Machine-based Shipboard Propulsion System

To lower the difficulty of fault protection,a doubly-fed induction machine based shipboard propulsion system(DFIM-SPS)that is partially power decoupled is presented.In such an intrinsically safe SPS architecture,a synchronous generator(SG)is employed for power generation,and the accuracy of the parameters of power generation unit(PGU)plays an important role in SPS stable operation.In this paper,the PGU parameter deviations are studied to evaluate the effects on system performance.The models of salient-pole SG,type DC1A excitation system(EXS)and DFIM are illustrated first.Besides,the corresponding control scheme is explained.For the 16 important parameters of PGU,up to 40%of parameter deviations are applied to implement parameter sensitivity analysis.Then,simulation studies are carried out to evaluate the parameter deviation effects on system performance in detail.By defining three parameter deviation effect indicators(PDEIs),the effects on the PGU output variables,which are the terminal voltage and output active power,are studied.Moreover,the increasing rates of PDEIs with different degrees of parameter deviations for the key parameters are analyzed.Furthermore,the overall system performance is investigated for the two most influential PGU parameters.This paper provides some vital clues on SG and EXS parameter identification for DFIM-SPS.

Brushless Doubly-Fed Induction Machine as a Variable Frequency Transformer

VFT （variable frequency transformer） has been recently used as art alternative to HVDC （high voltage direct current） 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 DFIM （doubly-fed induction machine） 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 BDFM （brushless doubly-fed machine） 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 BVFT （brushless variable frequency transformer）. A prototype machine is designed and simulated to verify the system validity.

The Effect of Clutch Wobbling and Mixed Eccentricity on Induction Machine Stator Currents

Faults and failures of induction machines can indeed lead to excessive costs, hence, there is a strong demand in the industry for adopting diagnosis techniques to assess and evaluate current condition of electrical machines. Eccentricity related faults as well as clutch wobbling constitute major portions of the faults related to induction motors. This paper presents the effect of clutch wobbling and mixed eccentricity on induction machine stator currents and the possibility of distinguishing between each ailment via comparing the abnormal harmonics contained in stator current spectrums in each case. In this paper, the current spectrum of a four pole-pairs, 550 kW, induction machine were calculated for the cases of full symmetry, clutch wobbling, and mixed eccentricity. The calculations involve integration of 93 electrical plus four mechanical ordinary differential equations. Electrical equations account for variable inductances affected by slotting and eccentricities. The calculations were followed by Fourier analysis of the stator currents. Zooms of the current spectrums, around the 50 Hz fundamental harmonic as well as of the main slot harmonic zone, of both calculated and measured currents are included. The spectrums presented in this paper rely on calculations that are performed with dedicated software which is owned by AGH University of Science and Technology.

Multi-area Frequency-constrained Unit Commitment for Power Systems with High Penetration of Renewable Energy Sources and Induction Machine Load

The increasing penetration of renewable energy sources(RESs)brings great challenges to the frequency security of power systems.The traditional frequency-constrained unit commitment(FCUC)analyzes frequency by simplifying the average system frequency and ignoring numerous induction machines(IMs)in load,which may underestimate the risk and increase the operational cost.In this paper,we consider a multiarea frequency response(MAFR)model to capture the frequency dynamics in the unit scheduling problem,in which regional frequency security and the inertia of IM load are modeled with high-dimension differential algebraic equations.A multi-area FCUC(MFCUC)is formulated as mixed-integer nonlinear programming(MINLP)on the basis of the MAFR model.Then,we develop a multi-direction decomposition algorithm to solve the MFCUC efficiently.The original MINLP is decomposed into a master problem and subproblems.The subproblems check the nonlinear frequency dynamics and generate linear optimization cuts for the master problem to improve the frequency security in its optimal solution.Case studies on the modified IEEE 39-bus system and IEEE 118-bus system show a great reduction in operational costs.Moreover,simulation results verify the ability of the proposed MAFR model to reflect regional frequency security and the available inertia of IMs in unit scheduling.

Quantitative Comparison of Electromagnetic Performance of Electrical Machines for HEVs/EVs

In this paper,various types of sinusoidal-fed electrical machines,i.e.induction machines(IMs),permanent magnet(PM)machines,synchronous reluctance machines,variable flux machines,wound field machines,are comprehensively reviewed in terms of basic features,merits and demerits,and compared for HEV/EV traction applications.Their latest developments are highlighted while their electromagnetic performance are quantitatively compared based on the same specification as the Prius 2010 interior PM(IPM)machine,including the torque/power-speed characteristics,power factor,efficiency map,and drive cycle based overall efficiency.It is found that PM-assisted synchronous reluctance machines are the most promising alternatives to IPM machines with lower cost and potentially higher overall efficiency.Although IMs are cheaper and have better overload capability,they exhibit lower efficiency and power factor.Other electrical machines,such as synchronous reluctance machines,wound field machines,as well as many other newly developed machines,are currently less attractive due to lower torque density and efficiency.

Recent Development of Linear Machine Topologies and Applications

Linear machines(LMs)produce linear motion without any intermediate transmission mechanisms,thus the whole electromechanical system has simple structure and its efficiency is high.Because of such merits,linear machines have been studied for a long time and rapidly developed in recent years.Due to the characteristic of open structure,linear machines have more diversity than rotary machines in terms of machine topologies.Accounting for the wide applications of linear machines,e.g.Maglev train,precision machine tools,semiconductor processing device,automatic equipment,logistic transport line,ropeless lifter,compressor,etc.,this paper reviews the most applied linear machines including machine topologies,operating principle and features.In addition,the influence of end effects and the corresponding reduction methods are also summarized.Finally,several commercial applications are exemplified.

Fuzzy-second order sliding mode control optimized by genetic algorithm applied in direct torque control of dual star induction motor

The direct torque control of the dual star induction motor(DTC-DSIM) using conventional PI controllers is characterized by unsatisfactory performance, such as high ripples of torque and flux, and sensitivity to parametric variations. Among the most evoked control strategies adopted in this field to overcome these drawbacks presented in classical drive, it is worth mentioning the use of the second order sliding mode control(SOSMC) based on the super twisting algorithm(STA) combined with the fuzzy logic control(FSOSMC). In order to realize the optimal control performance, the FSOSMC parameters are adjusted using an optimization algorithm based on the genetic algorithm(GA). The performances of the envisaged control scheme, called G-FSOSMC, are investigated against G-SOSMC, G-PI and BBO-FSOSMC algorithms. The proposed controller scheme is efficient in reducing the torque and flux ripples, and successfully suppresses chattering. The effects of parametric uncertainties do not affect system performance.

Feature extraction of induction motor stator fault based on particle swarm optimization and wavelet packet

To effectively extract the interturn short circuit fault features of induction motor from stator current signal, a novel feature extraction method based on the bare-bones particle swarm optimization （BBPSO） algorithm and wavelet packet was proposed. First, according to the maximum inner product between the current signal and the cosine basis functions, this method could precisely estimate the waveform parameters of the fundamental component using the powerful global search capability of the BBPSO, which can eliminate the fundamental component and not affect other harmonic components. Then, the harmonic components of residual current signal were decomposed to a series of frequency bands by wavelet packet to extract the interturn circuit fault features of the induction motor. Finally, the results of simulation and laboratory tests demonstrated the effectiveness of the proposed method.

Exponential response electrical pole-changing method for a five-phase induction machine with a current sliding mode control strategy

Electrical pole-changing technology leads to torque ripple and speed fluctuation despite broadening the constant power speed range of the multiphase induction machine （IM） system. To reduce the torque ripple and speed fluctuation of the machine, we investigate an exponential response electrical pole-changing method for five-phase IM with a current sliding-mode control strategy. This control strategy employs the dual-plane （dr-q1 and d2-q2） vector control method, which allows the IM to operate under different pole modes. Current sliding-mode controllers are applied instead of conventional proportional integral （PI） controllers to adjust the current vectors, and exponential current response achieves a smooth transition between the d1-q1 and d2-q2 planes. Compared with the step response pole-changing with PI control method, the proposed pole-changing method greatly reduces the torque ripple and speed fluctuation of the IM during the pole-changing process. Experimental results verify the ex- ceptional performance of the proposed electrical pole-changing strategy.

Implementation of Direct Torque Control Scheme for Induction Machines with Variable Structure Controllers

A torque control scheme for high-performance induction machine drives was developed to overcome some disadvantages of direct torque control （DTC）. In the improved DTC method, the stator flux and the torque controllers use variable-structure control theory which does not require information about the rotor speed. Space vector modulation is applied to the voltage source inverter to reduce the torque, stator flux, and current ripples. The digital signal processor-based implementation is described in detail. The experimental results show that the system has good torque and stator flux response with small ripples.

Experimental investigation and comparative study of interturn short-circuits and unbalanced voltage supply in induction machines

A transient model for an induction machine with stator winding turn faults on a single phase is derived using reference frame transformation theory. The negative sequence component and the 3rd harmonic are often considered as accurate indicators. However, small unbalance in the supply voltage and/or in the machine structure that exists in any real system engenders the same harmonics components. In this case, it is too difficult to distinguish between the current harmonics due to the supply voltage and those originated by inter-turn short- circuit faults. For that, to have the correct diagnosis and to increase the sensitivity and the reliability of the diagnostic system, it is crucial to provide the relationship between the inter-turn short-circuits in the stator winding and the supply voltage imbalance through an accurate mathematical model and via a series of experimental essays.

Modified sensorless vector control system of IM based on flux observer

This paper presents a speed sensorless vector control system for induction machine (IM),which is based on a flux observer. According to vector control theory of IM,the q-axis rotor flux converging on zero is utilized for speed estimation. Additionally this system solved the online identification of stator resistance by d-axis flux error. The advantages of the proposed system are simplicity and avoidance of the problems caused by only using a voltage model. The effectiveness of the proposed system has been verified by simulation and experimentation.

A New Hybrid Model Rotor Flux Observer and Its Application

A new hybrid model rotor flux observer, based on a new voltage model, is presented. In the first place, the voltage model of an induction machine was constructed by using the modeling method discussed in this paper and then the current model using a flux feedback was adopted in this flux observer. Secondly, the two models were com- bined via a filter and then the rotor flux observer was established. In the M-T synchronous coordinate, the observer was analyzed theoretically and several important functions were derived. A comparison between the observer and the traditional models was made using Matlab software. The simulation results show that the observer model had a better performance than the traditional model.

Modern improvement techniques of direct torque control for induction motor drives - a review

Conventional direct torque control (DTC) is one of the excellent control strategies available to control the torque of the induction machine (IM). However, the low switching frequency of the DTC causes high ripples in the flux and torque that leads to an acoustic noise which degrades the control performances, especially at low speeds. Many direct torque control techniques were appeared to remedy these problems by focusing specifically on the torque and flux. In this paper, a state of the art review of various modern techniques for improving the performance of DTC control is presented. The objective is to make a critical analysis of these methods in terms of ripples reduction, tracking speed, switching loss, algorithm complexity and parameter sensitivity. Further, it is envisaged that the information presented in this review paper will be a valuable gathering of information for academic and industrial researchers.

Reduction Algorithms Based on Discernibility Matrix:The Ordered Attributes Method

In this paper, we present reduction algorithms based on the principle of Skowron's discernibility matrix - the ordered attributes method. The completeness of the algorithms for Pawlak reduct and the uniqueness for a given order of the attributes are proved. Since a discernibility matrix requires the size of the memory of U2, U is a universe of objects, it would be impossible to apply these algorithms directly to a massive object set. In order to solve the problem, a so-called quasi-discernibility matrix and two reduction algorithms are proposed. Although the proposed algorithms are incomplete for Pawlak reduct, their opimal paradigms ensure the completeness as long as they satisfy some conditions. Finally we consider the problem on the reduction of distributive object sets.

Impact of increased wind power generation on subsynchronous resonance of turbine-generator units

With more and more wind power generation integrated into power grids to replace the conventional turbine-generator (T-G) units,how the subsynchronous resonance (SSR) of conventional T-G units is affected becomes an important technical issue.In this paper,a group of T-G units are interconnected with a series compensated transmission line,and some units are substituted by a nearby DFIG-based wind farm (WF).Under such circumstances,the SSR of power systems would change accordingly.This paper establishes the mathematical model to analyze the torsional interaction (TI) and the induction generator effect of the T-G units.Both eigenvalue analysis and time domain simulations demonstrate the impact of DFIG-based WF on SSR of power systems and how the control parameters of wind farms can affect the SSR.