Speed controller design of direct torque control system for induction motors by using adaptive supervisory Fuzzy-CMAC

A model-free approach was used to develop an adaptive supervisory Fuzzy-cerebellar model articulation controller (ASFCMAC) for a direct torque control system for an induction motor without shaft encoder. The two parts of the ASFCMAC are a supervisory controller for limiting tracking error to a bounded range and a Fuzzy-cerebellar model articulation controller subsystem for learning and approximating system dynamics. The ASFCMAC parameters are tuned according to adaptive rules derived from Lyapunov stability theory. Simulations and experimental comparisons with adaptive Fuzzy-cerebellar model articulation controller, adaptive cerebellar model articulation controller, fuzzy logic control, and proportional–integral control show that the proposed ASFCMAC has a superior root mean square error in operation over a wide range of speeds.     

Detection of outer raceway bearing defects in small induction motors using stator current analysis

We investigate the application of induction motor stator current spectral analysis (MCSA) for detection of rolling element bearing damage from the outer raceway. In this work, MCSA and vibration analysis are applied to induction motor to detect outer raceway defects in faulty bearings. Data acquisition, recording, and fast fourier transform (FFT) algorithms are done by using the Lab VIEW programming language. Experimental results verify the relationship between vibration analysis and MCSA, and identify the presence of outer raceway bearing defects in induction machines. This work also indicates that detecting fault frequencies by motor currents is more difficult than detecting them by vibration analysis. The use of intensive resolution FFT is recommended in MCSA for detecting faults easily. Reinstalling a faulty bearing can alter the characteristic frequencies and it is difficult to compare results from different bearings or even from the same bearing in different installations.     

Extraction from field models of the lumped parameters of induction motors

Mathematical background for the definition of the lumped parameters of the equivalent T-diagram of induction motors is described. It is shown how one can systematically extract the lumped parameters from a number of finite element transient simulations.     

Optimisation techniques for a hysteresis current controller to minimise torque ripple in switched reluctance motors

The switched reluctance (SR) motor has many benefits owing to its low cost, simple design, rugged construction and comparatively high torque-to-mass ratio. Unlike DC and induction motors, the SR motor is intended to operate in deep magnetic saturation to increase the output power density. Because of the saturation effect and the variation of magnetic reluctance with respect to rotor position, all the relevant characteristics of the machine are highly non-linear functions of both rotor position and phase current. The ultimate outcome of all these non-linearities is that the generated torque contains significant ripples. The non-linearities in the SR motor have been extensively studied and many control strategies to reduce the generated torque ripples have been proposed in the literature. Modulation of phase current profile for generating torque in the SR motor with minimum ripples was the focus of most of the research. However, the main challenge to minimise the torque ripple is to design a current controller that is able to track the modulated phase current. In this work, new techniques to optimise the widely used hysteresis current controller are studied, and experimental verifications under closed-loop speed control with the modulated reference current data are presented. The experimental results indicate that the torque ripple is reduced to lie within 5% of the desired steady torque using the proposed optimisation techniques.     

High-order terminal sliding mode control for induction motors based on current decoupling

为提高感应电机转速控制系统的性能,提出了速度环、电流环的高阶非奇异终端滑模控制方案.该方案通过设计非奇异终端滑模面来提高系统的响应速度和控制精度;通过设计高阶滑模控制律以直接获得平滑的控制信号,有效削弱常规滑模的抖振现象;对速度环,考虑了系统负载转矩和转动惯量的变化,所设计的高阶滑模控制律使系统具有良好的鲁棒性;对电流环,利用电压补偿实现交、直轴电流完全解耦,提高电流控制器的动态性能.仿真结果表明,该方案有效地消除了常规滑模存在的抖振现象,并且跟踪精度高,对负载扰动及转动惯量变化具有较强的鲁棒性.     

Synthesis study of magnetic torque sensors

There exist numerous solutions to measure the torque applied to a structure or a shaft, and we first present the available devices. They fall into two groups; some measure the torsion angle resulting from the applied torque, others use the shaft material property changes due to the induced stresses, We then present our contribution in this area: a synthesis study of torque sensors with variable-reluctance magnetic circuits excited by permanent magnets or coils. Among these sensors are new structures not only for stationary devices, but also for fully rotating devices. The advantages of structures of these types lie in their great design and implementation simplicity. The structures' study shows how to choose the different parameters of the sensors to meet specifications, It also demonstrates the advantages of some new designs in terms of performance-the ones using “overlapping” teeth for example     

Torque ripple reduction in direct torque controlled five-phase induction motor using modified five-level torque comparator

The five-phase induction motor inherently has the minimal torque ripple. However, when it is controlled by direct torque control (DTC) technique, the torque ripple increases due to the presence of a hysteresis torque comparator. The classical five-level torque comparator is presented in the previous literatures to control the torque ripple. However, this comparator has the drawback of wrong selection of zero voltage vectors inside the inner band on the positive side of the comparator, which enables the torque ripple to increase and dc-link utilization to decrease. In this paper, in order to reduce the torque ripple and to increase the dc-link utilization, a modified five-level torque comparator is proposed, which selects either medium or small voltage vectors instead of zero voltage vectors inside the inner band on the positive side of the comparator. In addition to torque ripple reduction and improvement in dc-link utilization, the proposed comparator significantly improves the quality of phase current. All the available 32 voltage vectors are selected through the proposed five-level torque comparator based on the location of x–y stator flux in order to eliminate the x–y stator flux so as to obtain reduced distortion in the phase current. By employing all the available voltage vectors, the freedom of utilization of all voltage vectors in the five-phase induction motor DTC drive is availed. The proposed five-level torque comparator is compared to its classical five-level counterpart through simulation and experimental results in order to validate the proposed DTC strategy.     

Thermal analysis of induction motors using 3D finite element method

Abstract

To design a reliable and economical induction motor, it is necessary to be able to predict accurately the temperature distribution within the motor. In this paper, a 3D thermal model of an induction motor is presented. Except for providing a more accurate representation of the problem, the proposed model can also reduce computer memory and time. The finite element method (FEM) is used to analyze the three dimensional (3D) heat flow equation which describes the thermal model. Galerkin's procedure is used to derive the element equations and first order tetrahedral elements are used to discretize the field region. Galerkin's time‐stepping scheme is employed to treat time differential terms. Values of surface heat transfer coefficients are obtained from the empirical formula and heat losses are revised by the factory test. Application of the proposed method to the analysis of a 9,000 HP induction motor yields temperature distribution very close to the experimental data.     

Unbalance and harmonics detection in induction motors using an optical fiber sensor

In this work, a new method for the detection of the negative effects of a particular unbalanced voltage and inverter harmonics on the performance of an induction motor using fiber sensors is proposed. Supplying a three-phase induction motor with unbalanced voltages causes an oscillating electromagnetic torque that generates vibrations, increased losses, efficiency reduction, and an extra temperature rise that leads to a reduction on insulation life of the machine. A new in-line fiber etalon accelerometer has been designed to detect these vibrations in the range DC-500 Hz. The in-line fiber etalon scheme used provides high robustness and stability, giving enough sensitivity to monitor the low-frequency and low-amplitude oscillations in the stator of the machine that exist in a voltage unbalance situation. To prove this claim, a 1.5-kW squirrel cage induction motor is analyzed under different unbalance levels. It is shown that a precise unbalance factor can be detected without accessing to the electric part of the machine and an accurate monitoring can be obtained using the high-resolution analysis proposed.     

Analysis of tubular linear induction motors, using the concept of surface impedance

By using the surface-impedance method, equivalent circuit for an axial-flux tubular induction motor is obtained. This circuit is used to determine the performance characteristics of a laboratory model. The calculated results are compared with experimental results. The voltages and currents in the equivalent circuit are related directly to the field quantities within the actual device.     

Design of vibration-insensitive Sagnac fiber-optic current sensors using spun high-birefringence fibers

A novel fiber-optic current sensing element is proposed to enhance sensor performance using spun high-birefringence fibers. Such element includes three fiber sections. Two terminal sections with a varying spin rate along the fiber are utilized to replace the fiber quarter-wave plates, each converting the light polarization state from linear to circular and vice versa. The middle section with a uniform spin rate is utilized as the current sensing fiber that maintains the circular polarization state during the light propagation. The fiber is also wound into a special geometric structure so that the Sagnac phase shift can be inherently eliminated, and the sensing result does not depend on the position of the current conductor. The evolution of the light polarization state was analyzed using coupled-mode theory with different polarization state incidents in the sensing fiber. A sensor scheme based on this type of spun fiber is also proposed.     

Performance calculation for single-sided linear induction motors with a double-layer reaction rail under constant current excitation

A method for computing the performance of a single-sided linear induction motor (SLIM) with a double-layer reaction rail, under constant current excitation, is presented. This method takes into account the reaction of secondary eddy currents on the airgap field, transverse edge and longitudinal end effects, together with skin effect, saturation, nonlinear magnetic permeability, and hysteresis in the solid steel core of a reaction rail. In an equivalent circuit of the machine, the mutual and secondary impedances are found from a solution of the two-dimensional electromagnetic field distribution. Modifying factors account for configurations in which the width of the secondary conductive layer is different from that of the steel core, and in which the thickness of the conductive overhand is different from that over the steel core. Good correlation is obtained between analysis and test results from a large-scale linear induction motor (LIM) at Queen's University. The developed expressions are appropriate for small and large LIM's and may also be used for constant voltage excitation conditions.     

A fast method for determining electrical and mechanical qualitiesof induction motors using a PC-aided detector

A unique computer-aided detector is presented that determines the mechanical and electrical qualities of single-phase and three-phase induction motors. Measurements of voltage, current, power factor, active power, and reactive power as well as evaluations of centrifugal switch and airgap eccentricity, i.e., misalignment between rotor and stator, of induction motors can be rapidly conducted, and test results are available on the screen within a few seconds. The feasibility and usefulness of this detector are impressively demonstrated through application examples     

A weak magnetic field measurement system using micro-fluxgate sensors and delta-sigma interface

This paper presents a weak magnetic field measurement system using micro-fluxgate (FG) sensors and a sensor signal processing technique using the delta-sigma modulation in the negative feedback loop. The feedback of the lowpass filtered bitstream output of a delta-sigma modulator to the magnetic field improves system linearity, hysteresis, and stability. In spite of the fact that the second-order delta-sigma modulator is used, the third-order noise shaping can be obtained in the digital output bit-stream by the use of an integrator in the loop. This improves the SNR of the digital output. The measured noise of the implemented system meets the measured noise of the FG sensing element itself. The weak magnetic field in the range of the Earth's magnetic field is successfully measured. The nonlinearity error is less than 0.4% in the range of /spl plusmn/100 /spl mu/T.     

Improving the stability of amorphous silicon ultraviolet sensors

In this paper we present an improved structure of an amorphous silicon/amorphous silicon carbide ultraviolet sensor, previously presented in literature, whose overall performances have been enhanced by growing a very thin layer of chromium silicide film on the top of the sensor. The sensor is a n-type amorphous silicon/intrinsic amorphous silicon/p-type amorphous silicon carbide stacked structure deposited on a glass substrate. The substrate is covered with a chromium film that acts as back metal contact. The top metal contact is a grid shaped chromium/aluminum/chromium metal stack that allows the incident radiation to reach the active p-type layer.The responses of two sets of sensors fabricated with and without the alloy film under ultraviolet radiation have been studied. The role of the very thin chromium silicide layer is to increase the conductivity of the top surface without attenuating the UV radiation absorbed in the device active layer. The increased top-surface conductivity ensures a better collection of the photogenerated carriers and hides the resistivity variation of the underlying p-doped layer under ultraviolet light caused by dopant activation, leading to a stable and linear behavior. Comparing the photocurrent values obtained on sensors with different area and distance between the grid electrodes, we found that the presence of the chromium silicide film extends the charge collection length by a factor of 10, allowing a better device photoresponse.     

Transient modeling of multiparallel tubular linear induction motors

In this paper, we model single and multiparallel generator driven tubular linear induction motors by the current filament method, in transient and dynamic states. Using a previously written code for transient and dynamic modeling of a single motor, we simulate a sample motor noted in a reference paper and compare the results with those obtained by using our current filament method. This comparison confirms the accuracy of our method. Finally, we model a system of two or more parallel motors and show that it is feasible to achieve greater muzzle velocities by paralleling certain designs of motors.     

Effect of magnet segmentation on the cogging torque in surface-mounted permanent-magnet motors

We present a method that minimizes the cogging torque in rotor surface mounted permanent-magnet motors. The key idea is to set the distribution of the air-gap flux density by segmenting the magnet pole into several elementary magnet blocks. By choosing either the appropriate elementary magnet block span or the relative position of the magnet blocks, the cogging torque may be significantly reduced. Our analytical approach uses Fourier series to predict the cogging torque harmonics, and finite-element computations. Our numerical results confirm the analytical conclusions.     

A new theory of development of force and torque in variable reluctance stepping motors

This paper presents a new theory of force and torque production in doubly slotted magnetic structures encountered in variable reluctance machines. This general theory is applicable to any point on the B-H curve of iron. It is capable of explaining all known phenomena including those for which satisfactory explanations are not available in existing theories. It enables optimization of all dimensions defining the rotor geometry to be carried out. It thus lays a sound theoretical basis for designing variable reluctance machines.     

Calculation and effects of end-ring impedance in cage induction motors

This paper describes a method for calculating the end-ring impedance of a squirrel-cage induction motor using the method of images. The method is verified by using finite-element analysis. A second method is also discussed, although it was found to be too simple to be accurate. The second part of the paper addresses the effect of this impedance variation on the motor performance with particular attention to the starting torque.     

Modelling of squirrel-cage induction motors for electromagnetic transient programs

The authors discuss the modelling of the squirrel-cage induction motor. The experimental measurements on motors of different rated power, 1-90 kW, clearly show that the single-cage model does not fit the torque-speed curve adequately. Consequently, when the speed varies in a wide range, only the double-cage model can fit the curve well with the squirrel-cage induction motor. The equivalence between the two most commonly used double-cage models in the literature is studied, and a method to find the equivalent parameters is developed. In addition, the induction motor modelling in the PSCAD/EMTDC and EMTP-RV simulation programs is examined, and the inaccuracies resulting from the use of manufacturer data are discussed.