Transient harmonic torques in induction machines: measurement and impact on motor performance

This paper focuses on the measurement of transient torques produced by the field harmonics in three phase squirrel cage motors and on the assessment of the operating conditions under which these torques might become significant. The paper presents first a model of the induction machine with any stator and rotor phase number and configuration, fed by arbitrary voltage waveforms and taking into account the space harmonics. Then, very much attention is paid to a reliable model validation against actual transient torques measurements. In this sense, the actual and great difficulties of measuring pulsating electromagnetic torques of several hundreds of Hertz are brought into light, the possible measurement techniques are critically reviewed and the solution chosen is discussed. Once the model accuracy has been experimentally confirmed, it is used to carry out a systematic plan of more than 250 simulations under clearly distinct operating conditions on five different motors. The analysis of these simulations yields a main practical conclusion: field harmonics may have (depending on the motor structure) a significant impact on electromagnetic torque, but only during transients characterized by high instantaneous frequencies of the rotor currents. For low slip transients, their impact is negligible. This conclusion is also theoretically justified in the paper.Echeverria Villar, JA.; Martínez-Román, J.; Serrano Iribarnegaray, L. (2012). Transient harmonic torques in induction machines: measurement and impact on motor performance. Electrical Engineering. 94(2):67-80. doi:10.1007/s00202-011-0216-4S6780942White D, Woodson H (1959) Electromechanical energy conversion. Wiley, LondonTaegen F, Hommes E (1972) Das allgemeine Gleichungssystem des Käfigläufermotors unter Berücksichtigung der Oberfelder. Teil I and II. 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SENSORLESS SPEED ROTOR FLUX ORIENTED CONTROL OF THREE PHASE INDUCTION MOTOR

Sensorless speed rotor flux oriented control of induction motor drives it is known to produce high performance because of decoupling rotor flux and torque producing current components of stator currents. This paper describes a simple and robust sensorles speed rotor flux oriented control system for three phase induction motor drives that it is adequate for high dynamic applications. To control the rotor speed of the induction motor drives, a PI controller is included in the speed control system. A hysteresis current controllers are applied for changing the magnitude and the frequency of the output voltage of the PWM voltage source inverter which fed the induction motor. In order to verify the proposed sensorlees speed control system, the model of the system is implemented in MATLAB Simulink software, which is suitable for testing the dynamic simulation. Simulation results shows that the reference and rotor speed of induction motor are very closed to each-other under step load torque changes

Data-driven online temperature compensation for robust field-oriented torque-controlled induction machines

Squirrel-cage induction machines (IMs) with indirect field-oriented control are widely used in industry and are frequently chosen for their accurate and dynamic torque control. During operation, however, temperature rises leading to changes in machine parameters. The rotor resistance, in particular, alters, affecting the accuracy of the torque control. The authors investigated the effect of a rotor resistance parameter mismatch in the control algorithm on the angular rotor flux misalignment and the subsequent deviation of stator currents and motor torque from their setpoints. Hence, an online, data-driven torque compensation to eliminate the temperature effect is proposed to enable robust torque-controlled IMs. A model-based analysis and experimental mapping of the temperature effect on motor torque is presented. A temperature-torque lookup-table is subsequently implemented within the control algorithm demonstrating the ability to reduce the detrimental effect of temperature on torque control. Experimental results on a 5.5 kW squirrel-cage induction motor show that the proposed data-driven online temperature compensation method is able to reduce torque mismatch when compared to having no temperature compensation. Up to 17% torque mismatch is reduced at nominal torque and even up to 23% at torque setpoints that are lower than 20% of the nominal torque. A limited torque error of <1% remains in a broad operating range

Harmonic current sideband indicators (HCSBIs) for broken bar detection and diagnostics in cage induction motors

Induction motor bar breakages have been increasingly studied in the last decades because of economic interests in developing techniques that permit on-line, non-invasive, early detection of motor faults in power plants. This work is specifically focused on broken bar detection and fault severity assessment in three phase power cage motors fed by non-sinusoidal voltage sources. In this work some new fault indicators for rotor bar breakages detection in squirrel cage induction motors are proposed, mathematically developed and experimentally proved. They are based on the sidebands of phase current upper harmonics, and they are well suited especially for converter-fed induction motors. The ratios I(7-2s)f/I5f and I(5+2s)f/I7f , I(13-2s)f/I11f and I(11+2s)f/I13f are examples of such new indicators, and they are not dependent on load torque and drive inertia, as classical indicators do. Their frequency-dependence has been also examined both theoretically and experimentally, and it was found less remarkable with respect to other indicators. Moreover, their values increase linearly with the quantity of consecutive broken bars, almost for not too much advanced faults; on 4-poles motors they were found quietly like the per-unit number of broken bars (ratio on total bar number). An original formulation is presented for motor mathematical modeling, based on the Generalized Symmetrical Components Theory, for sidebands amplitude computation. A complete motor model (involving all the elementary machine electrical circuits, as stator belts and rotor mesh loops) has been used for computer simulations; the same model was then transformed by using some complex Fortescue’s matrices to obtain a steady-state linear solution, solvable for stator and rotor currents, in healthy and faulty conditions. By exploiting the model, the formal definition of a set of new broken bar indicators was finally obtained. Machine simulations carried out by running the complete numerical model confirmed the accuracy of the model, and the theoretical previsions. Experimental work was performed by using a square-wave inverter-fed motor with an appositely prepared cage, for easy testing with increasing number of broken bars and without motor dismounting. Moreover, extensive experimentation was carried out on three industrial motors with different power and poles number, with increasing load, frequency and fault gravity for methodology validation. Finally, the ideas exposed in this work led to a patent application, owned by the University of Rome “Sapienza”

Estimation of rotor flux of an induction machine

The objective of this dissertation is to estimate rotor flux of an IM. Some of the material is focused on the functional block of the IM i.e. Torque estimator, Speed estimator etc. while a subsequent part deals with estimation of rotor flux. The dissertation is organized as follows:Chapter 1 describes background information of the machines then it focuses on the methodology how on to approach the task on a particular time with the help of Gantt chart.Chapter 2 presents the basic principals of rotating magnetic field of the IM and asserts brief overview of the AC machines. Later it talks about different kinds of IM rotors suggesting which one is good. It is crucial to start with good and appropriate reviews which were verified by numerous journals. Literature review is presented by analysing the previous work. (Busawan et al., 2001) summarises that a nonlinear observers for the estimation of the rotor flux and the load torque in an induction motor. The observers are designed on the basis of the standard alpha - beta Park's model. Finally, fuzzy logic is mentioned in more detailed way and Membership functions were also discussedChapter 3 explains the dynamic model of induction machine plant and the model was presented. Then the model is analysed, developed in MATLAB-SIMULINK which was discussed in Chapter 4. By considering following assumptions, dynamic model is implemented i.e. it should be symmetrical two-pole, three phase windings. Slotting effects are neglected, Permeability of the iron part is infinite, and iron losses are neglected. Dynamic d-q model and Axes transformation is implemented on stationary reference frame (a-b-c). Lastly torque equation is derived.Chapter 4 is the heart of this project by scrutinizing the model thoroughly and by introducing fuzzy controller logic using MATLAB-SIMULINK; simulations are performed to estimate the functional block such as torque, speed, flux, resistance with and without fuzzy logic. Results were obtained for different blocks and the m-file, DTC, Flux table were obtained and presented in the Appendixes.Chapter 5 concludes the simulation results and concentrates mainly on the future direction what more can be done to improve the platform in a more efficient manner

Motor generator dynamometer setup

The motor-generator set is widely used in the industry for converting large amounts of power energy to a different form of energy although the topic for this project motor-generator is smaller than usually utilized by an industrial company. The primary purpose of this small version motor-generator is for learning tool used by students associated with Electrical Power Engineering or Industrial Computer System Engineering at Murdoch University. The equipment is located in 1.003 Pilot Plant Engineering & Energy Building and was used in previous years by students at Murdoch University. The fundamental aim of the project is to get the apparatus operating correctly and establish accurate communication and control. Investigate the effects of Variable Speed Drive on the motor, the effects of rotor speed and loads on the generator. To design and implement a working communication and control program in the system using LabVIEW software, it should display the following outputs; Field Voltage, Armature Voltage, Current, Power, Synchronous Speed of Motor, Rotor Speed, Force, and Torque. It will be discussed in this report the fundamentals of motor-generator, National Instrument Data Acquisition card, and the LabVIEW software that being used and also the different components used as communication for the motor-generator. The major equipment of the system that will investigate are the following; Variable Speed Drive (VSD), Induction Motor, DC Generator, and the NI DAQ card. With understanding these pieces of equipment, it would determine accurate data information in the outputs. Allen Bradley variable speed drive powered and control the induction motor’s speed, while the National Instrument Data Acquisition card receives the systems information and addresses the controls. The four-kilowatt three-phase induction motor with 415 Voltage and 7.7 Amps which runs at 1455 revolution per minute. The DC generator converts mechanical energy into electrical energy and produces the measured DC voltage output with a variable load bank. The software control for this project is LabVIEW, which reads and writes to different components of the project through NI 6013, 50 pin DAQ card. To ensure the implementation of the communication and control program, it was run with many trials that produced accurate results. The output results of Voltage, Current and Power are displayed in the waveform were expected, the Strain Gauge that measured force were also shown as well as the torque concerning the level arm of the generator. The rotor speed was calculated based on the synchronous speed and slip of the motor and not measured by a proximity sensor. The calculated values of rotor speed were compared to the tachometers measured value

Estimating power factor of induction motors using regression technique

Induction motors are one of the largest power consumption in electrical systems. Since induction motors are inductive loads, they produce a lot of power quality issue in the electrical systems. Solving the power quality problem, monitoring power factor of induction motors is important because at no load or light load condition power factor is low and consequently low power factor not only provide a penalty charge, but also generates a huge current and losses in the grid systems. To measure the power factor, zero crossing and instantaneous power methods can be used. Both methods require motor voltage and current waveforms at operating times. Those methods may have a huge cost in terms of requiring the motor to be out of service for connecting devices. In this research, regression analysis will be applied to estimate the power factor of induction motor at any loading condition. The results of the proposed method will be compared with the measured power factor of induction motor in order to substantiate the feasibility of the proposed method

Induction motor’s rotor slot variation measurement using logistic regression

Rotor slots in induction motor expand due to thermal imbalance and create magnetic stress. Magnetic stress is a force that develops on the laminated surface of the rotor due to the curving or stretching magnetic flux. Traditional motor fault detection methods never measure magnetic stress on the rotor; a significant problem frequently arises in the motor. Magnetic stress is proportional to slot size variations in the rotor. High slot size variations on the laminated surface of the rotor lead to more curving and stretching magnetic flux and damage the rotor and stator, reducing their efficiency and induce harmonics. In this paper, the Average rotor Slot Size Variation (ASSV) in the rotor is predicted during the running condition of the motor through logistic regression. Logistic regression predicts ASSV by multimodal sensor signal sub-band energy values and measures rotor slot sizes from microscope images. Multimodal sensor signal is obtained from various sensors, such as vibration, temperature, current and Giant Magneto Resistance (GMR). Signal sub-band energy is obtained from Over complete Rational-Dilation Wavelet Transform (ORaDWT). From experimental results, ASSV is more than 75% from standard size, damaging the rotor and stator. The accuracy of ASSV prediction is about 92%