DSP implementation of the multiple reference frames theory for the diagnosis of stator faults in a DTC induction motor drive

This paper deals with the use of a new diagnostic technique based on the multiple reference frames theory for the diagnosis of stator winding faults in a direct-torque-controlled (DTC) induction motor drive. The theoretical aspects underlying the use of this diagnostic technique are presented but a major emphasis is given to the integration of the diagnostic system into the digital-signal-processor (DSP) board containing the control algorithm. Taking advantage of the sensors already built in the drive for control purposes, it is possible to implement this diagnostic system at no additional cost, thus giving a surplus value to the drive itself. Experimental results show the effectiveness of the proposed technique to diagnose stator faults and demonstrate the possibility of its integration in the DSP board.     

Characterization of coil faults in an axial flux variable reluctance PM motor

Variable-reluctance (VR) and switch-reluctance (SR) motors have been proposed for use in applications requiring a degree of fault tolerance. A range of topologies, of brushless SR and VR permanent-magnet (PM) motors are not susceptible to some types of faults, such as phase-to-phase shorts, and can often continue to function in the presence of other faults. In particular, coil-winding faults in a single stator coil may have relatively little effect on motor performance but may affect overall motor reliability, availability, and longevity. It is important to distinguish between and characterize various winding faults for maintenance and diagnostic purposes. These fault characterization and analysis results are a necessary first step in the process of motor fault detection and diagnosis for this motor topology. This paper examines rotor velocity damping due to stator winding turn-to-turn short faults in a fault-tolerant axial flux VR PM motor. In this type of motor, turn-to-turn shorts, due to insulation failures, have similar I-V characteristics as coil faults resulting from other problems, such as faulty maintenance or damage due to impact. In order to investigate the effects of these coil faults, a prototype axial flux VR PM motor was constructed. The motor was equipped with experimental fault simulation stator windings capable of simulating these and other types of stator winding faults. This paper focuses on two common types of winding faults and their effects on rotor velocity in this type of motor.     

Induction motor stator faults diagnosis by a current Concordia pattern-based fuzzy decision system

This paper deals with the problem of detection and diagnosis of induction motor faults. Using the fuzzy logic strategy, a better understanding of heuristics underlying the motor faults detection and diagnosis process can be achieved. The proposed fuzzy approach is based on the stator current Concordia patterns. Induction motor stator currents are measured, recorded, and used for Concordia patterns computation under different operating conditions, particularly for different load levels. Experimental results are presented in terms of accuracy in the detection of motor faults and knowledge extraction feasibility. The preliminary results show that the proposed fuzzy approach can be used for accurate stator fault diagnosis if the input data are processed in an advantageous way, which is the case of the Concordia patterns.     

Experimental investigation and comparative study of inter-turn 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.     

Comparison of the performance of a linear reluctance oscillatingmotor operating under AC supply with one under DC supply

The performance of the linear reluctance oscillating motor operating under AC and DC supplies is presented. The motor under AC supply must be equipped with a capacitor connected to the stator coil. It operates on the basis of the resonance in stator circuit and is known as a self-oscillating motor. When supplied from a DC source, it must be equipped with a controlled switch connected to the stator circuit. Operating under such conditions it is called a linear switched reluctance oscillating motor. The formulation of the mathematical models of the motor is followed by the simulation results. These are compared to experimental ones, obtained from tests carried out on a real motor. The motor under DC supply demonstrates much higher efficiency, 47%, than under AC supply     

A Reconfigurable Motor for Experimental Emulation of Stator Winding Interturn and Broken Bar Faults in Polyphase Induction Machines

The benefits and drawbacks of a 5-hp reconfigurable induction motor, which was designed for experimental emulation of stator winding interturn and broken rotor bar faults, are presented in this paper. It was perceived that this motor had the potential of quick and easy reconfiguration to produce the desired stator and rotor faults in a variety of different fault combinations. Hence, this motor was anticipated to make a useful test bed for evaluation of the efficacy of existing and new motor fault diagnostics techniques and not the study of insulation failure mechanisms. Accordingly, it was anticipated that this reconfigurable motor would eliminate the need to permanently destroy machine components such as stator windings or rotor bars when acquiring data from a faulty machine for fault diagnostic purposes. Experimental results under healthy and various faulty conditions are presented in this paper, including issues associated with rotor bar-end ring contact resistances that showed the drawbacks of this motor in so far as emulation of rotor bar breakages. However, emulation of stator-turn fault scenarios was successfully accomplished.      

A review of stator fault monitoring techniques of induction motors

Condition monitoring of induction motors is a fast emerging technology for online detection of incipient faults. It avoids unexpected failure of a critical system. Approximately 30-40% of faults of induction motors are stator faults. This work presents a comprehensive review of various stator faults, their causes, detection parameters/techniques, and latest trends in the condition monitoring technology. It is aimed at providing a broad perspective on the status of stator fault monitoring to researchers and application engineers using induction motors. A list of 183 research publications on the subject is appended for quick reference.     

Online rotor mixed fault diagnosis way based on spectrum analysis of instantaneous power in squirrel cage induction motors

Broken rotor bars and eccentricity are common faults in squirrel cage induction motors. These two faults usually occur simultaneously. This paper will deal with this kind of mixed fault. It is well known that the characteristic frequency of broken bars in the stator line current of a squirrel cage induction motor is very near to that of the fundamental component. In the spectrum of the stator line current, the characteristic components related to broken rotor bars are always submerged by the fundamental one, and it is difficult to detect the broken bar fault at an early stage. In our work, instantaneous power of the motor is used as the quantity to be monitored. Theoretical analysis indicates that the spectrum of ac level of the spectrum of the instantaneous power is clear from any component at the fundamental supply frequency, and the fault characteristics can be highlighted, which is effective toward the separation of mixed faults and the quantification of the fault extent. Experimental results have demonstrated the effectiveness of the proposed technique.     

Pattern recognition-a technique for induction machines rotor brokenbar detection

A pattern recognition technique based on Bayes minimum error classifier is developed to detect broken rotor bar faults in induction motors at the steady state. The proposed algorithm uses only stator currents as input without the need for any other variables. Initially, rotor speed is estimated from the stator currents, then appropriate features are extracted. The produced feature vector is normalized and fed to the trained classifier to see if the motor is healthy or has broken bar faults. Only the number of poles and rotor slots are needed as pre-knowledge information. A theoretical approach together with experimental results derived from a 3 hp AC induction motor show the strength of the proposed method. In order to cover many different motor load conditions, data are obtained from 10% to 130% of the rated load for both a healthy induction motor and an induction motor with a rotor having 4 broken bars     

Multiple reference frame analysis of an unsymmetrical inductionmachine

Due to the asymmetry of the stator windings of an unsymmetrical induction motor, the equations which describe this device cannot be expressed in a frame of reference where the state variables are constant in the steady state. This prevents linearization and thereby places a stumbling block in the development of a transfer function which could be used in linear control analysis, as in servo applications. The work presented in this paper provides a means to accomplish this goal. This is achieved by eliminating the position-dependent terms brought about due to asymmetry by recognising a unique property of a combination of reference frames and by employing an averaging procedure. The resulting equations are shown to predict the performance of the unsymmetrical induction motor with the accuracy of the detailed equations. The stage is now set to develop accurate reduced-order models and linear transfer functions for unsymmetrical induction motors     

Mechanical fault detection in a medium-sized induction motor using stator current monitoring

This paper presents the results of an experimental study of the detection of mechanical faults in an induction motor. As is reasonably well known, by means of analysis of combinations of permeance and magneto-motive force (MMF) harmonics, it is possible to predict the frequency of air gap flux density harmonics which occur as a result of certain irregularities in an induction motor. In turn, analysis of flux density harmonics allows the prediction of induced voltages and currents in the stator windings. Reviewing this theory, equations which may aid in the identification of mechanical faults are presented. These equations include both those which indicate eccentric conditions and those which have been suggested to help identify bearing faults. The development of test facility to create eccentricity faults and bearing fault conditions is described. This test facility allows rapid access to the motor bearings, allowing an investigation into the ability to detect faulted bearing conditions using stator current monitoring. Experimental test results are presented, indicating that it may be possible to detect bearing degradation using relatively simple and inexpensive equipment.     

An induction machine model for predicting inverter-machineinteraction

The conventional qd induction motor model typically used in drive simulations is very inaccurate in predicting machine performance, except perhaps for the fundamental component of the current and the average torque near rated operating conditions. Predictions of current and torque ripple are often in error by a factor of two to five. This work sets forth an induction machine model specifically designed for use with inverter models to study machine-inverter interaction. Key features include stator and rotor leakage saturation as a function of current and magnetizing flux, distributed effects in the rotor circuits, and a highly computationally efficient implementation. The model is considerably more accurate than the traditional qd model, particularly in its ability to predict switching frequency phenomena. The predictions of the proposed model are compared with those of the standard qd model and to experimental measurements on a 37 W induction motor drive     

Detection of stator short circuits in VSI-fed brushless DC motors using wavelet transform

The paper presents methodologies to detect and locate short-circuit faults on the stator winding of VSI-fed PM brushless dc motors. Normal performance characteristics of the motor are obtained through a discrete-time lumped-parameter network model. The model is modified to accommodate short-circuit faults in order to simulate faulty operation. Fault signatures are extracted from the waveforms of electromagnetic torque and phase-voltage summation using wavelet transform. Three independent detection techniques are introduced. Experimental measurements agree acceptably with simulation results, and validate the proposed methods. This work sets forth the fundamentals of an automatic fault detector and locator, which can be used in a fault-tolerant drive.     

Machine modeling and universal controller for vector-controlled induction motor drives

Developments of machine model and a universal controller for vector-controlled induction motor drives are presented in this paper. The machine representations associated with vector-control methods referring to various frames, including stator, rotor, and air-gap flux frames, can be derived simply by selecting different state variables; thereby clearly identifying the relationship between machine modeling and vector control. Moreover, a universal vector controller for induction motor drives fed by a voltage-controlled voltage source inverter is presented. It is shown in this paper that various vector controllers, including rotor flux-oriented controller, stator flux-oriented controller and air-gap flux-oriented controller, can be realized by simply changing few parameters. It is demonstrated by experimental results that the developed universal vector controller for various vector-control approaches can be implemented using the same hardware with a minor change to software associated with parameters; and thereby confirming the theoretical analysis.     

On the Choice of Phase-Balancer Capacitance for Induction Motors Fed from Single-Phase Supply

This paper presents analytical evaluation for performance characteristics of a three phase induction motor when fed from a single phase supply. Starting as well as running of such motor are achieved by connecting a capacitor across two of stator phases in a way to act as a phase converter. Symmetrical components concept was employed in the analysis. The influence of capacitor value on motor characteristics is being investigated showing that there exists an optimum value of capacitor for a specific characteristic. Formulas are then derived for calculating these optimum values and recommendations are given for proper choice of capacitor rating and value.     

A new and best approach for early detection of rotor and stator faults in induction motors coupled to variable loads

Today, induction machines are playing, thanks to their robustness, an important role in world industries. Although they are quite reliable, they have become the target of various types of defects. Thus, for a long time, many research laboratories have been focusing their works on the theme of diagnosis in order to find the most efficient technique to predict a fault in an early stage and to avoid an unplanned stopping in the chain of production and costs ensuing. In this paper, an approach called Park’s vector product approach (PVPA) was proposed which was endowed with a dominant sensitivity in the case in which there would be rotor or stator faults. To show its high sensitivity, it was compared with the classical methods such as motor current signature analysis (MCSA) and techniques studied in recent publications such as motor square current signature analysis (MSCSA), Park’s vector square modulus (PVSM) and Park-Hilbert (P-H) (PVSM_P-H). The proposed technique was based on three main steps. First, the three-phase currents of the induction motor led to a Park’s vector. Secondly, the proposed PVPA was calculated to show the distinguishing spectral signatures of each default and specific frequencies. Finally, simulation and experimental results were presented to confirm the theoretical assumptions.     

推进电机分体式安装技术探讨

介绍了船舶推进电机分体进舱安装的工艺过程,以及每个工艺过程,如基座位置的确定,轴承与转子的安装,定转子气隙的调整等,需重点注意的一些问题,为推进电机分体进舱安装提供技术支持.     

转子-定子系统松动-碰摩耦合故障的动态响应分析

建立了考虑定子与基础之间的连接刚度和阻尼(包括定子本身运动)的转子-定子系统发生松动-碰摩时的动力学模型和微分方程，对系统在运行过程中的非线性行为进行了数值仿真分析，发现随着转速的变化过程，此类系统响应主要以拟周期或阵发性分岔进入混沌，而由拟周期或倍周期倒分岔离开混沌。在超临界转速区，系统的响应以混沌和周期k的分频运动为主要运动形式。该结果为转子-定子系统的故障诊断提供了依据和参考。     

Speed control of a three-phase induction motor based on robust optimal preview control theory

A synthesized method for speed control of a three-phase induction motor (IM) based on optimal preview control system theory is implemented in this article. An IM model comprises three-input variables and three-output variables that coincide with the synchronous reference frame that is implemented using the vector method. The input variables of this model are the stator angular frequency and the two components of the stator space voltage vector, whereas the output variables are the rotor angular speed and the two components of the stator space flux linkage. The objective of the synthesized control system is to achieve motor speed control, field orientation control, and constant flux control. A novel error system is derived and introduced into the control law to increase the robustness of the system. The preview feed-forward controller, which includes the desired and disturbance signals, is used to improve the transient response of the system. A space vector pulse-width modulation (PWM) control technique for voltage source-fed IM is prepared for microprocessor-based control. Spectral analysis of the output voltage is evaluated to predict the effect of the proposed space vector modulation technique on the dynamic performance of the IM. The optimal preview controlled system is implemented, and its applicability and robustness are demonstrated by computer simulation and experimental results.