ANFIS-based diagnosis and location of stator interturn faults in PM brushless DC motors

An automatic scheme for fault diagnosis and location of stator-winding interturns in permanent-magnet brushless dc motors is presented. System performances under healthy and faulty operation are obtained via a discrete-time model. Waveform of the electromagnetic torque is monitored and processed using discrete Fourier transform and short-time Fourier transform to derive proper diagnostic indices. Two adaptive neuro-fuzzy inference systems (ANFIS) are developed to automate the fault diagnosis process. Test results show an acceptable performance for ANFIS in detecting the fault.     

Automatic diagnosis and location of open-switch fault in brushless DC motor drives using wavelets and neuro-fuzzy systems

The faulty performance of permanent-magnet (PM) brushless dc motor drives is studied under open-switch conditions. The wavelet transform is used to extract diagnostic indices from the current waveform of the motor dc link. An intelligent agent based on adaptive neuro-fuzzy inference systems (ANFIS) is developed to automate the fault identification and location process. ANFIS is trained offline using simulation results under various healthy and faulty conditions obtained from a lumped-parameter, network model. ANFIS testing shows that the system could not only detect the open-switch fault, but also identify the faulty switch. Good agreement between simulation results and measured waveforms confirms the effectiveness of the proposed methodology.     

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.     

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.     

Analytical calculation of air-gap magnetic field distribution and instantaneous characteristics of brushless DC motors

This paper derives the relative air-gap-specific permeance distribution function by Schwarz-Christoffel transformation, considering the effect of slotting. Neglecting the iron saturation, and employing the analytical algorithm for partial differential equations, efficient and effective analytical calculations of no-load air-gap magnetic field distribution, armature field distribution, and phase electromotive force (EMF), are demonstrated, considering the stator slots. Subsequently, based on the main circuit topology of a brushless DC motor (BLDCM), the field-circuit coupling model is constructed for the motor, and then the phase current waveforms and load air-gap magnetic field distribution at any time are determined. Consequently, the instantaneous electromagnetic torque is computed, which underpins the quantitative analysis of torque ripple and the pulsation induced by commutation. Hence, the present work paves the way to precise prediction of the motor's performance and acoustic noise. It is a powerful tool for the design of surface permanent magnet brushless DC motors.     

Analysis of torque developed in axial flux, single-phase brushless DC motor with salient-pole stator

An analysis of the torque developed by a single-phase disc brushless permanent magnet motor with salient-pole stator is presented. The machine represents a new family of brushless disc motors with the starting torque issue appearing to be most challenging. To produce a starting torque, the permanent magnets on one of the rotor discs are distributed nonuniformly. However, this significantly distorts a shape of the cogging torque versus rotational angle characteristic which, in turn, affects a waveform of the overall torque. A three-dimensional (3-D) finite-element model is used for the purpose of determining of angular variations of the torque developed by the motor. To find how the torque varies with time, a model of the source-inverter-motor circuit is developed. A simulation study on an influence of the commutation angle on the electromagnetic torque is also a subject of this paper. The results obtained show that the motor performance can be improved by a proper selection of the current commutation angle to reach the maximum efficiency. The simulation results are in good agreement with measurements obtained from a prototype motor.     

Analyses and compensation of rotor position detection error in sensorless PM brushless DC motor drives

In a permanent-magnet (PM) brushless DC motor, the waveform of back electromotive force (EMF) is related to the rotor position; hence, the back EMF can be used for position sensorless control. However, in practical implementation, the terminal voltage or phase voltage is used instead, as the back EMF is difficult to be sensed directly. Thus, detection error of the rotor position can occur. This paper documents the calculations and analyses on the detection error and the motor commutation angle, and presents an error compensation circuit to ensure proper commutation. Finite-element field simulation and experimental results are also given to verify the calculations as well as the compensation circuit.     

Three dimensional magnetic field computation by a coupledvector-scalar potential method in brushless DC motors with skewedpermanent magnet mounts-the formulation and FE grids

A three dimensional finite element (3D-FE) method for the computation of global distributions of 3D magnetic fields in electric machines containing permanent magnets is presented. The formulation of this 3D-FE method including 3D permanent magnet modeling, which is based on a coupled magnetic vector potential-magnetic scalar potential (CMVP-MSP) approach, is given. The development of the necessary 3D-FE grids and algorithms for the application of the method to an example brushless DC motor, whose field is three dimensional due to the skewed permanent magnet mounts on its rotor, is also given here. A complete set of results of application of the method to the computation of the global 3D field distributions and associated motor parameters under no-load and load conditions are detailed in a companion paper     

Three dimensional magnetic field computation by a coupledvector-scalar potential method in brushless DC motors with skewedpermanent magnet mounts-the no-load and load results

The coupled magnetic vector potential-magnetic scalar potential (CMVP-MSP) method of computation of 3D magnetic fields by finite elements (3D-FE) is applied here to a brushless DC motor with skewed permanent magnet mounts on its rotor. Results of the CMVP-MSP and 3D-FE computation of the magnetic field and associated motor parameters (EMFs and armature inductances) are detailed in this paper. These results demonstrate vividly the three dimensional nature of the computed flux distributions, caused by the torque ripple reduction design employing skewed magnet mounts on the rotor. Experimental evidence supporting the validity of the BD-FE field computations, through comparison between computed and measured armature EMF waveforms is also provided in this paper     

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.     

A thermometric approach to the determination of iron losses insingle phase induction motors

This contribution describes a novel technique for evaluating the iron loss density distribution in a single phase induction motor using the temperature time method. This is achieved by measuring the temperature gradient which exists at any point within the machine when it is isolated from the supply. This method was used when the motor was lightly loaded. The measurements were carried out on a 200 W, 220 V, 4-pole, 1.6-A single phase induction motor     

Method for in-field evaluation of the stator winding connection of three-phase induction motors to maximize efficiency and power factor

The performance of the oversized three-phase induction motors can be improved, both in terms of efficiency and power factor, with the proper change of the stator winding connection, which can be delta or star, as a function of their load. A practical method is proposed to quickly and easily evaluate which stator winding connection is more appropriate for the actual motor load profile, in order to increase the motor efficiency and power factor. This new method is suitable for in-field evaluation, because it requires only the use of inexpensive equipment and has enough accuracy to allow a proper decision to be made. The automatic change of the stator winding connection, as a function of the motor line current, is also analyzed. When properly applied, these methods can lead to the improvement of the efficiency and power factor of permanently oversized motors, motors with a load variation between low load and near full load during their duty cycle, and/or motors driving high-inertia, low duty cycle loads. The proposed methods are particularly suitable to industrial plants where typically many electric motor systems are oversized and/or can have a wide load variation. In these conditions, the active and reactive electrical energy bill can be significantly reduced.     

Improved transient simulation of salient-pole synchronous generators with internal and ground faults in the stator winding

An improved model for simulating the transient behavior of salient-pole synchronous generators with internal and ground faults in the stator winding is established using the multi-loop circuit method. The model caters for faults under different ground conditions for the neutral, and accounts for the distributed capacitances of the windings to ground. Predictions from the model are validated by experiments, and it is shown that the model accurately predicts the voltage and current waveforms under fault conditions. Hence, it can be used to analyze important features of faults and to design appropriate protection schemes.     

Detection and location of interturn short circuits in the statorwindings of operating motors

One major cause of motor failures is breakdown of the turn insulation leading to puncture of the groundwall. Early detection of interturn shorts during motor operation would eliminate consequential damage to adjacent coils and the stator core reducing repair costs and motor outage time. In addition to the benefits gained from early detection of turn insulation breakdown, significant advantages would accrue by locating the faulted coil within the stator winding. Fault location would not only increase the speed of the repair, but would also permit more optimal scheduling of the repair outage. This work was successful in practically implementing a theory to predict changes in the axial leakage flux resulting from stator winding interturn shorts and in developing an algorithm to locate the position of the faulted coil. An experimental setup consisting of a 200 hp motor loaded by a generator was used to validate this theory. Suitable transducers were developed and installed on this motor. Measurement using this experimental configuration clearly validated the theoretical model. On the basis of this experimental work an instrument to continuously monitor for shorted turns is under development     

The available matching of solar arrays to DC motors having both constant and series-excited field components

This paper presents a procedure for increasing the daily output mechanical energy supplied by DC motors directly connected to solar cell arrays (SCA). The technique is based on the use of DC motors with two components of magnetic field: a constant component that can be provided by a permanent magnet (or a separately excited winding) and a second one produced by a series field winding. It will be shown that through properly selecting the parameters of the motor's magnetic circuit, (i.e., the value of the constant field and the mutual inductance as well as their relative directions), an improved matching between the PV-array and the dc motor can be achieved. Based on assessing and minimizing an expression used to quantify the power mismatch between the SCA and the dc motor, the optimal parameters will be identified. A comparison will then be made between this suggested motor design and tooth the separately excited and series motors.     

A novel exact and universal approach for calculating the differential leakage related to harmonic waves in AC electric motors

In this paper, the distribution pattern of harmonic waves in AC electric motors is investigated. On the basis of this, a novel exact and universal approach for calculating differential leakage related to the harmonic waves was developed. This approach applies to any AC electric motor, regardless of winding type, single-phase or three-phase, regular or nonregular, integral-slot or fractional-slot, symmetrical or asymmetrical. Since this novel approach substitutes the approximation method adopted by conventional approaches with an exact one, it distinguishes itself by offering precise results, general applicability, and fast calculation.     

Advanced analytics for detection and diagnosis of false alarms and faults: A real case study

Onshore and offshore wind farms require a high level of advanced maintenance. Supervisory control and data acquisition (SCADA) and condition monitoring systems are now being employed, generating large amounts of data. They require robust and flexible approaches to convert dataset into useful information. This paper presents a novel approach based on the correlations of SCADA variables to detect and identify faults and false alarms in wind turbines. A correlation matrix between all the SCADA variables is used for pattern recognition. A new method based on curve fittings is employed for detecting false alarms and abnormal behaviours or faults in the components. The study is done in a real case study, validated with false alarms.     

A new approach to determine transient generator winding and dampercurrents in case of internal and external faults and abnormal operation.III. Results

For pt.II see IEEE Winter Meeting, New Orleans, LA, 1986. A novel method for analyzing the steady-state and transient currents in the stator, rotor, and damper windings of a large generator is discussed, and the application of the method to five classes of problems of practical importance is described. These are (1) internal phase-to-phase fault in a two-circuit machine; (2) 180° out-of-phase synchronization; (3) three-phase short circuit at generator terminals; (4) clearing of a three-phase system fault; and (5) unbalanced steady-state negative phase sequence load of 6%. The authors show the individual damper bar currents and energies or electric power loadings for these cases and, for one example, the time variations of stator and damper winding currents. The investigation was conducted on a standard two-pole generator that was designed for 60 Hz operation and has a rating of 700 MW     

A new method to approximate stator transients of synchronousmachines in power system simulation

This paper presents a new method to approximate the effects of stator transients of synchronous machines in power system transient stability simulations during unsymmetrical faults. This method can approximate the DC offset currents which arise from the stator and network transients during faults. However, the method is based on the traditional model with stator and network transients neglected     

直流输电的优点及交-直流改造的节能效果

介绍了高压直流输电提高传输能力,节能降耗的优点,并相应叙述了高压交流输电线路改造为高压直流输电线路的做法和应考虑的问题。