Epaminondas D. Mitronikas

Asynchronous Machine Rotor Fault Diagnosis Technique Using Complex Wavelets

This paper introduces a novel approach for the detection of rotor faults in asynchronous machines, based on wavelet analysis of the stator phase current. To be more specific, the measured stator phase current is filtered through a complex wavelet. Theoretical analysis validates that the spectrum of the modulus of the result of the filtering is free from the fundamental supply frequency component, and the fault characteristics can be highlighted. This is advantageous, especially if the induction machine operates at low slip values, where the characteristic frequency components of the rotor fault are very close to the fundamental frequency component. At the same time, by matching the wavelet function to the frequencies of the faulty components, a narrow bandpass filter at the frequency region of the fault characteristic spectral components is obtained. Furthermore, in the context of this paper, features extracted using the proposed technique are used as input to a support vector machine classifier that is employed for the detection of the rotor fault. Simulation and experimental results demonstrate the effectiveness of the proposed technique.

A new stator resistance tuning method for stator-flux-oriented vector-controlled induction motor drive

Field-oriented-controlled induction motor drives have been widely used over the last several years. Conventional direct stator-flux-oriented control schemes have the disadvantage of poor performance in the low-speed operating area when the stator flux is calculated using the voltage model, due to the stator resistance uncertainties and variations. In this paper, a new closed-loop stator-flux estimation method for a stator-flux-oriented vector-controlled induction motor drive is presented in which the stator resistance value is updated during operation. This method is based on a simple algorithm capable of running in a low-cost microcontroller, which is derived from the dynamic model of the induction machine. The effects of stator resistance detuning, especially in the low-speed operating region, are investigated and simulation results are shown. The motor drive system as well as the control logic and the resistance estimator are simulated and characteristic simulation results are derived. In addition, the proposed control scheme is experimentally implemented and some characteristic experimental results are shown. The simulation as well as the experimental results reveal that the proposed method is able to obtain precise flux and torque control, even for very low operating frequencies.

A Novel Approach for Broken Bar Fault Diagnosis in Induction Motors Through Torque Monitoring

The cracked or broken bar fault constitutes about 5-10% of total induction motor failures and leads to malfunction as well as reduction of the motors life cycle. This is the reason why there is continuous research on techniques for prompt detection. In this study, a study of the influences of the broken bar fault to the electromagnetic characteristics of the induction motor is presented, using an asynchronous cage motor and finite element method analysis. To this direction, two models have been created and studied: a healthy and one with a broken bar. Additionally, a new approach on the detection of the broken rotor bar fault through the electromagnetic torque monitoring is suggested and validated through experimental results.

Detection of Induction Motor Faults in Inverter Drives Using Inverter Input Current Analysis

Broken rotor bar/end-ring and eccentricity are common faults in squirrel-cage induction motors and have been thoroughly investigated in the case of ac grid supply. In this paper, these types of faults are studied in the case of inverter-driven motors. More specifically, a novel investigation in inverter input current spectrum is made in order to reliably detect the fault-indicative frequency components. These harmonics give the ability for fault detection and classification, even under low load and low motor severity fault condition in steady-state or transient operation. The proposed diagnostic method has been particularly designed for open-loop controlled variable frequency induction motor drives, which is a usual case in low-cost industrial drives where precise speed control of the motor is not required. Moreover, an alternative technique is also presented in case the stator current is measured.

An improved sensorless vector-control method for an induction motor drive

In the present paper, a new improved sensorless vector-control method for an induction motor drive is presented. The proposed method is based on an improved closed-loop stator-flux estimator, based on the dynamic model of the asynchronous motor, which achieves precise stator-flux estimation over a wide area of operation. This new stator-flux estimator ensures stability of the overall control scheme in a very-wide-speed operation area, as it will be shown in this paper. The rotor-speed-estimation method is based on an observer based on the model reference adaptive systems (MRAS) theory. The control scheme is based on a stator-flux-oriented direct vector-control method, where both flux and speed controllers are optimal tuned. In addition, implementation of the proposed method is based on a simplified algorithm capable of running in a low-cost microcontroller, which is discussed in detail. Also, the motor-drive system, including the stator-flux estimator, the speed estimator, and the control logic are simulated and some characteristic simulation results are presented. These results reveal that the proposed method is able to obtain precise flux and speed control over a wide operation area, including very low operating frequencies.

Open-Circuit Fault Diagnosis for Matrix Converter Drives and Remedial Operation Using Carrier-Based Modulation Methods

A novel monitoring system, designed to detect open-circuit (OC) faults that occur in the matrix converter (MC) topology, is proposed in this work. In this monitoring system, a new diagnosis method is implemented which is based on the discrete wavelet transform analysis of the measured output current waveform. In order to ensure the effectiveness of the proposed method and its resistivity to erroneous fault detections, a fuzzy expert system is used in the designed monitoring system. The main advantages of the proposed method are that the implementation cost is minimized because no extra sensors are used and that no information from the control algorithm about the modulation parameters or the applied pulse sequence is required, reducing its implementation complexity and facilitating a more modular design. Additionally, it can be easily adapted to modified matrix topologies. A simple and robust method for the localization of the open-circuited transistor(s) within the identified faulty leg is also proposed. The proposed techniques are validated by simulation and experimental tests. The remedial operation of MC drives after the occurrence of an OC fault by using a redundant leg is also studied. The use of carrier-based modulation methods for this operation is experimentally validated, and related issues are discussed.

Automatic Pattern Identification Based on the Complex Empirical Mode Decomposition of the Startup Current for the Diagnosis of Rotor Asymmetries in Asynchronous Machines

This paper presents an advanced signal processing method applied to the diagnosis of rotor asymmetries in asynchronous machines. The approach is based on the application of complex empirical mode decomposition to the measured start-up current and on the subsequent extraction of a specific complex intrinsic mode function. Unlike other approaches, the method includes a pattern recognition stage that makes possible the automatic identification of the signature caused by the fault. This automatic detection is achieved by using a reliable methodology based on hidden Markov models. Both experimental data and a hybrid simulation-experimental approach demonstrate the effectiveness of the proposed methodology.

Detection of Backlash Phenomena Appearing in a Single Cement Kiln Drive Using the Current and the Electromagnetic Torque Signature

Fault diagnosis in electromechanical drives has been widely investigated over the last decades, and many diagnostic methods have been proposed based on the reported faults. Additionally to already published works which have dealt with gear faults inside low reduction ratio gearboxes, this paper aims to present a simple and effective method for the early diagnosis of evolving faults in a high reduction ratio gear transmission system used in cement kiln drives. The under study system basically consists of a three-phase induction motor mechanically connected to a gearbox. The output shaft of the gearbox drives a gear pinion which, in turn, rotates a girth gear rim surrounding the cement kiln. The identification of mechanical vibrations due to backlash phenomena appearing between the pinion gear and the girth gear rim of the kiln is realized using the motor current signature analysis and processing the motor electromagnetic torque. The proposed diagnostic method is presented, analyzing the experimental results from an under-scale laboratory simulating system.

A comparative study of induction motor current signature analysis techniques for mechanical faults detection

This paper provides a comprehensive comparison of motor current signature analysis techniques for broken rotor bars and air gap eccentricity detection in induction motors. Four characteristic categories of processing methods are investigated, which are Fourier based analysis of the phase currents, parametric and eigenanalysis methods for spectrum estimation of the phase currents, wavelet analysis of the phase currents and current space vector analysis. The analysis is at first performed through simulation of a faulty asynchronous machine in Matlab-Simulink. Subsequent to the simulation results analysis, an experimental fault test rig was designed and implemented for the investigation of the aforementioned malfunctions. In this preliminary investigation, each analysis technique along with its advantages and disadvantages is presented and briefly discussed.

A Novel Control Strategy Applicable for a Dual AC Drive With Common Mechanical Load

The use of a dual electromechanical drive is a well-established and an efficient solution especially when high-power systems are considered. A very important requirement in such systems is the accomplishment of a load balance between the two drives in order to prevent a potential overloading of the one drive in relation to the other one. Additionally, the appearance of mechanical oscillations must be avoided as it will be catastrophic for the mechanical equipment, particularly in the case of mechanical resonance. In this paper, a general analysis of the existing control strategies already used in dual ac drives is being realized first, and a new hybrid control method is proposed based on the need of equal load and power distribution between the two drives. The efficiency of the proposed method is examined for a cement kiln which is a typical system whose large size and imperative uninterrupted operation enforce the use of such a dual drive. A theoretical analysis is being realized developing a corresponding mathematical model and using Matlab/Simulink. Finally, the proposed method is verified using a low-power laboratory system which has been appropriately designed to experimentally simulate a dual drive cement kiln operation.