Thomas M. Wolbank

Bio: Thomas M. Wolbank is an academic researcher from Vienna University of Technology. The author has contributed to research in topics: Stator & Inverter. The author has an hindex of 17, co-authored 143 publications receiving 1181 citations.

Stator-Current Spectrum Signature of Healthy Cage Rotor Induction Machines

Abstract: Before applying current-signature-analysis-based monitoring methods, it is necessary to thoroughly analyze the existence of the various harmonics on healthy machines. As such an analysis is only done in very few papers, the objective of this paper is to make a clear and rigorous characterization and classification of the harmonics present in a healthy cage rotor induction motor spectrum as a starting point for diagnosis. Magnetomotive force space harmonics, slot permeance harmonics, and saturation of main magnetic flux path through the virtual air-gap permeance variation are taken into analytical consideration. General rules are introduced giving a connection between the number of stator slots, rotor bars, and pole pairs and the existence of rotor slot harmonics as well as saturation-related harmonics in the current spectrum. For certain combinations of stator and rotor slots, saturation-related harmonics are shown to be most prominent in motors with a pole pair number of two or more. A comparison of predicted and measured current harmonics is given for several motors with different numbers of pole pairs, stator slots, and rotor bars.

Using PWM-Induced Transient Excitation and Advanced Signal Processing for Zero-Speed Sensorless Control of AC Machines

Abstract: The sensorless control of induction machines, particularly for operation at low speed, has received significant attention in recent years. To realize a field-oriented control of AC machines that is able to work at zero speed, the most commonly used methods are either sensor-based models or transient-signal-excitation methods. The major disadvantage of present signal-injection methods is that they are intrusive to pulsewidth modulation (PWM). An additional switching sequence has to be embedded in the control that will cause a torque and current ripple. In order to overcome these problems, a new flux-estimation algorithm that uses the phase current derivative to extract the flux-position information is presented. In contrast to previously introduced methods, this new approach operates without additional transient excitation of the machine and requires only fundamental-wave excitation using standard PWM or slightly modified PWM. Furthermore, only the current response in the two active states of PWM is used. This makes it possible to use sensorless control for the whole speed range including overmodulation and removes the distortion and parasitic influence of the zero switching states during the estimation of the flux. Experimental results are presented to validate the applicability of the presented approach.

Sensorless rotor temperature estimation of permanent magnet synchronous motor

Abstract: The work proposes a method for estimation of the magnet temperature in permanent-magnet synchronous machines by exploiting the d-axis saturation effects in the steel stator core produced by the d-current and rotor flux excitation. The method implies an intermittent injection of a voltage pulse in the d-axis of the motor. The resulting d-current response is a function of both the initial value of the d-current itself and the magnetization level of the magnets. Thus, a temperature dependent variation in the magnetization level of the permanent magnets is reflected in a variation of the d-current slope upon the voltage pulse. Experimental validation of the method is demonstrated with surface permanent-magnet motor.

Current-controller with single DC link current measurement for inverter-fed AC machines based on an improved observer-structure

Abstract: In modern industrial applications even low-cost drives have excellent dynamic behavior, which is achieved by field-oriented control combined with high-dynamic current regulation. Usually at least two phase-current sensors are necessary to realize such an operation. In this paper, a new current-control scheme is presented, which enables high-dynamic control of ac machine-line currents with improved accuracy by measuring only the current of the dc-link. The controller is based on three individual and adaptive phase-current observers, which guarantee very accurate phase-current estimates even at low-modulation indices. Thus, operation is possible even at low-speed without modifying the switching pattern of the controller and the necessary modification at zero-speed can be clearly reduced. Different realizations of the proposed scheme are given and a comparison is made to previously published schemes which are also based on a single dc-link current sensor. Measurements performed on an induction-machine drive at different points of operation show the applicability of the proposed structure. It is shown that the long-term accuracy is clearly increased and the maximum deviation of the observer estimate from the actual phase-current is reduced when using the proposed scheme.

Induction Machine Insulation Health State Monitoring Based on Online Switching Transient Exploitation

Abstract: Today's variable-speed drives are usually operated close to their maximum tolerable conditions. The fast switching of modern power electronic devices leads to high stress of the winding insulation. As a result, an insulation breakdown may lead to sudden breakdown and high economic loss. To avoid unpredictable downtimes and enable repair on demand, monitoring of the insulation health state is getting more and more important. This paper proposes a method to monitor changes in the insulation health state by evaluating the machine high-frequency properties. The deterioration of the insulation condition is usually linked with a change of insulation capacity and thus also influences high-frequency properties. Initiating a voltage step excitation of the machine by the switching of the inverter, the high-frequency properties can be identified by measuring the resulting current response. This response is usually seen as current signal ringing and contains the machine high-frequency information. By applying signal processing tools, changes in the high-frequency information are extracted, and an insulation state indicator is derived. The applicability of the method is verified by measurements on two test machines (5.5 kW and 1.4 MW) having different power ratings as well as different insulation systems.

A Survey of Fault Diagnosis and Fault-Tolerant Techniques—Part I: Fault Diagnosis With Model-Based and Signal-Based Approaches

Abstract: With the continuous increase in complexity and expense of industrial systems, there is less tolerance for performance degradation, productivity decrease, and safety hazards, which greatly necessitates to detect and identify any kinds of potential abnormalities and faults as early as possible and implement real-time fault-tolerant operation for minimizing performance degradation and avoiding dangerous situations. During the last four decades, fruitful results have been reported about fault diagnosis and fault-tolerant control methods and their applications in a variety of engineering systems. The three-part survey paper aims to give a comprehensive review of real-time fault diagnosis and fault-tolerant control, with particular attention on the results reported in the last decade. In this paper, fault diagnosis approaches and their applications are comprehensively reviewed from model- and signal-based perspectives, respectively.

State of the Art of Finite Control Set Model Predictive Control in Power Electronics

Abstract: This paper addresses to some of the latest contributions on the application of Finite Control Set Model Predictive Control (FCS-MPC) in Power Electronics. In FCS-MPC , the switching states are directly applied to the power converter, without the need of an additional modulation stage. The paper shows how the use of FCS-MPC provides a simple and efficient computational realization for different control objectives in Power Electronics. Some applications of this technology in drives, active filters, power conditioning, distributed generation and renewable energy are covered. Finally, attention is paid to the discussion of new trends in this technology and to the identification of open questions and future research topics.

A Survey of Condition Monitoring and Protection Methods for Medium-Voltage Induction Motors

Abstract: Medium-voltage (MV) induction motors are widely used in the industry and are essential to industrial processes. The breakdown of these MV motors not only leads to high repair expenses but also causes extraordinary financial losses due to unexpected downtime. To provide reliable condition monitoring and protection for MV motors, this paper presents a comprehensive survey of the existing condition monitoring and protection methods in the following five areas: thermal protection and temperature estimation, stator insulation monitoring and fault detection, bearing fault detection, broken rotor bar/end-ring detection, and air gap eccentricity detection. For each category, the related features of MV motors are discussed; the effectiveness of the existing methods are discussed in terms of their robustness, accuracy, and implementation complexity. Recommendations for the future research in these areas are also presented.

Recent Advances in Modeling and Online Detection of Stator Interturn Faults in Electrical Motors

Abstract: Online fault diagnosis plays a crucial role in providing the required fault tolerance to drive systems used in safety-critical applications. Short-circuit faults are among the common faults occurring in electrical machines. This paper presents a review of existing techniques available for online stator interturn fault detection and diagnosis (FDD) in electrical machines. Special attention is given to short-circuit-fault diagnosis in permanent-magnet machines, which are fast replacing traditional machines in a wide variety of applications. Recent techniques that use signals analysis, models, or knowledge-based systems for FDD are reviewed in this paper. Motor current is the most commonly analyzed signal for fault diagnosis. Hence, motor current signature analysis is a topic of elaborate discussion in this paper. Additionally, parametric and finite-element models that were designed to simulate interturn-fault conditions are reviewed.

Advances in Electrical Machine, Power Electronic, and Drive Condition Monitoring and Fault Detection: State of the Art

Abstract: Recently, research concerning electrical machines and drives condition monitoring and fault diagnosis has experienced extraordinarily dynamic activity. The increasing importance of these energy conversion devices and their widespread use in uncountable applications have motivated significant research efforts. This paper presents an analysis of the state of the art in this field. The analyzed contributions were published in most relevant journals and magazines or presented in either specific conferences in the area or more broadly scoped events.