M. A. Samonig

A method to detect missing magnetic slot wedges in AC machines without disassembling

In high voltage induction machines the stator slots usually are wide opened to facilitate the assembling of the stator winding coils. Thus the magnetically effective air gap and higher order harmonics are rising, the power factor is decreasing. To compensate this negative effect magnetic stator slot wedges are frequently applied. During operation these slot wedges can get loose and eventually fall out totally. Currently a detection of fallen out slot wedges is only possible by time consuming partially disassembling the machine and optical inspection. Simple and reliable testing methods can thus increase the reliability and reduce costs due to unnecessary disassembling of the machine. For such testing methods high frequency or transient electrical properties of an electrical machine suit very well as the base. When high frequency or transient voltage signals are applied to the terminals of the machine the resulting current response contains information about the machines magnetic state. Therein superposed are the magnetic material properties, several inherent asymmetries such as spatial saturation or slotting, as well as fault induced asymmetries. This paper introduces a new signal processing chain to detect and isolate the fault induced asymmetries caused by fallen out stator slot wedges. The chain consists of data capturing by collecting current response values due to voltage pulses and following Fast Fourier transformations. Measurements for several slot wedge fault cases are presented. The measured and calculated results show the high sensitivity and reliability of the proposed method.

Analysis of rotor fault detection in inverter fed induction machines at no load by means of finite element method

This paper analyzes a new method for detecting defective rotor bars at zero load and standstill by means of modeling using the finite element method (FEM). The detection method uses voltage pulses generated by the switching of the inverter to excite the machine and measures the corresponding reaction of the machine phase currents, which can be used to identify a modulation of the transient leakage inductance caused by asymmetries within the machine. The presented 2D finite element model and the simulation procedure are oriented towards this approach and are developed by means of the FEM software ANSYS. The analysis shows how the transient flux linkage imposed by voltage pulses is influenced by a broken bar leading to very distinct rotor-fixed modulation, that can be clearly exploited for monitoring. Simulation results are presented to show the transient flux paths. These simulation results are supported by measurements on a specially manufactured induction machine.

Sensorless position estimation from PWM-induced transient excitation in induction machines

This paper investigates the feasibility of sensorless position estimation from PWM-induced transient excitation sequences, present during inverter-driven operation of induction machines (IM) with standard space vector PWM (SVPWM). The applied method exploits existing machine saliencies and their correlation to the current slopes measured in response to a voltage pulse at the machine terminals. Determination of this quite linear current response and its position dependent slope modulation allows for extraction of the flux/rotor position information. However, an initial transient oscillation process delays the first possible measurement instant, what imposes minimum pulse duration and limits the possible operational range of SVPWM-integrated transient excitation for sensorless methods. Previous publications showed, that by application of current signal high frequency sampling it is possible to estimate the current derivative before these oscillations decay, thus further reducing the minimum pulse duration requirement. The paper at hand contributes an analysis of different signal processing algorithms and their capabilities when used for this purpose. The investigations include: mean value evaluation (MVE), Theil-Sen regression (TSR), least-squares regression (LSR) and maximum-likelihood estimation (MLE). In a first step an offline comparison is carried out with previously sampled measurement data. The second part features an online evaluation to verify the possibilities for SVPWM-integration.

Prediction of slotting saliency in induction machines with respect to high-frequency-excitation based sensorless control

Sensorless field oriented control (FOC) strategies have found their place in industry applications during the last few years. Stimulated by this development scientific research continues to improve their performance, which is directly linked to the estimation accuracy of flux and rotor position without a mechanical sensor by means of high frequency or transient excitation. The influence of induction machine (IM) design parameters on the rotor saliency, originating from interactions of rotor and stator slotting, is investigated with a focus on transient electrical machine behavior. As this saliency is often used to estimate rotor position in sensorless control schemes, effects attenuating or sustaining it have a straight impact on the controls quality. The present study features finite element (FE) simulations that are compared to measurements for a number of test machines, to validate the results. In a second step it aims at generating a more comprehensive view on the dependencies between saliency and machine design by conducting parameter variations by means of FE simulations, with a focus on stator short pitching and rotor skewing.

Prediction of rotor slotting harmonics in induction machines in the presence of air-gap eccentricity

The paper analyses the influence of induction machine (IM) design on rotor slotting harmonics used for sensorless control strategies. These harmonics have a direct impact on flux and rotor position estimation accuracy. Therefore prediction of their magnitude helps in selecting suitable machine designs with regard to stator/rotor slotting and winding configuration. The paper at hand focuses on the effects that lead to the formation of the rotor slotting harmonic, by analyzing them with a simplified inductance phasor model, finite element (FE) simulations and measurement results. These three means are used to prove the existence of certain machine slotting and winding configurations that result in rotor slotting harmonic mitigation, or even complete cancelation. As will be shown, the magnitude of this mitigation effect is directly linked to a fault induced asymmetry originating from mixed (static and dynamic) rotor eccentricity within the machine.

Transient magnetic analysis of voltage pulse excited induction machines with respect to diagnosis and fault detection

A new fault detection method for induction machines (IM) is analyzed with respect to transient magnetic material behavior by means of finite element (FE) modeling. The detection method uses the machines inverter to excite the IM with transient voltage pulses and measures the corresponding phase current responses. To account for the material behavior transient BH curves are identified from measurements on a demagnetized magnetic circuit and included in the FE model to accurately simulate pulsed voltage excitations.

Interactive simulation for teaching the influence of power management on hybrid electric cars overall energy consumption

Usage of sustainable energy is a key factor for solving future environmental issues. The purpose of the project SustEner is to modernize sustainable electrical energy vocational training by enhancing existing or establishing new training methods in enterprises and education. This paper presents the SustEner module power management techniques in hybrid electrical cars. Increasing market demand for hybrid electric vehicle (HEV) leads to a higher effort on training and education of high qualified engineers in this field. Beside the development and design of different HEV components also the interaction and efficiency of the entire system is a key factor. Understanding the power flow from one component to the other improves the ability of developing high efficiency HEV. Online teaching tools provide the possibility of teaching complex technical problem in an easy way and with high approval. Thus an interactive simulation tool was developed teaching power management techniques for HEV. In the following an interactive online tool is presented based on a MATLAB/Simulink HEV model enabling configuration of a HEV and efficiency analysis for a specific drive cycle.

Teaching power management techniques for hybrid electric cars by a interactive simulation

Usage of sustainable energy is a key factor for solving future climate issues. The purpose of the project SustEner is to modernize Sustainable Electrical Energy vocational training by enhancing existing or establishing new training methods in enterprises and education. This paper presents the SustEner module power management techniques in hybrid electrical cars.

Exploiting rotor slotting harmonics to determine and separate static and dynamic air-gap eccentricity in induction machines

The paper investigates the influence of pole-pair number on the mixed eccentricity related fault indicators extracted by means of high-frequency or transient signal injection. The method exploits the transient current response to track eccentricity- and slotting-related machine saliencies. By using the fault indicators locus, a separation of mixed eccentricity components is performed, without comparison to additional reference measurements of the faultless case (no eccentricity). It is shown, that the fault indicator related to certain machine designs can be used to extract a reliable reference from the eccentric machine. This allows for the separation of static and dynamic proportions from the overall mixed eccentricity.