M. Ebrahimi

Detection of stator winding faults in induction motors using three-phase current monitoring.

The objective of this paper is to propose a new method for the detection of inter-turn short circuits in the stator windings of induction motors. In the previous reported methods, the supply voltage unbalance was the major difficulty, and this was solved mostly based on the sequence component impedance or current which are difficult to implement. Some other methods essentially are included in the offline methods. The proposed method is based on the motor current signature analysis and utilizes three phase current spectra to overcome the mentioned problem. Simulation results indicate that under healthy conditions, the rotor slot harmonics have the same magnitude in three phase currents, while under even 1 turn (0.3%) short circuit condition they differ from each other. Although the magnitude of these harmonics depends on the level of unbalanced voltage, they have the same magnitude in three phases in these conditions. Experiments performed under various load, fault, and supply voltage conditions validate the simulation results and demonstrate the effectiveness of the proposed technique. It is shown that the detection of resistive slight short circuits, without sensitivity to supply voltage unbalance is possible.

Clonk : an onomatopoeic response in torsional impact of automotive drivelines

Abstract Vehicular driveline is a lightly damped non-linear dynamic system that is prone to noise and vibration response when subjected to excitation. There are many sources of excitation such as torsional impact caused by the take-up of backlash in the powertrain system. Such sources of excitation exist in transmission backlash, in driveline splines and in pinion-ring gear contact in the differential. Abrupt application or release of the throttle in slow moving traffic or rapid engagement of the clutch can be followed by an onomatopoeic response of the driveshafts, referred to in the industry as clonk. This is a disagreeable, audible and tactile response in some vehicles and can also coincide with every cycle of low-frequency longitudinal vehicle response, commonly referred to as shuffle or shunt. This paper describes the phenomenon of clonk and investigates its occurrence both by an experimental technique and by detailed modal analysis of driveshaft pieces. It is shown that finite element predictions agree well with the experimental findings and that the high-frequency structural modes can lead to discernible radiated noise. The preliminary findings reported here point to a need for a more detailed elasto-acoustic analysis.

Vibration analysis of distributed-lumped rotor systems

In this paper a distributed-lumped model for the analysis of the flexural vibrations of a rotor-bearing system is considered. A general formula for the determinant of the tri-diagonal partitioned matrix description of the system is derived. This enables the irrational characteristic determinant of the system model to be obtained by the dynamic stiffness matrix method. The results obtained are compared to those acquired from the transfer matrix method. The error source in the computation of the natural frequencies by the dynamic stiffness matrix method is discussed. It is shown that by implementing the transfer matrix method the natural frequencies obtained are of greater accuracy. A numerical example illustrating the two methods, is presented and the results achieved are commented upon.

Modelling and simulation of the milling action

Abstract The paper describes the mathematical modelling and simulation of the whole milling action in a milling machine. The mathematical model includes: (a) a model of the dynamics of the X axis drive, (b) a model of the dynamics of the spindle drive, (c) a model of the dynamics of the cutting process itself with cutting forces and torques and (d) the interconnection of (a), (b) and (c) to form the complete model of the milling action. The model uses both z and s plane transfer functions in order to model discrete and continuous parts of the system. The models of the X axis drive dynamics and spindle drive dynamics include models of the digital filter and analog converter in the velocity and position loop control. Friction is modelled in the machine table (part of the X axis drive) as a combination of stiction, coulomb and viscous friction. The model of the X axis drive dynamics is explained in detail whereas the model of the spindle drive dynamics is derived from the former. The model of the cutting process dynamics, which connects the other two models, is based upon a relatively simple analysis of the forces generated during face milling. The model is designed to be simulated by an existing computer simulation package and for this reason some dynamic equations are reoriented in order to avoid differentiation. This part of the paper concludes with an overall block diagram to represent the model of the whole milling action. The simulation of the mathematical model is then described, as are the tests carried out on the model and the actual machine in order to validate the model.

Optimization of the high-frequency torsional vibration of vehicle driveline systems using genetic algorithms:

Abstract Vehicle drivelines with manual transmissions are exposed to different dynamic engine torques under driving conditions. Engine torque can dramatically vary with throttle demand from coast to drive condition and, conversely, with throttle release from drive to coast. Abrupt application or release of throttle in slow moving traffic or rapid engagement of the clutch can be followed by an audible response, referred to in industry as the clonk noise. This paper presents a complete dynamic model of a vehicle driveline for the optimization of high-frequency torsional vibration by the distributed-lumped (hybrid) modelling technique (DLMT). The model used is first validated against experimental tests. Parameter sensitivity studies have been carried out using the model to identify the important components affecting clonk. Three key parameters have been chosen from the parameter study. To optimize these key factors, genetic algorithms (GAs) have been used in this multi-parameter optimization problem. The GAs show significant reduction in the driveline noise, vibration and harshness (NVH).

Automotive gas turbine regulation

A multivariable model of an automotive gas turbine, obtained from the linearized system equations is investigated. To facilitate vehicle speed changes, whilst protecting the system against thermal damage, control of the power turbine inlet gas temperature and gas generator speed is proposed by feedback regulation. Fuel flow and the power turbine nozzle area variations are the selected, manipulatable inputs. Owing to the limited control energy available for regulation purposes a multivariable, optimum, minimum control effort strategy is employed in the inner loop controller design study. Simulated, open and closed loop system responses are presented for purposes of comparison. Significant improvements in the transient response interaction reaction times and low steady state output interaction achieved using passive compensation and output feedback alone. Simplification of the closed loop configuration is proposed in the final implementation without performance penalties.

Machine Tool Axis Dynamics

Abstract The independent axis dynamics of machine tools that employ long slender lead screws, bearings, and workpiece saddles, mounted on supporting slides, will be considered. Distributed-lumped parameter techniques will be used for system analysis and in the model formulation procedures. Realizations that encompass combined torsional and tension loading will be incorporated. Specific, integrated, distributed-lumped machine tool configurations will be derived and described in block diagram form. Simulation studies illustrating the dynamic signature of a machine tool axis drive, when operated at various feed rates, together with the measured results will be presented. The effect of changes in the effective lead-screw length on the workpiece surface finish will be commented on.

Analytical solution of distributed-lumped parameter network models

Abstract System models for distributed-lumped parameter processes are derived. Procedures leading to the Smith normal form and thereafter to the admittance matrix of these models are presented. General results for interconnected distributed-lumped parameter models are provided and a typical application study is included.

Model-based fault diagnosis of induction motor eccentricity using particle swarm optimization

Abstract Much research works address model-free or signal processing and spectral analysis-based fault detection schemes for rotor eccentricity fault in induction motors. Nevertheless, despite existing reliable fault-embedded eccentricity mathematical models such as the winding function method an integrated model-based fault detection algorithm for detecting this fault yet has not been fully explored. This article presents model-based mixed-eccentricity fault detection and diagnosis for induction motors. The proposed algorithm can successfully detect faults and their severity using stator currents. To determine the values of the fault-related parameters, an adaptive synchronization-based parameter estimation algorithm is introduced using particle swarm optimization. Simulation and experiments demonstrate the ability of the algorithm to detect and diagnose these faults. The proposed algorithm can be employed to estimate the parameters, in addition to slowly time varying and abruptly changing parameters.

Multivariable System Regulation

Abstract The regulation of multivariable systems which are subjected to input set point changes and disturbances is considered. A regulation strategy, for analysis purposes, employing both an inner- and an outer-loop feedback structure is proposed. Prescribed, closed-loop, dynamic behaviour using minimum control effort while confining steady-state output coupling is achieved. Output recovery, following disturbance perturbations, via proportional, outer-loop control is advocated. Elementary procedures enabling the computation of conventional pre and feedback compensators are provided, facilitating thereby cost-effective implementation. Stability assessment via established frequency domain techniques is acknowledged. Application studies, enabling comparisons with existing controller design methods, are outlined.