Diagnosis of Inter-Turn Short Circuit for a Polyphase Induction Motor in Closed-Loop Vector-Controlled Drives

The main objective of this paper is to develop and experimentally verify a new technique to detect an inter-turn short circuit in one phase of a stator winding of an induction motor energized from a vector-controlled drive. This is in order to overcome the fault masking difficulties associated with the concept of depending on the actual magnetic field pendulous oscillation between the conventional voltage and current space vectors with respect to a reference that is unaltered by the compensation action of the drive. This technique is based on the flux pendulous oscillation phenomenon. This flux pendulous oscillation is also described in this paper, this in addition to the magnetic field pendulous oscillation previously addressed in prior publications. The new approach has been verified through experimental results which are represented here

Establishing the Relative Merits of Interior and Spoke-Type Permanent-Magnet Machines With Ferrite or NdFeB Through Systematic Design Optimization

In this paper, a multiobjective design optimization method combining design-of-experiments techniques and differential-evolution algorithms is presented. The method was implemented and utilized in order to provide practical engineering insights for the optimal design of interior and spoke-type permanent-magnet machines. Two combinations with 12 slots and 8 poles and 12 slots and 10 poles, respectively, have been studied in conjunction with rare-earth neodymium-iron-boron (NdFeB) and ferrites. As part of the optimization process, a computationally efficient finite-element electromagnetic analysis was employed for estimating the performance of thousands of candidate designs. Three optimization objectives were concurrently considered for minimum total material cost, power losses, and torque ripple, respectively. Independent variables were considered for both the stator and rotor geometries. A discussion based on a systematic comparison is included, showing, among other things and despite common misconception, that comparable cost versus loss Paretos can be achieved with any of the rotor topologies studied

Automated Multi-Objective Design Optimization of PM AC Machines Using Computationally Efficient FEA and Differential Evolution

The design optimization methods described in this paper are employing an ultrafast computationally efficient finite element analysis technique. A minimum number of magnetostatic solutions are used for the analysis, which makes possible the study of thousands of candidate motor designs with typical PC-workstation computational resources. A multi-objective differential evolution algorithm that considers a large number of independent stator and rotor geometric variables and performance criteria, such as average and ripple torque, losses, and efficiency, is used. The optimization method is demonstrated on different permanent magnet (PM) ac synchronous motors in the kilowatt and megawatt power ranges. For the low-power PM ac machine study, a nine-slot six-pole topology is considered. For the high-power PM ac machines, four case studies were carried out with the following: fractional-slot embedded surface PM (SPM), fractional-slot interior PM (IPM), integer-slot SPM, and integer-slot IPM, respectively. Four motor topologies are systematically compared based on optimal Pareto sets. The design optimization of IPM motors includes an additional search for an optimum operating torque angle corresponding to the maximum-torque-per-ampere condition

Calculation of Magnet Losses in Concentrated-Winding Permanent-Magnet Synchronous Machines Using a Computationally Efficient Finite-Element Method

The proposed hybrid method combines computationally efficient finite-element analysis (CE-FEA) with a new analytical formulation for eddy-current losses in the permanent magnets (PMs) of sine-wave current-regulated brushless synchronous motors. The CE-FEA only employs a reduced set of magnetostatic solutions yielding substantial reductions in the computational time, as compared with the conventional FEA. The 3-D end effects and the effect of pulsewidth-modulation switching harmonics are incorporated in the analytical calculations. The algorithms are applied to two fractional-slot concentrated-winding interior PM motors with different circumferential and axial PM block segmentation arrangements. The method is validated against 2-D and 3-D time-stepping FEA

Analysis and Diagnostics of Adjacent and Nonadjacent Broken-Rotor-Bar Faults in Squirrel-Cage Induction Machines

In this paper, faults associated with the rotor of an induction machine are considered. More specifically, effects of adjacent and nonadjacent bar breakages on rotor fault diagnostics in squirrel-cage induction machines are studied. It is shown that some nonadjacent bar breakages may result in the masking of the commonly used fault indices and, hence, may lead to a possible misdiagnosis of the machine. A discussion of the possible scenarios of these breakages as well as some conclusions regarding the types of squirrel-cage induction machines (number of poles, number of squirrel-cage bars, etc.) that may be more prone to these nonadjacent types of failures are presented. This discussion is supported through both simulation and experimental results. It is also shown that secondary fault effects can be used to diagnose such nonadjacent bar breakages

Multi-Objective Tradeoffs in the Design Optimization of a Brushless Permanent-Magnet Machine With Fractional-Slot Concentrated Windings

In this paper, a robust parametric model of a brushless permanent magnet machine with fractional-slot concentrated windings, which was developed for automated design optimization is presented. A computationally efficient finite-element analysis method was employed to estimate the dq-axes inductances, the induced voltage and torque ripple waveforms, and losses of the machine. A method for minimum effort calculation of the torque angle corresponding to the maximum torque per ampere load condition was developed. A differential evolution algorithm was implemented for the global design optimization with two concurrent objectives of minimum losses and minimum material cost. An engineering decision process based on the Pareto-optimal front for 3,500 candidate designs is presented together with discussions on the tradeoffs between cost and performance. One optimal design was finally selected, prototyped and successfully tested

A Reconfigurable Motor for Experimental Emulation of Stator Winding Inter-Turn and Broken Bar Faults in Polyphase Induction Machines (Journal article)

The benefits and drawbacks of a 5-hp reconfigurable induction motor, which was designed for experimental emulation of stator winding interturn and broken rotor bar faults, are presented in this paper. It was perceived that this motor had the potential of quick and easy reconfiguration to produce the desired stator and rotor faults in a variety of different fault combinations. Hence, this motor was anticipated to make a useful test bed for evaluation of the efficacy of existing and new motor fault diagnostics techniques and not the study of insulation failure mechanisms. Accordingly, it was anticipated that this reconfigurable motor would eliminate the need to permanently destroy machine components such as stator windings or rotor bars when acquiring data from a faulty machine for fault diagnostic purposes. Experimental results under healthy and various faulty conditions are presented in this paper, including issues associated with rotor bar-end ring contact resistances that showed the drawbacks of this motor in so far as emulation of rotor bar breakages. However, emulation of stator-turn fault scenarios was successfully accomplished

Analysis, Modeling, and Diagnostics of Adjacent and Nonadjacent Broken Rotor Bars in Squirrel-Cage Induction Machines

In this thesis, faults associated with squirrel-cage rotor structures will be considered. More specifically, diagnostics of adjacent and nonadjacent squirrel-cage rotor bar breakages will be addressed. Effects of such faults on machine performance will be studied through a number of modeling approaches. Namely, an example of a simple 8-bar squirrel-cage induction machine will be used to visualize the effects of both adjacent and nonadjacent rotor bar faults on the magnetic field distribution in the induction machine. Then, more sophisticated models such as the magnetic equivalent circuit, and time-stepping finite element models of a case-study 5-hp induction machine will be developed. These models will be used to verify the assumptions used in the simple 8-bar example as well as to provide a more detailed picture of the fault effects on the motor performance. A number of both adjacent and nonadjacent fault scenarios will be considered. It will be shown that some nonadjacent rotor bar breakages may result in the masking of the commonly used indices of fault signals, hence, leading to possible misdiagnosis of the machine. It will also be shown that secondary effects that appear during such nonadjacent rotor faults can be utilized for purposes of fault identification using conventional rotor fault diagnostic approaches with modified indices. Moreover, a new rotor fault diagnostics technique based on the vibration signal obtained using a low-cost piezoelectric vibration sensor will be introduced. This technique will be used for successful diagnostics of both adjacent and nonadjacent squirrel-cage rotor faults. Both of these findings show a good deal of promise in practical applications

Comparison of Torque Ripple Minimization Control Techniques in Surface-Mounted Permanent Magnet Synchronous Machines

In this paper, three calculation methods of torque for Surface-Mounted Permanent Magnet Synchronous Machines (SPMSMs) are performed, and the results including the average torque and the torque ripple from each method are compared. This is in order to enable one to choose an effective torque estimation technique for further torque ripple minimization in these machines. Accordingly, a vector controlled motor-drive model, including torque ripple minimization techniques, was developed. In this paper, a current harmonics injection and an adaptive internal model algorithm were developed for the torque ripple minimization in the vector control drive system. The corresponding simulation results are given and compared in this paper. An equivalent circuit model coupled to a Time-Stepping Finite Element (TSFE) model of the motor-drive system built in Ansoft-Maxwell V14.0 was developed to verify the above mentioned torque ripple minimization control techniques, which reduce the torque pulsations as well as eliminate the need for skewing the stator windings or the rotor permanent magnet (PM) mounts in SPMSMs

Magnetic Equivalent Circuit Modeling of Induction Machines Under Stator and Rotor Fault Conditions

In this paper, stator and rotor failures in squirrel-cage induction machines are modeled using the magnetic equivalent circuit (MEC) approach. Failures associated with stator winding and rotor cage are considered. More specifically, stator inter-turn short circuit and broken rotor bar failures are modeled. When compared to conventional modeling techniques, the MEC modeling approach offers two main advantages: 1) relatively high speed of execution, and 2) high accuracy. The developed MEC model is validated here with respect to the experimental tests and time-stepping finite-element simulations for healthy and various faulty conditions