A comprehensive assessment of PM motor topology impact on magnet defect fault signatures

This paper presents a detailed study on topology dependent magnet defect fault signatures in permanent magnet (PM) motors. A new mathematical approach is introduced to analyze the fault signature behaviors in PM motors with different design specs such as combinations including winding types, number and location of stator coils / magnet defects etc. Thanks to the flexible features of the proposed method, it is possible to analyze various winding configurations (including full, short and fractional pitch, single and double layer, delta and star connection) and combination of multiple magnet defect effects on the motor variables' frequency spectrum. It is shown that depending on the motor topology, the corresponding spectrum can be different from others and the generalized fault models may not be valid. In addition, current or back-emf spectrums do not include any fault related harmonics in some cases or the fault components showing up in the stator back-emf do not show up in the stator current. Comparative 2-D Finite Element (FE) simulation and experimental results justify the theoretical magnet defect fault analysis and show the efficacy of proposed approach

A Comprehensive Magnet Defect Fault Analysis of Permanent-Magnet Synchronous Motors

In this paper, magnet defect faults and their corresponding reflections on permanent-magnet (PM) motor stator variables are investigated. An analytical approach based on a partitioned magnetic equivalent circuit is developed to determine the influence of magnet defect faults on PM motor variables. Due to the flexibility of the proposed method, the effect of each rotor magnets on each stator coil can be calculated to obtain the induced back electromotove force under faulty cases and observe the fault-related signatures in the frequency spectrum. The proposed tool significantly reduces the computational burden and provides sufficient accuracy, which significantly eases to simulate several magnet fault scenarios and examine detailed topology dependence relations in shorter time. Different cases, including various numbers and locations of defected magnets, winding configurations, and crack direction effects, are studied to understand the magnet defect influences comprehensively. The experiments and simulations are carried out at different speeds and load conditions to fully characterize the fault signatures. Comparative 2-D finite-element simulations and experimental results justify the theoretical magnet defect fault analysis and show the efficacy of the proposed approach

A comprehensive analysis of magnet defect faults in permanent magnet synchronous motors

Condition monitoring of permanent magnet synchronous motors (PMSMs) is the process which identifies and averts any serious fault and is of critical importance for reliability and robustness of the system. In this study, broken/crack magnet fault in PMSMs and the consequence effects of such failure on stator back-emf and current wave forms are investigated. For this purpose, a three phase, 8-pole permanent magnet surface mounted (PMSM) motor is modeled using 2-D Finite Element (FE) analysis. Three types of cracks with the same area and different directions are created on one rotor magnet to investigate the effect of the direction of the cracks on the fault signatures. Fast fourier transform (FFT) is used to analyze the stator current and back-emf signatures. Both faulty and healthy motors are simulated at different speed and load to scrutinize the effect of these two parameters on the fault signatures. To verify the analysis results, an experimental setup is used to support the results

Separation of broken magnet and static eccentricity failures in PMSM

This paper deals with the separation of broken magnet failures from static eccentricity (SE) fault using phase current information in permanent magnet synchronous motors (PMSMs). Broken magnet and SE faults exhibit very similar fault patterns in back-emf and flux spectrums. Therefore, these two faults should be discerned from each other for accurate diagnosis. In this paper, phase current waveforms are exhaustively analyzed at different speed and torque profiles to discriminate broken magnet from SE in PMSMs. In order to specify the behavior of sideband harmonics, 2-D Time Stepping Finite Element Method (TSFEM) is used. Simulation and experimental results show that some distinctive harmonics such as 0.25th, 0.5th and 0.75th can define the fault type in PMSMs

A simplified numerical approach to analyze magnet defects in permanent magnet synchronous motors

Condition monitoring of permanent magnet synchronous motors (PMSMs) is the process that identifies and averts impending faults and is of critical importance for reliability and robustness of overall system. In this study, magnet defect fault in PMSMs and the consequence effects of such failure on stator back-emf and current wave forms are investigated through modified magnetic equivalent circuit (MEC). The proposed analytical approach is used to investigate the effect of magnet faults on the stator back-emf which significantly reduces the computational burden and provides high enough accuracy while predicting the additional harmonics in motor variables. The 2-D Finite Element (FE) results support the potential use of the proposed method for fault signature analysis. Simulations are also carried out at different speed and load condition to expose the faulty signature. Comparative experimental results conducted at the same conditions to show the efficacy of the proposed method

Discernment of Broken Magnet and Static Eccentricity Faults in Permanent Magnet Synchronous Motors

This paper deals with the discernment of broken magnet and static eccentricity faults in permanent magnet synchronous motors through the stator phase current. Broken magnet and static eccentricity faults exhibit very similar fault patterns in back-electromotive force (emf) and flux spectrums. Therefore, it is essential to separate these faults from each other for a true diagnosis. In this study, stator emf and phase current waveforms are analyzed in detail to identify the discerning components and characterize their dynamic behaviors. Two-dimensional time-stepping finite-element simulations and experimental results show that the fault classification process can be implemented by using fault-dependent in-phase current fault signatures

A New Method for Leakage Inductance Calculation of Transverse Flux Machines

This paper presents a new analytical method for leakage inductance calculation of transverse flux permanent magnet machines. In this method, leakage flux paths are predicted base on the finite element results, and then all paths would be modeled by flux tubes. Finally, the inductance of the machine would be obtained by calculation of the permeance of flux tubes. The validity of the proposed model is verified by comparing the Finite Element results with the results obtained from the proposed approach. Comparing the results shows that the proposed model is able to accurately estimate the leakage inductance of the machine with an average error less than 9%

Severity Estimation of Interturn Short Circuit Fault for PMSM

This paper presents a novel method to estimate the number of shorted turns in a permanent magnet synchronous machine (PMSM) following the detection of interturn short-circuit (ITSC) fault and its location. In this proposed method, PMSM is excited through a low sinusoidal voltage at standstill condition to obtain the winding resistance and synchronous inductance by current response. It is shown that the ITSC fault introduces variation in the current response, which can be used to calculate the number of shorted turns under zero fault resistance assumption. Using this practical procedure, the fault severity can be estimated directly in a straight-forward manner. In other words, the severity estimation for a given machine can be done without complex machine modeling or experiments on ITSC prototype with multiple taps. The findings in this paper are essential for a comprehensive solution including fault mitigation algorithms and postfault operations. In order to verify the findings, a three-phase equivalent circuit model supported by finite element analysis results is used to take saturation and space harmonics into account. In addition, experimental results are presented to demonstrate the validity and practicability of the severity estimation

Separation harmonics for detecting broken bar fault in case of load torque oscillation

This paper presents separation harmonics to discriminate rotor failure from low frequency load torque oscillations in three phase induction motors. The most common method for detecting broken rotor bar faults is to analyze the corresponding sidebands through motor current signature analysis (MCSA). If a motor is subjected to load fluctuation, then the oscillation related sidebands exhibit similar behaviors as well. Particularly, when the load fluctuation frequency is close or equal to that of broken bars, the stator current spectrum analysis can be misleading. In this study, torque and motor phase voltage waveforms are exhaustively analyzed to discriminate broken rotor bar fault from low frequency load torque oscillation in three phase induction motors. In order to extract and justify the separation patterns, 2-D Time Stepping Finite Element Method (TSFEM) is used. The simulation and experimental results show that the proposed approach can successfully be applied to fault separation process in star connected motors