Taner Goktas

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 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.

Modeling and Dynamic Behavior Analysis of Magnet Defect Signatures in Permanent Magnet Synchronous Motors

In this paper, a motor specific fault severity assessment method is proposed to calculate the amplitude of magnet defect fault signatures in the stator current and back-electromotive force (EMF) through machine and controller parameters of permanent magnet synchronous motor (PMSM) drive. A detailed mathematical analysis is developed based on the linear model of PMSM to predict the behavior of fault signatures in motor variables at various operating points. In order to understand and decouple the effects of motor controllers and operating points, the derivations are further extended to clarify the effects of current loop gains. Under the light of findings, the fault severity impact on the current and back-EMF fault signatures is investigated exhaustively. For this purpose, the fault intensity imposed to a motor is increased in four steps by removing 25% of one magnet at each step. Throughout each fault level, the changes in the corresponding spectrums are analyzed, which provides an essential information to design accurate threshold to minimize false alarms. The theoretical derivations are validated through comparative finite element analysis (FEA) simulations and experiments.

Comprehensive Analysis of Magnet Defect Fault Monitoring Through Leakage Flux

This paper presents a detailed magnet defect fault detection analysis through fluxgate sensors by monitoring the leakage flux around permanent magnet synchronous motors. The flux spectra of electric machines contain direct and most critical information to monitor and characterize magnet defect faults and their progressions. In the mainstream diagnosis techniques based on phase current and back-EMF analysis, the fault corresponding signature characteristics may vary and cause misleading results depending on motor topology, winding configuration, number and location of defective magnets, and controller parameters. In this paper, it is shown that leakage flux analysis provides some superior results for magnet defect diagnosis. For this purpose, the fault patterns in the leakage flux spectrum are exhaustively analyzed at different torque/speed profiles. Simulation and experimental results show that the deployment of a direction sensitive fluxgate sensor in magnet defect fault detection yields very promising results both in time and frequency domain analyses.

A simplified mathematical approach to model and analyze magnet defects fault signatures in permanent magnet synchronous motors

This paper deals with modeling and analysis of broken magnet fault signatures in permanent magnet surface mounted (PMSM) motor variables. A detailed mathematical analysis based on the linear model of PMSM motor is developed to predict the behavior of different fault signatures in stator current and back-emf for various motor operation points. In order to verify the results, a three phase, 8-pole PMSM motor is modeled using finite element analysis (FEA) and 7% of one magnet is cut using a fine cutter on the rotor to model the broken magnet fault. This paper also presents a comprehensive fault severity analysis and its impacts on the current and voltage fault signatures. For this purpose, the fault intensity imposed to the motor is increased in four steps by removing 25% of one magnet at each step. Throughout each fault level, the changes in the spectrum are analyzed which provides an essential information to design threshold fault detection.

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.

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.

Broken rotor bar fault monitoring based on fluxgate sensor measurement of leakage flux

Broken rotor bar fault in induction motors significantly affects the motor dynamic performance and increases the mechanical oscillations in torque and speed. Motor current signature analysis has widely been used to detect such fault, yet it has some shortcomings due to motor topology, stator winding and load type dependencies. In this paper, radial leakage flux which contains most critical fault related information is analyzed using a fluxgate sensor to detect broken bar fault in induction motors (IMs). The 2D-Time Stepping Finite Element Method (2D-TSFEM) is used to analyze fault patterns in leakage flux. A 2-Dimensional (2D) finite element analysis and experimental results show that using leakage flux can provide superior and more reliable results than classical motor stator current analysis in IMs.

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.

Diagnosis of broken rotor fault in inverter-fed IM by using analytical signal angular fluctuation

The aim of this paper is to detect broken rotor bar fault at the presence of low frequency load torque oscillation in inverter-fed induction motors. The low frequency load torque oscillation in induction motor may sometimes have the same effect as broken rotor bar fault on the stator current. Especially, when load torque oscillation frequency is close to twice the slip frequency, additional processing need to be done to separate these two effects from each other. To discern these two effects, Analytical Signal Angular Fluctuation (ASAF) spectrum is used. Experimental results are presented for separating broken rotor bar fault from low frequency load torque oscillation.