Condition Monitoring Techniques for Permanent Magnet Synchronous Motors
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Due to the variety of electric motor applications in critical service systems, they need precise control and accurate health monitoring in order to operate reliably and safely. Fault diagnosis, as the earliest step of system health management, identifies impending faults through pre-specified indexes. This is a critical process as it provides early warnings for catastrophic failures well beforehand and enables preventive maintenance schedule updates. The most important advance in this field is the implementation of fault diagnosis system embedded to drive system. In this technology, the health monitoring system is programmed in the main CPU used for controlling purposes. Also, there is no need to install any additional sensor since the same measurement used for control is sent for monitoring. This technology is growing up and still is not mature enough to be used in industries widely. In this study, rotor related faults such as magnet defect and eccentricity 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 rotor related faults on PM motor variables. Stator winding configuration, winding connection type and location of damaged rotor magnets are some of the physical properties affecting the fault signature characteristics. Several cases with different numbers of pole and slot are investigated through the proposed method. In addition, different winding connections (including star and delta connection), different winding configurations (including single and double layer, fractional and full coil pitch), and different magnet defect numbers and locations are scrutinized. 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 dependencies in shorter times. At the last part of this research, a motor specific fault severity assessment method is proposed to calculate the amplitude of magnet defect fault signatures in the stator current and back-emf through machine and controller parameters of 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.