Time-stepping Finite-element Simulations Research Articles

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.

Impact of Rotor Design on Interior Permanent-Magnet Machines With Concentrated and Distributed Windings for Signal Injection-Based Sensorless Control and Power Conversion

This paper examines the relationship between rotor design, saliency-based signal injection sensorless control, and power conversion properties for four industrially relevant interior permanent-magnet machine configurations: a 36-slot 6-pole stator with v bar rotor, a 36-slot 6-pole stator with flat bar rotor, a 9-slot 6-pole stator with v bar rotor, and a 9-slot 6-pole stator with flat bar rotor. The influence of rotor geometric design variables over the range of current densities at the maximum torque per ampere angle was found using a design of experiments' methodology and standardized regression coefficients. Tradeoffs between sensorless control and power conversion properties are found using a Monte Carlo methodology. Power conversion and sensorless control properties were analyzed using hybrid static and time-stepping finite-element simulations.

Stator Harmonic Currents in VSI-Fed Synchronous Motors With Multiple Three-Phase Armature Windings

Electric motors equipped with multiple three-phase windings are often used for the advantages they offer in terms of reliability, performance, and inverter power segmentation. When the windings are fed by independent voltage-source inverters (VSIs), circulation harmonic currents can occur in stator phases. If the motor is an induction machine, circulation currents are known to originate form transient imbalances in the applied voltages due to inverter switching. This paper investigates the problem when a synchronous machine is used and shows how additional (and possibly major) sources for circulation currents can arise in this case (even with a round-rotor design) due to the nonsinusoidal air-gap flux distribution. The phenomenon is illustrated for a 45-MW quadruple three-phase synchronous motor supplied by four medium-voltage (MV) multilevel VSIs. Its circulation currents are predicted with two alternative methods, i.e., analytically and from time-stepping finite-element simulation. The results obtained in both ways are shown to well match measurement results collected on the actual motor during full-load system testing.