This paper addresses the diagnostics of inter-turn short-circuits in the stator windings of symmetrical six-phase induction motors supplied by an unbalanced voltage three-phase system. A new approach based on the analysis of the power zero-sequence component is proposed. Both simulation and experimental results are presented, that show the effectiveness of the proposed approach for discriminating between healthy and faulty motor operation, independently of the balanced/unbalanced nature of the supply voltage system.
This paper presents a comparison between two low voltage permanent magnet synchronous motors dedicated to an electric boat. One motor has a distributed winding and the other one an original concentrated winding developed in our laboratory. The originality of these two windings consists in the use of cylindrical solid bars. The AC additional losses due to the solid bars are considered. To compare the two windings, two prototypes were designed and manufactured. The both types of windings are presented and characterized with a developed test bench.
Eccentricity is a critical fault in permanent magnet (PM) machines. In this article, an eccentricity diagnosis method is proposed for dual three-phase PM (DTPPM) machines based on detecting the difference of zero-sequence voltage component (ZSVC) between two sets of three-phase windings. The research is carried out by finite-element method, and 10-pole/12-slot surface-mounted DTPPM machines with different winding configurations are modeled. Eccentricity significantly affects the ZSVC difference in DTPPM machines where a single set of three-phase windings is rotationally asymmetric. The fundamental component and fractional harmonics dominate in the ZSVC difference under static eccentricity (SE) and dynamic eccentricity (DE), respectively. Both the fault characteristic components appear under mixed eccentricity (ME). Moreover, the ZSVC in a single set of three-phase windings is analyzed for comparison. It shows that detecting ZSVC difference has better sensitivity to eccentricity. Furthermore, the effectiveness of the proposed method is verified under different load conditions and eccentricity conditions.
The transmission of a constant torque from zero to synchronous speed with low torque ripple via simple electromechanical devices is an important requirement for a wide range of industrial applications. Hysteresis couplers or clutches can be useful to improve the aforementioned performance indexes, thanks to their unique features. This paper analyzes the influence of the cost functions in the design optimization of magnetic hysteresis couplings. After a brief re-call of a fast method of analysis, several configurations are compared by optimizing the coupler geometry in order to maximize the average torque and minimize the amount of rare-earth material. The obtained results are then deeply analyzed allowing to draw general design guidelines with special emphasis on the influence of the number of poles, cost functions, outer envelope as well as the airgap thickness on the main performance indexes.
When the grid-side converter (GSC) is switched on, a large inrush current may occur if the synchronization between the grid and the GSC is not performed well. Hence, a grid voltage and GSC output voltage vectors must be synchronized before the GSC is switched on. This study proposes a novel sensorless synchronization method based on discontinuous currents induced by the grid voltage after applying a series of controlled short circuits to the GSC terminals. Grid voltage angle is estimated using sampled current, a discrete sliding mode observer, and a double generalized second-order integrator with frequency locked loop in both discontinuous and continuous mode. The proposed method ensures the proper synchronization and GSC operation in the continuous operating mode under load conditions. The effectiveness of the proposed method is verified by simulations in Plexim PLECS.
