J. T. Chen

Advanced Flux-Switching Permanent Magnet Brushless Machines

This paper overviews the recent development and new topologies of flux-switching (FS) machines, with particularly emphasis on the permanent magnet (PM) type. Specific design issues, including winding configurations, combinations of stator and rotor pole numbers, rotor pole width, split ratio, etc., are investigated, while the torque capability of selected FSPM machines is also compared.

Winding Configurations and Optimal Stator and Rotor Pole Combination of Flux-Switching PM Brushless AC Machines

A simple analytical method is developed to compare the combinations of stator and rotor pole numbers in flux-switching permanent magnet (PM) machines in terms of back electromotive force (EMF) and electromagnetic torque. The winding connections and winding factors of machines having all poles and alternate poles wound, and different numbers of phases, from two to six, are determined by the coil-EMF vectors. Their differences from analyzing the conventional fractional-slot PM machines with concentrated nonoverlapping windings are highlighted. The general conditions are established for balanced symmetrical back-EMF waveform. It shows that the optimized rotor pole number should be close to the number of stator poles, whereas larger torque can be obtained by the machine with relatively higher rotor pole number. The analysis is validated by finite-element analyses and experiment.

Analysis of a Novel Multi-Tooth Flux-Switching PM Brushless AC Machine for High Torque Direct-Drive Applications

A three-phase, multi-tooth flux-switching permanent magnet brushless ac machine is analyzed, its electromagnetic performance, viz., the phase flux-linkage and back-EMF waveforms, the self- and mutual-inductances, the cogging torque, the electromagnetic torque, and the torque-current characteristic, are predicted by 2-D and 3-D finite-element analyses and validated experimentally. Compared with a conventional flux-switching machine, a multi-tooth machine requires a significantly smaller volume of magnet material, since only half the number of permanent magnets is required, and it exhibits a higher torque density at low excitation currents as well as a lower torque ripple. However, since it saturates more quickly as the current is increased due to the higher armature reaction, and at very high electric loadings its torque capability is lower than that of a conventional flux-switching machine.

Comparison of All- and Alternate-Poles-Wound Flux-Switching PM Machines Having Different Stator and Rotor Pole Numbers

The influence of stator and rotor pole numbers, viz. 6/5, 6/7, 12/10, 12/11, 12/13, and 12/14 stator/rotor poles, etc., on the electromagnetic performance of three-phase flux-switching permanent-magnet (FSPM) machines with all and alternate poles wound is investigated in this paper. It shows that the back-EMF waveform, winding inductance, unbalanced magnetic force, and torque density in an FSPM machine are all significantly affected by the stator and rotor pole numbers and winding configurations, as confirmed by both finite-element analyses and measurements.

Online Multiparameter Estimation of Nonsalient-Pole PM Synchronous Machines With Temperature Variation Tracking

The ill-convergence of multiparameter estimation due to the rank-deficient state equations of permanent-magnet synchronous machines (PMSMs) is investigated. It is verified that the PMSM model for multiparameter estimation under id = 0 control is rank deficient for simultaneously estimating winding resistance, rotor flux linkage, and winding inductance and cannot ensure them to converge to the correct parameter values. A new method is proposed based on injecting a short pulse of negative id current and simultaneously solving two sets of simplified PMSM state equations corresponding to id = 0 and id ≠ 0 by using an Adaline neural network. The convergence of solutions is ensured, while the minimum |id| is determined from the error analysis for nonsalient-pole PMSMs. The proposed method does not need the nominal value of any parameter and only needs to sample the winding terminal currents and voltages, and the rotor speed for simultaneously estimating the dq-axis inductances, the winding resistance, and the rotor flux linkage in nonsalient-pole PMSMs. Compared with existing methods, the proposed method can eliminate the estimation error caused by the variation of rotor flux linkage and inductance as a result of state change due to the injected d-axis current in the surface-mounted PMSM. The method is verified by experiments, and the results show that the proposed method has negligible influence on output torque and rotor speed and has good performance in tracking the variation of PMSM parameters due to temperature variation.

Influence of Skew and Cross-Coupling on Flux-Weakening Performance of Permanent-Magnet Brushless AC Machines

A method is proposed for predicting the flux-weakening performance of permanent-magnet (PM) brushless ac machines accounting for skew and d-q axis cross-coupling. The method is based on a d-q-axis flux-linkage model, a hybrid 2-D finite-element (FE)-analytical method being used to predict the d- and q-axis inductances. However, it only requires 2-D FE analysis of the magnetic field distribution over a cross section of the machine. The developed method is used to predict the torque-speed characteristic of an interior PM brushless ac machine with one stator slot-pitch skew. This is compared with predictions from a direct FE analysis of the machine and validated by measurements.

Cogging Torque in Flux-Switching Permanent Magnet Machines

The influence of manufacturing tolerances on the cogging torque waveforms, as well as the back-EMF waveforms, in 3- and 5-phase flux-switching permanent magnet (FSPM) machines having different numbers of stator/rotor poles is investigated by finite element analyses and experiments. The cause of excessive cogging torque in the prototype FSPM machines has been identified. It is due to modular stator structure which makes it mechanically weak, leading to the intrusion of C-core into the airgap and an uneven inner stator bore. The analyses presented in the paper should be useful to the design and analysis of modular PM machines in general.

A Novel E-Core Switched-Flux PM Brushless AC Machine

A novel E-core switched-flux permanent-magnet (SFPM) brushless machine is proposed, and its electromagnetic performance is compared with that of the conventional SFPM brushless machine. The operation principle of the E-core SFPM machine will be first described, and the influence of stator and rotor pole number combinations is investigated, while the electromagnetic performance of the optimized E-core SFPM machine is predicted by finite-element analyses and validated by experiment. It is shown that the number and volume of magnets in the E-core SFPM machine is significantly reduced, only half of that in the conventional machine, while the phase back electromotive force and torque of the E-core machine are ~15% larger than those of the conventional machine.

Influence of Slot Opening on Optimal Stator and Rotor Pole Combination and Electromagnetic Performance of Switched-Flux PM Brushless AC Machines

The significant influence of slot opening on the optimal stator and rotor pole combination and on the electromagnetic performance of the switched-flux permanent magnet (SFPM) machine is observed and investigated in this paper. A new SFPM brushless machine with remarkable slot opening relative to the magnet thickness is developed to reduce the magnet usage and to increase the slot area. Its stator slot opening is almost several times of that in the conventional SFPM machine, but its magnet usage is only half. However, the new machine exhibits ~ 40% larger back EMF and electromagnetic torque than those of the conventional machine, while its cogging torque and torque ripple are significantly lower.

Stator and Rotor Pole Combinations for Multi-Tooth Flux-Switching Permanent-Magnet Brushless AC Machines

A simple analytical method is developed for determining the optimal combination of stator pole and rotor pole numbers for a multi-tooth flux-switching permanent magnet (FSPM) machine, and the optimal design of the stator teeth for maximum torque. In addition, the rotor pole width and the split ratio are optimized by finite element analysis. The optimized multi-tooth FSPM machine exhibits a significantly higher torque capability and requires a significantly lower volume of magnet material than a conventional FSPM machine. The performance of the proposed multi-tooth FSPM machine is validated experimentally.