Direct torque control of brushless DC drives with reduced torque ripple

The application of direct torque control (DTC) to brushless ac drives has been investigated extensively. This paper describes its application to brushless dc drives, and highlights the essential differences in its implementation, as regards torque estimation and the representation of the inverter voltage space vectors. Simulated and experimental results are presented, and it is shown that, compared with conventional current control, DTC results in reduced torque ripple and a faster dynamic response

Analysis of air-gap field modulation and magnetic gearing effect in fractional slot concentrated winding permanent magnet synchronous machines

In this paper, the torque production of fractional slot concentrated winding (FSCW) permanent magnet synchronous machines (PMSM) are analyzed from the perspective of the air-gap field harmonics modulation accounting for slotting effect. It is found that the average torque of FSCW PMSM is produced by both the principle of conventional PMSM and the magnetic gearing effect. A finite element analysis (FEA)-based equivalent current sheet model and harmonic restoration method is firstly used in FSCW PM machines with different slot-pole number combinations to quantify the respective contribution of the conventional PMSM and the magnetic gearing effect to the average torque. The influence of slot opening on the magnetic gearing effect, cogging torque and torque ripple is analyzed. The results show that the magnetic gearing effect makes a non-ignorable contribution to the average torque when a large slot opening stator is used. The expression of the gear ratio in FSCW PMSMs is derived. The influence of gear ratio on the contribution of the magnetic gearing effect to the total torque is investigated by FEA. The FEA predicted torques are validated by experiments on the prototypes

Influence of PWM on the proximity loss in permanent magnet brushless AC machines

The winding copper loss can be significantly increased due to skin and proximity eddy current effects. The skin and proximity losses due to fundamental frequency current has been investigated in literature, but the influence of PWM on the skin and proximity losses has not been reported. In this paper, 2-D finite element method is employed to analyze the skin and proximity losses in a permanent magnet brushless AC machine, in which significant proximity loss exists due to high frequency current ripples induced by the PWM, as confirmed by both theoretical calculation and experiment. The analyses should be generally applicable to other machines

Design and analysis of novel asymmetric-stator-pole flux reversal PM machine

This paper proposes a novel flux reversal permanent magnet (FRPM) machine with asymmetric-stator-pole (ASP) configuration. Different from the conventional FRPM machine with uniform “NS-NS-NS” PM sequence, the proposed ASP-FRPM machine is characterized by a “NSN-S-NSN” magnet arrangement. Hence, the interpolar flux leakage is significantly reduced with the developed design, which can improve the torque capability. The machine topologies, features and operating principle are introduced, respectively. A simplified magnetic circuit model is established to reveal the underlying flux leakage reduction mechanism of the ASP design, and the rotor pole number is analytically optimized as well. The design parameters are then globally optimized so as to improve the torque quality. In addition, the electromagnetic characteristics of the ASP- and conventional FRPM machines are compared. Finally, experiments have been carried out to validate the theoretical results

Influence of stator and rotor pole number combinations on the electromagnetic performance of stator slot-opening PM hybrid-excited machine

A new type of three-phase stator hybrid excited machine with permanent magnets (PMs) located at the slot openings of field winding slots is presented in this paper. It has the advantage of good flux regulation capability due to the field excitation. The machines with different stator/rotor pole combinations, i.e., 6-stator pole and 7-/8-/10-/11-/13-/14-rotor poles, have been comparatively investigated in terms of the open-circuit and on-load characteristics, as well as the influence of dc current and the unbalanced magnetic forces. The 2-D finite element analysis (FEA) has been employed for analysis and optimization of the machines together with experimental validation

A high-power factor Vernier machine with coil pitch of two slot pitches

In this paper, an 18-slot/26-pole vernier permanent magnet synchronous machine (VPMSM) with coil pitch of two slot pitches is proposed based on a nine-slot/18-flux-modulation-pole/26-pole VPMSM with concentrated tooth-coil windings. Compared with the original VPMSM, the number of slots is doubled and the phase winding connection is adjusted to reduce the space harmonic content, the phase inductance, and hence, improve the power factor. This paper shows that the proposed VPMSM increases power factor from 0.73 to 0.95 with better torque and flux-weakening capability. Moreover, a series of VPMSMs with high-power factor is proposed from the same design principle and given design guidelines

Online parameter estimation for permanent magnet synchronous machines : an overview

Online parameter estimation of permanent magnet synchronous machines is critical for improving their control performance and operational reliability. This paper provides an overview of the recent achievements of online parameter estimation of PMSMs with examples. The critical issues in parameter estimation are firstly analysed, especially the rank-deficient issue and inverter nonlinearities. Then, the state-of-the-art online parameter estimation modelling techniques are reviewed and assessed. Finally, some typical applications and examples are outlined, e.g. estimation of mechanical parameters, improvement of sensored and sensorless control performance, thermal condition monitoring, and fault diagnosis, together with future research trends

Comparative study of air-gap field modulation in flux reversal and Vernier permanent magnet machines

In this paper, the torque production mechanisms of flux-reversal permanent magnet (FRPM) machine and Vernier permanent magnet (PM) machine are analyzed and compared based on air-gap field modulation. Working harmonics of PM magnetomotive force (MMF) and air-gap permeance in two machines are analytically identified and compared, indicating that the fundamental PM MMF together with all permeance harmonics contribute to the torque production of Vernier machine whereas all PM MMF harmonics but only fundamental permeance in FRPM machine produces the torque. Thanks to the utilized large dc component of air-gap permeance, the torque density of Vernier machine is revealed to be better. Influence of critical parameters on machine performance, such as PM thickness and slot width ratio of the modulation pole, is also investigated. It shows that FRPM machine is more sensitive to the design parameters. Both finite-element analysis and experimental validation are conducted to verify the conclusion

Magnetoresistance of 2D and 3D Electron Gas in LaAlO3/SrTiO3 Heterostructures: Influence of Magnetic Ordering, Interface Scattering and Dimensionality

Magnetoresistance (MR) anisotropy in LaAlO3/SrTiO3 (LAO/STO) interfaces is compared between samples prepared in high oxygen partial pressure (PO2) of 10-4 mbar exhibiting quasi-two-dimensional (quasi-2D) electron gas and low PO2 of 10-6 mbar exhibiting 3D conductivity. While MR of an order of magnitude larger was observed in low PO2 samples compared to those of high PO2 samples, large MR anisotropies were observed in both cases. The MR with the out-of-plane field is always larger compared to the MR with in-plane field suggesting lower dissipation of electrons from interface versus defect scattering. The quasi-2D interfaces show a negative MR at low temperatures while the 3D interfaces show positive MR for all temperatures. Furthermore, the angle relationship of MR anisotropy for these two different cases and temperature dependence of in-plane MR are also presented. Our study demonstrates that MR can be used to distinguish the dimensionality of the charge transport and various (defect, magnetic center, and interface boundary) scattering processes in this system.Comment: 14 pages, 5 figure

Improved Dynamic Mechanical Properties of Modified PTFE Jet Penetrating Charge with Shell

A modified polytetrafluoroethylene (PTFE) was produced by the addition of copper powder to improve the mechanical properties and penetration performance of conventional PTFE. Static compression and split Hopkinson pressure bar test analyses verified the improved mechanical properties of the modified PTFE. Shaped charge structure was designed with by applying modified PTFE to liner material, the formation of modified PTFE jet and the process of jet penetrating shell charge were researched by numerical simulation. As compared to Teflon, results demonstrated that the mechanical properties of the modified PTFE have been significantly improved to achieve greater consistency of jet formation, stronger penetration, broadened pore size, and increased damage performance in the absence of a charge shell explosion