Influence of Stator MMF Harmonics on the Utilization of Reluctance Torque in Six-Phase PMA-SynRM with FSCW

Although fractional-slot concentrated winding (FSCW) offers many significant advantages, such as short end-turn windings, high slot filling factor, and low cogging torque, it is frequently limited by excessive stator magnetomotive force (MMF) harmonics which will induce high eddy losses in the permanent magnets (PMs). What is more, in the literature, it can be observed that the reluctance torque of the salient-pole machine with FSCW is usually much lower than that obtained with integral slot winding. To explore the underlying reason why the reluctance torque in a salient machine with FSCW significantly decreases, a new six-phase FSCW with 24 slots and 10 poles, which can significantly reduce the undesirable stator MMF harmonics, is obtained by using the concept of stator shifting. Then, two permanent-magnet-assisted synchronous reluctance machines (PMA-SynRMs) with the proposed winding layout and conventional asymmetric 12-slot/10-pole six-phase winding layout are designed and simulated by the finite-element method (FEM). The reluctance torque, total torque, and d/q-axis inductances with different current phase angles are also compared under different loaded conditions. The results show that a reduction in stator MMF harmonics can indeed lead to a significant enhancement in reluctance torque under heavy loaded conditions, while the dominance will diminish under light loaded conditions

A Novel Sensorless Control Strategy for Brushless Direct Current Motor Based on the Estimation of Line Back Electro-Motive Force

In this paper, a novel sensorless control strategy based on the estimation of line back electro-motive force (BEMF) is proposed. According to the phase relationship between the ideal commutation points of the brushless direct current motor (BLDCM) and the zero-crossing points (ZCPs) of the line BEMF, the calculation formula of line BEMF is simplified properly and the commutation rule for different positions of the rotor is presented. The estimation error of line BEMF caused by the freewheeling current of silent phase is analyzed, and the solution is given. With the phase shift of the low-pass filter considered, a compensation method using “60°-α” and “120°-α” is studied in this paper to eliminate the error. Finally, the simulation and experimental results show that the rotor-position-detection error is reduced effectively and the motor driven by the accurate commutation signal can work well at low and high speed

Phase-field investigation of intergranular corrosion mechanism and kinetics in aluminum alloys

The resistance to intergranular corrosion (IGC) is crucial for 7xxx series high-strength aluminum alloy. The grain boundary characteristics and nanoscale intergranular precipitates are the most significant factors affecting the IGC performance of alloys. Exploring the influences of the two factors on the mechanism and kinetics of corrosion is a fundamental issue for IGC processes. In this paper, the multi-phase field model for electrochemical corrosion is employed to study the IGC processes. The effects of grain size, GB overpotential, and the status of nano-precipitates on the mechanism and kinetics of IGC are systematically and quantitatively investigated. Polycrystalline alloys with the averaged grain sizes in micrometer and nanoscale show typical IGC (GB network propagation) regime and massive corrosion regime respectively. The IGC tendency of micrometer-sized grains increases with the average grain size, while that of nanoscale grains exhibits the opposite trend due to different corrosion mechanisms. For the IGC in the presence of nano-precipitates, our simulations quantify that the orientation, size, and distribution of precipitates could substantially affect the corrosion rate. Nanoscale precipitates exhibit completely different corrosion regimes in the process of IGC, with trenching and penetrating corrosion patterns depending on the overpotential. The multi-phase field model lays a foundation for revealing the corrosion mechanism as well as designing new corrosion resistant materials