Dezhi Liu

Influence of magnet shape on torque behavior in surface-mounted permanent magnet motors

This paper discusses influence of magnet shape on torque behavior in surface-mounted permanent magnet (SPM) motors. The effect of pole embrace optimization, magnet-skew and magnet shaping have been analyzed in different 8-pole, 24-slot, three phase SPM motors which having the same stator configuration. Finite-element method (FEM) is used to predict Back-EMF and torque ripple. The result shows magnet-skew can reduce cogging torque efficiently. Magnet sharping with 3rd harmonic increases average torque compared with sine magnet shaping and lower torque ripple compared with magnet-skew with optimized pole embrace.

Design of Novel Shaftless Pump-Jet Propulsor for Multi-Purpose Long-Range and High-Speed Autonomous Underwater Vehicle

Owning to its extremely long endurance, small size, cost-effective employment, easy, and fast transported properties, the merits of autonomous underwater vehicles (AUVs) exceed those of manned underwater vehicles. Therefore, it has become an indispensable member in navies throughout the world, as well as with oceanographic research, commercial resource explorations, and especially the underwater search and rescue (SAR) sectors. Up to date, the tragic MH370 and QZ8501 flight incidents have dramatically increasing the awareness of high-performance SAR equipment, which in turn will stimulate the states party to the incident to urgently upgrade their shallow- and deep-sea SAR equipment. To extend the range (endurance) and shorter the searching period for the next generation SAR AUV, a sea water cooled high-power density magnetically slotless permanent magnet brushless motor is proposed and integrated with pump-jets impeller to achieve designated shaftless pump-jet propulsor. In this paper, the developed shaftless pump-jet propulsion system is applied in Naval University of Engineering series multi-purpose long-range and high-speed deep-sea AUV, which could provide excellent performance as a SAR platform.

Small disturbance stability analysis of multiphase inverter-fed induction motor drive system

The inverter-fed induction motor drive system may become unstable at low frequencies and light load. Taking the inverter-fed five phase induction motor drive system as an example, the small disturbance mathematic model of whole system is deduced, based on small disturbance model of induction motor and switching model of inverter system, the three-dimensional unstable region is presented and discussed by Hurwitz stability criterion of modern control theory, the results of mathematic analysis, simulation and experiments are identical. The effect of variant induction motor parameters, filter-inverter parameters, and operation conditions on system stability is studied in details. The analysis method and the conclusion obtained in the paper may contribute to the design of parameters and stable operation of inverter-fed multiphase induction motor drive system.

Modeling and parameter measurement scheme for double primaries coupling Linear Induction Motors

In order to improve the redundancy performance, Linear Induction Motor (LIM) could be designed to have m primaries (m is an integer and m≥2) and just one secondary. When anyone of the primaries runs in failure model, other remanent primaries could accomplish the scheduled target. The paper represents equivalent circuit of double primaries coupling (m=2) LIM based on the research of mathematic model. Test data of no load and locked mover for single primary excited and double primaries excited with the same current are used for parameter measurement. Calculation results of the machine performance (e.g., terminal voltage and force) based on the motor model are presented and compared to test data from a prototype LIM. Result of compare shows that motor model and parameter measurement scheme for double primaries coupling LIM is efficient and accurate. Result of calculation and test indicates that when excited with the same current, efficiency and thrust density of double primaries coupling LIM are improved.

Experimental and Simulation Research on the Low-Frequency Oscillation of a 4-wire 12-Phase Generator-Rectifier-load system

A 15~20Hz low-frequency oscillation (LFO) will badly harm the safety of 4-wire multi-phase generator-rectifier-load systems. This paper studies the LFO in a 4-wire 12-phase generator-rectifier-resistance load system by simulation and experiment. The simulation model of 12-phase generator is programmed in FORTRAN language by secondary development with PSCAD/EMTDC software, and validated by a hardware experiment. The effects on the LFO from various system parameters, such as capacitance of filter capacitor, load resistance, leakage inductances of armature windings and field winding, saturation, and resistances of damper windings, are studied with the simulation model and hardware system. The extracted rules in this paper provide a reference for correlative research and design.

Analysis of 3D thermal field in the stator of high-capacity and high-torque-density motor with forced evaporative-cooling system

Forced evaporative-cooling (FEC) system has the advantages of simple structure, less cooling medium dosage and good cooling performance. It can realize the efficient cooling of the high-capacity and high-torque-density motor. It is worthy to simulate the thermal field of the stator in order to have a deep research on the cooling performance and the distribution of the thermal field. Based on analysis of a high-capacity and high-torque-density motor stator with the FEC system, a complete simulation model in 3D for temperature calculation of the stator was developed of stator concerned with the change of stator segmentation ratio, thickness of sealed gel on the inner stator surface and area ratio between stator tooth body and back-iron was also analyzed. Distribution rule of stator temperature field has been obtained and result of emulation was tested agree well with experiment. Conclusion of this paper can be provided as academic foundation for more application in high-capacity motor with FEC system.

Magnetic circuit calculation of non-salient pole synchronous generator based on distributed magnetic circuit method

Due to low-accuracy of traditional magnetic circuit method with single magnetic loop and some approximate empirical formulas in the magnetic circuit calculation of non-salient pole synchronous generator, the distributed magnetic circuit method (DMCM) is put forward and adopted. The comparison of the results among traditional magnetic circuit method, DMCM and finite-element method (FEM) shows the validity and high-accuracy of DMCM. Furthermore, DMCM is more suitable for some special rotor configuration with subsidiary slots, ventilation slots or the slots for q-axis windings.