Multiwavelength fiber laser in four mode fiber

Multiwavelength fiber laser is a nonlinear phenomenon that has a great potential for optical communication system. A stable triple-wavelength fiber laser in four mode fiber had been demonstrated experimentally by employing Sagnac filter in a simple close loop laser cavity. The Sagnac loop filter configuration was constructed using a 2 m of polarization maintaining fiber (PMF), a 3 dB coupler and a polarization controller. The laser is able to sustain triple-wavelength laser generation at 13.1 dBm output power of Erbium-Doped Fiber Amplifier (EDFA) as all laser wavelengths produced less than 0.25 nm fluctuation for over 20 min of unstoppable lasing operation. This laser configuration also has flexibility to perform single, dual and triple wavelength laser by controlling the EDFA output power

Nonlinear Analytical Model for Predicting Magnet Loss in Surface-Mounted Permanent-Magnet Motors

This article develops a nonlinear analytical model (NAM) for predicting the magnet loss of surface-mounted permanent-magnet (PM) motors considering nonlinearity effect and slotting effect. The analytical expression of vector magnetic potential in the PM region is derived from Hague's equation for slotless air-gap, and then, it is extended for slotted air-gap based on the conformal mapping method. The PMs, iron nonlinearity, and winding current contributing to the eddy current are all represented by equivalent current in the analytical model. The key of the proposed model is to solve the equivalent current of iron nonlinearity from the improved magnetic circuit model (IMCM) of iron region, where the air flux source is proposed to replace the air reluctance. It is found that the iron saturation can decrease the amplitude of flux density and therefore reduce the magnet loss. Based on the NAM, the magnet loss can be obtained with high accuracy and high efficiency, which is a powerful tool for the optimization of magnet loss in the motor design. The effectiveness of the proposed model is verified by the finite-element method

Dovetail rotor poles in synchronous permanent magnet and reluctance machines

Robust synchronous permanent magnet and reluctance machine designs are developed. In the designs, the rotor structure is simple and strong and the leakage flux is relatively small. For the new design solution, a dovetail form-blocked rotor structure, specific analyzing principles are also developed. The dovetail designs are shown to be good solutions with their lower leakage flux and at least the same strength against centrifugal forces as the conventional rotor solutions. The compared conventional solutions considered have inseparable rotor sheets in which the parts of the rotor are kept still by using bridges between them. In the dovetail rotor, the forms of the rotor parts keep them together and no bridges between them are needed for support. The simplicity of the dovetail solution has also been kept the same or better. In addition, the manufacturing method is the same for both solutions. The dovetail design can also be used for saving the magnetic material of permanent magnet synchronous machines because it has a smaller leakage flux than the conventional V-shaped designs with supporting bridges. The problem of how to compare the dovetail designs to the conventional ones is considered in depth. The strength of the dovetail structure has to be defined in a different way than in the conventional design with supporting bridges. In bridge-fixed design, the strength of the bridges is critical for rotor durability but in the dovetail design wider areas of the rotor affect the strength of the rotor. However, the basic electrical properties could be defined with the same method. Additional methods for defining the electrical properties of dovetail designs are also considered. One method is that the load angle can be defined only from the forms of phase currents in delta-connected synchronous machines and phase voltage and current in star-connected synchronous machines. The load angles defined are successfully used to find a good model for the test results. The other method is to view the normalized local torque density in the air gap as a function of time. In this work, several dovetail synchronous reluctance and permanent magnet machines are designed, manufactured, tested, and analyzed. The design, manufacturing, testing, and analysis methods are defined and developed especially for dovetail designs

INVESTIGATION OF PERMANENT MAGNET SYNCHRONOUS MACHINES FOR DIRECT-DRIVE AND INTEGRATED CHARGING APPLICATIONS IN ELECTRIC VEHICLES

Electrified vehicles have proven to be potential candidates in the future for disrupting the automotive industry which is dominated by conventional gasoline vehicles. Electric vehicle (EV) technology has evolved rapidly over the last decade with new designs of EV drivetrain systems and components but no specific design has been able to serve as a solution that is affordable, reliable and performance-wise similar to existing gasoline vehicle equivalent. Extended driving range and overall cost of the vehicle still remain major bottlenecks. Understanding the state-of-the-art technologies and challenges in existing electric vehicle powertrain and charging systems, with major focus on permanent magnet synchronous machines & drives, this dissertation presents the following

デュアルインバータ駆動オープン巻線誘導電動機の位相制御変調を用いた低負荷領域における高調波低減に関する研究

国立大学法人長岡技術科学大

Design and Multi-physical Fields Analysis of High Speed Permanent Magnet Machines

Due to the advantages of high power density, high efficiency and compact size, high speed permanent magnet machines (HSPMMs) have found wide application in industrial areas. Compared with a conventional speed permanent magnet machine, a HSPMM rotor can reach speeds of more than 10,000 rpm, which brings challenges with regard to electromagnetic, thermal and mechanical aspects of machine design. The higher power density also results in larger power loss per unit volume; due to the small machine size, machine thermal dissipation becomes difficult. Moreover, air frictional loss rises dramatically when the rotor is in high speed operation and this may also further increase rotor temperature. Therefore, research into HSPMM power losses and improving machine thermal dissipation capability is of significant interest. HSPMM mechanical issues also need to be considered to ensure safe and reliable machine operation. As rotor speeds rise, rotor strength becomes prominent and critical as the permanent magnets are vulnerable to the large centrifugal force. In addition, the machine rotor should also have enough rigidity and avoid operating at critical speeds. As such, this dissertation focuses on HSPMM design and research. Multi-physical fields analysis of a HSPMM is carried out to calculate machine power losses and temperature distribution, with factors influencing machine performance considered; HSPMM rotor mechanical research and analysis are also carried out and presented in this study. Firstly, the HSPMM design methodology and process are illustrated with machine rotor parameters, PM material, pole numbers and rotor sleeve considered for a 150 kW, 17000 rpm HSPMM. Then, HSPMM performance for different machine stator structures and PM pole arc pole pitches is investigated using the Finite Element Method (FEM) for the machine operating at both no load and full load conditions; HSPMM electromagnetic performance and how it is impacted by machine parameters is also studied. HSPMM power losses are comprehensively investigated in the following chapter. As machine core loss can be significantly increased with increasing machine frequency, it is critical to accurately estimate HSPMM iron loss. Based on the machine iron core magnetic field variation that is obtained by FEM analysis, machine steel iron core loss estimation for HSPMM is performed using an improved method with the influences of alternating and rotating magnetic fields, as well as harmonics effects, considered for high precision. Then the HSPMM air gap magnetic flux density distribution considering machine stator slotting effect is also analytically calculated with its effectiveness verified by FEM results. Then rotor eddy current loss is studied by time-stepping FEM, while the effects of rotor sleeve dimensions and properties, copper shielding composite rotor structure, air gap length, as well as slot opening width are further researched in depth. A PM bevelling method is also proposed and investigated to reduce HSPMM rotor eddy current loss while having little effect on machine output torque. Then a fluid field analysis is carried out to study HSPMM rotor air frictional loss when the rotor is in high speed operation. According to the characteristics of a machine axial forced air cooling system, the HSPMM temperature distribution is investigated by 3-D fluid–thermal coupling CFD modelling with the calculated power losses results. The machine thermal analysis theory and modelling method are also detailed and further explained. HSPMM thermal performance variation due to impacting factors of cooling air velocity, rotor eddy current loss and sleeve thermal conductivity are also comprehensively investigated and studied in this dissertation. The designed HSPMM is prototyped, and temperature experimental tests are also carried out to verify the effectiveness of the research and analysis for HSPMM. Then, thick-walled cylinder theory is introduced to study rotor mechanical strength analytically, while it also verifies the FEM calculation results. Then based on FEM analysis, HSPMM rotor stress distribution is investigated with sleeve material effects on rotor strength discussed. In order to alleviate the rotor sleeve stress, three pole filler materials are comparatively studied, while the temperature impacts on rotor mechanical stress is further considered; sleeve thickness and the interference between PM and sleeve are investigated in an integrated fashion for HSPMM rotor strength analysis, with some conclusions also drawn for HSPMM rotor mechanical design. HSPMM rotor critical speeds are also calculated by the established 3D rotor dynamic analysis FEM model to ensure the rotor is operating in a desirable condition

Thermal management of the permanent magnets in a totally enclosed axial flux permanent magnet synchronous machine

Elevated magnet temperature in Axial Flux Permanent Magnet Synchronous Machines (AF PMSM) adversely affects torque production, material cost, and the risk of demagnetisation. These machines show promise in applications requiring high power density, however the factors which affect magnet temperature have rarely been investigated. This is therefore the focus of the thesis. A multiphysics numerical model was formulated which predicted the loss, flow, and temperature fields within an AF PMSM. A criterion for estimating the relative importance of the fluctuating component of a periodic heat source on the temperature response of a device was proposed and validated. In this work it was used to justify a steady state, rather than transient, thermal analysis. Thermometric and electrical measurements were taken from an instrumented AF PMSM to validate the numerical predictions. A novel magnet loss measurement technique was implemented; losses were determined by measuring the initial temperature rise rate of the magnets. This was achieved via a calibration relating temperature rise to voltage constant. It was found that 99% of the heat generated in the magnets was convected to the inner cavity of the machine, due to the inner cavity’s recirculating flow structure this heat was dissipated to the casing and core. As a proportion of all heat entering the inner cavity 56-62% left to the casing while 28-41% left to the core. Magnet hot spots were found to be up to 13% greater than the mean temperature rise. Their location was influenced by the distribution of losses and the direction of shaft rotation. Temperature gradients within the inner cavity caused the magnet’s trailing edge to incur a 10% greater temperature rise than the leading edge. As increasing temperature decreases the coercivity of magnet materials these findings are a crucial contribution to the understanding of devices where local demagnetisation is of concern.Open Acces