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ABSTRACT: A new noncontact drive system has been developed employing a consequent-pole-type bearingless permanent magnet (PM) motor and a thrust magnetic bearing. This bearingless motor has a wide magnetic gap. The wide magnetic gap may cause a decrease in radial magnetic suspension force because of an increase in magnetic reluctance. A thrust magnetic bearing is installed at the end of the shaft because strong thrust force exists in centrifugal pump applications. In this paper, the magnetic suspension forces and rotation characteristics of the experimental prototype are evaluated while the rotor is magnetically suspended. Experimental results are also compared to the calculated ones using the finite-element method. It is demonstrated that the developed consequent-pole-type bearingless PM motor possesses sufficient magnetic suspension force for noncontact operation.
IEEE Transactions on Energy Conversion 01/2011; · 2.27 Impact Factor
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ABSTRACT: Displacement sensors are necessary for bearingless motors and magnetic bearings. A sensor target ring is needed in a rotor shaft, thus, the axial length has to be extended. The shaft extension is considerable when a gap length is large because a wide gap sensor needs a large diameter in a sensor head coil. To solve this problem, search coils have been installed in a stator for rotor displacement estimation. However, there is serious interference between suspension winding current and search coils. In this paper, the interference is theoretically and experimentally investigated. Two search coil connections are compared. Sensor output characteristics of one of the proposed connection are found to be effective in the interference elimination, even though suspension windings are driven by a three-phase inverter.
IEEE Transactions on Industry Applications 01/2011; · 1.66 Impact Factor
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ABSTRACT: In this paper, a comparison of efficiencies is put forward for a set of test machines constructed from several different types of low-loss magnetic steels. These are laminated amorphous alloys, 6.5% high silicon steel, and general-purpose low-loss silicon steel. Efficiency and characteristics are compared by experiment. The test switched reluctance motors are shown to have more than 95% efficiency at an output of about 2 kW. The effectiveness of an enhanced winding slot fill factor is also evaluated. The use of the high silicon steel is more practical at improving the efficiency as opposed to the use of increased slot fill factor.
IEEE Transactions on Energy Conversion 01/2010; · 2.27 Impact Factor
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ABSTRACT: Thrust magnetic bearings, which can regulate axial displacement of a rotor shaft, have been used for high-speed rotation. However, conventional thrust magnetic bearings have many problems in manufacturing and assembling caused by a large disk rotor of itself. Therefore, we have proposed a novel structure of a thrust magnetic bearing without the large disk rotor. A cylindrical rotor, that has a small diameter as well as a simple shape, is used in the proposed thrust magnetic bearing. This paper introduces the structure and the principle of the proposed thrust magnetic bearing. In addition, it is shown with experiments on high-speed operation that the proposed thrust magnetic bearing is equipped with the sufficient performance in order to make for practical use.
IEEE Transactions on Magnetics 11/2009; · 1.36 Impact Factor
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ABSTRACT: Bearingless motors are characterized by integration of electrical motors and magnetic bearings. These motors can realize magnetic suspension of rotor shafts without mechanical contacts. Recently, non-contact canned motor pumps without expendable parts by means of using these motors have been vigorously developed. In these pumps, the large magnetic gap length of about 5 mm or more is required of the bearingless motors, because fluid flows into the gap. It becomes difficult to generate sufficient suspension force for magnetic suspension, as the magnetic gap length is increased. Therefore, a novel structure of a 5-axis active control type bearingless motor which can generate the sufficient suspension force under wide-gap condition has been proposed by the principal authors. In general, thrust disks with large outside diameters are used in thrust magnetic bearings. However, in the canned motor pump application, rotational speed is limited to prevent cavitation caused by the large thrust disks. Accordingly, the proposed novel structure is equipped with a cylindrical rotor instead of the large thrust disk, and can generate sufficient suspension force in the axial direction, also. This paper introduces magnetic suspension characteristics of the proposed novel structure with experiments.
Energy Conversion Congress and Exposition, 2009. ECCE 2009. IEEE; 10/2009
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ABSTRACT: A novel bearingless disk motor for a possible application of implantable centrifugal artificial hearts is proposed in this paper. To reduce a motor height, C-shaped stator cores with radially expanded coil windings are employed. End windings are not located in the axial direction. The motor height and an outer diameter are designed to be 10 mm and 70 mm, respectively. Magnetic suspension characteristics of the bearingless disk motor are analyzed by using finite element method. The design consideration of a suspension winding configuration has been discussed especially on radial suspension force variations. A prototype machine is fabricated and tested. Experimental results have provided the feasibility of the design of the bearingless disk motor.
Energy Conversion Congress and Exposition, 2009. ECCE 2009. IEEE; 10/2009
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ABSTRACT: Multi-consequent-pole bearingless motors have been developed for low rotational speed and swinging stages used in monitoring system and vacuum process chambers. The motor has flat shape and two degrees of freedom are actively controlled in the radial x-y directions. The suspension windings have a novel structure of a toroidal coil wound around the stator yoke. The structure realizes a short axial length with compact coil end-windings. In this paper, the toroidal winding design is compared with conventional distributed winding design. The design process indicates a consideration of magnetic saturation in the stator yoke with three dimensional finite element analysis. A special design consideration for the stator yoke is required because of significant leakage flux caused by the toroidal winding. It is shown that a compact axial length is realized. It is also shown that a wide cross sectional area is required in the stator yoke compared with conventional distributed windings.
Energy Conversion Congress and Exposition, 2009. ECCE 2009. IEEE; 10/2009
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ABSTRACT: In this paper, a design-optimization method for a consequent-pole bearingless motor with a rather large air-gap length is presented. A rotor iron and permanent-magnet structure is proposed which enhances the suspension-force capability during startup. Magnetic saturation in the rotor-iron pole area is solved, and the stator iron is designed so that magnetic saturation is avoided. The design optimization is based on finite-element-method analysis. It is shown that startup is achieved from the touch-down condition in the experiments.
IEEE Transactions on Industry Applications 09/2009; · 1.66 Impact Factor
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ABSTRACT: A bearingless motor is a motor that combines a motor function with a magnetic bearing function. A prototype machine is an outer rotor bearingless motor, which is actively controlled in two perpendicular radial movements. The other three degrees of freedom, i.e., axial and conical movements, are supported by passive magnetic bearings (PMBs). In this paper, the results of rotation tests in a bearingless motor with and without PMBs are presented. The experimental results of the rotational characteristics are presented. The measured results of static torque are reported. The measurement results are compared to the calculated ones using three-dimensional finite element method (3D-FEM). It is presented that a bearingless motor is stably rotated thank1s to PMBs.
Power & Energy Society General Meeting, 2009. PES '09. IEEE; 08/2009
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ABSTRACT: A thrust magnetic bearing having a conventional thrust magnetic disk is usually installed in five-degree-of-freedom controlled bearingless drive systems. The thrust disk has a larger diameter than a rotor diameter of the bearingless motor. Therefore, a geometrical shape of the rotating part becomes convex. The convex-shaped rotating shaft causes complicated assembly and disassembly processes and increases its peripheral velocity, which results in a limitation of a maximum rotational speed. In this paper, a thrust magnetic bearing having a cylindrical-shaped rotor has been proposed and designed by using finite element method. The simulated results have shown that the proposed thrust magnetic bearing employing a permanent magnet rotor and a coreless coil stator has a sufficient thrust force.
Power & Energy Society General Meeting, 2009. PES '09. IEEE; 08/2009
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ABSTRACT: A bearingless permanent magnet (PM) motor combines functions of non-contact magnetic suspension and torque generation together, thus it can drive without mechanical contact. Unlike conventional bearingless PM motors, such as a surface-mounted PM motor, a consequent-pole type of bearingless PM motor has inherent advantages. It can regulate the radial rotor positions independently of the motor drive and has no tradeoff between radial suspension force and torque. In the consequent-pole bearingless PM motors, distributed or concentrated windings can be employed to the motor winding structure. However, relationship between voltage characteristics and the winding design has not yet been revealed. In this paper, the induced electromotive force (EMF) of the consequent-pole bearingless PM motor is numerically calculated on the basis of the magnetic flux distribution in the airgap around the rotor. It is found that the EMF is distorted by the second harmonic at a specific slot number in a consequent-pole rotor. The calculated EMFs are confirmed with the experimental results in the fabricated test machines.
IEEE Transactions on Magnetics 07/2009; · 1.36 Impact Factor
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ABSTRACT: A multi-consequent-pole bearingless motor which is adapted to low speed rotation is presented. The bearingless motor can be used in swinging stages (or platforms) under specific conditions. Two degrees of freedom (2DOF) are actively controlled in the radial x-y directions. A gap sensor is required to control each DOF. Although 2DOF bearingless motors almost have a flat rotor so that axial length of the rotor is small, the device needs gap sensors and its target. In this paper, a novel stator structure is proposed and a design procedure considers the installation of the gap sensors on the stator. Three dimensional finite element analyses are carried out. An amplitude pulsation and a direction error of the radial suspension force with respect to the rotor rotational angular position are evaluated. Two machines with a conventional stator and the proposed stator are tested and compared. It is shown the proposed machine has beneficial performance by experimental verification.
IEEE Transactions on Magnetics 07/2009; · 1.36 Impact Factor
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ABSTRACT: Bearingless PM motors which have additional suspension windings have been designed with 3D FEM. To verify satisfactions in practical application, a test machine has been built. In this paper, suspension force is measured with the static forces. Two experimental methods are proposed. It is proved that those procedures are suitable even if it is in limited conditions, only one shaft end can be used for static force applied. Furthermore, the relation of the suspension force and rotor rotational angle is shown.
IEEE Transactions on Magnetics 07/2009; · 1.36 Impact Factor
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ABSTRACT: Magnetic bearings, which can suspend rotor shafts by electromagnetic force without mechanical contacts and lubrication, have been developed and commercialized. In the various types of magnetic bearings, thrust magnetic bearings with thrust disks are generally used for active suspension control of thrust direction. However, the large thrust disks of the thrust magnetic bearings have caused various problems. Therefore, this paper proposes a novel structure of an active thrust magnetic bearing using a cylindrical rotor core without the large thrust disk, and it is shown with 3-D-FEA and experiment that the proposed thrust magnetic bearing with the cylindrical rotor core is effective in producing thrust force.
IEEE Transactions on Magnetics 12/2008; · 1.36 Impact Factor
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ABSTRACT: In this paper, a novel structure of a prototype machine is proposed for enhanced start-up characteristics in a bearingless motor. The bearingless motor has two-axis active position regulation with only one unit. Passive magnetic bearings are constructed for improved stiffness in passively regulated movements. The passive magnetic bearings have influence in active two axis movements. A serious situation occurs at a start-up process from touched down condition. An optimization of machine design has been carried out in 3D-FEM analysis and an improved structure is proposed. Based on the design, a prototype bearingless motor is developed. It is shown that a successful start-up is achieved from the touch down displacement of 0.3 mm in experiment.
IEEE Transactions on Magnetics 12/2008; · 1.36 Impact Factor
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ABSTRACT: This paper reports efficiency improvement of a doubly salient-pole homopolar machine with powder iron core. Powder iron core is composed of the metal magnetization powder with resin. It has advantages of low cost, isotropic magnetic property for three dimensions, a high flexibility of design, and low eddy-current loss at high frequency. This paper shows characteristics and performance comparisons between test machines composed of powder iron material and laminated silicon steel. Both machines are designed under the same specification except core material to evaluate the difference in materials. Experimental results demonstrate that the maximum efficiency is improved by about 1% at 9,000 r/min. In addition, it is shown that the machine efficiency can be influenced by flux pulsation in the thrust direction, through the three-dimensional (3-D) finite element method (FEM) analysis.
Electrical Machines and Systems, 2008. ICEMS 2008. International Conference on; 11/2008
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ABSTRACT: Bearingless motors (BelMs) have two kinds of stator windings composed of motor windings and suspension windings in the same stator. Not only torque but also electromagnetic suspension force can be simultaneously generated in the same stator. Therefore, rotor shaft suspension can be realized without mechanical contacts and lubricant. In addition to advantages of magnetic bearings, the BelMs are expected to have advantageous features such as small size, low cost and high critical speed. This paper introduces reduction effect of suspension input power using rotor eccentricity actively in the BelMs. It is verified experimentally that the rotor eccentricity is effective in reducing the suspension input power.
Electrical Machines and Systems, 2008. ICEMS 2008. International Conference on; 11/2008
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ABSTRACT: A new non-contact drive system has been developed employing a consequent-pole type bearingless permanent magnet (PM) motor. This bearingless motor has a much wider gap with respect to its rotor radius. Wide magnetic gaps can cause a decrease in radial magnetic suspension force of the bearingless motor because of an increase in magnetic reluctance. In this paper, the magnetic suspension forces of the fabricated wide gap bearingless drive system are evaluated, when the rotor is magnetically levitated. Experimental results are also compared to the calculated ones using the finite element method. It is demonstrated that the developed consequent-pole type bearingless PM motor with wide magnetic gaps possesses sufficient magnetic suspension force for non-contact operation.
Power and Energy Society General Meeting - Conversion and Delivery of Electrical Energy in the 21st Century, 2008 IEEE; 08/2008
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ABSTRACT: In order to produce high-efficiency motors at relatively low production costs, a layered block is made from amorphous iron sheets. From the block, stator and rotor cores of a test switched reluctance motor (SRM) are fabricated. The experimental results of the test machine are compared to another test machine made from low iron loss silicon steel type 35A300 in JIS standard. This silicon steel is equivalent to M-22, 300, and V300-35A in ANSI, BS601, and DIN46400, respectively. The validity of the test results is compared and verified through use of an analytical simulation software package. Approximately 6% improvement in efficiency is observed for the prototype SRM with the layered amorphous core material. The SRM test motor has an efficiency of 95.1% at a speed of 8500 r/min with an output of 2.4 kW.
IEEE Transactions on Industry Applications 06/2008; · 1.66 Impact Factor
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ABSTRACT: In this paper, we present new strategies of vibration suppression in flexible shaft of a motor with active and passive magnetic forces. Shaft magnetic damping originates from the principle of a bearingless motor having a radial magnetic force generation. Radial force is used for shaft vibration suppression to go through the first critical speed. Simplifications are described in a suppression force system. We propose the elimination of a power source with self-excitation, as well as the elimination of sensors, controllers, and inverters, although the effectiveness is limited.
IEEE Transactions on Industry Applications 06/2008; · 1.66 Impact Factor
