Consequent-pole Bearingless Motor Research Articles

A Novel Combined Winding and Test Result of a 20-Pole/24-Slot Consequent-Pole Bearingless Motor With Parallel Motor Winding

A novel consequent-pole bearingless motor is proposed with a unique combined winding structure of parallel motor windings for mixing applications, such as agitators used to mix fluids in the pharmaceutical or food industry. Bearingless motors can be used to achieve high purity and no contamination in these mixing applications. The principles of the magnetic suspension force and torque generation are presented by calculating the magnetomotive force (MMF) distributions with two different magnetic field. In addition, the error angle of the suspension force is evaluated in several pole/slot combinations with the proposed combined winding using 3-D finite element analysis. As a result, 20-pole/24-slot was found to be the best configuration, because it has the least direction and amplitude variations in the radial suspension force generation. A prototype of the proposed 20-pole/24-slot bearingless motor was built and tested. The stable magnetic suspension start-up and rotation can be successfully achieved in the experiment. The measured waveforms of the rotor displacement and the U-phase current while the rotor is magnetically suspended and rotated are shown. It is confirmed by calculations and experiments that the proposed combined winding is effective for stable radial magnetic suspension and rotation.

Development of a Compact Centrifugal Pump With a Two-Axis Actively Positioned Consequent-Pole Bearingless Motor

A novel centrifugal pump has been developed that employs a bearingless motor with two-axis radial active positioning control. The structure of this motor is an extension of a hybrid of consequent-pole and homopolar-type bearingless motors. Based on 3-D finite-element-method analysis, the influence of the permanent-magnet dimension and motor current on magnetic suspension characteristics has been investigated. The passive stiffness of this motor has been enhanced. The test pump was fabricated and found to provide a maximum pump output of 1 W with a flow rate of 4 L/min against a head pressure of water of 1.5 m. An impeller with a shroud contributes to a significant reduction in axial impeller movement caused by axial thrust. The rotor vibration is significantly smaller than the fluid gaps in the pump casing. The experimental results demonstrate that the proposed consequent-pole bearingless motor is feasible and effective for use with a centrifugal pump.

Suspension Performance of a Two-Axis Actively Regulated Consequent-Pole Bearingless Motor

The objective of this study is to investigate the suspension performance of a proposed two-axis actively regulated consequent-pole bearingless motor with C-shaped segmented cores. The motor is intended for use in compact, contamination-free centrifugal pumps. In this bearingless motor, the two-axis radial motion of the rotor is actively regulated. Additionally, the axial and tilting motions of the rotor are passively stabilized. In addition, rotating angle detection is not required for active magnetic suspension, unlike conventional permanent-magnet-type bearingless motors. The test machine is stably driven without any mechanical contact at a rated speed of 3000 r/min. The rotor vibration in the actively and passively regulated directions is less than 1/10th of the range of rotor motion. The test results demonstrate the feasibility of the proposed bearingless motor for centrifugal pump applications.

Design of Homopolar Consequent-Pole Bearingless Motor With Wide Magnetic Gap

A wide magnetic gap bearingless motor is required in canned pumps and chambers in the semiconductor manufacturing process. In two-axis actively regulated bearingless motors, having the wide magnetic gap causes decreases in radial magnetic suspension force, axial restoring force, and tilting restoring torque, as well as in rotational torque. In radial actively positioned bearingless motors, the passive stiffness of the axial and tilting movements is one of main concerns. In this paper, a homopolar consequent-pole bearingless motor has been improved with wide magnetic gap. Design improvement of the permanent-magnet arrangement is presented with a 3-D finite-element method analysis. The proposed structure of the homopolar consequent-pole bearingless motor is shown to enhance the passive stiffness and the radial suspension force as well as the rotating torque.

Reduction of force interference and performance improvement of a consequent-pole bearingless motor

Abstract A bearingless motor combines the functions of both magnetic suspension and torque generation together in a single motor. A consequent-pole type of bearingless motor has already been proposed. In contrast to conventional bearingless motors, it is free from the trade-off between suspension force and torque. In addition, stable suspension can be achieved without detecting the rotational angle. However, a part of the X -axis current generates undesirable force in the Y -axis. This force interference influences the performances of bearingless motors; thus, the interference should be eliminated. In this paper, the authors propose an optimal winding design of the consequent-pole bearingless motor to minimize the suspension force interference. Here, the suspension forces in the radial direction are numerically calculated using the magneto-motive force distribution of the bearingless motor, and are compared with the analytical results of finite element method. To verify the theory, static and dynamic performance tests were carried out. It was found that the improved winding configuration significantly reduced the suspension force interference by 90% compared with the previous winding configuration. It was also found that the radial shaft vibration and the power consumption were considerably decreased, by approximately 16% and 44%, respectively.

Development of a Four-Axis Actively Controlled Consequent-Pole-Type Bearingless Motor

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.

Outer Rotor Consequent-Pole Bearingless Motor With Improved Start-Up Characteristics

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.

Optimization of Stator Design in a Consequent-Pole Type Bearingless Motor Considering Magnetic Suspension Characteristics

In this paper, a design optimization method for a consequent-pole bearingless motor is presented. This produces stable magnetic suspension under motor torque generation. The suspension force reduction and direction error, which can be caused by torque generation, are limited in the proposed designs. In the optimization routine, the number of suspension and torque winding turns and air-gap length are carefully assessed. Three stators are constructed for experimental verification. The amplitude and direction errors for the suspension force are found to be within acceptable ranges and the operation of the magnetic suspension is acceptable

Basic characteristics of a consequent-pole-type bearingless motor

We describe the basic characteristics of a consequent-pole bearingless motor. The consequent-pole-type rotor has buried permanent magnets (PMs) polarized in the same radial direction. We carried out an analysis to find the optimum pole number for the machine to produce stable magnetic suspension. The results indicate that there is decoupling of the radial suspension forces from the drive torque when eight or more poles are used. Here, we compare the torque and suspension force generation with those of a conventional surface-mount PM rotor. The suspension force is several times higher for the consequent-pole rotor; however, the torque decreases by 12%. We built a test machine and confirmed the torque and suspension characteristics. We also compared the test machine with other conventional bearingless motors.

A Principle and Winding Design of Consequent-Pole Bearingless Motors

Recently, bearingless motors have been developed to enhance motor drive systems with magnetic suspension. Several types of motors have been proposed as bearingless motors, such as induction, surface mounted permanent magnet, inset permanent magnet, interior permanent magnet, buried permanent magnet, homopolar, hybrid, and switched reluctance bearingless motors. Permanent magnet bearingless motors have been attracting more interests in these years because of the high efficiency. In this paper, a consequent -pole bearingless motor is proposed. A rotor has buried permanent magnets, of which polarities are like. The radial force of a consequent-pole bearingless motor is generated by dc current. Thus, rotational angular position is not needed in a magnetic suspension controller. Radial force variations caused by a rotor rotation are minimized by improving arrangement of stator suspension conductors. A prototype bearingless motor and its controller are built. In experiment, principles of magnetic suspension in the proposed consequent pole bearingless drive are confirmed.