Bearingless Permanent Magnet Research Articles

Floating Capacitor Suspension Inverter for Parallel Combined Winding Bearingless Motors

Recent efforts to improve the performance of bearingless motors have focused on “combined winding” machine designs that use the same coils for torque and suspension force production. While combined winding designs have been successful in increasing the machine performance, they add substantial cost and complexity to the power electronics required for the bearingless drive system. This article presents a bearingless drive concept, which eliminates the additional power electronic hardware requirements for a parallel combined winding design. The resulting drive requires the same hardware components as a traditional, separated winding bearingless motor. The article proposes and explains the design and theory of operation, proposes a simple control implementation, and presents initial validation via simulation results. The theory and design presented are valid for both conventional $p\pm 1$ bearingless motor designs (i.e., bearingless permanent magnet designs) as well as $p_s=1$ bearingless motor designs (i.e., bearingless ac homopolar designs). Experimental results are provided that validate the proposed concept and demonstrate stable levitation of a bearingless motor.

A novel four degree-of-freedoms bearingless permanent magnet machine using modified cross feedback control scheme for flywheel energy storage systems

A novel four degree-of-freedoms bearingless permanent magnet machine using modified cross feedback control scheme for flywheel energy storage systems

Electromagnetic Performance Analysis on the Bearingless Permanent Magnet Synchronous Motor With Halbach Magnetized Rotor

In order to approximately obtain sinusoidal air-gap magnetic field and get larger radial levitation force of the bearingless permanent magnet synchronous motor (BPMSM), a novel BPMSM with Halbach magnetized rotor is proposed. Firstly, the suspension and rotation mechanisms of the BPMSM are introduced. The control mechanism of producing the radial levitation force in single direction and arbitrary direction is analyzed in detail. The mathematical models of the radial suspension force are given. Secondly, the comparative research on the BPMSMs with the Halbach magnetized rotor and parallel magnetized rotor is carried out. The air-gap magnetic field, back electromotive force (EMF), radial suspension force, and torque are calculated and compared. Finally, the prototype motor equipped with the Halbach magnetized rotor is constructed. Some experimental results are tested and the stable suspension operation of the proposed motor is realized.

Optimal Design and Performance Analysis for Interior Composite-Rotor Bearingless Permanent Magnet Synchronous Motors

The bearingless permanent magnet synchronous motor (BPMSM) is widely developed due to the advantages such as high speed, high power factor, high power density, and zero friction. In this paper, in order to provide more space for the placement of a permanent magnet (PM), a new type of BPMSM with interior composed magnetic structure is designed. The operation principles of the proposed BPMSM with the Maxwell force are introduced first. Then, by using of the finite element method (FEM), the pole-arc coefficient of BPMSM is optimized to reduce the cogging and increase the levitation force. In addition, the electromagnetic properties including magnetic field, levitation force, electromagnetic torque, loss, and cogging torque are simulated and analyzed. Finally, the static levitation experiment is carried out to verify the performance of levitation force. The research lays a foundation for further research about optimal design of the new type of BPMSM and also provides a mathematical model foundation for research of the control system.

A High-Precision Rotor Position and Displacement Prediction Method Specially for Bearingless Permanent Magnet Synchronous Motor

The high performance sensorless performance of the bearingless permanent magnet synchronous motor is the main direction to improve the reliability of the drive system and reduce the cost of the system, and the high-precision rotor position and displacement prediction method is the key technology to realize the high performance sensorless operation. In view of the above problems, a rotor displacement and position prediction method based on kernel extreme learning machine is studied in this paper. On the basis of the mathematical model of BPMSM, this method predicted the position and displacement of the rotor according to the current and flux linkage of suspension windings and torque windings by KELM. The construction method of rotor position and displacement prediction model was described; meanwhile the implementation steps of offline training and online prediction were given. Finally, the error between the method and the actual value was compared by simulation and experiment. The results showed that the proposed method had high accuracy and could achieve real-time rotor position and displacement and then provides the basis for realizing sensorless operation control of BPMSM.

Simple Driving Method for a 2-DOF Controlled Bearingless Motor Using One Three-Phase Inverter

In this paper, we propose a simple driving method that uses only one three-phase inverter for an actively controlled 2-DOF bearingless motor. This motor has a six-slot/six-pole structure, including two separated windings for the single-phase six-pole motor and the three-phase four-pole suspension. The stator core has a staggered-tooth structure to produce starting torque. The single-phase motor winding is connected between the neutral point of the three-phase suspension winding and the midpoint of the dc power sources. The radial suspension force is calculated analytically and verified using the finite-element method. In addition, we introduce a ripple compensation method for the suspension force. A prototype of a bearingless permanent magnet motor with 2-DOF active suspension was built and tested. The results of experiments demonstrated that the rotor, which was driven at speeds up to 8000 r/min, could be levitated successfully, using only one three-phase inverter.

1 kW/60,000 min−1bearingless PM motor with combined winding for torque and rotor suspension

A comprehensive description of a bearingless permanent magnet synchronous machine is presented including simulation, design, control and measurement focusing on a 1 kW/60,000 min -1 machine. A combined six-phase winding is used for the excitation of the two-pole motor field wave and the four-pole levitation field wave by applying two parallel three-phase current systems. The decomposition into the individually controllable current systems for motor torque and lateral rotor position control and the calculation of the relevant control parameters is explained. Measurements give an insight on the controlled motor performance. Thus, it is shown that the combination of torque and lateral force production with a single six-phase winding, fed by two three-phase inverters, not only leads to advantages in winding manufacturing but can be operated with a conventional field-oriented control also at high speed.

Design and Analysis of a Novel Bearingless Motor for a Miniature Axial Flow Blood Pump

In this paper, a novel design for the axial flow blood pump is proposed, based on the bearingless permanent magnet (PM) motor concept. The design of the impeller, the rotor, and the stator is explained. The axial length of the impeller is optimized based on the finite-element analysis (FEA), and because of reduced axial length of the rotor, only one radial active magnetic bearing is used, whose functionality is embedded in the same stator, which is used for generating motor torque. A novel design of the rotor and the stator is proposed for measuring the radial position of the rotor using four linear Hall effect sensors. This sensor assembly can measure the radial position of the rotor with good accuracy. The angular position of the rotor is measured with two Hall effect sensors. The 3-D FEA of the complete system is performed, and suspension forces, stiffness, and torques are evaluated under various control conditions. The control strategy for the bearingless PM motor based on the Hall effect position sensors is explained. The experimental setup is built in order to guide the process of design. The experimental results of the system are evaluated under different operating conditions and compared with FEA results.

Modeling and Analysis of Hybrid Permanent Magnet Type Bearingless Motor

The traditional bearingless permanent magnet synchronous motor has complex decoupling control problems. To overcome the drawbacks above, a novel hybrid permanent magnet type bearingless motor (HPMTBM) is proposed in this paper, which has integrated the merits of hybrid excitation permanent magnet motor and magnetic bearings. The main advantages of this HPMTBM are the simple control mechanism and the low power consumption. First, the principle and theoretical background of this motor are introduced. Then, the mathematical models of radial suspension force and torque are established using Maxwell stress tensor method, and air-gap magnetic fields, radial suspension forces are calculated by finite-element analysis. Finally, the prototype motor is designed and constructed. The radial suspension forces and rotor radial displacements are tested. The simulation and experimental results show the feasibility of the proposed HPMTBM.

Speed Control of Bearingless Permanent Magnet Synchronous Motor Based on Flux Strengthening and Voltage Regulation

In order to reduce the speed fluctuation of bearingless permanent magnet synchronous motors (BPMSMs) and considering the effect of suspension force load on the suspension performance, a novel speed control method of the BPMSM based on flux strengthening and voltage regulation is presented in this paper. First, the structure of the BPMSM and the principle of suspension force generation are introduced. Second, based on the mathematical models of the BPMSM, the principles of the flux strengthening and voltage regulation control are analyzed. Besides, the effect of the flux strengthening control method on the suspension performance is illustrated. Third, the control system of the BPMSM is designed on the foundation of the proposed control method, and the cooperation strategy of the flux strengthening and voltage regulation control is proposed to improve the speed performance. Finally, the experimental results on the BPMSM prototype confirm that the proposed control strategy can reduce the speed fluctuation and improve the suspension performance of the BPMSM effectively.

Thermal modeling and analysis of bearingless permanent magnet synchronous motors

Thermal modeling and analysis of bearingless permanent magnet synchronous motors

An improved rotating HF signal injection method based on FIR filters for state estimation of BPMSM sensorless control

An improved rotating high-frequency signal injection method based on a finite impulse-response filter for state estimation of bearingless permanent magnet synchronous motor sensorless control is developed in this article. A novel equiripple optimal approximation finite impulse-response filter, which can achieve that the maximum error of pass-band and stop-band is minimum than other finite impulse-response filter under the conditions of the same-order magnitude, is introduced to extract the high-frequency current signal and realize minimum extraction error. The rotor position error signal can be extracted using heterodyning processing to the high-frequency current. The proposed method can effectively eliminate the synchronous shaft filter and reduce the complexity of the system. Linear-phase compensation is used in the finite impulse-response filter to achieve minimum delay of rotor speed and position estimation. The BPMSM sensorless vector control system is set up based on this estimation approach. Simulation results indicate that the proposed method integrated off-line optimization of a finite impulse-response filter and linear-phase compensation can accurately estimate the rotor position and speed in the full-speed range.

Design and analysis of interior composite-rotor bearingless permanent magnet synchronous motors with two layer permanent magnets

Abstract In this paper, a new type of interior composite-rotor bearingless permanent magnet synchronous motors (BPMSMs) with two layer permanent magnets (PMs) is proposed. In order to reduce the torque ripple of this kind of motors, the sizes of PMs are optimized. Moreover, the magnetic field analysis of the interior composite-rotor BPMSM with two layer PMs is carried out by the finite element method (FEM). The corresponding static electronic magnetic characteristics at no load, including magnetic field, PM flux linkage and inductance, are studied in detail. In addition, electromagnetic torque characteristics and suspension force characteristics are also investigated thoroughly. The results of the analysis and simulation lay a significant foundation for further research on the interior composite-rotor BPMSMs with two layer PMs.

Analysis of Winding Forms for Bearingless Flux-Switching PM Motor with U-core Stator Laminations

Due to low-cost and magnet-free rotor structure, bearingless flux-switching permanent magnet motors (BFSPMs) are more applicable to high-temperature and/or disposable applications. A BFSPM with U-core stator laminations is investigated in this paper. First, the operational principle is analyzed in accordance with the influence of winding connection manners on torque and radial forces, and then the basic winding arrangement for torque windings and radial force windings is determined. The mathematical models of torque and radial forces are derived based on the basic winding arrangement. Followed by that, a method to select winding terminal connection manners is proposed by taking into account control scheme and power inverter topologies. A promising terminal connection is found from three possible candidates and a detailed current model for torque and radial force control are given for the promising winding forms. Finally, relevant electromagnetic properties of the motor are verified and analyzed by finite element analysis.

Design and Analysis of a Novel Bearingless Flux-Switching Permanent Magnet Motor

Conventional bearingless permanent magnet motors have magnets on their rotor, and their maximum electric loading performance may be restricted by thermal instability and lack of mechanical integrity. To overcome such drawbacks, a novel bearingless motor with magnets, suspension force windings, and torque windings in the stator is proposed; the proposed motor is called bearingless flux-switching permanent magnet motor. First, the structure and winding configuration of the bearingless flux-switching permanent magnet motor are designed and introduced. Second, the operation principle of radial suspension force is illustrated based on the principle of reverse direction magnetization for symmetrical rotor teeth. Third, the corresponding electromagnetic characteristics, including flux field distributions, torque, and controllability of radial suspension forces, are investigated. Finally, the decoupling characteristics between suspension force windings and torque windings are discussed and analyzed comprehensively. High power per permanent magnet volume, good controllability of radial suspension forces, and excellent decoupling characteristics are achieved with the proposed bearingless flux-switching permanent magnet motor. Analytical results are validated through finite-element analysis and experimentation.

Compensation control of suspension force for LS‐BLPMSM

To overcome the difficulty in start-up of bearingless permanent magnet synchronous motor (BLPMSM), a novel structure of line-starting BLPMSM (LS-BLPMSM) is presented in this study, which has the ability of self-starting. First, the operation principle of the LS-BLPMSM is expounded and the suspension operation condition is deduced. Since two sets of windings are arranged in the stator of bearingless motor, different pole-pair cooperation between two sets of windings cause breaking or driving torque, and the theory of pole-pair cooperation is analysed. Second, the interference of squirrel-cage on suspension force magnetic field is studied based on the T-type equivalent circuit model of the equivalent induction motor formed by the suspension force windings and squirrel-cage bars, and a suspension force compensation strategy is presented. Finally, an experimental prototype with 2-pole-pair torque windings and 1-pole-pair suspension force windings is tested under different working conditions with the proposed control strategy. The rotation speed and the displacements in x and y axes are provided. The simulation and experimental results have shown that the motor has good rotation and suspension performance, and the validity and feasibility of this control strategy are confirmed.

Modeling and control of a bearingless permanent magnet synchronous motor

This paper presents a suspension force modeling method of BPMSMs based on Maxwell stress tensor method. By deducing the magnetic flux density of the airgap in BPMSMs using magnetic circuit analytic approach, the suspension force model with rotor eccentricity is established. And then the suspension force of a surface-mounted BPMSM is computed by the finite element method. Furthermore, in order to confirm the performance of the BPMSM and the magnetic suspension in real time, a prototype machine and its control scheme is set up and then corresponding experimental study is carried on. Rotor stabilization with magnetic levitation by using Maxwell tensor modeling method is verified by the simulation and experimental results.

Experimental verification of an angle-sensorless control scheme for bearingless permanent magnet machines

Experimental verification of an angle-sensorless control scheme for bearingless permanent magnet machines

Internal Model Control for a Bearingless Permanent Magnet Synchronous Motor Based on Inverse System Method

To effectively enhance the control accuracy and dynamic performance of a bearingless permanent magnet synchronous motor (BPMSM), this paper presents a novel control scheme combining the inverse system method and the internal model control. By cascading the inverse model of the BPMSM with the original BPMSM system, a decoupling pseudo-linear system is constituted. Moreover, in order to improve the robustness of the whole system and reject the influence of the unmodeled dynamics and system noise to the decoupling control accuracy, the internal model control scheme is employed for the pseudo-linear system to design extra closed-loop controllers. Consequently, the proposed decoupling control scheme incorporates the advantages of both the inverse system method and the internal model control. The effectiveness of the proposed control scheme is verified by experimental results at various operations.

Suspension Force Modeling for a Bearingless Permanent Magnet Synchronous Motor Using Maxwell Stress Tensor Method

Bearingless permanent magnet synchronous motors (BPMSMs) have been received more and more attention during the past few decades. To realize the high-performance control for rotation and levitation, we will first need to obtain the accurate suspension force model of a BPMSM. In this work, different from conventional suspension force models, a modeling scheme for the suspension force of a BPMSM is presented by taking into account rotor eccentricity with the Maxwell stress tensor modeling scheme. The theoretical value of a suspension force model is compared by the two-dimensional finite element (FE) analysis, and calculation results reveal that the theoretical value closely agree with the FE computed one. Furthermore, the digital control system is devised by taking advantage of TMS320F2812, and a test platform for experiments is then set up. In accordance with the corresponding findings of the experiments, the rotor stabilization with magnetic levitation can be achieved. The results lay a theoretical and experimental foundation for further study of the BPMSM.