In this paper, a hybrid magnetic bearing (HMB) prototype system is designed and analyzed. Two compact bearings are used to suspend the rotor in five degrees of freedom. Electromagnets are used for axial suspension of the rotor, while permanent magnets are used for the passive radial stability. A brushless DC motor is designed in order to rotate the shaft around its axis. The 3-D finite-element model of the HMB system is established and distribution of magnetic fields in the air gaps and magnetic forces on the rotor under various control currents and displacements is calculated. A nonlinear adaptive sliding-mode controller is designed for the position control of the rotor in axial direction. Since the control characteristics of the active magnetic bearing system are highly nonlinear and time varying with external interference, a radial basis function compensator is designed first, and then, a sliding-mode control law is used to generate the control input. The stability analysis for the designed controller is given based on the Lyapunov theorem. Experimental setup is built to guide the design process. The performance of the HMB system based on the designed control algorithm is evaluated under different operating conditions.

Design and Adaptive Sliding-Mode Control of Hybrid Magnetic Bearings

In order to improve the performance of the high-speed brushless direct current motor drives, a novel high-precision sensorless drive has been developed. It is well known that the inevitable voltage pulses, which are generated during the commutation periods, will impact the rotor position detecting accuracy, and further impact the performance of the overall sensorless drive, especially in the higher speed range or under the heavier load conditions. For this reason, the active compensation method based on the virtual third harmonic back electromotive force incorporating the SFF-SOGI-PLL (synchronic-frequency filter incorporating the second-order generalized integrator based phase-locked loop) is proposed to precise detect the commutation points for sensorless drive. An experimental driveline system used for testing the electrical performance of the developed magnetically suspended motor is built. The mathematical analysis and the comparable experimental results have been shown to validate the effectiveness of the proposed sensorless drive algorithm.

High-Precision Sensorless Drive for High-Speed BLDC Motors Based on the Virtual Third Harmonic Back-EMF

The vibration suppression in the presence of gyroscopic effects is an important issue for safe operations in magnetic bearing levitated varying speed rotor system. This paper proposes a synchronous vibration control method with a two-stage notch filter for the magnetically suspended rotor system with strong gyroscopic effects. First, the dynamics of the magnetically suspended rotor system with synchronous vibrations in the rotational motion is modeled. Then the proposed two-stage notch filter is designed and the solution of the two-stage switching point is derived to distinguish low speed and high speed. Stability analysis is also presented in the low-speed region and the high-speed region, respectively. Finally, simulation results demonstrate that the stability can be guaranteed by adjusting the phase shift angle of the notch filter over the entire speed range. Further experimental results confirm the effectiveness of the proposed suppression method.

A Two-Stage Synchronous Vibration Control for Magnetically Suspended Rotor System in the Full Speed Range

The successful industrial application of flexible rotors supported on active magnetic bearings (AMBs) requires careful attention not only to rotordynamic design aspects, but also to electromagnetic and feedback control design aspects. This paper describes the design, construction and modeling process for an AMB test rig which contains a 1.23m long flexible steel rotor, with a mass of 44.9 kg and two gyroscopic disks. The rotor typifies a small industrial centrifugal compressor designed to operate above 12,000 rpm and the first bending natural frequency. There are four AMBs — two AMBs at the shaft ends to support the shaft with a combined load capacity of 2600N and two additional AMBs at the mid and quarter spans to allow for the application of simulated destabilizing fluid or electromagnetic forces to the rotor. Simulated aerodynamic cross coupling stiffness values are to be applied to the rotor through these two internal AMBs with the goal of developing stabilizing robust controllers. The unique design allows multiple support and disturbance locations providing the ability to represent a variety of machine configurations, e.g., between bearing and overhung designs. The shaft transfer function in lateral movement has been developed with finite element model and then verified by experimental frequency response measurements. Models for the power amplifiers, position sensors, signal conditioning and data converter hardware were developed, verified experimentally and included in the overall system model. A PID controller was developed and tuned to levitate the rotor and enable further system characterization.Copyright © 2010 by ASME

Design, Construction and Modeling of a Flexible Rotor Active Magnetic Bearing Test Rig

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.

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

This paper proposes a phase compensator design for the flexible rotor in the high-energy-density magnetically suspended motor (HEDMSM), whose rated rotational speed is above the first bending critical speed. The optimum phase and magnitude of the control system nearby the critical speed are analyzed. Additionally, the coil inductance of the large-power HEDMSM is always large. That will lead to large phase lag and make optimum compensator design more difficult. Therefore, an effective phase-leading compensation method is presented to compensate the large phase lag of the switching power amplifier. Then, the optimum compensator is designed and carried out in the 315-kW HEDMSM. The experimental results show that the optimum compensator can minimize the displacement resonance peak, when the rotor passes the first bending critical speed with low amplifier current.

Optimum Compensator Design for the Flexible Rotor in Magnetically Suspended Motor to Pass the First Bending Critical Speed

The active surge suppression is a challenging topic in the industrial compressor systems. This paper addresses the two issues on the surge detection approach for magnetically suspended centrifugal compressors (MSCCs) utilizing the signal monitoring capabilities of magnetic bearings. An adaptive frequency estimator is proposed to extract the surge signal, and a judgment criterion is establish to the surge state. First, the derivation of a surge disturbance transfer model for the fluctuating pressure and rotor displacement was presented, and the characteristics of surge signal in the MSCC system is analyzed. Then, a conventional notch filter (NF) is used to eliminate the synchronous disturbance in the surge signal, and a modified adaptive notch filter (ANF) method is used to estimate the frequency of surge signal. The convergence analysis of the modified ANF shows that the linearized system is asymptotically stable. The mild surge detection technology and judgement criterion are also discussed. Experimental results on both the 100 kW and 315 kW MSCC systems show that the proposed method can rapidly detect the surge before the MSCC systems develops into the modified surge.

Surge Detection Approach for Magnetically Suspended Centrifugal Compressors Using Adaptive Frequency Estimator

The eddy current displacement (ECD) sensors used for displacement measurement are the core component of the magnetically levitated rotor (MLR) system. The temperature compensation of the ECD sensor is an important condition to ensure the stable operation of the MLR system in a wide temperature range. This article proposes a simultaneous compensation solution based on an improved signal extraction circuit to the issue of temperature drift for the ECD sensor. First, according to the operating principle of the ECD sensor, the generating mechanism and effect of the temperature drift are analyzed. Then, the principle of the simultaneous compensation method based on an auxiliary temperature sensor is expounded, which has a simple structure and strong universality. Furthermore, in order to determine the resistance ratio parameters, the procedure of designing a temperature self-compensation circuit is given in detail. Finally, the experimental results on an ultrahigh-speed magnetically levitated centrifugal compressor validate the effectiveness of the proposed method.

Yin Zhang

Papers

Optimum Compensator Design for the Flexible Rotor in Magnetically Suspended Motor to Pass the First Bending Critical Speed

Surge Detection Approach for Magnetically Suspended Centrifugal Compressors Using Adaptive Frequency Estimator

Simultaneous Temperature Drift Compensation for Eddy Current Displacement Sensors Used in Magnetically Levitated Rotor