Self-sensing Active Magnetic Bearing Research Articles

A Multifrequency Disturbances Identification and Suppression Method for the Self-Sensing AMB Rotor System

The self-sensing active magnetic bearing (SAMB) rotor systems own the benefits of reduced cost and better system integration, from the substitution of rotor displacement estimation for external sensors. However, the self-sensing errors between the real and estimated rotor displacement, together with the unbalance force and sensor runout, will act as disturbances that affect the SAMB rotor system, inducing current fluctuations and rotor vibrations. This paper presents a disturbance suppression method for the modulation-type SAMB rotor systems, in which both the amplitude and phase of disturbances are identified and real-time updated. A lumped multifrequency disturbances model is established. And a disturbances identification algorithm with object function value-based step vectors is proposed. The system stability and method convergence conditions are analyzed. The convergence rate, overshoot and antinoise capacity of the method are verified through simulations. In the end, the effectiveness and performance of the suppression method are validated through steady state and varying rotational speed experiments on a 4-DOF radial SAMB rigid rotor platform.

Feedback linearization of an active magnetic bearing system operated with a zero–bias flux

AbstractInput-output linearization by state feedback is applied to a flux-controlled active magnetic bearing (AMB) system, operated in the zero-bias mode. Two models of the AMB system are employed. The first one is described by the third-order dynamics with a flux-dependent voltage switching scheme, whereas the second one is the fourth-order system, called self-sensing AMB, since it does not require the measurement of the rotor position. In the case of that system we had to find the flat outputs to guarantee its stability. The proposed control schemes are verified by means of numerical simulations performed within the Matlab environment.

A Self-Sensing Active Magnetic Bearing Based on a Direct Current Measurement Approach

Active magnetic bearings (AMBs) have become a key technology in various industrial applications. Self-sensing AMBs provide an integrated sensorless solution for position estimation, consolidating the sensing and actuating functions into a single electromagnetic transducer. The approach aims to reduce possible hardware failure points, production costs, and system complexity. Despite these advantages, self-sensing methods must address various technical challenges to maximize the performance thereof. This paper presents the direct current measurement (DCM) approach for self-sensing AMBs, denoting the direct measurement of the current ripple component. In AMB systems, switching power amplifiers (PAs) modulate the rotor position information onto the current waveform. Demodulation self-sensing techniques then use bandpass and lowpass filters to estimate the rotor position from the voltage and current signals. However, the additional phase-shift introduced by these filters results in lower stability margins. The DCM approach utilizes a novel PA switching method that directly measures the current ripple to obtain duty-cycle invariant position estimates. Demodulation filters are largely excluded to minimize additional phase-shift in the position estimates. Basic functionality and performance of the proposed self-sensing approach are demonstrated via a transient simulation model as well as a high current (10 A) experimental system. A digital implementation of amplitude modulation self-sensing serves as a comparative estimator.

Self-sensing active magnetic bearing using real-time duty cycle

In a self-sensing active magnetic bearing (AMB) system driven by pulse width modulation (PWM) switching power amplifiers, the rotor position information can be extracted from coil current and voltage signals by a specific signal demodulation process. In this study, to reduce the complexity of hardware, the coil voltage signal was not filtered but measured in the form of a duty cycle by the eCAP port of DSP (TMS320F28335). A mathematical model was established to provide the relationship between rotor position, current ripple, and duty cycle. Theoretical analysis of the amplitude-frequency characteristic of the coil current at the switching frequency was presented using Fourier series, Jacobi-Anger identity, and Bessel function. Experimental results showed that the time-varying duty cycle causes infinite side frequencies around the switching frequency. The side frequency interval depends on the varying frequency of the duty cycle. Rotor position can be calculated by measuring the duty cycle and demodulating the coil current ripple. With this self-sensing strategy, the rotor system supported by AMBs can steadily rotate at a speed of 3000 r/min.

Magnetic levitation of a one DOF system using simultaneous actuation and displacement sensing technique

This paper discusses the development of a displacement self-sensing estimator for a one degree of freedom (DOF) magnetically levitated system using the parameter estimation technique. Current demodulation technique is known to be capable of extracting the air gap length from the coil current with demodulation filters. However, one of its main disadvantages is that its output is a function of the air gap length and the duty cycle of the PWM amplifiers. It is therefore demonstrated here, through computer simulation and experimental investigation, that the self-sensing parameter estimation technique is capable of removing the variable duty cycle from the estimated output. It is composed of two identical demodulation filters, one coil inductance simulator and one PI convergence controller. Benefiting from the closed loop characteristics of the self-sensing parameter estimation, not only is the influence of the duty cycle removed, but the dynamic characteristics of the selfsensing system are also greatly enhanced. The design of the analogue circuitries implementing the algorithm of the self-sensing parameter estimator is described. Very good agreement in the static and dynamic calibrations of the estimator output is observed, when compared with a dial gauge and commercial eddy current probe. While the self-sensing active magnetic bearing (AMB) system is levitated, excellent signal tracking capability of the parameter estimator is noted.

Improvement of Frequency Characteristic of Self-Sensing Active Magnetic Bearing with Zero-Bias Current Control

An improvement of frequency characteristic of self-sensing active magnetic bearings (AMBs) with zero-bias current control is proposed. In the self-sensing AMBs non-liner magnetic characteristic of electromagnet degrades the frequency characteristic of the position sensing. Furthermore noise is observed due to alternations of electromagnet's excitation. This also degrades the frequency characteristic. In this paper, current-interference compensation and linearizing current disturbance are utilized. The method achieves improvement of the frequency characteristic of the position sensing.

ゼロバイアス電流方式によるセルフセンシング磁気軸受

A zero-bias-current self-sensing active magnetic bearing is proposed. One degree-of-freedom (DOF) of the rotor is controlled by a pair of electromagnets which are alternatively energized by the proposed circuit. The rotor position of the one DOF is measured by using both electromagnets: the nonenergized electromagnet also contributes to the position sensing. The proposed method gives good linearity in the position estimation. The controller of the magnetic levitation consists of a digital signal processor, DSP, which compensates the nonlinearity of the magnetic force and achieves good damping. In the experiment, the rotor can run at 45,000 min-1. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 165(2): 69–76, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20616

Self-Sensing Active Magnetic Bearings Using a New PWM Amplifier Equipped with a Bias Voltage Source

In this paper, a self-sensing active magnetic bearing (AMB) with a new PWM amplifier is proposed. This amplifier employs two DC sources: one supplies a control current and the other supplies a bias current. A pair of electromagnets driven by this amplifier also works as a position sensor based on bridge measurement. In the experiment, a rotor running at 45,000 min-1 is suspended by the proposed 5-axis AMB without any position sensors. The experimental system is still stable even if the length of the cables between the PWM amplifiers and the electromagnets is varied within 45 meters.

704 セルフセンシング磁気軸受の実用化の研究(関東支部 茨城講演会)

Active magnetic bearing (AMB) requires multiple displacement sensors. Separate sensors cause several problems; high sensor cost, installing space and non-collocation between the actuators and the sensors. To overcome these problems, self-sensing technique has been proposed. In this paper, nonlinear characteristics of the differential transformer type displacement estimation are analyzed. Then the compensation method is developed which is applied to the internal PM type self-sensing AMB with good results.