Special Issue "Active Magnetic Bearing Actuators"

A special issue of Actuators (ISSN 2076-0825).

Deadline for manuscript submissions: closed (30 November 2016).

Special Issue Editor

Dr. Eric H. Maslen
E-Mail Website
Guest Editor
Department of Integrated Science and Technology, James Madison University, Harrisonburg, VA 22807, USA
Interests: magnetic bearings; active control; rotordynamics; machine design; magnetics modeling; inverse magnetics; self-sensing

Special Issue Information

Dear Colleagues,

As active magnetic bearings become a mature commercial technology, the range of application and sophistication of design steadily increases. This has produced many different magnetic topologies, design optimization strategies, and field control schemes. This Special Issue is aimed at taking stock of this art, with a particular emphasis on the actuator: The magnetic component and the associated drive electronics. Although passive and electrodynamic magnetic bearings are also increasingly important, the focus here will be on fully active actuators which use some combination of magnetically permeable materials, permanent magnets, and powered coils to produce forces on a rotor or other suspended object. Contributions are particularly encourage related (but not limited) to: scaling issues, low and high pole count, loss estimation and mitigation, high and very low flux density designs, high and very low temperature designs, amplifier schemes, such as transconductance and transpermeance, coupled switching arrays, inversion, and control of coupled actuators.

Dr. Eric H. Maslen
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Actuators is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Active magnetic bearings
  • Inverse magnetics
  • Design optimization
  • Power amplifiers
  • Magnetic losses
  • Low temperature magnetics
  • High temperature magnetics

Published Papers (12 papers)

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Editorial

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Editorial
Actuators for Active Magnetic Bearings
Actuators 2017, 6(4), 31; https://doi.org/10.3390/act6040031 - 27 Oct 2017
Viewed by 3576
Abstract
The literature of active magnetic bearing (AMB) technology dates back to at least 1937 when the earliest work that clearly describes an active magnetic bearing system was published by Jesse Beams [...]
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(This article belongs to the Special Issue Active Magnetic Bearing Actuators)

Research

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Article
Modeling and Testing Strategies for an Interconnected Four-Pole Magnetic Bearing
Actuators 2017, 6(3), 21; https://doi.org/10.3390/act6030021 - 23 Jun 2017
Cited by 2 | Viewed by 4692
Abstract
An unusual idea for the construction of active magnetic bearings has been recently discussed in the literature. Theoretical results predict a greater equivalent stiffness for it, when compared with traditional active magnetic bearings. The development of a mathematical model that allows these predictions [...] Read more.
An unusual idea for the construction of active magnetic bearings has been recently discussed in the literature. Theoretical results predict a greater equivalent stiffness for it, when compared with traditional active magnetic bearings. The development of a mathematical model that allows these predictions and the use of recently-built prototypes for testing if the expectations hold true are the main goals of this paper. Full article
(This article belongs to the Special Issue Active Magnetic Bearing Actuators)
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Article
Development of a Compact Axial Active Magnetic Bearing with a Function of Two-Tilt-Motion Control
Actuators 2017, 6(2), 14; https://doi.org/10.3390/act6020014 - 30 Mar 2017
Cited by 4 | Viewed by 5604
Abstract
A compact axial active magnetic bearing with a function of two-tilt-motion control is fabricated which has a new configuration of magnetic poles. They consist of four cylindrical poles with coils and a single common pole whose opposite plane of the rotor has a [...] Read more.
A compact axial active magnetic bearing with a function of two-tilt-motion control is fabricated which has a new configuration of magnetic poles. They consist of four cylindrical poles with coils and a single common pole whose opposite plane of the rotor has a permanent magnet to achieve multi-degree-of-freedom zero power control. Modal control is applied because local zero power control may make the whole system unstable when the number of control channels is larger than the number of freedoms of motion to be controlled. In the developed system, a disk-shape rotor is sandwiched between two axial magnetic bearing stators that are operated differentially. Such a configuration makes it possible to rotate the rotor without disturbing the axial motion. The characteristics of the fabricated magnetic bearing system including rotation are studied experimentally. Full article
(This article belongs to the Special Issue Active Magnetic Bearing Actuators)
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Article
A System Identification Technique Using Bias Current Perturbation for the Determination of the Magnetic Axes of an Active Magnetic Bearing
Actuators 2017, 6(2), 13; https://doi.org/10.3390/act6020013 - 28 Mar 2017
Cited by 2 | Viewed by 4613
Abstract
Inherent in every Active Magnetic Bearing (AMB) are differences between the expected geometric axes and the actual magnetic axes due to a combination of discrepancies, including physical variation from manufacturing tolerances and misalignment from mechanical assembly, fringing and leakage effects, as well as [...] Read more.
Inherent in every Active Magnetic Bearing (AMB) are differences between the expected geometric axes and the actual magnetic axes due to a combination of discrepancies, including physical variation from manufacturing tolerances and misalignment from mechanical assembly, fringing and leakage effects, as well as variations in magnetic material properties within a single AMB. A method is presented here for locating the magnetic axes of an AMB that will facilitate the accurate characterization of the bearing air gaps for potential improvement in field tuning, performance analyses and certain shaft force measurement techniques. This paper presents an extension of the application of the bias current perturbation method for the determination of the magnetic center to the determination of magnetic axes for the further development of accurate current-based force measurement techniques. Full article
(This article belongs to the Special Issue Active Magnetic Bearing Actuators)
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Article
Modeling and Realization of a Bearingless Flux-Switching Slice Motor
Actuators 2017, 6(2), 12; https://doi.org/10.3390/act6020012 - 27 Mar 2017
Cited by 8 | Viewed by 5371
Abstract
This work introduces a novel bearingless slice motor design: the bearingless flux-switching slice motor. In contrast to state-of-the-art bearingless slice motors, the rotor in this new design does not include any permanent rotor magnets. This offers advantages for disposable devices, such as those [...] Read more.
This work introduces a novel bearingless slice motor design: the bearingless flux-switching slice motor. In contrast to state-of-the-art bearingless slice motors, the rotor in this new design does not include any permanent rotor magnets. This offers advantages for disposable devices, such as those used in the medical industry, and extends the range of bearingless slice motors toward high-temperature applications. In this study, our focus is on the analytical modeling of the suspension force torque generation of a single coil and the bearingless motor. We assessed motor performance in relation to motor topology by applying performance factors. A prototype motor was optimized, designed, and manufactured. We also presented the state-of-the-art nonlinear feedback control scheme used. The motor was operated, and both static and dynamic measurements were taken on a test bench, thus successfully demonstrating the functionality and applicability of the novel bearingless slice motor concept. Full article
(This article belongs to the Special Issue Active Magnetic Bearing Actuators)
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Article
The Proposal of Magnetic Suspension using Laterally Control Flux-Path Mechanism
Actuators 2017, 6(1), 11; https://doi.org/10.3390/act6010011 - 21 Mar 2017
Cited by 4 | Viewed by 4658
Abstract
A novel flux control magnetic suspension system that places control plates beside the magnetic source (permanent magnet) is proposed. In a conventional flux-path control magnetic suspension system, the control plates were inserted between the magnetic source and the suspended object (floator). In contrast, [...] Read more.
A novel flux control magnetic suspension system that places control plates beside the magnetic source (permanent magnet) is proposed. In a conventional flux-path control magnetic suspension system, the control plates were inserted between the magnetic source and the suspended object (floator). In contrast, the control plates were placed beside the magnetic source in the proposed system. In such a configuration, the effective gap becomes larger than in the conventional system. Basic characteristics of the proposed magnetic suspension system were studied both numerically and experimentally. The numerical analyses show that the attractive force acting on the floator increases as the position of the lateral ring-shape control plate increases. The variation of the attractive force is sufficient for the stabilization of the suspension system. It is also shown that lateral force can be generated by dividing the plates into halves and moving them differentially. The predicted characteristics are confirmed experimentally in a fabricated apparatus with a three-axis force sensor and a gap adjustment mechanism. Full article
(This article belongs to the Special Issue Active Magnetic Bearing Actuators)
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Article
Transpermeance Amplifier Applied to Magnetic Bearings
Actuators 2017, 6(1), 9; https://doi.org/10.3390/act6010009 - 15 Feb 2017
Cited by 7 | Viewed by 4968
Abstract
The most conventional approach of controlling magnetic forces in active magnetic bearings (AMBs) is through current feedback amplifiers: transconductance. This enables the operation of the AMB to be understood in terms of a relatively simple current-based model as has been widely reported on [...] Read more.
The most conventional approach of controlling magnetic forces in active magnetic bearings (AMBs) is through current feedback amplifiers: transconductance. This enables the operation of the AMB to be understood in terms of a relatively simple current-based model as has been widely reported on in the literature. The alternative notion of using transpermeance amplifiers, which approximate the feedback of gap flux rather than current, has been in commercial use in some form for at least thirty years, however is only recently seeing more widespread acceptance as a commercial standard. This study explores how such alternative amplifiers should be modeled and then examines the differences in behavior between AMBs equipped with transconductance and transpermeance amplifiers. The focus of this study is on two aspects. The first is the influence of rotor displacement on AMB force, commonly modeled as a constant negative equivalent mechanical stiffness, and it is shown that either scheme actually leads to a finite bandwidth effect, but that this bandwidth is much lower when transpermeance is employed. The second aspect is the influence of eddy currents. Using a very simple model of eddy currents (a secondary short-circuited coil), it is demonstrated that transpermeance amplifiers can recover significant actuator bandwidth compared with transconductance, but at the cost of needing increased peak current headroom. Full article
(This article belongs to the Special Issue Active Magnetic Bearing Actuators)
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Article
Applying Standard Industrial Components for Active Magnetic Bearings
Actuators 2017, 6(1), 8; https://doi.org/10.3390/act6010008 - 04 Feb 2017
Cited by 4 | Viewed by 5512
Abstract
With the increasing number of active magnetic bearing applications, satisfying additional requirements is becoming increasingly more important. As for every technology, moving away from being a niche product and achieving a higher level of maturity, these requirements relate to robustness, reliability, availability, safety, [...] Read more.
With the increasing number of active magnetic bearing applications, satisfying additional requirements is becoming increasingly more important. As for every technology, moving away from being a niche product and achieving a higher level of maturity, these requirements relate to robustness, reliability, availability, safety, security, traceability, certification, handling, flexibility, reporting, costs, and delivery times. Employing standard industrial components, such as those from flexible modular motion control drive systems, is an approach that allows these requirements to be satisfied while achieving rapid technological innovation. In this article, we discuss technical and non-technical aspects of using standard industrial components in magnetic bearing applications. Full article
(This article belongs to the Special Issue Active Magnetic Bearing Actuators)
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Article
Fractional Order PID Control of Rotor Suspension by Active Magnetic Bearings
Actuators 2017, 6(1), 4; https://doi.org/10.3390/act6010004 - 13 Jan 2017
Cited by 25 | Viewed by 6611
Abstract
One of the key issues in control design for Active Magnetic Bearing (AMB) systems is the tradeoff between the simplicity of the controller structure and the performance of the closed-loop system. To achieve this tradeoff, this paper proposes the design of a fractional [...] Read more.
One of the key issues in control design for Active Magnetic Bearing (AMB) systems is the tradeoff between the simplicity of the controller structure and the performance of the closed-loop system. To achieve this tradeoff, this paper proposes the design of a fractional order Proportional-Integral-Derivative (FOPID) controller. The FOPID controller consists of only two additional parameters in comparison with a conventional PID controller. The feasibility of FOPID for AMB systems is investigated for rotor suspension in both the radial and axial directions. Tuning methods are developed based on the evolutionary algorithms for searching the optimal values of the controller parameters. The resulting FOPID controllers are then tested and compared with a conventional PID controller, as well as with some advanced controllers such as Linear Quadratic Gausian (LQG) and H controllers. The comparison is made in terms of various stability and robustness specifications, as well as the dimensions of the controllers as implemented. Lastly, to validate the proposed method, experimental testing is carried out on a single-stage centrifugal compressor test rig equipped with magnetic bearings. The results show that, with a proper selection of gains and fractional orders, the performance of the resulting FOPID is similar to those of the advanced controllers. Full article
(This article belongs to the Special Issue Active Magnetic Bearing Actuators)
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Article
Active Magnetic Bearing Online Levitation Recovery through μ-Synthesis Robust Control
Actuators 2017, 6(1), 2; https://doi.org/10.3390/act6010002 - 08 Jan 2017
Cited by 13 | Viewed by 5268
Abstract
A rotor supported on active magnetic bearings (AMBs) is levitated inside an air gap by electromagnets controlled in feedback. In the event of momentary loss of levitation due to an acute exogenous disturbance or external fault, reestablishing levitation may be prevented by unbalanced [...] Read more.
A rotor supported on active magnetic bearings (AMBs) is levitated inside an air gap by electromagnets controlled in feedback. In the event of momentary loss of levitation due to an acute exogenous disturbance or external fault, reestablishing levitation may be prevented by unbalanced forces, contact forces, and the rotor’s dynamics. A novel robust control strategy is proposed for ensuring levitation recovery. The proposed strategy utilizes model-based μ-synthesis to find the requisite AMB control law with unique provisions to account for the contact forces and to prevent control effort saturation at the large deflections that occur during levitation failure. The proposed strategy is demonstrated experimentally with an AMB test rig. First, rotor drop tests are performed to tune a simple touchdown-bearing model. That model is then used to identify a performance weight, which bounds the contact forces during controller synthesis. Then, levitation recovery trials are conducted at 1000 and 2000 RPM, in which current to the AMB coils is momentarily stopped, representing an external fault. The motor is allowed to drive the rotor on the touchdown bearings until coil current is restored. For both cases, the proposed control strategy shows a marked improvement in relevitation transients. Full article
(This article belongs to the Special Issue Active Magnetic Bearing Actuators)
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Article
A Generalized Unbiased Control Strategy for Radial Magnetic Bearings
Actuators 2017, 6(1), 1; https://doi.org/10.3390/act6010001 - 08 Jan 2017
Cited by 8 | Viewed by 5033
Abstract
The present work extends a method of unbiased control originally developed for three-pole radial magnetic bearings into a generalized unbiased control strategy that encompasses bearings with an arbitrary number of poles. By allowing the control of bearings with more than three poles, the [...] Read more.
The present work extends a method of unbiased control originally developed for three-pole radial magnetic bearings into a generalized unbiased control strategy that encompasses bearings with an arbitrary number of poles. By allowing the control of bearings with more than three poles, the applicability of the approach is broadened to the case of large rotors. Other ramifications of this generalized unbiased control strategy are fault tolerant unbiased bearings, control of bearings with more than three poles using 3-phase drives, and a novel approach to the unbiased control of eight-pole magnetic bearings. Full article
(This article belongs to the Special Issue Active Magnetic Bearing Actuators)
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Review

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Review
Homopolar Permanent-Magnet-Biased Actuators and Their Application in Rotational Active Magnetic Bearing Systems
Actuators 2016, 5(4), 26; https://doi.org/10.3390/act5040026 - 16 Dec 2016
Cited by 18 | Viewed by 7099
Abstract
Active Magnetic Bearings (AMBs) are already widely used in rotating machinery and continue to gain popularity due to the ever-present push to higher rotational speeds and decreasing prices of associated electronic components. They offer several advantages over conventional mechanical bearings including non-contact rotor [...] Read more.
Active Magnetic Bearings (AMBs) are already widely used in rotating machinery and continue to gain popularity due to the ever-present push to higher rotational speeds and decreasing prices of associated electronic components. They offer several advantages over conventional mechanical bearings including non-contact rotor support (thus eliminating mechanical wear and the need for lubricants), ability to tune bearing parameters through software for optimum machine performance, remote monitoring and health diagnostic, etc. In some applications, such as in a vacuum or in aggressive environments, they are often the only viable solution. An electromagnetic actuator, along with a position sensor and control electronics, is a key component of AMBs. While there is a variety of actuator designs described in the literature, most of the AMBs built commercially use heteropolar radial electrical actuators in combination with a dedicated electrically-biased axial actuators. On the contrary, since its inception in 1998, Calnetix Technologies mainly uses homopolar permanent magnet (PM)-biased radial actuators along with a homopolar PM-biased combination radial/axial actuators. In this paper, we provide an overview of the research we have done over the last 15 years in this area focusing on the advantages and disadvantages of this approach and explaining why we have made certain design choices. Full article
(This article belongs to the Special Issue Active Magnetic Bearing Actuators)
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