IEEE TRANSACTIONS ON MAGNETICS, VOL. 50, NO. 11, NOVEMBER 2014 8300404
Design and Static Performance Analysis of a
Novel Axial Hybrid Magnetic Bearing
Xianxing Liu, Jinyue Dong, Yi Du, Kai Shi, and Lihong Mo
School of Electrical and Information Engineering, Jiangsu University, Zhenjiang 212013, China
This paper proposes an axial permanent magnet-biased hybrid magnetic bearing, which possesses the advantages of low power
consumption, simple structure, and easy control. The structure and operation principle are introduced. Then, the mathematical
models, including the suspension force expression, are built based on traditional equivalent magnetic circuit. In addition, the basic
principle of structure parameter design is presented, based on which the key parameters are given. Due to the inaccuracy of the
traditional equivalent magnetic circuit, an improved method for magnetic circuit is introduced. Last, the accuracy of the analytical
method is validated by finite element analysis and it also has an important reference value for other types of magnetic bearings
design.
Index Terms—Equivalent magnetic circuit method, finite element analysis (FEA), hybrid magnetic bearing, permanent magnet
biased.
I. INTRODUCTION
C
OMPARED with conventional bearings, a magnetic bear-
ing has a lot of advantages, such as no friction, no abra-
sions, no lubrication, high speed, small noise, high precision,
long life, and so on [1]–[3]. Since there is no mechanical
contact between the stator and rotor, magnetic bearing can
achieve a very high speed, which means it is suitable for
applications such as high speed electrical machines, energy
storage flywheels for energy transmission, precision machining
spin-spindles, and so on. Based on the different producing
principle of the suspension force, magnetic bearings can be
classified as passive magnetic bearing (PMB), active magnetic
bearing (AMB), and hybrid magnetic bearing (HMB). Since
the permanent magnets (PMs) biased HMB combines the
merits of PMB and AMB [4]–[6], it has aroused general
interest in magnetic bearing areas [7].
In this paper, an axial permanent magnet-biased hybrid
magnetic bearing (APMHMB) is proposed, which has the
features of lower power consumption, simple structure, and
easy control. Since some distribution of magnetic field cannot
be correctly analyzed by traditional equivalent magnetic circuit
methods, a method for improving the magnetic path is adopted
based on analysis of the magnetic circuit, which not only can
be applied in the proposed APMHMB design, but also has an
important reference value for other types of magnetic bearings
design. Combining improvement to the magnetic path and the
given structure parameter design method, the analysis accuracy
can be effectively enhanced.
II. C
ONFIGURATION AND OPERATION PRINCIPLE
Fig. 1 shows the proposed APMHMB, which consists of a
disc-shaped rotor and tubular stator. The stators are composed
of two E-shaped iron cores of which the two PM rings and two
control coils are inset in the slots, respectively. In addition,
the rotor is designed as a simple plane iron core, which is
sandwiched between the two E-shaped stator iron cores. In
order to ensure that the rotor can rotate freely, two air gaps
are arranged between two stator iron cores and rotor. Thus,
Manuscript received March 7, 2014; revised May 22, 2014; accepted
May 25, 2014. Date of current version November 18, 2014. Corresponding
author: X. Liu (e-mail: liuxianxing@ujs.edu.cn).
Color versions of one or more of the figures in this paper are available
online at http://ieeexplore.ieee.org.
Digital Object Identifier 10.1109/TMAG.2014.2327165
Fig. 1. Configuration of proposed APMHMB. (a) Cross section of proposed
APMHMB. (b) Enlarged view.
the proposed HMB has symmetrical structures in the above
and below sides. In addition, the NdFeB PM ring is polarized
axially to produce the magnetic field axially. The dashed lines
and solid lines denote the flux paths generated by the PMs
and control coils, respectively.
The static resulting forces generated by PMs can levitate
the rotor in the ideal equilibrium position with neither external
disturbance nor load. When a disturbance force is exerted on
rotor in the positive y-direction, the rotor will be displaced
from the balance position toward upside, which results in
the length variation of the two air gaps. Consequently, the
magnetic flux density in the upper air gap around the rotor
will become stronger, and that in the lower air gap will
be depressed. In order to achieve the rotor suspension, an
appropriate current should be fed into the two control coils
to generate the control flux according to the control demand.
Thus, the control flux can be superposed with the PM-biased
flux, hence achieving the flux density reduction and increase
in the upper and below air gaps, respectively. As a result, the
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