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 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.
Highlights
Electromagnetic Actuators as Part of Active Magnetic Bearing SystemsThe operational principle of the Active Magnetic Bearings (AMB) is rather simple [1]: An electromagnetic actuator is configured to exert forces on a supported ferromagnetic object.The object position in space is monitored by a position sensor.The position sensor provides information about the object position to a control system.The control system adjusts the current in the actuator in response to changes in the position and an application specific control input.Force is applied by the actuator on the object to maintain the object in the desired position in space without coming into mechanical contact.This operational principle is schematically illustrated in Figure 1 using a simple Horse-Shoe electromagnet as an example of an electromagnetic actuator
That most often an alternative solution—a combination radial and axial homopolar permanent magnet (PM)-biased electromagnetic actuator—is a better fit for a practical industrial magnetic bearing application
In order to facilitate a rapid design process, we developed an automated approach in which the design process is driven by analytical equations, the parameters of which are constantly adjusted based on Finite Element Analysis (FEA) results
Summary
The operational principle of the Active Magnetic Bearings (AMB) is rather simple [1]:. 2, or or any any other be adjusted adjusted so so that that the the object object deflection deflection from from other type type of of magnetic magnetic bearings, bearings, is is that that the the current current II can can be the the desired desired position position would would remain remain as as zero zero regardless regardless of of the the value value of of the the external external force force acting acting on on the the object (the external force has to be static or slowly changing and not to exceed the load limit of the object (the external force has to be static or slowly changing and not to exceed the load limit of the actuator)
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