Active Magnetic Bearing Online Levitation Recovery through μ-Synthesis Robust Control

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 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.

An Improved Equivalent-Input-Disturbance Method for Uncertain Networked Control Systems with Packet Losses and Exogenous Disturbances

“…An exogenous disturbance was d(t) = 30 tanh 0.1t + 50 sin 0.1πt + 20 cos(0.3/πt). (46) According to the reference (45), the parameters of the internal model ( 9) were chosen as…”

“…This study takes a magnetic levitation ball system as an example to further illustrate the effectiveness and applicability of this method [46]. The system (Figure 8) contains an electromagnet, a power amplifier, a laser sensor, a hollow steel ball, a local controller, the main controller, and network communication.…”

Condition Monitoring of Active Magnetic Bearings on the Internet of Things

“…Active Magnetic Bearings (AMBs) support a rotor with a magnetic field such that the rotor is levitated [1]. AMBs are an alternative to other types of bearings such as rolling element bearings and fluid film bearings [2]. AMBs have advantages over other types of bearings such as the potential for higher efficiency and rotational speeds.…”

Actuators for Active Magnetic Bearings

“…References [13,14] explore some specific practical directions of control. Pesch et al [13] look at the problem of recovery from momentary contact with the touch-down bearing, using a robust µ-synthesis approach.…”

“…References [13,14] explore some specific practical directions of control. Pesch et al [13] look at the problem of recovery from momentary contact with the touch-down bearing, using a robust µ-synthesis approach. Anatachaisilp et al [14] explore the use of fractional order control (as opposed to more familiar integer-order control) to achieve desired control shaping with substantially reduced controller complexity.…”