Cascaded Position-Flux Controller for an AMB System Operating at Zero Bias

Abstract

The paper reports on the implementation and the design of a controller for a fuel cell blower (FCB) with active magnetic bearings (AMBs). The cascaded position-fluxcentralized controller is comprised of a centralized position control loop and an inner flux control loop. The last one is based on state estimation without explicit flux measurements. As the position control is not dependent on the magnetic field nonlinearities, such a control structure enables operation under a zero bias. The practical working implementation of a flux control for the industrial levitated rotor is shown for the first time. The flux control gives better results than current control for both normal and zero bias operation. The system is analyzed fully, combining rotor dynamics and power amplifier analyses simultaneously. The importance of using the coil voltage in addition to current and practical treatment of the flux control is revealed. The centralized position-flux controller is compared with a state-of-the-art cascaded position-current control, which has inner current control loops. The proposed control solution with a zero bias can achieve a dynamic performance comparable that of a controller with the classical bias current.

A Generalized Unbiased Control Strategy for Radial Magnetic Bearings

“…The operation of magnetic bearings with zero bias flux has been a subject of several recent works such as [10,11]. These works consider eight-pole horseshoe-type magnetic bearings and treat each axis as a separate one-degree-of-freedom (1-DOF) system.…”

“…By comparing Equation (6) to Equation (10), the conditions that W must obey to convert the current-to-force equation to the desired i 2 form are…”

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

“…Note that the possibility to linearize all state equations depends on restrictive integrability conditions and as such the approach is applicable only to a limited non-zero bias mode (see, e.g., Lindlau and Knospe, 2002;Chen and Knospe, 2005;Jastrzebski et al, 2014). There exist many papers that apply feedback linearization to make the system equations exactly linear; see a brief overview below.…”

“…Moreover, the application of the flux-based control decreases the force estimation error, and the controller can achieve a larger bandwidth than a classical current-controlled AMB system. For a detailed comparison between flux-and current-control of the AMB system, with experimental verification, we refer the reader to Jastrzebski et al (2014).…”

The Proposal of Magnetic Suspension using Laterally Control Flux-Path Mechanism

“…The current of the electromagnet is controlled to produce a restoring force and damping. In several systems, direct field control using flux feedback has been applied [5][6][7][8]. One of the problems of this method is that a large current is necessary to achieve wide-gap suspension.…”