Design, Construction and Modeling of a Flexible Rotor Active Magnetic Bearing Test Rig

Abstract

The successful industrial application of flexible rotors supported on active magnetic bearings (AMBs) requires careful attention not only to rotordynamic design aspects, but also to electromagnetic and feedback control design aspects. This paper describes the design, construction and modeling process for an AMB test rig which contains a 1.23m long flexible steel rotor, with a mass of 44.9 kg and two gyroscopic disks. The rotor typifies a small industrial centrifugal compressor designed to operate above 12,000 rpm and the first bending natural frequency. There are four AMBs — two AMBs at the shaft ends to support the shaft with a combined load capacity of 2600N and two additional AMBs at the mid and quarter spans to allow for the application of simulated destabilizing fluid or electromagnetic forces to the rotor. Simulated aerodynamic cross coupling stiffness values are to be applied to the rotor through these two internal AMBs with the goal of developing stabilizing robust controllers. The unique design allows multiple support and disturbance locations providing the ability to represent a variety of machine configurations, e.g., between bearing and overhung designs. The shaft transfer function in lateral movement has been developed with finite element model and then verified by experimental frequency response measurements. Models for the power amplifiers, position sensors, signal conditioning and data converter hardware were developed, verified experimentally and included in the overall system model. A PID controller was developed and tuned to levitate the rotor and enable further system characterization.

Optimization Strategy for PID-Controller Design of AMB Rotor Systems

“…For parallel-and tiltingmode control, the same controller structure is used. Because of the limitation of the DSP system, the PID controller slightly differs from the commonly used PID-controller structure as given in (9). The PID controller (Fig.…”

“…The controller structure is given in (9). It includes five filters: two second-order filters (number 4 in Table V), one all-pass filter (number 3), and two low-pass filters of second order (number 2).…”

“…A drawback of this method is that the robustness properties are not taken into account explicitly, and all states are required for feedback (therefore, an observer becomes necessary). Robust control methods (H ∞ -controller [8], μ-synthesis [9]) have been developed to compensate for some of the drawbacks of the LQ method, focusing on both performance and robustness of the controlled system. In [9], a test rig designed to investigate rotordynamic instability due to aerodynamic loads is supported by two AMBs, which are controlled by μ-synthesis controller.…”

“…Robust control methods (H ∞ -controller [8], μ-synthesis [9]) have been developed to compensate for some of the drawbacks of the LQ method, focusing on both performance and robustness of the controlled system. In [9], a test rig designed to investigate rotordynamic instability due to aerodynamic loads is supported by two AMBs, which are controlled by μ-synthesis controller. Compared with a proportional-integral-derivative (PID) controller, the μ-synthesis controller shows an improved stability and performance.…”

Imbalance compensation for an AMB system with adaptive immersion & invariance control

“…The feedback linearized system of the original system (1) by (4) is given by (16) which is in the form of (8) and (9) with…”