The undesired synchronous vibration due to rotor mass imbalance is a main disturbance source in all rotating machinery including active magnetic bearing (AMB)-rotor systems. In the AMB-rotor system, imbalance compensation, which causes the AMB actuators to spin a rotor about its geometric axis, and automation balancing, which spins a rotor about its inertial axis, are two kinds of common control aim for the rotor imbalance control. In this study, the internal relation between the imbalance compensation and the automation balancing is analyzed and a uniform control method is proposed. With the identical control algorithm, the proposed control method can realize the automation balancing or the imbalance compensation, respectively, by switching the controller’s junction position in the original control loop. The proposed control method does not depend on the dynamic plant model, because its algorithm is based on the real-time identification for the Fourier coefficient of the rotor imbalance disturbance. In this paper, the process of identification algorithm is given in detail and all the possible junction forms of the controller are illustrated. By the simulations, the identification performances of the control algorithm are compared in the conditions with three variable factors, including the signal noise ratio (SNR), the imbalance phase and the identification delay time. The noise level has considerable influence on the identification precision, but the imbalance phase has little. To prolong the identification delay time will be of benefit to improve the identification precision but slow down the identification process. Experiments, which are carried out on an AMB-rigid rotor test rig, indicate that by switching the junction position of the controller in control loop, both kinds of rotor imbalance control can achieve the good effectiveness.

A Uniform Control Method for Imbalance Compensation and Automation Balancing in Active Magnetic Bearing-Rotor Systems

It is necessary to reduce the vibration of rotors supported on active magnetic bearings (AMBs) with high displacement precision requirement in operation. An unbalance compensator for an AMB-rigid rotor system is studied. The dynamic model of an AMB-axially symmetric rigid rotor system was first established. Then, the specific form of compensating currents in the AMBs was obtained. At last, an unbalance compensator based on real-time variable step size (VSS) polygonal iterative seeking algorithm for equivalent unbalance coefficients of the rotor at the AMBs positions was proposed. With the compensator, the AMBs produce additional forces that are of same magnitudes but opposite phases as the equivalent unbalance forces at the AMBs positions to reduce the rotor vibration. Since the equivalent unbalance coefficients, which represent the equivalent imbalance of the rotor at the AMBs positions, are independent of the rotating speed, thus, the compensator is suitable for application in both steady state and varying-speed operations. With the VSS method, both the accuracy and the convergence rate of the identification algorithm could be realized. Numerical simulations and experiments confirmed the effectiveness of the proposed method for suppressing the unbalance vibration of the AMB-rotor system in steady states and varying-speed operations.

Unbalance Compensation for Active Magnetic Bearing Rotor System Using a Variable Step Size Real-Time Iterative Seeking Algorithm

Multi-frequency periodic vibration suppressing in active magnetic bearing-rotor systems via response matching in frequency domain

In this study, we focus on the error of estimated frequency of disturbance and present a new adaptive frequency tracking and new modification law after examining relation between the error of frequency and output level in detail. We also develop a multiple frequency estimation algorithm, which is insensitive to observation noise and prove the asymptotic stability for adaptive nonlinear algorithm and adaptive frequency tracking method theoretically. The results of simulation show that when estimated frequency by difference equation method approach to the true value, then the output error converges to zero (or equilibrium point) asymptotically. This corresponds to the asymptotic stability condition. The effectiveness of this method and the theoretical proof are verified by simulation. The experimental results show that the proposed algorithm is effective for achieving unbalance vibration suppression.

Adaptive unbalance vibration control of magnetic bearing system using frequency estimation for multiple periodic disturbances with noise

As the actuators of active magnetic bearings (AMB) are open loop unstable a feedback control system is essential for their successful operation and for ensuring good performance. In addition, when rotor systems utilizing AMBs are operated at high speeds there will be synchronous vibrations due to unavoidable rotor mass unbalances, which generate synchronous disturbance forces. These forces and vibrations can often lead to severe problems in rotating machines including collision with the touchdown bearings at high speed and the possible risk of causing damage to the internal parts of the machines. In this paper, a new ''direct" adaptive feedforward algorithm is proposed for minimizing selected vibration performance measures which is based on the filtered-x LMS adaptive filter algorithm. This new adaptive algorithm has been used for adjusting the amplitude and phase of a synchronous signal injected at the summing junction of the bearing feedback control loop. The experimental results reported in this work show the effectiveness of the proposed method.

The direct method for adaptive feed-forward vibration control of magnetic bearing systems

This study is concerned with the adaptive forced rejection approach for a single periodic output disturbance with an unknown period and its application to unbalance vibration suppression in rotor-magnetic bearing systems.A discrete recursive technique is applied to estimate the unknown disturbance period and then to internally and adaptively generate a pseudofeedforward reference signal such as that this disturbance is eliminated.Simulations are carried out.The results indicate that both the estimation algorithm of an unknown period and reference signal adaptive generation algorithm are stable.Finally, the approach is applied to a problem of unbalance vibration suppression in rotor-magnetic bearing systems.Approximately 20 dB and 7 dB reductions in unbalance vibrations were experimentally obtained in the horizontal and vertical directions of the front and rear sides of the rotor, respectively.The experimental results show that the proposed algorithm is effective for achieving unbalance vibration suppression.

Fan Qi-fu

Papers

Unbalance Vibration Control of Magnetic Bearing Systems Using Adaptive Algorithm with Disturbance Frequency Estimation

Unbalance Vibration Control of Magnetic Bearing Systems Using Adaptive Algorithm with Disturbance Frequency Estimation.