Control Of Magnetic Bearing System Research Articles

Nonlinear vibration control of magnetic bearing system considering positive and negative stiffness

The nonlinear dynamics are studied for an active magnetic bearing (AMB) system under the low-frequency sinusoidal excitation, which can affect the operational stability of a high-speed magnetic bearing. A single-degree-of-freedom nonlinear dynamics model of magnetic bearing was developed with a c-type active magnetic bearing as the research target. The characteristics of the magnetic bearing system show positive and negative stiffness for different feedback gains. The amplitude–frequency response curves of the vibration characteristics of the positive stiffness magnetic bearing system were obtained by using the method of multiple scales. The influence of each parameter on the resonance amplitude and nonlinearity of the magnetic bearing system is understood by analyzing the amplitude–frequency response curve. The bifurcation diagram for the rotor with rotor mass, and control parameters is derived from the numerical simulation of the negative stiffness magnetic bearing system. The parameter intervals that cause single-cycle vibration, double-cycle vibration, and chaotic state of the magnetic bearing rotor are discovered by analyzing the bifurcation diagrams of each parameter. The simulation results show that the magnetic bearing system exhibits complex nonlinear dynamic characteristics when it is a negative stiffness system.

Design of Neuro Fuzzy Sliding Mode Controller for Active Magnetic Bearing Control System

Design of Neuro Fuzzy Sliding Mode Controller for Active Magnetic Bearing Control System

Design and Implementation of a Fault-Tolerant Magnetic Bearing Control System Combined With a Novel Fault-Diagnosis of Actuators

Although magnetic bearings are generally reliable, an important concern for machine applications is fault tolerance. The fault-tolerant operation of a magnetic bearing system can be realized through the identification and isolation of fault actuators and subsequent support reconstruction via residual actuators. In this study, a novel fault-diagnosis algorithm for electromagnetic actuators (EMAs) is proposed. The equivalent slope of the load current is defined as a fault-diagnosis threshold by theoretically analyzing the variation characteristics of the current in the modulation. The synchronous sampling of the current and its processing algorithm are designed. By combining these algorithms with the generalized bias current linearization theory reported previously, a fault-tolerant control (FTC) system for magnetic bearings is developed, and control of multi-position and multi-current loops is realized by using two digital signal processors (DSP). The FTC of the rotor motion and the fault-diagnosis of actuators are executed in parallel. The proposed control system is verified by the experiments, and experimental results demonstrate that the proposed system can cope with EMA fault in an extremely short time of less than 5 ms. Thus, the support can be reconstructed by employing the FTC to maintain rotor stability.

Design and Analysis of Second-Order Sliding Mode Controller for Active Magnetic Bearing

An active magnetic bearing (AMB) is a kind of high-performance bearing that uses controllable electromagnetic force to levitate the rotor. Its control performance directly affects the operation characteristics of high-speed motors and other electromechanical products. The magnetic bearing control model is nonlinear and difficult to control. Sliding mode control algorithm can be used in the magnetic bearing control system, but the traditional sliding mode control has the problem of high-frequency chattering, which affects the operation stability of magnetic bearings. Based on the second-order sliding mode control algorithm, a new second-order sliding mode controller for active magnetic bearing control was designed, and the stability of the designed sliding mode control law was proven by Lyapunov criterion. On the basis of the established active magnetic bearing control model, the numerical analysis of the designed controller was carried out, and the control effect was compared with that obtained by the exponential reaching law for the sliding mode control algorithm. The experimental results show that the designed sliding mode controller has better dynamic performance and stability than the exponential reaching law for the sliding mode controller.

3/2-Order Dual-Mode Fractional Repetitive Control for Harmonic Vibration Suppression in Magnetically Suspended Rotor

Harmonic currents in magnetically suspended rotor systems are usually caused by mass unbalance and displacement sensor errors, which will produce harmonic vibrations. Repetitive control (RC) is used to eliminate harmonic currents in the control system, but for the magnetic bearing control system, the odd harmonics often dominates, and the characteristics of the even harmonic frequency are not expected to change greatly. At the same time, the ratio of the sampling frequency to the rotor frequency is required to be an integer in the conventional repetitive controller (CRC), which greatly limits its range of application. Therefore, a 3/2-order dual-mode fractional-order repetitive control scheme with a three-parallel structure is proposed. The three branches in the scheme can not only eliminate odd and even harmonics independently,but also improve the robustness of frequency fluctuations. In addition, this method converts the fraction into an integer polynomial by Lagrange interpolation, which can accurately suppress the harmonic current at any frequency. The system delay is reduced to 0.5N sampling periods, and the system dynamic response rate is accelerated. Simulation results show that the proposed algorithm can effectively achieve harmonic vibration suppression at any frequency.

A novel iterative learning control method and control system design for active magnetic bearing rotor imbalance of primary helium circulator in high-temperature gas-cooled reactor

As one of the key technologies of high-temperature gas-cooled reactor, primary helium circulator–equipped active magnetic bearing provides driving force for primary helium cooling system. However, repetitive periodic vibration produced by rotor imbalance may introduce risks to primary helium circulator (even for high-temperature gas-cooled reactors). First, this article analyzes a periodic component extraction algorithm which is widely used in active magnetic bearing rotor unbalance control methods and points out the problem that the periodic component extraction algorithm occupies numerous computing resources which cannot satisfy the real-time request of active magnetic bearing control system. Then, a novel iterative learning control algorithm based on the iteration before last iteration of system information (iterative learning control-2) and a plug-in parallel control mechanism based on the existing control system are put forward, meanwhile, an integrated independent distributed active magnetic bearing control system is designed to solve the problem. Finally, both the simulation and experiment are carried out, respectively. The corresponding results show that the control method and control system proposed in this article have significant suppression effect on the repetitive periodic vibration of the active magnetic bearing system without degrading the real-time requirement and can provide important technical support for the safe and stable operation of the primary helium circulator in high-temperature gas-cooled reactor.

Active Surge Control for Magnetically Suspended Centrifugal Compressors Using a Variable Equilibrium Point Approach

Surge is one of the main rotor dynamic instabilities limiting the operation of centrifugal compressors. This paper proposes an active surge control scheme for magnetically suspended centrifugal compressors using a variable equilibrium point approach. Multiple uncertainties caused by magnetic air gap adjustment are considered for the active magnetic bearing (AMB) control systems. By using the combination of an analytical model and a finite-element method, the perturbation of bearing force parameters, including the force-current factor and the force-displacement factor, is analyzed. The model uncertainties caused by the perturbation of the power amplifier parameters are identified through the online frequency sweep excitation. Based on the uncertainty analysis of the AMB control system, a μ-synthesis-based controller is designed for the axial magnetic bearing system to suppress the vibration caused by surge. The experiments demonstrate that the proposed method can suppress surge and improve the reliability of the system by using automatic magnetic air gap adjustment of the AMB-rotor system.

Hopf Bifurcation and Control of Magnetic Bearing System with Uncertain Parameter

In this paper, the Hopf bifurcation and control of the magnetic bearing system under an uncertain parameter are investigated. Firstly, the two‐degree‐of‐freedom magnetic bearing system model with uncertain parameter is established. The method of orthogonal polynomial approximation is used to obtain the equivalent magnetic bearing model which is deterministic. Secondly, combining mathematical analysis tools and numerical simulations, the Hopf bifurcation of the equivalent model is analyzed. Finally, a hybrid feedback control method (linear feedback control method combined with nonlinear stochastic feedback control method) is introduced to control the Hopf bifurcation behavior of the magnetic bearing system.

Design of Magnetic Bearing Control System Based on Active Disturbance Rejection Theory

At present, most of the magnetic bearing system adopts the classical proportional–integral–derivative (PID) control strategy. However, the external disturbances, system parameter perturbations, and many other uncertain disturbances result in PID controller difficult to achieve high performance. To solve this problem, a linear active disturbance rejection controller (LADRC) based on active disturbance rejection controller (ADRC) theory was designed for magnetic bearing. According to the actual prototype parameters, the simulation model was built in matlab/simulink. The step and sinusoidal disturbances with PID and LADRC control strategies were simulated and compared. Then, the experiments of step and sinusoidal disturbances were performed. When control parameters are consistent, the experiment showed that the rotor displacement fluctuation decreased by 28.6% using the LADRC than PID control under step disturbances and decreased by around 25.8% under sinusoidal disturbances. When the rotor is running at 24,000 r/min and 27,000 r/min, the displacement of rotor is reduced by around 15% and 13.7%, respectively. Rotate the rotor with step disturbances and sinusoidal disturbances. It can also be seen that LADRC has the advantages of fast response time and good anti-interference. The experiments indicate that the LADRC has better anti-interference performance compared with PID controller.

Magnetic Bearing Control System based on PI and PID Controllers

Magnetic Bearing Control System based on PI and PID Controllers

Model-free adaptive control for three-degree-of-freedom hybrid magnetic bearings

Mathematical models are disappointing due to uneven distribution of the air gap magnetic field and significant unmodeled dynamics in magnetic bearing systems. The effectiveness of control deteriorates based on an inaccurate mathematical model, creating slow response speed and high jitter. To solve these problems, a model-free adaptive control (MFAC) scheme is proposed for a three-degree-of-freedom hybrid magnetic bearing (3-DoF HMB) control system. The scheme for 3-DoF HMB depends only on the control current and the objective balanced position, and it does not involve any model information. The design process of a parameter estimation algorithm is model-free, based directly on pseudo-partial-derivative (PPD) derived online from the input and output data information. The rotor start-of-suspension position of the HMB is regulated by auxiliary bearings with different inner diameters, and two kinds of operation situations (linear and nonlinear areas) are present to analyze the validity of MFAC in detail. Both simulations and experiments demonstrate that the proposed MFAC scheme handles the 3-DoF HMB control system with start-of-suspension response speed, smaller steady state error, and higher stability.

Dynamic conditions to destabilize persistent Rotor/touchdown bearing contact in AMB systems

It is now common practice to supplement a magnetic bearing with a touchdown bearing to protect the rotor and stator components. Rotor/touchdown bearing contact may arise from rotor drop, caused by power loss or emergency shutdown. This paper considers the control options that are viable when the magnetic bearing is still functional should contact arise from intermittent faults or overload conditions. The problem is that bi-stable rotor responses are possible, with and without contact. If rotor contact should become persistent, the desirable course of action is to destabilize the rotor response and induce a return to contact-free levitation. In order to achieve this, it is appropriate to gain an understanding of the rotor dynamic behavior. This is determined from analytical and simulated results to reveal suitable control actions. These may be applied through the magnetic bearing control system, or by activating the touchdown bearing through a separate control loop. The issue is that standard control action for a contact-free rotor state will not be appropriate for a rotor in persistent contact since the basic plants to be controlled are significantly different. The required control action should be activated only when contact is detected. The results demonstrate that appropriately phased synchronous forcing could destabilize synchronous forward rub responses. Alternatively, small whirl motions of a touchdown bearing could also be beneficial without disturbing the main magnetic bearing control loop.

Dynamics Modeling and Measurement of the Microvibrations for a Magnetically Suspended Flywheel

Microvibrations produced by high-speed flywheels can highly degrade the performance of precision instruments on satellites. Magnetically suspended flywheel (MSFW) is a promising attitude actuator for the ultraprecision satellites due to the convenient and effective microvibration suppression algorithm. The comprehensive microvibration characteristics of an MSFW are important for designing the microvibration suppression algorithm. This paper focuses on studying the microvibration characteristics of an MSFW with a specific magnetic bearing structure. A complete microvibration dynamical model of the MSFW, including the rotor dynamics, the magnetic bearing control system, and the microvibration sources, is developed. Simulations are performed to predict the microvibration characteristics according to the proposed theoretical model and experimental tests are conducted to measure the comprehensive microvibrations of the practical MSFW. Simulation and experimental results are compared to prove the validity of the proposed microvibration dynamical model. Thus, the proposed theoretical model can predict the microvibration characteristics of the MSFW and can be used to design the microvibration suppression algorithm in the future work.

Adaptive backstepping control for magnetic bearing system via feedforward networks with random hidden nodes

This paper presents an adaptive backstepping neural controller (ABNC) to achieve precise rotor position tracking for a nonlinear active magnetic bearing (AMB) system with modeling uncertainties and external disturbances. In the proposed ABNC, the single-hidden layer feedforward networks (SLFNs) are used to approximate the unknown nonlinearities of dynamic systems and then based on the approximated models, the neural controller is constructed. Different from the existing methods, the hidden node parameters of the SLFNs are determined using the recently proposed neural algorithm named extreme learning machine (ELM), where these parameters are assigned randomly without adjusting. This simplifies the controller design process. Using the Lyapunov theory, stable tuning rules are derived for the update of the output weights of the SLFNs and a proof of stability in the uniformly bounded sense is given for the resulting controller. Moreover, to relax the online computation burden existing in the ABNC, a simplified ABNC (Simpl_ABNC) with less parameters to be adjusted online is proposed to improve the control performance. Finally the simulation results demonstrate that the proposed ABNC and Simpl_ABNC achieve better tracking performance comparing with other controllers including PID controller, conventional backstepping controller and adaptive backstepping sliding mode controller. Also the results show that the Simpl_ABNC has much less computation complexity and also better tracking performance than the ABNC.

The Design of the Simple Structure-Specified Controller of Magnetic Bearings for the High-Speed SRM

Magnetic bearing system controllers using H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> algorithms provide excellent interference rejection capability and robustness. However, in the conventional H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> control design, the order of the controller is much higher than that of the plant, making implementation in practical engineering applications difficult. To solve the problem, based on the requirements of the theory of mixed sensitivity design method, this paper designs a simple structure-specified controller of magnetic bearings for the highspeed magnetic levitated switched reluctance motor (SRM) using backpropagation neural network function approximation characteristics. The proposed controller is of lower order than the traditional H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> controller, and meets performance of H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> controller, which is more suitable for practical implementation. By contrast with the traditional mixed sensitivity controller, results of simulations verify that the controller is reasonable. The controller is applied on the high-speed magnetic levitated SRM platform, and experimental results verify that the controller can achieve control of magnetic bearing systems with good disturbance rejection and robustness.

Autobalancing of high-speed rotors suspended by magnetic bearings using LMS adaptive feedforward compensation

To suppress unbalanced vibrations of low-speed rotors suspended by magnetic bearings, such as a magnetically suspended flywheel, an autobalancing control method based on elimination of synchronous force has been applied. But its precision may decrease for high-speed rotors such as magnetically suspended control moment gyros. The reason is that the low-pass characteristic of an amplifier in a magnetic bearing control system causes errors in the force elimination. Moreover, this low-pass characteristic increases with rotational speed. To resolve this problem, we propose an autobalancing control scheme using adaptive feedforward compensation based on a least mean square (LMS) algorithm. In this LMS algorithm, two input signals are synchronous displacement and its orthogonal signal. The weights of the input signals are introduced into the algorithm. They are updated in the principle of least mean square to minimize the error between actual and reference values of synchronous current. In simulation and experiments, this method reduces synchronous vibration to less than 40% of that with conventional proportional feedforward. The results demonstrate that this method counteracts the negative effect of low-pass characteristics of an amplifier adaptively and suppresses the synchronous vibration force more precisely. Accordingly, high-precision autobalancing of high-speed rotors can be achieved.

Commissioning and Control of the AMB Supported 3.5 kW Laboratory Gas Blower Prototype

This paper presents the practical results of the design analysis, commissioning, identification, sensor calibration, and tuning of an active magnetic bearing (AMB) control system for a laboratory gas blower. The presented step-by-step procedures, including modeling and disturbance analysis for different design choices, are necessary to reach the full potential of the prototype in research and industrial applications. The key results include estimation of radial and axial disturbance forces caused by the permanent magnet (PM) rotor and a discussion on differences between the unbalance forces resulting from the PM motor and the induction motor in the AMB rotor system.

Overview of Development Plans for Magnetic Bearing Control System

Magnetic bearing is a new type bearing used in many fields. An appropriate controller can greatly improve its dynamic performance. With the development of software and hardware of computer, many new platforms appear suitable for studying of controller of magnetic bearing. Typical software platforms include universal operation systems, such as Dos, Windows, and some special operation systems, such as RTLinux. Some applications, such as Matlab/Simulink, can also be applied. And typical hardware platforms cover PC, DSP and some special embedded computers. The design mode of the controller also advances from code design to model design. Many new development plans of magnetic bearing controller based on these platforms and design mode have many advantages over old platforms. For designers, the development plans based on theses new platforms are good choices for bringing about a stable, short development period, low cost controller.

The Impact Analysis of Digital Controller Hardware Parameters of AMB on Control Precision

Digital control circuit for the hardware components, the impact of parameters on the control precision is analyzed. The digital control model is derived according to the requirements control of magnetic bearing system in this paper .Control accuracy and the prediction of control accuracy can be achieved by he theoretical estimates when numerical control system is given .For the future, it provides a simple and efficient method for estimating control accuracy of numerical controller.

Control Parameter Tuning of Magnetic Bearing PID Controller Based on Expansion Coefficient Critical Proportion

The digital PID controller system for magnetic bearing was described in this paper which combined Matlab technique with simulation of the magnetic bearing control to reach the influence of parameters of digital PID controller for magnetic bearing control system. The application of the expansion coefficient critical proportion for turning parameters of digital PID controller can achieve better results. Finally, provide a simple and efficient method for numerical controller of magnetic bearing.