Application Of Active Magnetic Bearings Research Articles

5-axes Levitation of a Rotor by Active Magnetic Bearings Employing Direct Output Feedback Control

In recent years the application of active magnetic bearings (AMB), as supporting element as well as vibration controller for rotors, has attracted considerable attention from researchers. In this work an attempt has been made for the complete levitation of a rotor weighing 4 kg, supported on two radial active magnetic bearings and two axial passive magnetic bearings (PMB) resulting in 5-axes levitation. The active bearings working in the mode of attraction make the system inherently unstable. Herein, a direct output feedback control scheme based on proportional and derivative of position signal has been employed to achieve stability. The active magnetic bearings consist of electromagnetic actuators, proximity probes for position measurement, feedback controller and current feedback type power amplifier. The passive bearings consisting of axially magnetized circular permanent magnets work in the mode of repulsion. The design of the electromagnetic actuator has been carried out considering load carrying capacity of the AMB, core loss and the resistive loss in the coil, so that the temperature rise in the core as well as in the coil is within allowable limit. Design of the feedback controller is based on direct output feedback control scheme, which makes the controller design easier and implementation of the controller hardware becomes simpler. The feedback controller parameters have been selected appropriately to generate required stiffness and damping in the AMBs for stable levitation of the rotor. The rotor has been driven up to a speed of 2000 rpm.

Robust Multi-Objective Optimization of a 3-Pole Active Magnetic Bearing Based on Combined Curves With Climbing Algorithm

With the extensive application of active magnetic bearings (AMBs), the robust multiobjective optimization of the structure seems to be a priority. However, it is a challenge due to the high dimension and huge computational cost of finite-element analysis. In this article, a robust multi-objective optimization method is proposed to pursue good performance for a three-pole AMB. To increase the efficiency of the optimization process, the Kendall correlation coefficient is applied to assist in determining the sensitivity. The parameters are divided into three layers, and a three-level multiobjective optimization structure is established. Meanwhile, Kriging model is employed to improve the optimization efficiency. The selection of the final solution in Pareto curves is always an issue. The proposed optimization structure can only ensure the performance of the AMB, rather than robustness. Thus, a robust solution selection method is proposed based on the climbing algorithm. The robustness can be easily shown in the Pareto curve obtained through the optimization structure. The final solution is selected with good robustness in terms of suspension force and force ripple. The experimental results based on a prototype are provided to verify the effectiveness of the proposed optimization method.

Experimental study on vibration control of spur geared rotor system with active magnetic bearings

The gearbox vibrations and noise caused by variation of contact forces often causes failure in the components of gearbox, which are then transmitted to the surrounding structures. The concept of active control of gearbox vibrations with piezoelectric actuators at the mounting points has been analysed earlier in several studies, then with certain limitations. There has been little research on how Active Magnetic Bearings (AMBs) might mitigate gear vibrations. AMBs are used in this study to investigate active internal shaft vibration control caused by rotor unbalance, gear runout, transmission error, which usually resides within the gearbox. Hence, minimizing the effect of vibrational amplitude at gear mesh frequency and its harmonics to have quieter gear operation. A mathematical model is developed for the torsional-lateral dynamic analysis of a spur geared rotor-AMB system. Responses are computed numerically with different gear-rotor faults. Based on the mathematical model, setted up an experimental test rig in the laboratory, and the effectiveness of the proposed model is compared with and without the application of AMBs. The approach is based on active control of the shaft transverse vibration with an electromagnetic actuator. The control forces are applied to the rotor shafts supported on conventional rolling element bearings by an eight-pole radial AMB, as an auxiliary component and a closed-loop linear output feedback control is employed for stable, reliable, and robust operation. A linear PID controller working on differential mode is used to generate the appropriate control signals and the experimental results are presented. It was found that there is a considerable amount of reduction in the geared rotor vibration levels and correspondingly in overall measured gear noise levels.

Application of active magnetic bearings in control and estimation of geared-rotor faults in high speed offset spur gear transmission system

This study is focused on the mathematical modelling, analysis, active transverse vibration control and fault analysis of a single-stage spur geared-rotor system. It uses Active Magnetic Bearings (AMBs) as an auxiliary bearing in addition to the conventional mechanical bearing in rotor fault detection considering the dynamic model with gyroscopic effects. The change in dynamic forces primarily due to the mesh deformation, gear runout, and variable transmission error are considered, which causes unwanted vibration and noise. To prevent the damage of gears and other supporting structures, these forced vibrations and control currents are meticulously investigated. From the dynamic responses of geared-rotor, the AMB control the stiffness and damping to minimize the transmission of forced vibrations to the mountings by closed-loop feedback control system. For an accurate modelling the dynamic transmission error is taken in two orthogonal transverse directions, which has asymmetric transmission error characteristics. Full spectrum is used for frequency domain analysis with tilting phenomena of the gears at high spin speed. An identification algorithm is developed for fault detection and estimation of system parameters from vibration and current of the proposed geared-rotor-AMB system. The robustness of the proposed algorithm is verified with different added percentage of noise and modeling errors.

Nonlinear dynamic simulation and parametric analysis of a rotor-AMB-TDB system experiencing strong base shock excitations

The application of active magnetic bearings (AMBs) enables turbomachinery to increase power density, controllability and resilience to external disturbances. However, due to the limited load capacity of AMBs, base shock excitations may result in contact between the rotor and the touchdown bearings (TDBs), which can seriously damage the machine. This paper presents a dynamic analysis of a rotor-AMB-TDB system experiencing strong base shocks while the AMBs are operating. The contacts between the rotor and the TDBs, and the rolling-ball contacts within the TDBs are modeled based on the Hertzian contact theory. A PD controller is designed, considering saturation. The dynamic equations were solved numerically, and the results showed three different rotor motion modes after base shocks. FFT spectra, STFT spectra, Poincaré maps and bifurcation diagrams were used for the dynamic analysis. Unsuitable system parameters, including unbalance eccentricity, radial clearance, equivalent stiffness and damping ratio, may lead to complex behaviors including periodic, KT-periodic, and quasi-periodic responses as well as jump phenomena. This study reveals the mechanism of nonlinear responses, provides a method for predictions, and helps with controller designs for rotor re-levitation.

Active Magnetic Bearing Design and Backstepping-Adaptive Control for High-Speed Rotors

Friction and vibrations hindering high-speed are the most pertinent problems facing the rotating machines. Thus, friction and vibration attenuation are essential in improving the overall performance of turbomachines. Conventionally, high-speed flywheel energy storage systems use Active Magnetic Bearings (AMB) to nullify friction losses and to deal with unbalances but, in the present era with increasing demand for high-speed machinery, the applications of AMBs are proliferating. They are not like the traditional bearings; they generate forces through magnetic fields with no contact between bearing and rotor thus decreasing the friction and providing the ability to counteract imbalances actively. This paper investigates an optimized design methodology along with backstepping adaptive control design of an 8-pole radial AMB used for flywheel energy storage systems. Design optimization using GA, along with analytical design constraints are presented. The design details along with finite element simulations are given to verify the optimization results and system requirements. Bearing parameters then obtained are used to develop a linearized mathematical model of the system, an adaptive back-stepping controller is designed for it to regulate the deviation of the rotating shaft from its equilibrium position.

Application of active magnetic bearings for in situ flexible rotor residual balancing using a novel generalized influence coefficient method

ABSTRACTAn identification algorithm for the estimation of residual unbalances is developed for a flexible rotor-bearing system integrated with an active magnetic bearing (AMB). The main advantage of the present methodology is that it can be applied in situ and also with safe traversal of resonances during run-up. The flexible rotor-AMB system is modelled by the finite element method, considering randomly distributed residual unbalances along with disc discrete residual unbalances. In order to obtain equivalent discrete unbalances at limited disc locations for the balancing of the flexible rotor system, a generalized influence coefficient method (GICM) is proposed. Equivalent unbalances obtained at discrete balancing planes are used to check the reduction in unbalance responses. The proposed algorithm is compared with the conventional influence coefficient method (CICM) without AMB to check the accuracy and consistency of the estimated values of residual unbalances. The values estimated by both methods are found to be consistent, while the GICM has an advantage of using AMB for the safe operation of the unbalanced rotor at high speeds during measurements. In order to have a suitable discrete position of AMB (for effective estimation of residual unbalances), various rotor system models are considered with different positions of the AMB.

Application of active magnetic bearings in flexible rotordynamic systems – A state-of-the-art review

Abstract In this paper a critical review of literature on applications of Active Magnetic Bearings (AMBs) systems in flexible rotordynamic systems have been presented. AMBs find various applications in rotating machinery; however, this paper mainly focuses on works in vibration suppression and associated with the condition monitoring using AMBs. It briefly introduces reader to the AMB working principle, provides details of various hardware components of a typical rotor-AMB test rig, and presents a background of traditional methods of vibration suppression in flexible rotors and the condition monitoring. It then moves on to summarize the basic features of AMB integrated flexible rotor test rigs available in literature with necessary instrumentation and its main objectives. A couple of lookup tables provide summary of important information of test rigs in papers within the scope of this article. Finally, future directions in AMB research within the paper’s scope have been suggested.

Adaptive multipopulation genetic algorithm based self designed fuzzy logic controller for active magnetic bearing application

Active magnetic bearings (AMBs) are contact less bearings where the stable suspension of the rotor depends on attractive forces produced by electromagnets. Further, these systems are subjected to system uncertainties, nonlinearities and speed dependent rotor dynamic conditions. Therefore, designing a controller to provide a desired dynamics for these systems is a challenging task. Various linear and nonlinear control techniques have been used to control AMBs. These techniques require detailed mathematical model of the system and are sensitive to modelling errors. Therefore, in the present work, human heuristic knowledge based nonlinear fuzzy logic controller (FLC) is designed for AMB. Zero-order Takagi–Sugeno controller (ZTSC) model of FLC is proposed over Mamdani model to reduce the computational time required to calculate the fuzzy output. However, deciding the fuzzy parameters such as rule base and range of operation of the membership functions to achieve desired performance is an iterative process. In order to automate this process and to improve the performance of controller, a self-designed zero-order Takagi–Sugeno controller (SZTSC) based on evolutionary genetic algorithm is proposed. Further, multipopulation genetic algorithm with adaptive tuning of its parameters (adaptive multipopulation genetic algorithm) is proposed over simple genetic algorithm, due to its ability to search better optimal solution at a higher convergence speed. Membership functions range of operation for the input variables and control rules of the SZTSC are generated automatically without any expert’s knowledge by adaptive multipopulation genetic algorithm based optimization method. Simulations are carried out to check the performance of SZTSC compared to the expert’s knowledge based ZTSC. SZTSC has shown better performance compared to ZTSC under different dynamic conditions of AMB.

Active Balancing Control of AMB-Rotor Systems Using a Phase-Shift Notch Filter Connected in Parallel Mode

The vibration controllability is an important feature in the applications of active magnetic bearings (AMBs). This paper addresses the two key challenges on the active balancing control of AMB-rotor systems: presenting a parallel-mode scheme to enhance the notch performance at high speeds, and proposing a phase-shift notch filter to ensure stable operations over the entire speed ranges. First, both the frequency characteristics of the simplified notch filter in series and in parallel mode are discussed. The analysis shows that the closed-loop system with a parallel-mode notch filter has a deeper notch depth and faster convergence. The capacities of the synchronous current elimination are also improved at high speeds. Then, an improved phase-shift notch filter connected in parallel with the controller is modeled and analyzed. In order to understand the sensibility of the proposed solution to phase-shift variations, the stability analysis of the closed-loop system in the entire operational speed range is performed using the frequency response method. Experimental results on a high-speed centrifugal air blower test rig show the effectiveness of the proposed solution.

Vibration suppression of a time-varying stiffness AMB bearing to multi-parametric excitations via time delay controller

The applications of active magnetic bearings are growing in industry due to its amazing advantages in reducing friction losses. In this research, the vibration of a two-degree-of-freedom rotor, active magnetic bearings system is suppressed via a nonlinear time delay controller at the confirmed worst resonance case. The selected resonance case is the simultaneous primary and sub-harmonic resonance case. The main aim of this paper was to study the effects of the nonlinear, time delay controller on the behavior of the vibrating system. The multiple time scale perturbation technique is applied to obtain an approximate solution to the second-order approximation. The steady-state solution is obtained around the worst resonance case. The stability of the system is studied applying both frequency response equations and phase-plane method. The worst resonance case is confirmed applying numerical technique. The effects of the different parameters on the steady-state response of the vibrating system are investigated. The obtained approximate solution is validated numerically. Some recommendations are given regarding the design of such system. At the end of the work, a comparison is made with the available published work.

Control of a flexible rotor active magnetic bearing test rig: a characteristic model based all-coefficient adaptive control approach

Active magnetic bearings (AMBs) have found a wide range of applications in high-speed rotating machinery industry. The instability and nonlinearity of AMBs make controller designs difficult, and when AMBs are coupled with a flexible rotor, the resulting complex dynamics make the problems of stabilization and disturbance rejection, which are critical for a stable and smooth operation of the rotor AMB system, even more difficult. Proportional-integral-derivative (PID) control dominates the current AMB applications in the field. Even though PID controllers are easy to implement, there are critical performance limitations associated with them that prevent the more advanced applications of AMBs, which usually require stronger robustness and performance offered by modern control methods such as H-infinity control and µ-synthesis. However, these advanced control designs rely heavily on the relatively accurate plant models and uncertainty characterizations, which are sometimes difficult to obtain. In this paper, we explore and report on the use of the characteristic model based all-coefficient adaptive control method to stabilize a flexible rotor AMB test rig. In spite of the simple structure of such a characteristic model based all-coefficient adaptive controller, both simulation and experimental results show its strong performance.

Rotor Crack Detection Using Active Magnetic Bearings

Well-established procedures exist to monitor and diagnose fairly severe problems with rotating machinery but little progress has been made in developing techniques to detect subtle changes in machine condition for both improved diagnostics, and to develop prognostic procedures for determining remaining service life. Of all machine faults, crack initiated problems present probably the most significant safety and loss hazard in modern turbomachinery, including aircraft engines and power generation units. Different approaches are used to model, detect, and localize crack-induced damage in rotating structures. This paper presents novel application of active magnetic bearings (AMBs) for on-line rotor crack detection. AMB-actuators provide convenient means to apply a broad spectrum of known dynamic forces and monitor responses in a rotor-bearing system, which facilitates more sensitive and precise diagnostics. The paper presents theoretical modeling and description of the experimental facility for proof-of-concept testing.

Application of Active Magnetic Bearings in Turbocompressors and Turboexpanders of the Gas Industry

Application of Active Magnetic Bearings in Turbocompressors and Turboexpanders of the Gas Industry

Analysis on dynamic performance for active magnetic bearing-rotor system

In the application of active magnetic bearings (AMB), one of the key problems to be solved is the safety and stability in the sense of rotor dynamics. The project related to the present paper deals with the method for analyzing bearing rotor systems with high rotation speed and specially supported by active magnetic bearings, and studies its rotor dynamics performance, including calculation of the natural frequencies with their distribution characteristics, and the critical speeds of the system. One of the targets of this project is to formulate a theory and method valid for the analysis of the dynamic performance of the active magnetic bearing-rotor system by combining the traditional theory and method of rotor dynamics with the analytical theory and design method based on modern control theory of the AMB system.

On-line evolution of robust control systems: an industrial active magnetic bearing application

An electrical pump running on active magnetic bearings (AMBs) is described.To overcome the difficulty of obtaining an accurate model of the system, the control system is designed on-line. An optimiser modifies controller parameters running on the controller (a digital signal processor) in real time and the resulting sensor data is recorded and processed. On-line optimisation of the controller is achieved from within a commercial CACSD software package using H 2 and H ∞ measures of tracking as design objectives. A multiobjective genetic algorithm is used to drive the optimisation for the AMB system. The resulting controller is compared with that of a manually tuned controller and significant improvements in performance and robustness are observed.

An Overview of Active Magnetic Bearing Technology and Applications

In this paper, the author presents a short history and general discussion of the operation of an active magnetic bearing, as well as specific applications of active magnetic bearings in both commercial and research scenarios. Although magnetic suspension devices have been used in nonrotating scenarios such as magnetically levitated trains, only applications associated with rotating equipment will be addressed. Commercial applications such as large turbomachinery and small-scale turbomolecular pumps will be discussed. Research applications, such as bearingless motors, flywheels for energy storage, micromachines, and biomedical applications, will be presented. Research topics associated with superconducting magnetic bearings are beyond the scope of this paper.

Experimental study of active magnetic bearing on a 150M3 turbo oxygen gas expander

This paper is concerned with the investigation, experiment and design analyses on the application of active magnetic bearings for a 150M3 turbo oxygen gas expander having 1.16 kg weight and 30 mm diameter rotor, which was supported by two aerostatic bearings formerly. Now, the machine can work steady at a rotation speed of 92,000 r/min, and can be run up to a maximum rotation speed of 104,000 r/min.

On-Line Genetic Auto-Tuning of PID Controllers for an Active Magnetic Bearing Application

A prototype large electrical machine running on active magnetic bearings is described. This rig is controlled by a digital signal processor connected by a custom interface to MATLAB/Simulink hosted by a PC. The on-line tuning of a PID controller is set up as an optimisation problem from MATLAB and a multiobjective genetic algorithm is used to drive the optimisation. The results of an optimisation are presented and analysed.