Active Magnetic Bearing Control Research Articles

Multi-objective optimization of bias current coefficient based on NSGA- III for active magnetic bearing with redundant electromagnetic actuators

PurposeThe multi-objective optimization configuration strategy is proposed due to the configuration of EMAs in fault-tolerant control of active magnetic bearing with redundant electromagnetic actuators involving high-dimensional, nonlinear, conflicting goals.Design/methodology/approachA multi-objective optimization model for bias current coefficients is established based on the nonlinear model of active magnetic bearings with redundant electromagnetic actuators. Based on the non-dominated sorting genetic algorithm III, a numerical method is used to obtain feasible and non-inferior sets for the bias current coefficient.Findings(1) The conflicting relationship among the three optimization objectives was analyzed for various failure modes of EAMs. (2) For different EMAs' failure modes, the multi-objective optimization configuration strategy can simultaneously achieve the optimal or sub-optimal effective EMF, flux margins, and stability of EMF. Moreover, the characteristics of the optimal Pareto front are consistent with the physical properties of the AMB. (3) Compared with the feasible configuration of C0, the non-inferior configurations can significantly improve the performance of AMB, and the advantages of the multi-objective optimization configuration strategy become more prominent as the asymmetry of the residual supporting structure intensifies.Originality/valuei) Considering the variation of the rotor displacement during the support reconstruction, a decision-making model that can accurately characterize the dynamic performance of AMB is presented. (ii) The interaction law between AMB and rotor under different failure modes of EMAs is analyzed, and the configuration principles for redundant EMAs are proposed. (iii) Based on the dynamic characteristics of AMB during the support reconstruction, effective EMF, energy consumption, and the Pearson correlation coefficient between the desired EMFs and the decoupled control currents are used as objective functions. iv. The NSGA-III is combined with the decision-making model to address the multi-objective optimization configuration problem of C0.

Control of Active Magnetic Bearings

Control of Active Magnetic Bearings

Double Five-Phase-Four-Leg Topology Converter for Five-Axis Active Magnetic Bearing With Optimized Current Control

Active magnetic bearing (AMB) is a kind of contactless bearing system for high-speed rotational machines. Power electronics converter is the key conversion unit for the electromagnetic force generation. However, there is no such kind of integrated power electronics converter to drive a typical five-axis magnetic bearing by considering the global optimization of power electronics devices. In order to cut the cost and increase the power density of AMB converter, this paper analyzes the development status of topology of AMB drive and proposes a novel converter with double five-phase-four-leg topology. The novel converter could control all the ten winding currents of five-axis AMB with only eight switches while the conventional topology needs twenty switches by further utilizing the freedom degree of the AMB control. Also, compared with the conventional topology, the switches of novel topology have same maximum voltage and current. Further, this paper proposes the optimized current control methods to minimize the bias current of the active magnetic bearing and applies it to the double five-phase-four-leg topology converter. With the optimized current control, actual current of each coil is decreased and difficulty of thermal design is reduced. The proposed double five-phase-four-leg topology can suspend the five-axis AMB by only using eight switches and eight diodes, which is the minimum compared with the state of the art.

Adaptive gain scheduling based event-triggering control design for robust performance of active magnetic bearing

This article proposes an efficient adaptive robust control for the eight-pole active magnetic bearing based on a heteropolar structure. Due to the uncertain behavior of active magnetic bearing, the mathematical model of active magnetic bearing is considered to be highly nonlinear and uncertain. As the rotor displacement and velocity are the measurable states, sliding mode control is designed to estimate state variables. Also, a matched disturbance term is used to deal with undesirable disturbances in the active magnetic bearing system. The controller is developed for an active magnetic bearing using the event-triggering-based sliding mode control technique. However, the stability of the proposed scheme has been achieved with the help of Lyapunov theory. Furthermore, the adaptive gain scheduling approach based on a neural network has been augmented to adjust the gain of the proposed controller for active magnetic bearing adaptively. The simulation studies have been performed in detail to demonstrate the use of proposed scheme for the robust control of active magnetic bearings. Finally, a comparative analysis of the proposed control design scheme with a conventional controller has been performed to achieve improved performance satisfying the plant constraints.

Decoupling Control of Six-pole Axial-radial Active Magnetic Bearing Based on Improved Linear Active Disturbance Rejection Optimized by Least Square Support Vector Machine

Decoupling Control of Six-pole Axial-radial Active Magnetic Bearing Based on Improved Linear Active Disturbance Rejection Optimized by Least Square Support Vector Machine

Division Linearization Zero-Bias Current Control for AMBs–Rotor System With Uncertainties and Saturation

Traditional constant current sum (CCS) distribution strategy is always employed in the nonlinear active magnetic bearing (AMB) system control for linearization, but the bias current in CCS causes extra power consumption and limits the AMBs' capacity. In this paper, a division linearization zero-bias current (DLZBC) distribution strategy is proposed as a substitution for CCS strategy. Under this strategy, a linear active disturbance rejection controller (LADRC) with a static anti-windup compensator (SAWC) is applied to deal with model uncertainties and current saturation. For different types of AMB-supported machines, a partial normalized nonlinear model is established. Subsequently, the performance of the CCS strategy is analyzed, and a DLZBC strategy is presented to reduce the power consumption and transform the system into a linear plant with a lumped uncertain parameter. Afterward, a LADRC is designed to enhance robustness, whose parameters are chosen according to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu -$</tex-math></inline-formula> synthesis framework and are convenient for adjustment practically. For anti-saturation, a SAWC is developed to help the system escape quickly from current saturation and enlarge the stability domain of the saturated system. Comparative simulations and experiments results show that the proposed control method can significantly reduce power consumption and achieve good response in AMB-rotor system.

The Influence of Speed Ratio on the Nonlinear Dynamics of a Magnetic Suspended Dual-Rotor System with a Fixed-Point Rubbing

Magnetic suspended dual-rotor systems (MSDS) provide the potential to significantly improve the performance of aero-engines by eliminating the wear and lubrication system, and solve vibration control issues effectively. However, the nonlinear dynamics of MSDS with rubbing is rarely investigated. In this work, the nonlinear support characteristics of active magnetic bearings (AMBs) are described by the equivalent magnetic circuit method, the impact force is characterized by the Lankarani–Nikravesh model, and the nonlinear dynamic model is established using the finite element method. On this basis, the influence of speed ratio on the nonlinear dynamics is investigated. Simulation results show that the fundamental sub-synchronous vibration of period n is the dominant motion of MSDS, where n is determined by the speed ratio. The frequency components of sub-synchronous vibrations of period k are integer multiples of the minimum dimensionless frequency component 1/k, where k is a positive integral multiple of n. Quasi-periodic and chaotic vibrations are more likely to occur near critical speeds, and their main frequency components can be expressed as a variety of combined frequency components of the rotating frequency difference and its fractional frequency. To reduce the severity of fluctuating stresses stemming from complicated non-synchronous vibrations, speed ratios, corresponding to smaller n and AMB control parameters attenuating vibration amplitude or avoiding critical speeds, are suggested.

Time-Scale Separation Control for a Class of Current Distribution Strategy in AMBs-Rotor System With Bounded Bus Voltage

In active magnetic bearings (AMBs) systems, good dynamic characteristics and low power consumption are two important concerns, which are difficult to be obtained simultaneously if considering bounded bus voltage. This paper proposes a universal current distribution constraint format and a related time-scale separation control scheme to achieve improvements in both aspects. Considering the bounded bus voltage and symmetrical configuration in one AMB control axis, a double-input three-order nonlinear model is established to describe the AMBs-rotor system. Subsequently, a constraint format is propounded to cover and improve existing current distribution strategies. The power consumption and voltage response are compared between different instances under this constraint format. Then, the double-input model is converted to a single-input cascaded nonlinear system, and a time-scale separation control scheme is designed accordingly. The scheme contains a nominal controller and a dynamic inversion. The nominal controller determines the dynamic characteristics of the AMBs-rotor system. The dynamic inversion compensates for the nonlinearity of the system based on the characteristics of the amplifier. This scheme can preserve the closed-loop stability by only adjusting the time-scale coefficient. Finally, experimental results demonstrate the advantages of the proposed method in aspects of dynamic performance, voltage response, and power consumption.

Multi-objective optimization configuration of redundant electromagnetic actuators in fault-tolerant control of active magnetic bearing system

Fault-tolerant control of active magnetic bearing (AMB) systems with redundant electromagnetic actuators (EMAs) based on generalized bias current linearization has become a practical technique to address EMA/amplifier faults. In this method, the configuration of multi-channel EMAs involves solving a high-dimensional and nonlinear problem containing complex constraints offline. This article develops a general framework for the EMAs multi-objective optimization configuration (MOOC) by combining the non-dominated sorting genetic algorithm III (NSGA-III) and the sequential quadratic programming (SQP) with the designing of objectives, handling of constraints, consideration of the iterative efficiency and the diversity of solutions. The numerical simulation results confirm the feasibility of the framework for searching the non-inferior configurations and reveal the function mechanism that intermediate variables of the nonlinear optimization model on AMB performance. Finally, the best configurations identified using the technique for order preference by similarity to an ideal solution (TOPSIS) are applied to the 4-DOF AMB experimental platform. Experiments further indicate that the work in this paper provides a novel way with good performance and high reliability for solving the EMAs MOOC problem in fault-tolerant control of AMB systems.

Design and speed control of U-type 3-coil active magnetic bearing

Design and speed control of U-type 3-coil active magnetic bearing

Research on Common Mode EMI and Its Reduction for Active Magnetic Bearings

Active magnetic bearing (AMB) with power electronics drive is an important technology for high-speed rotational machinery suspension. There were seldom literatures concerning the common mode (CM) electromagnetic interference (EMI) problems of the AMB system. In this article, we found that the power electronic converter used for AMB control will not only bring EMI to the devices but also influence the performance of the levitation control. To cope with this problem, the parasitic paths of the leakage currents in the five-degrees-of-freedom AMB system were analyzed. The control principle and the novel zero CM PWM (ZCMPWM) strategy for the AMB driven by a four-leg converter were presented to suppress the CM EMI. Experiment has been done on an AMB-based compressor. The proposed method can significantly reduce the CM EMI caused by the AMB controller and improve the performance of levitation.

Unbalanced vibration control of active magnetic bearing using an active disturbance rejection notch decoupling technique

Aiming at the position coupling, gyroscopic effect, and synchronized vibration caused by the unbalance mass in the magnetic bearing rotor, a linear active disturbance rejection notch decoupling control method is proposed. Firstly, a model with coupling and unbalanced vibration of the system was established. The terms of position coupling, gyroscopic effect, and unbalanced vibration in the system are estimated by Extended State Observer and the estimator is treated as the system disturbance to be compensated, then the radially existing coupled and unbalanced vibration systems are decoupled into four independent second-order series-integrated subsystems. The nonlinear state error feedback control law is designed to implement the decoupling control of each subsystem. For the problem of unbalanced vibration of the rotor after decoupling, the suppression method of the dynamic unbalanced force of the same frequency notch filter is designed, and then the closed-loop feedback structure of the new method is deduced, and its frequency characteristics are analyzed. Then the rules and principles of controller parameter selection are summarized using Bode diagram. The simulation results show that the designed linear active disturbance rejection notch decoupling controller not only achieves the decoupling control of the respective degrees of the magnetic bearing rotor but also suppresses the unbalanced vibration of the rotor. At the same time, it solves the influence of the gyroscopic effect on the control under the high-speed running of the magnetic bearing rotor.

Sliding Mode Control of Active Magnetic Bearings - A Cascaded Architecture

Accurate and robust positioning of rotor axle is essential for efficient and safe operation of high-speed rotational machines with active magnetic bearings. This study presents a cascaded nonlinear control strategy for vertical axial positioning of an active magnetic bearing system. The proposed scheme employs two sliding mode controllers for regulating rotor vertical position and current and an adaptive estimator to invert the nonlinear input mapping. Uniform asymptotic stability is proven for the closed-loop system and the efficacy and performance of the proposed design is evaluated in simulation.

Adapting the control of the magnetic bearings of a highly flexible and gyroscopic rotor to the excitations by the motor

A test rig was built to perform fatigue tests on thick-walled cylinders made of fibre reinforced plastic (FRP). During the fatigue test, the rotational speed of an FRP cylinder is periodically varied until it fails. The FRP cylinder is connected to a drive spindle that accelerates and decelerates it using a permanent magnet synchronous machine (PMSM). To avoid excessive wear, the rotor is supported by active magnetic bearings (AMB). After the fatigue test was finished with the first cylinder, a new cylinder was attached to the test stand. With this new specimen, previously uncritical radial vibrations became more severe. For high accelerations, these vibrations led to instability of the rotor. However, high accelerations are desirable to perform the fatigue tests in the shortest possible time. Hence, the AMB control should be made insensitive to these vibrations. Since the vibrations depend on the acceleration of the rotor, it is reasonable to assume that they are induced by the PMSM. To reduce the vibrations, these excitations from the PMSM are included in the model-based controller parametrization process for the radial AMB, in which the parameters are adjusted via optimization. With the adjusted control, the amplitude of the vibration was significantly reduced and higher accelerations were possible. The described parameter tuning process can easily be adapted to different AMB systems with disturbances and changes in the 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

An Improved Resonant Controller for AMB-Rotor System Subject to Displacement Harmonic Disturbance

The controller contains harmonic components due to the detection error of the displacement sensor. The harmonic component acts on the magnetic bearing coil in the form of harmonic current, resulting in undesirable harmonic vibration force, which is not conducive to the microvibration control of active magnetic bearing (AMB) rotor system. In order to solve the problems of slow response speed and limited harmonic frequency range in series mode, an improved resonant controller in parallel mode is proposed in this article, which greatly improves the response speed of the system and the suppression effect at harmonic frequency. In addition, the gain and phase angle at each harmonic frequency can be adjusted, so the robustness of each harmonic frequency can be independently controlled, and the system stability can be guaranteed in a wide range of operating speeds. Finally, the effectiveness of the proposed algorithm is verified by simulation and experiment, which has important significance and application value for harmonic current suppression of AMB-rotor system.

Magnetic Static Force Evaluation of Active Magnetic Bearing for a Hemocompatibility Assessment Device: Numerical and Experimental Approach

<h3>Purpose</h3> Development of pediatric left ventricular assist devices (LVADs) has severely lagged behind that of adult LVADs, primarily due to the size and hemocompatibility constraints of pediatric anatomy. To quantify sources of blood trauma within a device, we proposed a hemocompatibility assessment platform (HAP) that can evaluate the hemocompatibility of individual components of LVADs. To eliminate the hemolysis induced by the HAP itself, we incorporated passive magnetic bearings to suspend the rotor radially and an active magnetic bearing (AMB) to control the axial position. In this study, we evaluated AMB forces of 2 geometries and validated the model by comparing its predictions with experimental results. <h3>Methods</h3> The AMB comprises a stator with an electromagnetic coil and a rotor with a permanent magnet (PM) ring (1 mm and 2 mm thickness). The AMB numerical model was established in COMSOL 5.5 using the finite-element method. The magnetic forces generated by the AMB were evaluated by increasing the rotor-stator gap from 0.1 mm to 0.5 mm with a 0.1 mm increment and by varying the coil current from -2 A to 2 A with a 1 A increment. AMB force data was collected experimentally by a precision force transducer on an XYZ-micrometer-driven stage. <h3>Results</h3> The average error of the numerical models was 8.8% and 7.0% for 1 mm and 2 mm thick PM rings, respectively. Higher errors were seen at small (<0.2 mm) rotor-stator gaps. The change in magnetic force due to electrical current, or magnetic stiffness, is greater in the thicker PM ring. For both PM ring sizes, the AMB exhibits high magnetic stiffness from -1 A to 1 A, though it saturates for currents of -2 A and 2 A. This region of high current stiffness was identified as the optimal control region. <h3>Conclusion</h3> AMB force generation was characterized as a function of current and gap, both experimentally and numerically. In future work, this function will be used to tune a control algorithm to modulate current supplied to the AMB, ultimately stabilizing the rotor axially. Additionally, if design specifications such as PM ring thickness or material change, the numerical model can be used to quickly generate a new function for the AMB control algorithm.

Hybrid Active Disturbance Rejection Decoupling Control for Six-pole Active Magnetic Bearing Based on Improved Genetic Algorithm

Hybrid Active Disturbance Rejection Decoupling Control for Six-pole Active Magnetic Bearing Based on Improved Genetic Algorithm

Adaptive Backstepping Control of Active Magnetic Bearings with Slice Rotor

Adaptive Backstepping Control of Active Magnetic Bearings with Slice Rotor

Design and Modeling of 2 MW AMB Rotor With Three Radial Bearing-Sensor Planes

Active magnetic bearings (AMBs) provide reliable solution for high-speed rotors, where oil-free and reliable operation are crucial. In high-power applications benefits of AMBs, compared to traditional rolling element bearings or fluid film bearings, are highly valued. Typical AMB rotors comprise two radial AMBs, which are designed with compressor or generator wheels integrated on the rotor. AMB dimensions and locations are carefully selected for each new application. The system design is being iterated such that the nodes of the lowest frequency rotor bending modes are sufficiently far away from the AMB and sensor nodes to ensure robust AMB control. The design is very challenging and cost sensitive. This work focuses on electromagnetic design, modeling, and control of fully levitated AMB-rotor with three radial AMBs. The additional bearing ensures that the same design can be reused with different applications and regardless of the changes in locations of nodes of the first bending mode. The control plant is modeled based on flexible rotor dynamics; while bearing inductances and forces are modeled with 2-D and 3-D finite element method (FEM) electromagnetic simulations. The presented multi-input multi-output (MIMO) model-based control is coupled and centralized with three actuator-sensor pairs for radial suspension. The control design is verified in simulations using nonlinear engineering models. Additionally, experimental identification results are included.