Hybrid Magnetic Bearing System Research Articles

Optimization for vibration analysis in rotating machines

A not stable mechanical movement transmission between systems produces equilibrium losses, such as a rotor of motors that are coupled in rotating machines. This can be studied as a disturbance “vibration” either as characteristic of the movement transmission due to controlled displacement over rotors, which transmits the movement. Therefore, in this research is presented an analysis for an optimal control of the rotor axis displacement that includes “vibration” as the part of the movement transmission. It implies mathematical modelling and specific sensors selections to correlate the vibration in this control task. Furthermore, in order to verify the proposed analysis, it was simulated and tested in a hybrid magnetic bearing system.

Disturbance rejection based on iterative learning control with extended state observer for a four-degree-of-freedom hybrid magnetic bearing system

Iterative learning control (ILC) is an iterative control strategy which calculates a new input according to the error in previous cycles. It is widely used in industries with repetitive operations. Since magnetic bearing systems can be considered as running in a repetitive task, the ILC could be applied. Hence, this paper proposes a modified iterative learning control (ILC) strategy for a four degree-of-freedom (DOF) hybrid magnetic bearing system to reject the disturbance based on an extended state observer (ESO). The feasibility of applying the ILC to the four-DOF magnetic bearing system is analyzed firstly. It is proved that the tracking error can converge by selecting suitable controller parameters. Secondly, to accurately obtain the uncertainties in the operation process, an ESO is designed. As for a repetitive rotation process, the iteration variant disturbance may have a certain influence on the performance of the system which is not usually considered. Therefore, the iteration variant disturbance is introduced and the effectiveness is derived. Finally, simulations and experiments are carried out to demonstrate the effectiveness of the proposed method. The classical proportion-integration-differentiation (PID) control and an existing proposed neural network inverse (NNI) control are implemented for comparison. The results show that the proposed strategy can achieve better reference tracking and disturbance suppression ability than PID and NNI control.

Parameter Design of Six-Pole Hybrid Magnetic Bearing Considering Variable Stiffness

Six-pole hybrid magnetic bearing (HMB) which driven by an inverter is a kind of high performance bearing with the advantages of small size and low cost. In order to overcome the disadvantage of the six-pole HMB that the working point of the rotor deviating from the given reference point, which affects the stable operation of the six-pole HMB system, the parameter design of the six-pole HMB is carried out in combination with the steady region determined by variable stiffness coefficient. Firstly, the structure and working principle of the six-pole HMB are described, and mathematical model of the radial suspension force in the x direction which considers static working point offset is derived by equivalent magnetic circuit method. Secondly, variable stiffness of the six-pole HMB which considers the static working point offset is analyzed, and the steady region of the stable operation of the six-pole HMB is obtained. Thirdly, combined with the delineated steady region, the parameter design of six-pole HMB is carried out. Finally, simulation and experimental results show that the six-pole HMB system has well performance of anti-interference, which proved that variable stiffness analysis provides a theoretical basis for the parameter design of the six- pole HMB.

Rotor Displacement Self-Sensing Method for Six-Pole Radial Hybrid Magnetic Bearing Using Mixed-Kernel Fuzzy Support Vector Machine

In order to solve the problems of larger volume, higher cost and lower reliability caused by displacement sensors in a magnetic bearing system, a self-sensing method using mixed-kernel function fuzzy support vector machine (FSVM) displacement prediction model is proposed. Firstly, The structure and working principle of six-pole radial hybrid magnetic bearing (HMB) are introduced, and its suspension force mathematical model is deduced. Secondly, the FSVM displacement prediction model among control currents and rotor displacements is established, and the performance parameters of FSVM are optimized by genetic algorithm. Finally, a simulation test of the six-pole radial HMB system is constructed, the simulation results show that the performance of the prediction model using the mixed-kernel function FSVM is significantly better than that using other kernel functions, and the predicted values are about 93.35% and 95.5% of the actual values in the x- and y- direction. The anti-disturbance experiments are carried out and the feasibility of the method proposed is verified.

Design and Adaptive Sliding-Mode Control of Hybrid Magnetic Bearings

In this paper, a hybrid magnetic bearing (HMB) prototype system is designed and analyzed. Two compact bearings are used to suspend the rotor in five degrees of freedom. Electromagnets are used for axial suspension of the rotor, while permanent magnets are used for the passive radial stability. A brushless DC motor is designed in order to rotate the shaft around its axis. The 3-D finite-element model of the HMB system is established and distribution of magnetic fields in the air gaps and magnetic forces on the rotor under various control currents and displacements is calculated. A nonlinear adaptive sliding-mode controller is designed for the position control of the rotor in axial direction. Since the control characteristics of the active magnetic bearing system are highly nonlinear and time varying with external interference, a radial basis function compensator is designed first, and then, a sliding-mode control law is used to generate the control input. The stability analysis for the designed controller is given based on the Lyapunov theorem. Experimental setup is built to guide the design process. The performance of the HMB system based on the designed control algorithm is evaluated under different operating conditions.

Composite anti-disturbance controller for magnetically suspended control moment gyro subject to mismatched disturbances

To achieve the high-precision control for the hybrid magnetic bearing system in the magnetically suspended control moment gyro under voltage-controlled mode, this paper proposes a composite control approach combining robust control and a state-space disturbance observer. To handle the multiple disturbances, the hierarchical idea is used. The external disturbances are estimated and rejected by a state-space disturbance observer, while the norm-bounded uncertainties are attenuated by robust $${H_\infty }$$ strategy. On the other hand, to counteract the input-mismatched disturbances in the voltage-controlled mode, different equilibrium points are designed for various state variables. That is, the mismatched influence is transferred to the state variable that is not paid much attention. The proposed method exhibits the attractive advantage that it retains the baseline robust controller performance. The effectiveness and superiority of the proposed control method are demonstrated by both simulations and experiments.

Magnetic Field and Specific Axial Load Capacity of Hybrid Magnetic Bearing

Permanent magnet bias hybrid magnetic bearing (HMB) which combines active and passive actuators in one unit is very suitable for rotational applications in spacecraft. In the past, numerous studies focusing on the active actuator have been widely reported. However, few have addressed on the passive unit which is essential to the suspension system. In this paper, a sufficiently precise and concise analytical method which is based on the conformal transformation is proposed for the analysis and design of the HMB with specific axial load capacity. With this approach, important parameters used for optimal MB designing, such as magnetic leakage coefficient, as well as the flux density of main flux and fringing flux are given as simple formulas, which educe the axial restoring magnetic force and the axial passive stiffness. The coupling effect of these two units of the HMB is analyzed. The torque generated by the control current of the radial bearing is educed. Experimental investigation via an experimental apparatus to measure the axial specific capacity is introduced. Flywheel prototypes suspended by this kind of HMB system are tested, and the consequence is compared with the analytical data and the finite-element method data to get a final conclusion, which demonstrates the specific load capacity and the conciseness and accuracy of the analytical method.

하이브리드 자기베어링 시스템의 강인 안정도 해석

This paper propose the robust stability algorithm for controlling a hybrid magnetic bearing system. The control object in the magnetic bearing system enables the rotor to rotate without any physical contact by using magnetic force. Generally, the system dynamics of the magnetic bearing system has severe nonlinearity and uncertainty so that it is not easy to obtain the control objective. For solving these problems, we propose the fuzzy modelling and robust control algorithm for hybrind magnetic bearing system. The sufficient conditions for robust controller are obtained in terms of solutions to linear matrix inequalities (LMIs). Simulation results for HMB are demonstrated to visualize the feasibility of the proposed method.

A contribution on the investigation of the dynamic behavior of rotating shafts with a Hybrid Magnetic Bearing Concept (HMBC) for blower application

Within a subproject of the RAPHAEL-Program, which was part of the 6th EURATOM Framework Program supervised by the European Commission, it was investigated whether the use of a Hybrid Magnetic Bearing Concept (HMBC) will be beneficial for a blower application. Within the RAPHAEL program, the subproject “Component Development” is dealing with R&D of components of High Temperature Reactor Technology (HTR), where a major focus is on safety- and reliability-related issues. That implies special requirements for the support of high speed rotating shafts in HTR-Applications that only can be satisfied by using Active Magnetic Bearings (AMB). Regarding safety and competitiveness, AMBs are considered to be key components for the support of rotating HTR-components due to their technical features. AMBs are characterized by an electromagnetic actuator that is generating the bearing force depending on the clearance between stator and rotor, in which the rotor is levitated. Therefore an active control of the coil current is necessary. Furthermore, Touch Down Bearings (TDB) are needed to avoid damages in case of an emergency shut down or in case of energy supply losses. This contribution provides an internal insight on the advantages of a Hybrid Magnetic Bearing Concept that is characterized by a completely Active Magnetic Bearing-supported vertical arranged rotor and an additional permanent magnetic radial orientated bearing. One benefit of the HMBC is an additional radial guidance of the shaft that may reduce the loads while dropping into the Touch Down Bearings e.g. in case of energy supply losses of the AMBs. Reduced loads on the TDBs will increase their life cycle and the availability of the AMB supported component. The scope of this R&D-Project, which will be described more detailed in this contribution, includes: the analytical modeling and simulation of the dynamic behavior of the Hybrid Magnetic Bearing System; the modification of the completely AMB-supported test facility FLP 500 with a radial PMB; the experimental tests and validation of the analytical models to provide recommendations for the investigated blower application as a HTR-component. Furthermore, the effects occurring during the modification of the test facility and the approach that was necessary to solve unexpected problems will be described.

Design Analysis and Performance Assessment of Hybrid Magnetic Bearings for a Rotary Centrifugal Blood Pump

A hybrid magnetic bearing system was designed for a rotary centrifugal blood pump being developed to provide long-term circulatory support for heart failure patients. This design consists of two compact bearings to suspend the rotor in five degrees-of-freedom with single axis active control. Permanent magnets are used to provide passive radial support and electromagnets to maintain axial stability of the rotor. Characteristics of the passive radial and active thrust magnetic bearing system were evaluated by the electromagnetic finite element analysis. A proportional-integral-derivative controller with force balance algorithm was implemented for closed loop control of the magnetic thrust bearing. The control position is continuously adjusted based on the electrical energy in the bearing coils, and thus passive magnetic forces carry static thrust loads to minimize the bearing current. Performance of the magnetic bearing system with associated control algorithm was evaluated at different operating conditions. The bearing current was significantly reduced with the force balance control method and the power consumption was below 0.5 W under various thrust loads. The bearing parameters predicted by the analysis were validated by the experimental data.

Parameter Estimation and Actuator Characteristics of Hybrid Magnetic Bearings for Axial Flow Blood Pump Applications

Axial flow blood pumps are generally smaller as compared to centrifugal pumps. This is very beneficial because they can provide better anatomical fit in the chest cavity, as well as lower the risk of infection. This article discusses the design, levitated responses, and parameter estimation of the dynamic characteristics of a compact hybrid magnetic bearing (HMB) system for axial flow blood pump applications. The rotor/impeller of the pump is driven by a three-phase permanent magnet brushless and sensorless motor. It is levitated by two HMBs at both ends in five degree of freedom with proportional-integral-derivative controllers, among which four radial directions are actively controlled and one axial direction is passively controlled. The frequency domain parameter estimation technique with statistical analysis is adopted to validate the stiffness and damping coefficients of the HMB system. A specially designed test rig facilitated the estimation of the bearing's coefficients in air-in both the radial and axial directions. Experimental estimation showed that the dynamic characteristics of the HMB system are dominated by the frequency-dependent stiffness coefficients. By injecting a multifrequency excitation force signal onto the rotor through the HMBs, it is noticed in the experimental results the maximum displacement linear operating range is 20% of the static eccentricity with respect to the rotor and stator gap clearance. The actuator gain was also successfully calibrated and may potentially extend the parameter estimation technique developed in the study of identification and monitoring of the pump's dynamic properties under normal operating conditions with fluid.

Effect of the repulsive force in the HTSC–permanent magnet hybrid bearing system

Magnetic levitation using the pinning force of the YBaCuO high- T c bulk superconductor (HTSC) materials has an advantage to achieve stable levitation without control. To increase levitation force, the HTSC–permanent magnet hybrid magnetic bearing system is introduced. A circular shaped three phase Nd–Fe–B permanent magnet is installed on the rotor, and HTSC bulk superconductor is set on the stator. The additional permanent magnet is installed under the HTSC. Repulsive force of the permanent magnet is used for levitation, and pinning force between the HTSC and permanent magnet is used for guidance force of the bearing. In this system, relationship between permanent magnet and the HTSC is important. When repulsive force of the permanent magnet is large, pinning force of superconductor is used to keep the rotor position. As a result, stability for the lateral direction is decreased with hybrid system. For levitation force, effect of the hybrid system is not observed with column HTSC. Compared with the ring HTSC results, the following thing is considered. Because there is no space that flux of one permanent magnet acts on the other one with the column HTSC configuration, interaction between two permanent magnets becomes small.

Improvement of levitation characteristics in a magnetic bearing system using HTSC‐permanent magnet hybrid structure

AbstractMagnetic bearing using pinning force of a permanent magnet and a high‐temperature superconductor has been developed. Additional permanent magnet is introduced to increase the levitation force of the magnetic bearing. In this hybrid magnetic bearing system, levitation force is mainly given by the repulsive force of the permanent magnets, and stability for the lateral direction is given by pinning force of the superconductor.The experimental device is developed. A ring‐type superconductor and a bulk one are examined. Levitation characteristics of the hybrid magnetic bearing are measured. The bulk superconductor shows better characteristics of both levitation and lateral stability than the ring one. Levitation force of the hybrid system becomes about twice as large as that of the nonhybrid one. Although, the repulsive force of the permanent magnet decreases the lateral stability of the system, its influence becomes small by choosing an adequate position of the permanent magnets and the superconductor. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 150(1): 71–77, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10350

Improvement of the Levitation Characteristics in the Magnetic Bearing System Using HTSC-Permanent Magnet Hybrid Structure

Magnetic bearing using pining force of a permanent magnet and a high-temperature superconductor has been developed. Additional permanent magnet is introduced to increase the levitation force of the magnetic bearing. In this hybrid magnetic bearing system, levitation force is mainly given by the repulsive force of the permanent magnets, and stability for the lateral direction is given by pining force of the superconductor. The experimental device is developed. A ring type superconductor and a bulk one are examined. Levitation characteristics of the hybrid magnetic bearing are measured. A bulk superconductor shows better characteristics both levitation and lateral stability than ring one. Levitation force of the hybrid system becomes about twice as large as that of the no-hybrid one. Although repulsive force of the permanent magnet decreases lateral stability of the system, its influence becomes small by choosing adequate position of the permanent magnets and the superconductor.

Modeling and control of a new horizontal-shaft hybrid-type magnetic bearing

This paper reports on the development of a new horizontal-shaft hybrid-type magnetic bearing system. The bearing system will be used for a horizontal-shaft machine. The rotor is levitated due to the repulsive force between a stator and a rotor permanent magnet (PM). A lower cost and higher radial stiffness have been achieved by using a strontium-ferrite magnet on the rotor and an Nd-Fe-B PM above and below the rotor magnet. A finite-element analysis was performed to calculate the levitation force and radial stiffness. An upper stator magnet subtending an angle of 45/spl deg/ provides the best compromise between a large levitation force and radial stiffness. A model for the horizontal-shaft hybrid magnetic bearing system has been developed and includes the effect of the rotor dynamics and the electromagnetic forces. An integral servocontroller was designed to stabilize the axial position. The controller has been implemented in a digital signal processor. Experimental results performed on a prototype system are in agreement with the theoretical results.