Study and analysis on some design aspects in single and multi-axis active magnetic bearing (AMB)

Active magnetic bearing (AMB) is a substitute of conventional bearing, which provides electromagnetic force to support the rotating part respecting the stator. The utilization of electromagnetic force makes this bearing “active”. The attraction force of an AMB system can be control by manipulating the input so that the rotor can be levitate at required position. As lot of limitation exist in passive magnetic bearing, the AMB is very useful in modern applications. Due to frictionless nature of magnetic bearing and non-necessity of lubricants, now-a-days AMB is taking place as the alternate of any other bearing in multiple applications of growing industry. Adequate knowledge of essential components is necessary for successful implementation of any active magnetic bearing design. So, In this paper, the magnetic analysis has been analyzed for the different types of single and multi-axis AMB using ANSYS Maxwell with extensively reviewed components.

Optimization of Active Magnetic Bearings’ Power Supply System for Main Helium Fan in High Temperature Gas-Cooled Reactor

High temperature gas-cooled reactor (HTR) is a kind of reactor with inherent safety developed by Institute of Nuclear Energy and New Energy Technology of Tsinghua University. In the first circuit, pure helium is used as coolant and the main helium fan is used to promote the coolant circulation. In order to meet the requirements of service environment and performance, the main helium fan adopts the non-lubricant active magnetic bearing (AMB) system as its support system. For the high-speed rotating equipment supported by AMBs, losing power would lead to bearing failure and cause serious damage to the equipment. In this paper, the power supply system of AMBs is optimized. The power supply of AMB system is connected with the DC-link of the motor converter through DC/DC converter. During normal operation, the AMB system is supplied by external power supply, and the DC/DC converter is used as the backup redundant power supply. In the event of a power failure accident, the DC/DC converter is put into operation, converting the remanet kinetic energy of the motor into stable power to maintain the normal operation of the AMB system. The DC/DC converter adopts two-stage topology structure of the former BUCK converter and the later LLC converter, and completes the voltage stabilization control of the latter LLC converter through the digital signal processor (DSP). Experimental results show that this scheme can realize the power loss protection function of the rotating equipment supported by AMBs.

Investigation of a 2-DOF Active Magnetic Bearing Actuator for Unmanned Underwater Vehicle Thruster Application

In this work, a novel application of Active Magnetic Bearing (AMB) is proposed to integrate AMB in the Magnetically Coupled Thruster (MCT) assembly for underwater application. In this study, a 2-Degree-Of-Freedom (DOF) AMB is developed and investigated for the MCT of an Unmanned Underwater Vehicle (UUV). The paper presents the detailed electro-mechanical modeling of the in-house developed AMB system. The intractable problem of rotor suspension and rotation with opposing pairs of electromagnets is considered. A Linear Quadratic Gaussian (LQG) controller is designed and analyzed in the frequency domain for the stabilization of the open-loop unstable AMB for MCT. The performance specifications of the controller, such as reference tracking and disturbance rejection are achieved and evaluated through real-time implementation of the controller. The compensator also performed reasonably well during the dynamic operations, i.e., when the rotor-propeller assembly was spun at 1500 rpm. This rotor speed is needed to generate a thrust of 40–45 N and up to 1 m/s forward velocity, which is necessary to propel the UUV under consideration. By deploying AMB in MCT assembly, it is anticipated that problems associated with the conventional directly coupled thruster operating in harsh underwater environment, such as water ingress into electronics compartment, rusting, lubrication, and vibrations would be eliminated.

Pseudospectral method-based optimal control for a nonlinear five degree of freedom active magnetic bearing system

Active magnetic bearings (AMB) are used to suspend the rotor freely inside the stator to avoid any physical contact between them. Thus, it helps in significantly reducing the wear and tear that may cause a system breakdown. With the advancement of power electronics and the implementation of advanced control techniques, the use of AMB in industrial applications has increased. This paper proposes an optimal control strategy for the five degree of freedom (DOF) AMB system. The time-energy consumption of input is minimized by the application of a relatively new optimal control method called the pseudospectral method (PSM). Since the AMB is a nonlinear system, therefore the implementation of classical optimal control strategies becomes challenging. Thus, the PSM first transforms the optimal control problem at non-uniform nodes and converts it into a nonlinear programming problem, which is relatively easier to tackle. The PSM, as demonstrated in this paper, is able to find optimal solutions using relatively fewer grid points which in turn reduces the computational time and converges to the solution faster. The simulation analysis for the AMB system using two different types of PSM, that is, Legendre PSM and the Chebyshev PSM illustrates the optimal performance of the proposed strategy.

Modelling, Analysis and Identification of the Parallel and Angular Misalignments in a Coupled Rotor-Bearing-AMB System

The standard techniques used to detect the misalignment in rotor systems are loopy orbits, multiple harmonics with predominant 2X component, and high axial vibration. This paper develops a new approach for the identification of misalignment in coupled rotor systems modelled using 2-node Timoshenko beam finite elements. The coupling connecting the turbine and generator rotor systems is modelled by a stiffness matrix, which has both static and additive components. While the magnitude of static stiffness component is fixed during operation, the time varying additive stiffness component displays a multi-harmonic behaviour and exists only in the presence of misalignment. To numerically simulate the multi-harmonic nature coupling force/moment as observed in experiments, a pulse wave is used as the steering function in the mathematical model of the additive coupling stiffness (ACS). The representative TG system has two-rotor systems, each having two discs and supported on two flexible bearings - connected by coupling. An active magnetic bearing (AMB) is used as an auxiliary bearing on each rotor for the purposes of vibration suppression and fault identification. The formulation of mathematical model is followed by the development of an identification algorithm based on the model developed, which is an inverse problem. Least-squares linear regression technique is used to identify the unbalances, bearing dynamic parameters, AMB constants and importantly the coupling static and additive stiffness coefficients. The sensitivity of the identification algorithm to signal noise and bias errors in modelling parameters have been tested. The novelty of paper is the representation and identification of misalignment using the ACS matrix coefficients, which are direct indicators of both type and severity of the misalignment.