Model-Based Levitation Control of A 100 kW Bearingless Electric Motor

The use of magnetically levitated rotors for various applications, especially in pumps and compressors, has seen an unprecedented rise in the last few years. Bearingless motors combine levitation and torque production capabilities. They offer more compact footprint and require less power electronics compared to more traditional active magnetic bearing supported motors. A lot of significance has been attached to reducing cost, complexity and broadening applicability of the magnetically levitated rotors. Hence, the levitation control of rotors in such bearingless machines has become quite an interesting topic of research. Digital control strategies need to be adopted for proper levitation control of rotors. Furthermore, it has to be kept in mind that these rotors cannot afford to have too many oscillations under different environmental conditions because oscillations can eventually lead to instability and heavy losses. This thesis presents a state-of-the-art model-based digital control of the levitation of a 100 kW bearingless electric motor where the point-mass of the rotor is considered. This motor has a rated speed of 22000 rpm. The entire bearingless motor system is converted into state-space models by taking into account the bearingless machine's nominal operating points and conditions. Then, a model-based controller with Pincer's conditions, coupled with an estimator with Kalman filtering, integral action and state-command path, is implemented and tested for the levitation control. FEM derived Simulink model of the bearingless motor is tested to verify the proposed control strategies. The closed-loop poles and zeroes, step responses of the closed-loop system and the frequency responses are also recorded from the simulations. In the end, the control of the rotor is investigated with five different combinations involving controller, estimator, integrator and state-command path. Comparisons are conducted on the the proposed control strategies and conclusions are drawn based on the findings

Analysis and simulation of vector controlled bearingless induction motors

The concept of bearingless motors, which combine both motoring and rotor bearing capabilities, is appealing especially in high speed and high power machine applications. Although extensive research has been carried out on permanent magnet and reluctance types of bearingless motors, studies on the induction motor type are less successful. This thesis addresses the bearingless induction motor based on the concept of dual-pole windings, one controlling the motor torque and the other the generated radial forces. A modelling approach is undertaken to investigate the effect of induction machine design on radial force generation and motor levitation under both steady state and transient conditions. The simulation is based on the dynamic reluctance mesh model embedded in vector control systems for the decoupled control of torque, flux and radial force. This is achieved through modification of a previously developed computer software for modelling induction motors in order to model the control of bearingless induction motors. Both the squirrel cage and wound rotor induction motors are investigated and their suitability for generating controlled bearing relief forces assessed. Vector control schemes for the bearingless cage and wound rotor induction motors were also designed and simulated. A mixed field oriented vector control scheme, which incorporates the simple rotor field orientation for motoring control and an airgap field orientation for rotor levitation control, is introduced and found to be advantageous in bearingless induction motor control. Apart from investigating totally bearingless conditions, the study also investigates bearing relief capabilities for a vector controlled cage and wound rotor induction motor in which the rotor movement is restricted by bearings but with the bearing load cancelled by suitably directed radial force. The effects of real winding topologies, stator and rotor slotting and iron saturation on the performance of bearing relief and bearingless induction motors are also presented. Finally, suggestions for future work is included In order to further investigate bearingless induction motors and its applications

Field Weakening Control of Interior Permanent Magnet Synchronous Motor Employing Model Order Reduction

Various control strategies have been adopted for the field weakening control of the interior permanent magnet synchronous motors. Most of these either use the magnetic model parameters or utilize the approaches like the look up tables to minimize the effects of parametric sensitivity. The variation of the inductance values due to the magnetic saturation or the cross-coupling and fluctuation in the stator resistance and the permanent magnet flux due to the temperature difference can significantly affect the control performance especially at high speeds. In this thesis, the field weakening algorithm has been proposed that employs one of the model order reduction technique, i.e. orthogonal interpolation method. This technique obtained from reducing the order of the finite element model of the machine takes the stator current components as input and outputs the corresponding flux linkage components. At first, the control design was implemented utilizing the reduction technique that contained the motor parameters to test the validity of the orthogonal interpolation method in the field weakening operation. Thereupon, the technique was designed operating independent of any machine parameter that put into place the orthogonal interpolation method and its inversion for the references calculation. The simulink feature, ‘algebraic constraint’, was used in combination with the reduction technique to produce the required current components. The control techniques were implemented in the field oriented control scheme. The methods were at first tested through simulations in the MATLAB/Simulink environment and then the experiments were performed in the dSPACE laboratory for validity of the results. The results provided in the end confirm the feasibility of the approach used. The motor operates well in the field aweakening region and can operate in the wide speed range. The results also confirm that the approach operating independent of the machine parameters exhibit better control performance

Magnetic Bearings

The term magnetic bearings refers to devices that provide stable suspension of a rotor. Because of the contact-less motion of the rotor, magnetic bearings offer many advantages for various applications. Commercial applications include compressors, centrifuges, high-speed turbines, energy-storage flywheels, high-precision machine tools, etc. Magnetic bearings are a typical mechatronic product. Thus, a great deal of knowledge is necessary for its design, construction and operation. This book is a collection of writings on magnetic bearings, presented in fragments and divided into six chapters. Hopefully, this book will provide not only an introduction but also a number of key aspects of magnetic bearings theory and applications. Last but not least, the presented content is free, which is of great importance, especially for young researcher and engineers in the field

Third International Symposium on Magnetic Suspension Technology

In order to examine the state of technology of all areas of magnetic suspension and to review recent developments in sensors, controls, superconducting magnet technology, and design/implementation practices, the Third International Symposium on Magnetic Suspension Technology was held at the Holiday Inn Capital Plaza in Tallahassee, Florida on 13-15 Dec. 1995. The symposium included 19 sessions in which a total of 55 papers were presented. The technical sessions covered the areas of bearings, superconductivity, vibration isolation, maglev, controls, space applications, general applications, bearing/actuator design, modeling, precision applications, electromagnetic launch and hypersonic maglev, applications of superconductivity, and sensors