Jose Andres Santisteban

Vector control methods for induction machines: an overview

In the last three decades, different vector control methods (field-oriented control (FOC), field acceleration method (FAM), universal field orientation (UFO), direct self control (DSC) and Takahashi method among others) have been proposed. It is difficult for students and nonspecialists to understand the drawbacks and advantages of each one. With this in mind, the objective of this paper is to propose a clear classification and comparison of them.

Superconducting-electromagnetic hybrid bearing using YBCO bulk blocks for passive axial levitation

A superconducting/electromagnetic hybrid bearing has been designed using active radial electromagnetic positioning and a superconducting passive axial levitator. This bearing has been tested for an induction machine with a vertical shaft. The prototype was conceived as a four-pole, two-phase induction machine using specially designed stator windings for delivering torque and radial positioning simultaneously. The radial bearing uses four eddy-current sensors, displaced 90° from each other, for measuring the shaft position and a PID control system for feeding back the currents. The stator windings have been adapted from the ones of a standard induction motor. The superconducting axial bearing has been assembled with commercial NdFeB permanent magnets and a set of seven top-seeded-melt-textured YBCO large-grain cylindrical blocks. The bearing set-up was previously simulated by a finite element method for different permanent magnet-superconductor block configurations. The stiffness of the superconducting axial bearing has been investigated by measuring by a dynamic method the vertical and transversal elastic constants for different field cooling processes. The resulting elastic constants show a linear dependence on the air gap, i.e. the clearance between the permanent magnet assembly and the set of superconducting large-grain blocks, which is dependent on cooling distance.

Development of hybrid bearing system with thrust superconducting magnetic bearing and radial active electromagnetic bearing

A superconducting/electromagnetic hybrid bearing system is currently under development and test. This system consists of a thrust superconducting magnetic bearing and a double radial active electromagnetic bearing/motor devices. The thrust bearing has been designed using NdFeB permanent magnets levitating on a set of superconducting monoliths of YBCO, prepared by top seeded melt texturing technique, which supports the weight of the rotor. The bearing/motor devices were conceived as 4-pole 2-phase induction machine using stator windings for delivering torque and radial positioning simultaneously. Using this superconducting axial bearing and the active bearings for the rotor radial positioning, a fully levitating vertical-shaft inductive machine has been tested. The tests were successful in reaching a controlled levitation up to 6,300 rpm.

Proposal of New Strain Transducers Based on Piezoelectric Sensors

The high sensitivity of piezoelectric materials to mechanical stress has turned them suitable for use in transducers capable of detecting very slight strains. In this sense, the objective of this paper is the proposal of new configurations of strain transducers based on lead zirconate titanate piezoelectric sensors. Aiming practical applications, for the measurement of dynamic strains in the structures of machines, some transducer prototypes have been developed. For their optimization, the finite-element simulations were performed. The experimental results, obtained with a prototype installed in the bearing house of a rotating machine fault simulator, show the effectiveness of these devices to measure slight dynamic strains. In this way, the measurement of the small dynamic strains in this structure can provide useful information about the machine condition.

Design and implementation of a digital control system for an axial flux switched reluctance motor

Nowadays, besides the rapid growth of different areas like the mechanical and electrical ones, it is possible to identify a particular effort to develop new motors including new electrical drives and control systems. Additionally, these equipments are being designed to give them the maximum efficiency as the energy cost is continuously increasing. With this in mind, some results related to a particular switched reluctance motor, are presented. The airgap between its poles are distributed in such a way that they are parallel to the rotation axis. Such structure is little studied by researchers. On the other hand, in order to maintain a low ripple torque, a particular algorithm is proposed which consists in imposing motor currents with a special format. The implementation of this strategy was made using two microcontrollers, one to determine the position and speed of the rotor while the second impose the appropriated current to the motor windings. This strategy has been successfully tested to control the speed of the rotor in a simple feedback loop.

The Finite Element Method as an Effective Control Design Tool

The finite element method (FEM) has shown its reliability when it deals with electromagnetic design. In this work, it is shown that the FEM can also be effective as a control design tool for nonlinear structures like active magnetic bearings. This work suggests the permanent introduction of the FEM in a regular electrical engineering programme.

Hybrid bearing for induction machine with controlled electromagnetic positioning and superconducting levitation

A frictionless electromagnetic-superconducting hybrid bearing for induction machine has been designed and is currently in development and tests. The vertical and radial stiffnesses have been investigated by dynamic method for different air gaps of the axial superconducting bearing. The measured low value of the radial elastic constant appeared to be responsible for the instability of the rotating shaft. That instability has been controlled using double motor-bearing devices assembled on the same shaft. This fully frictionless system reached a spinning speed of 6300 RPM.

Design and Simulation of an Automatic Positioning System for Antennas Installed on Ships

Due to the advancement of technology, war or civil ships are carrying more and more antennas and sensors, both for entertainment (TV antennas) as well as for everyday tasks (navigation radar antennas, positioning, arms and communication). This article describes a proposal for a digital control system aiming the positioning of a digital TV antenna mounted on a ship. In this case, beside the electrical signal of usual sensors, the data provided by a GPS (Global Positioning System) receiver are utilized to design the control system. Simulation results confirm the feasibility of this approach.

A simple PID controller for a magnetic bearing with four poles and interconnected magnetic flux

The conventional structures of active magnetic bearings to support rotors dispose of eight poles operating in such a way that two adjacent poles share the same magnetic flux. In this work, a different electromagnetic structure is presented which is based on the so named bearingless motor with split windings. While this device is originally supplied by alternate electrical currents, in this case, as the purpose is to generate only radial forces, the windings are supplied by continuous currents forming a magnetic flux with four equivalent poles. To test this approach, a conventional induction motor was used and its rotor was appropriately modified. It will be shown that although the magnetic fluxes are coupled, for low speed rotation, all the controlled plant can be modeled as an unstable second order system, so PID controllers can be appropriately designed. In order to test this approach, a workbench consisting of displacement sensors, signal conditioners and two microcontrollers development boards was implemented. For different radial loads and changes of displacement references, the experimental results were well succeeded.

Mutual Inductances Effect on the Torque of an Axial Magnetic Flux Switched Reluctance Motor

This paper evaluates the performance of a 6/4 axial flux switched reluctance motor (AFSRM), with only one stator, considering the contribution of the mutual inductances on the torque. To estimate the self and mutual inductances, one computational approach based on the three-dimensional finite element method, was implemented. Different from the most conventional models of the radial flux SRM, this study shows that the contribution of mutual inductances is important in the performance of the axial flux SRM when its control strategy considers two phases simultaneously energized, as verified by dynamic simulation results.