Joseph Vithayathil

Microprocessor-Based Field-Oriented Control of A CSI-Fed Induction Motor Drive

This paper describes the method of field orientation of the stator current vector with respect to the stator, mutual, and rotor flux vectors, for the control of an induction motor fed from a current source inverter (CSI). A control scheme using this principle is described for orienting the stator current with respect to the rotor flux, as this gives natural decoupling between the current coordinates. A dedicated micro-computer system developed for implementing this scheme has been described. The experimental results are also presented.

DC Link Filter Design Considerations in Three-Phase Voltage Source Inverter-Fed Induction Motor Drive System

The dc link filter elements in a three-phase voltage source inverter-fed induction motor system can affect the performance of the drive system if not properly chosen. The requirements, design considerations, and a simplified procedure for the selection of filter component values based on minimization of voltage and current ripple currents in the dc link, damping effects, and on resonant frequency considerations are formulated. Typical computational results and experimental waveforms are presented.

A New PWM Control Method for Three-Phase Autosequentially Commutated Current Source Inverters

A new current pulsewidth modulation (PWM) method is presented which uses the principle of creating zero three-phase currents at selected instants of time, through which the load current harmonic content can be controlled along with the magnitude of its fundamental content. This gives rise to reduction of motor torque ripples through the selection of suitable PWM patterns and a fast current control in the inverter by varying the pulsewidths of the PWM pattern. Under this new PWM mode of operation, the autosequentially commutated inverter (ASCI) circuit can be modified easily so that a higher number of pulses can be accommodated within a half-cycle, compared to the normal ASCI circuit. The experimental oscillograms verify the effectiveness of the new PWM method.

A New Three-Phase Current Source Inverter with Flexible PWM Capability

A new three-phase current source inverter topology is presented, consisting of three single-phase bridge inverters connected in series and feeding the isolated windings of a standard three-phase induction motor. Because a current zero in one phase now does not affect the others, it enables the implementation of a wide range of current PWM patterns for the reduction and selective elimination of torque pulsations. Furthermore, this system allows for very fast control of the fundamental load current through the use of sinusoidal PWM, a method that was not possible to implement on existing inverter topologies.

Field Oriented Control (Vector Control) of 3 Phase Squirrel Cage Induction Motors

Vector control, also described as field oriented control, is being increasingly used for the speed control of induction motors. This is because, with vector control, it is possible to achieve high dynamic (transient) performance, equalling that of the separately excited DC motor, in variable speed AC drives. Therefore, vector control makes it possible to use, in place of a DC motor, a 3 phase induction motor, which is smaller, mechanically more sturdy, less expensive, and does not have the commutator or other rubbing contacts, and is therefore free of associated maintenance requirements and sparking problems. Vector control, however, requires on-line computation of certain control variables using inputs from sensing elements which continually sense operating motor variables such as motor line currents, motor shaft position or speed. These computed control variables serve as feedback values, which are compared with the appropriate reference values. The errors are continuously corrected by appropriately del...

A fast acting detector for abnormal output voltages of an UPS system

A new method of sensing the abnormal output voltage conditions of a single phase UPS system is presented, which provides the information almost instantaneously, so that a fast load transfer can be initiated. A continuous monitoring of the UPS output instantaneous voltage is used so that any under/over voltage, transients, or waveform distortion present can be detected.

A Current Source Inverter Fed Induction Motor Drive with Power Factor Angle Control Using Microprocessor

This paper describes a method of adjusting the stator power factor angle for the control of an induction motor fed from a current source inverter (CSI) based on the concept of space vectors (or park vectors). It is shown that under steady state, if the torque angle is kept constant over the entire operating range, it has the advantage of keeping the slip frequency constant. This can be utilized to dispose of the speed feedback and simplify the control scheme for the drive, such that the stator voltage integral zero crossings alone can be used as a feedback for deciding the triggering instants of the CSI thyristors under stable operation of the system. A closed-loop control strategy is developed for the drive based on this principle, using a microprocessor-based control system and is implemented on a laboratory prototype CSI fed induction motor drive.