V. Rajagopalan

Expert systems for fault diagnosis of VSI fed AC drives

The use of a rule-based expert system for fault diagnosis of a voltage source inverter (VSI) feeding an induction motor are presented. Interactive session between the user and the expert system is employed to determine the faulty device(s) of the VSI fed drive. Based on the response of the operator, the functional and connectivity information coded in the knowledge base of the expert system diagnoses a fault and corrective measures and advice are given. This could result in an increase in the system availability, reliability, safety, and a reduction in maintenance cost and down time.<<ETX>>

Nonlinear control for STATCOM based on differential algebra

This paper presents a nonlinear controller for GTO based static compensators (STATCOM). This controller permits achievement of high transient performances for this kind of compensator. The design of the control system is based upon the differential algebra theory. Such a control system enables global stabilization of the compensation system and thus helps to improve largely the transient performance of the global system. The system is simulated using the averaged model for inverters in order to validate the controller performance.

Economical Equidistant Pulse Firing Scheme for Thyristorized DC Drives

From the literature published, six different gate firing schemes are available for three-phase thyristor Graetz bridge converters employing equidistant pulses. All these thyristor firing schemes have been developed with particular attention to the special control requirements of converters used in a high voltage dc transmission scheme. Herein is described a new simple equidistant pulse firing scheme intended to be economically quite competitive to the presently existing individual phase control circuits used in three-phase converter circuits for industrial applications. The princidple of operation and the circuit details of the firing circuit are described. Experimental results obtained on a laboratory dc drive of capacity 3 KVA are discussed.

Analysis by finite element method of a coupled inductor circuit used as current injection interface

In the case of three-phase diode bridge rectification, the harmonic content of the input currents can be reduced by injecting a calculated amount of third harmonic current on the AC side. The paper presents an analysis, by the finite element method, of a magnetic device (coupled three-phase inductor) used as current injection interface in a third harmonic modulation circuit. The magnetic device is designed to block fundamental currents and to offer least resistance to third harmonic currents. In order to reduce its zero sequence inductance, which may affect the operation of the diode bridge, a conductive shield is added to cover the coupled inductor. On the other hand, the conductive shield produces excessive power losses due to high eddy currents induced by the third harmonic field. The electrothermal aspect of the coupled inductor is therefore investigated. The analysis is performed using a realistic 3D model of the magnetic device.

A learning aid for power electronics with knowledge based components

In this paper we have presented a self-study expert system based power electronics instruction aid for selection and analysis of suitable power electronic converter configurations. Converter input output specifications, analysis, and converter design methodologies are interactively pursued with extensive graphical aid to guide the user (student, engineers, etc.) in the study process. Furthermore, transient, steady-state, and harmonic analysis are possible with an integrated simulator within the instruction module. A fault diagnosis expert system based module for converter-fed motor-drives, which can be chained with the expert learning aid, has also been developed. This is in the process of development to diagnose faults on all converters available in the package. >

Diagnosis and monitoring for AC drives

An expert system-based fault detection, diagnosis, and monitoring for a voltage source inverter (VSI) fed AC motor drive called EXDIMPED (expert system for diagnosis and monitoring of power electronic drives) is presented. A unique integration of symptom and topology based reasoning has been employed to diagnose a fault. A method of expert system-based monitoring is also presented. The technique of diagnosis used in the present study could be applied to any drive system with minor modifications.<<ETX>>

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.

Analysis and design of a dual series resonant converter for utility interface

The use of a dual series resonant converter with phase-shifted operation for photovoltaic utility interface is presented. The analysis, sequence of operation and detailed design for a 5 kW system are presented. The inverter operates at a fixed frequency above the resonant frequency in order to reduce the switching losses in the devices. A general purpose Simulation program AT0SEC5 has been used to predict the performance of the converter and experimental results are given confirming the validity of the simulation results.

Modeling and simulation of power electronic converters for power supplies

This paper is an update on four earlier papers that were published on the subject of modeling and simulation of power electronic converters. This paper gives an update on the micro and macro-modeling of power semiconductor devices and reviews the new simulation tools and user-friendly environment that are available for the simulation of power electronic converters with special emphasis on the analysis and design of power electronic converters that are used for power supplies. The paper discusses the subject of efficient computation of steady state and the use of symbolic math analysis for the generation of design curves. An example of a novel DC power supply with low AC current distortion is chosen to illustrate the application of the symbolic math analysis. Finally the paper suggests the addition of a benchmark 12-pulse converter scheme that is generally used for high power DC supply.

An EPROM-based PWM modulator for a three-phase soft commutated inverter

A fully digital erasable programmable ROM (EPROM)-based pulse width modulator (PWM) that receives voltage and frequency control commands independently at the input and could be used in AC variable-speed drives is described. This modulator is simpler and dynamically better than one built using a microcomputer. A high-1 resolution (one in 256) is obtained, and up to eight different PWM switching strategies can be easily implemented. Changes in the voltage or frequency commands are transient free. Some experimental results are presented. >