R.M. Stephan

Modeling adjustable-speed drives with long feeders

This paper presents the modeling of different topologies of electric drive systems when the cable that connects the converter to the motor has a significant length. The long feeder together with converter harmonics decrease the performance of the motor. To correctly assess the voltage and the current throughout the drive system, frequency-dependent models for the cable and the motor should be used. A frequency-dependent cable model is necessary for an accurate voltage evaluation while a frequency-dependent motor model responds for accuracy in the current. The models were validated through experimental results carried out on an actual oil platform and from a prototype system. The latter system was used to test the systems performance when very long motor leads (longer than 5 km) are involved.

Adaptive and robust cascade schemes for thyristor driven DC-motor speed control

Abstract This paper is concerned with the development of improved cascaded speed control systems for thyristor driven DC-motors. The main features of the work can be summarized in the following four points: (1) Development of a digital dual-mode adaptive controller for the inner current control loop and of a model reference adaptive controller for the outer speed control loop, thus making the entire system adaptive. (2) Development of robust controllers both for the inner current loop and also for the outer speed loop, thus making the entire system robust. (3) Implementation of the above control strategies, adaptive and robust, in a 16-bit single board computer with floating-point coprocessor. (4) Comparison of the results of both robust and adaptive improved cascaded schemes with a commercially available controller. The obtained results showed that the model reference adaptive control concept and the robust control strategy can be applied with success for the speed control of a DC-motor.

Vector Control Methods for Induction Machines: An Overview

Abstract 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 a difficult task for students and non specialists 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.

Analysis of a long distance drive for an induction motor

Pumping crude oil from wells on deep ocean waters is a challenge that the oil industry is facing. To achieve this goal, a better assessment of the electrical and mechanical parts involved in the process is needed. This paper analyses the behaviour of a special type of induction motor, the ESP (electrical submersible pump) motor, when supplied by an inverter 3 km away. This configuration is widely used for oil pumping processes. Digital simulation is carried out under EMTP. To validate the system model, the simulation results were compared against experimental ones.

Modelling a static VAr compensator using EMPT

A digital simulation of a static VAr compensator (SVC) using a thyristor controlled reactor (TCR) and fixed capacitor (FC) is presented. This configuration is widely used in power system applications. The model is tested under EMTP (ATP version).

Comparison of overvoltage mitigation methods in industrial drives with long cables

This work analyses via simulation and experimental results the impact on the motor terminal voltage of inverter-fed industrial drives. After the validation of the modeling some overvoltage mitigation techniques are implemented and evaluated. In several industrial plants the cable connecting the converter and the machine may have a length of some hundreds of meters. While for conventional steady-state studies a lumped-circuit may be used to represent the cable, this is not true for power electronics application where harmonics exist in steady-state. The effect on the machine terminal voltage is increased with the length of the cable. To accurately access the motor terminal overvoltage and to implement an efficient mitigation method one needs to model the cable with the highest precision possible. In this paper a detailed frequency dependent cable is used to analyse the motor terminal voltage. Experimental results are carried out to validate the simulation models of cable and the plant. Some filter solution are analysed together with another converter configuration in order to minimize the inverter terminal voltage.

Robust Current Control for a Thyristor Driven DC-motor

Abstract A new approach to the armature current control of a thyristor driven DC-motor, based on robust pole-placement concepts, is proposed. The principal difficulty in this control problem arises due to the two different conduction modes of the current. As long as the current is continuous the armature may be modelled practically as a first order system, but as the current becomes discontinuous it exhibits nonlinear gain behaviour. These plant variations are classicaly compensated with a dual-mode adaptive current controller. It will be shown that the proposed scheme can substitute with success the old one. Moreover, because the robust controller has fixed structure and coefficients, independently of the current operation mode, its realization is simpler than that of a dual-mode adaptive controller. Simulation as well as experimental results are presented.

An Integrated Laboratory for Teaching Electrical Engineering

Abstract The modem tendency towards interdisciplinary work, the increasing demand on laboratory classes in Electrical Engineering courses and the necessity to overcome the limited financial support for education have been solved with the expanded use of a Power Electronics Teaching laboratory at UFRJ. This paper describes the equipment hardware/software and exemplifies the teaching process.

Adaptive and Robust Cascade Schemes for Thyristor Driven DC-Motor Speed Control

Improved cascaded speed control schemes for a thyristor driven DC-motor are presented. The main features of the work are the following: - Development of a digital dual-mode adaptive controller for the inner current control loop and of a model reference adaptive controller for the outer speed loop, thus making the entire system adaptive. - Development of robust controllers both for the inner current loop and also for the outer speed loop, thus making the entire system robust. - Implementation of the above control strategies, adaptive and robust, in a 16-bit single board computer with floating-point coprocessor. - Comparison of the results of both robust and adaptive improved cascaded schemes with a commercially available controller. The obtained results showed that the model reference adaptive control concept and the robust control strategy can be applied with success for the speed control of a DC- motor.