Showing papers by "Jose Rodriguez published in 2000"

Regenerative drives in the megawatt range for high performance downhill belt conveyors

Abstract: Downhill transport of ore from the mine to the beneficiation plant by means of belt conveyors introduces important advantages both for the personnel and for the equipment. Furthermore, if the conveyor is equipped with a regenerative AC drive, the system will generate an important amount of electrical energy for use in the process. This paper discusses the technical alternatives and the criteria used to select a solution, using modern converter-inverter drives in the megawatt and medium-voltage range. The considered drive alternatives are: (1) an AC wound-rotor induction motor drive with additional resistors; (2) an AC synchronous motor with cycloconverter; (3) an AC induction motor with current-source inverter; and (4) an induction motor with multilevel voltage-source inverter. The study reveals that, considering the main technical criteria, the use of a three-level active front end feeding a voltage-source three-level inverter is the most appropriate alternative.

A high performance vector control of a 11-level inverter

Abstract: This paper presents a switching strategy for multilevel cascade inverters, based on the space vector theory. The proposed high performance switching strategy generates a voltage vector across the load with minimum error respect to the sinusoidal reference, with very low harmonic distortion and reduced switching frequency, without the use of traditional sinusoidal PWM techniques or more sophisticated vector modulation methods.

Reduced switching frequency active front end converter for medium voltage current-source drives using space vector modulation

Abstract: This paper proposes an active front end (AFE) converter for medium voltage current source drives. The converter comprises a 12-pulse isolation transformer and two PWM current source rectifiers (CSR) with GTO thyristors. The converter operates with a switching frequency of 100 Hz (2 p.u.), thus reducing its commutation losses by 66% compared to previous PWM approaches. Also, the converter independently controls its active and reactive power flow, thus being able to operate as a VAr compensator to the power system. Under this scheme, unity power factor is achieved by setting the reactive power reference to zero. The converter's control system is built over an inner d-q axes synchronous frame current loop, and a DC link current and reactive power outer loops to control the d and q axes respectively. Linear controllers are used in all loops except the DC link. A nonlinear controller is employed to linearize this loop, hence avoiding instabilities during regenerative operation. All these features were achieved using staggered sampling space vector modulation (SVM), which assures harmonic cancellation between both PWM-CSR through the feeding transformer. Moreover, the use of SVM avoids all complications associated with selective harmonic elimination techniques (usually employed in these converters). Specifically, solving nonlinear equations and distributing shorting pulses. Simulation results obtained under different operating conditions validate the proposed AFE converter for medium voltage current source drives.

A regenerative cell with reduced input current harmonics for multilevel inverters

Abstract: This work presents a basic unit for a medium voltage multilevel inverter, capable of regeneration of power from the load to the three-phase source. This basic cell uses a single-phase PWM rectifier to reduce the input current harmonics. The work is focused on the control, modeling and simulation of the regenerative cell, which generates practically sinusoidal currents at the output and at the input and works with near unity power factor. Experimental results obtained in the series parallel connection of two regenerative cells confirm the simulation studies.

Modelling and analysis of common-mode voltages generated in medium voltage PWM-CSI drives

Abstract: Common-mode voltages appear in PWM-CSI drives due to the working principles of the input rectifier and the output inverter. This work presents the modelling and analysis of the drive, by using the Matlab software to study this problem. The results of the model are in close agreement with experimental results, which show overvoltages of up to 100%, generating an important stress to the motor.

Simulation of a 12-pulse cycloconverter with the Alternative Transient Program (ATP)

Abstract: Transient phenomena in the distribution system can cause severe problems in the behavior of high power cycloconverter-fed synchronous motor drives. The study of these problems have motivated this work, which presents the simulation of a three-phase 12-pulse cycloconverter with the Alternative Transient Program (ATP). This study exploits the capability of ATP to produce a satisfactory interaction between the power circuits and the control logic. Special attention has been paid to the generation of firing pulses for the thyristors, to operate without circulating current. The results obtained with this simulation thoroughly describes the operation of the cycloconverter. These results include input and output voltages and currents.