Hiroshi Uchino

An Approach to Flux Control of Induction Motors Operated with Variable-Frequency Power Supply

A new speed control system for induction motors has been developed which is capable of controlling with quick field weakening and superior response and stability. This method is to control the stator current as a vector quantity on the basis of slip frequency control. More specifically, it is designed to calculate the commanded stator current of the induction motor by corresponding to flux and torque commands on the basis of motor constants and use the calculated commands to control the stator current.

Which is better at a high power reactive power compensation system, high PWM frequency or multiple connection?

In general, higher PWM frequency gives better performance at small or medium capacity inverters. This paper deals with the comparisons between two systems, SB and MB at a multi-10 MVA GTO power converter for reactive power compensation from the viewpoints of desired switching frequency and converter connections. SB is a single bridge system consisting of a three-phase bridge power converter unit and a transformer and its PWM frequency varies from 450 Hz to 1800 Hz. The line frequency is 50 Hz. 1 MB or 3 MB is a multiple bridge system consisting of plural single- or three-phase power converter units and transformers. Two kinds of systems using different transformer windings are considered. Type A uses conventional but complicated zigzag windings and type B simple star and delta windings. The switching frequencies are chosen the lowest, 50 Hz for 1 MB and 150 Hz for 3 MB. The evaluated items are harmonic distortion, power loss, GTO utilization factor and control response. A simulation study shows that MB is superior to SB in any case, even in the case of severe line faults where very quick response is requested. A new control strategy is adopted for obtaining quick response. Type B system has almost the same characteristics as type A system and can easily conquer the DC magnetization of the power converter transformers that may be encountered at a line voltage disturbance.<<ETX>>

Converter configurations and switching frequency for a GTO reactive power compensator

This paper compares two converter configurations for a multi-10 MVA gate-turn-off (GTO) reactive power compensator (STATCOM) from the viewpoints of converter connection and switching frequency. One is a single-bridge system consisting of a three-phase bridge converter unit and a transformer. Its pulsewidth modulation (PWM) frequency varies from 450 to 1800 Hz, and its line frequency is 50 Hz. The other is a multiconnected converter system consisting of plural, single-, or three-phase converter units and transformers. Its switching frequencies are chosen to be the lowest possible. The evaluated items are harmonic distortion, power loss, GTO utilization factor, and control response. Our simulation study shows that the multiconnected converter system with the lowest switching frequency is superior to the single-bridge system with the higher switching frequency in every case, even when there are severe line faults requiring very quick response. A new control strategy is adopted for obtaining quick response.

Parallel operation of active and passive filters for variable speed cycloconverter drive systems

The authors prepared a digital simulation program consisting of a passive filter, active filter, cycloconverter, and power supply system, and they studied a variety of combinations of passive and active filters in terms of harmonic compensation, parallel resonance suppression, and series resonance suppression. It is shown that the harmonic compensation equipment with a combined use of active and passive filters can effectively compensate a variable-frequency harmonic current generated by the cycloconverter over a wide operation range and can suppress the parallel and series resonance phenomena. The authors analyze the characteristics of three types of arrangement of the active and passive filters. The total harmonic current compensation and total current feedback compensation show good characteristics in terms of harmonic compensation and resonance suppression.<<ETX>>