Nagataka Seki

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.

Power converter with a failure detector of a self-turn-off semiconductor element

A power converter including a plurality of serially connected self-turn-off semiconductor elements, including a first control circuit for producing a plurality of control signals, and a plurality of second control circuits is connected to receive respective of the control signals to supply a non-conduction control signal to a respective of the self-turn-off semiconductor elements to turn off the respective semiconductor element. The power converter further includes a plurality of failure detectors and blocking circuits. Each of the failure detectors is connected to a respective of the self-turn-off semiconductor elements for detecting a fault thereof to produce a fault detection signal when the respective self-turn-off semiconductor elements has failed. Each of the blocking circuits is connected to the respective failure detector and to the first control circuit for blocking either the respective control signal or the respective non-conduction control signal based on the respective fault detection signal.

Multimicrocomputer-based controller for 12 MW GTO power conditioning systems

A multimicrocomputer controller was fabricated for a 12 MW power conditioning system (PCS). The configuration of the PCS, which consists of a 12 MW GTO (gate-turn-off) inverter, series reactors, output transformers, AC circuit breakers, and a PCS controller, is described. The functions of the controller are outlined. Results of performance tests that were conducted on a 20 kW PCS model and on the 12 MW PCS are reported, reflecting the excellent performance of the controller.<<ETX>>

Gating circuit developed for high power thyristors

Gate turn off thyristor (GTO) gating circuits, especially off-gating circuits, are the most important for reliable operation of GTO equipment. This paper describes a new gating circuit for high power GTO of 600A class. The off-gating circuit can provide a negative pulse of 200A with its rate of rise of 30A/us. Its power dissipation decreases to 20 percent of a previous type. The on-gating and negative bias circuits are also described.

New GTO uninterruptible power supplies with self-diagnosis functions

There is an increasing demand on the uninterruptible power supply (UPS) equipment for reduced energy consumption and installation space and improved reliability. This paper describes the system construction of the microprocessor-based UPS system using turn-off thyristors (GTO). The constant voltage control is performed by a GTO step-up chopper, and the GTO inverter normally is run at a fixed pulsewidth of 120°. During the overcurrent limitation operation, the PWM control on the GTO inverter is done in software. New functions are incorporated into the control circuit, such as operation procedure guidance, fault recording and fault diagnostic functions, to realize easy operation and shorten MTTR.

High power gate turn-off thyristors (GTO'S) and GTO-VVVF inverter

Three types of high power GTOs with voltage ratings of 600 to 1300V, and maximum gate turn-off currents of 200 to 600A were developed. Design considerations for realizing these devices will be described. In addition, various results will be demonstrated relating to the development of a VVVF inverter using these devices.