Electric power conversion systems – Current conversion – With condition responsive means to control the output...
Patent
1997-04-17
1998-12-22
Berhane, Adolf
Electric power conversion systems
Current conversion
With condition responsive means to control the output...
363 54, 363128, H02M 704
Patent
active
058525564
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a power converter for converting an alternating current to a direct current, or vice versa.
BACKGROUND ART
FIG. 2 shows a conventional power converter comprising a thyristor valve and a controller for controlling the thyristor valve. As shown in FIG. 2, the thyristor valve has a plurality of light-triggered thyristor (hereinafter referred to as "thyristor") LLT which are connected in series. The thyristor is used as a switching element, which allows an electric current to flow in only one direction. In order to equalize the voltages applied to the thyristors of the thyristor valve, one voltage divider is connected in parallel to each thyristor. The voltage divider is a serial circuit being consisted of a capacitor C and a resistor R. Two reactors L are connected to the ends of the serial circuit of the thyristor LTT.
They control the current flowing into each thyristor LTT. The Reactors L also alleviate the rising curve of a surge voltage VS applied from the outside to the thyristors LTTs when the surge voltage VS is applied to the thyristor LTT.
Each thyristor LTT is connected in parallel with light emitting diodes LEDF and LEDR. The diode LEDF emits light when a forward bias voltage is applied to the thyristor LTT, and the diode LEDR emits light when a reverse voltage is applied to the thyristor LTT. The currents flowing into the light-emitting diodes LEDF and LEDR are controlled by a resistor RD. The light beams emitted from the LEDF and LEDR are transmitted through light guides LGs to a pulse generator PG which is set at a ground potential.
The pulse generator PG comprises a light-electric converter LEC for converting the light signals transmitted from the light emitting diodes LEDF and LEDR into a forward voltage signal FV and a backward voltage signal RV. The forward voltage signal FV and reverse voltage signal RV are used to determine a timing when the pulse generator generates a pulse to control the gate of the thyristor LTT.
The pulse generator PG includes serially connected light emitting diodes LEDs in the same number as the thyristors LTTs. The serial circuit of the light emitting diodes LEDs is connected to a power source E through a switching element S1 and an impedance Z1 in series.
Turning on the switching device S1, current I1 flows to the LEDs connected to the switching device S1, in series whereby each LEDs simultaneously emit light. Each light emitted from the light emitting diodes LEDs is applied to one of the gates of the thyristors LTTs through the light guides LGs. In short, when the switching device S1 is turned on, the serially connected thyristors LTTs can be simultaneously turned on. LG1 is a logic circuit for controlling the switching device S1, AMP1 is an amplifier for outputting an ON/OFF signal for turning on and off the switching device S1, upon receipt of the output of the logic circuit LG1.
The thyristor valve has an arrester Ar. The arrester Ar controls the level of a surge voltage VS applied externally to coordinate with the withstand voltage of the thyristor LTT (abbreviated VDRM).
FIG. 3 shows a timing chart representing the relationship between the waveforms of voltage and currents and the gate pulse. FIG. 3 is prepared to explain the feature of the present invention, but is used here to explain the conventional art. The timing chart shows the waveforms comprising the thyristor valves of FIG. 2 which are bridged in a three-phase system and operated as an inverter.
AA describes the voltage between the terminals of the thyristors LTTs, and IT describes a thyristor valve current. BB describes a transient withstand voltage during the period between the time that the thyristor valve current IT is cut off and the time that the forward withstand voltage BB reaches the rated value VDRM.
The thyristors LTTS are turned off in a reverse voltage period T1 between the time that the thyristor valve current IT is cut off and the time that the voltage AA recovers to the forward voltage. In general, the reverse voltage period T1 is set at
REFERENCES:
patent: 3838332 (1974-09-01), Hopengarten
patent: 4547843 (1985-10-01), Hucker
patent: 4868731 (1989-09-01), Hobi
patent: 5155673 (1992-10-01), Takahashi et al.
T. Takahashi, et al., IPEC-Tokyo, pp. 1268-1272, Apr. 2-6, 1990, "The Thyristor Valve Design Considering The Critical Dynamic Conditions".
Berhane Adolf
Kabushiki Kaisha Toshiba
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