Power-electronic circuit arrangement for compensating for...

Details Power-electronic circuit arrangement for compensating for... Power-electronic circuit arrangement for compensating for...

1999-04-02

2001-01-23

Jackson, Stephen W. (Department: 2836)

Electricity: electrical systems and devices

Safety and protection of systems and devices

With specific voltage responsive fault sensor

C361S115000, C307S102000, C307S064000, C323S207000

Reexamination Certificate

active

06178076

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to the field of power electronics,wherein mains system disturbances and mains voltage reductions occur in a voltage supply system.
2. Discussion of Background
Circuit arrangements of this type, also known as Dynamic Voltage Restorers (DVR), supply a separate voltage, in series with the disturbed voltage supply mains system, in order to compensate for mains voltage reductions and mains system disturbances. In consequence, only insignificant changes and disturbances can be recorded on the load. To this end, the feeder converter must react very quickly, which means that the power semiconductor switches in the converter have to have a high clock frequency. This also results in the requirement that the filter connected on the mains system side of the feeder transformer must be kept as small as possible. In conventional systems for low and medium power levels, it is possible to use IGBTs and a comparatively low intermediate-circuit voltage. During operation at the required clock frequencies in such configurations, the switched-on losses of the elements are typically the governing factor, to such an extent that no further measures can be taken to reduce the overall losses significantly. At higher power levels, it is on the one hand increasingly more difficult to use IGBTs, and on the other hand the intermediate-circuit voltage must be increased in order that the currents that occur can still be coped with well. In addition, conventional GTOs have the disadvantage that they cannot be switched fast enough. In general, the switching losses in silicon semiconductor switches tend to increase at higher voltage loads. This applies to both IGBTs and GTOs. Modern, hard-driven GCTs (Gate Commutated Thyristors) can, furthermore, be produced with lower switched-on losses than IGBTs. The ratio of the switched-on losses to the switching losses is thus shifted to a major extent toward the switching losses for high-power applications, particularly with respect to the use of GCTs.
SUMMARY OF THE INVENTION
Accordingly, one object of the invention is to provide a novel circuit arrangement for compensating for mains system disturbances and mains voltage reductions, which can also be used economically for high-power applications. In particular, the intention is to make it possible to keep the switching losses in operation low, while increasing the overall efficiency of the system and the load capacity of the semiconductors.
This object is achieved by a power-electronic circuit arrangement for compensating for mains system disturbances and mains voltage reductions in a voltage supply system, the circuit arrangement comprising a feeder converter, which is connected via a feeder transformer to the voltage supply mains system, is fed from a first auxiliary voltage source with a first auxiliary voltage Ul and which, when mains system disturbances or mains voltage reductions are present, is designed to feed a compensating voltage into the voltage supply mains system, and the circuit arrangement further comprising a filter which can be connected in parallel with the feeder transformer, on the mains system side, and wherein at least one second auxiliary voltage source is provided, with a second auxiliary voltage U
2
which can be coupled to the feeder converter instead of the first auxiliary voltage source, in which case the second auxiliary voltage U
2
is chosen to be less than the first auxiliary voltage U
1
.
The essence of the invention is thus to provide a second auxiliary voltage source, whose voltage is chosen to be lower than that of the first auxiliary voltage source. The second auxiliary voltage source can be coupled to the feeder converter with the aid of a switch. The circuit according to the invention can thus operate in two different modes: when the first auxiliary voltage source is coupled to the feeder converter, the available voltage is sufficiently high to compensate for mains system undervoltages or overvoltages. On the other hand, when less severe disturbances occur, the second, lower auxiliary voltage source is coupled to the feeder converter, and mains system disturbances can in consequence be compensated for without any major switching losses. The circuit then operates in a regulated mode, and the switching losses of the semiconductor switches in the feeder converter can be kept at an acceptable level, which is typically less than the losses when switched on. A further option for influencing the voltage is achieved by pulsing, in particular by pulse-width modulation of the switches, in the regulated mode.
Further advantageous embodiments result from the corresponding dependent claims.


REFERENCES:
patent: 5329222 (1994-07-01), Gyugyi et al.
patent: 5343139 (1994-08-01), Gyugyi et al.
patent: 5485075 (1996-01-01), Mori et al.
patent: 5610501 (1997-03-01), Nelson et al.
patent: 5729120 (1998-03-01), Stich et al.
patent: 5754035 (1998-05-01), Sen
patent: 5949221 (1999-09-01), Edwards

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