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.