HIGH-POWER FACTOR THYRISTORS GTO MIXED CY CLOCONVERTERS

This paper deals with a reactive power suppression technique inside ph ase-controlled structures such as rectifier bridges and cycloconverter s. The concept is based on an association between dual-switching cells by means of thyristors (natural zero current switching) and reverse b locking abilities GTOs (natural zero voltage switching). Thyristor cel ls work with a lagging phase shifting control and draw a positive reac tive power. On the contrary, GTO cells use a leading phase shifting co ntrol and draw a negative reactive power. The total average reactive p ower in the power system is zero and the power factor is only given by the line current form factor. The application of this concept to cycl oconverters gives three basic structures. Two of them have a natural c urrent reversibility. These two structures use, either a mixed full br idges association with a pulse number of 6, or a mixed bridges associa tion with a pulse number of 3. The first one gives a high power factor but draws a low frequency fluctuating reactive power. The second one yields no reactive power but with a less power factor. The study and t he comparison of these structure have been carried out on a 20 kVA thr ee-phase laboratory prototype.