A novel facility with thyristor rectifiers and direct current distribution board for a hydro power plant supply

Thyristor rectifiers from the series DRI-PT with analogue control electronics printed circuit board "DIGISP 09" and serial diodes towards the load represent an additional improvement of the existing rectifiers based on the programmable logic controller (PLC). Along with the concomitant direct current distribution board it represents the redundunt system for the direct current supply of consumers in a hydro power plant. New implemented functions are the output voltage compensations depending on the battery temperature and the battery cables voltage drop, active sharing of the load current during the parallel operation of two rectifiers, manual battery presence check, automatic and manual battery state check (periodical automatic discharging of the predefined battery capacity in the adjusted moment) and limited operation time in the equalize charging mode. Maximum battery current ripple was reduced to 5% of the nominal value utilizing the double LC filter in the power circuit. Digital controllers were implemented in the form of adjustable PID regulators with the linear adaptive gain scheduling. Beside the basic digital regulators, control electronics also possess an analogue PI regulator, enabling the reliable rectifier operation in the float charging mode even in the case of PLC fault. In the paper were presented results of the examinations of rectifier's power factor, total harmonic current distortion and the overall efficiency. High values of overall efficiency for nominally loaded thyristor rectifiers of approximately 95.5% were measured.