Frequency and time domain analysis of unit connected generators to HVDC converters

The steady-state performance of the ´direct connection´ of a synchronous generator to an HVDC converter, without AC filters or AC bus bar, is analysed. This system is also referred to as a unit connection´ (UC). Despite the existence of subtransient saliency, the distorted terminal voltage of the machine and its harmonic components could be fully determined by simple analytical expressions. The harmonic components and the operation limits of the converter are also derived. The rectified voltage in UC systems has been shown to be essentially as in conventional HVDC converters. Some time domain simulation results of the unit connected system voltages waveforms are presented to confirm the validity of the analytical model obtained. Also, it is shown that it is possible to determine the actual firing delay angle of the converter and the limits of the minimum firing angle due to the UC operation. The analysis presented is highly useful in assessing the machine terminal voltage waveform and its harmonics.