Harmonic Analysis of CLCC-HVDC Based on Switching Function

The new Controllable Line-Commuted Converter (CLCC) with controllable turn-off capability employs a hybrid design of thyristors, combining the low cost and high reliability of conventional converters. During AC faults or disturbances, it uses a flexible DC auxiliary circuit to achieve forced commutation, thereby addressing the commutation failure issues of LCC converters and enhancing the stability and reliability of high-voltage direct current (HVDC) transmission systems. To study the characteristics of electric power quality and improvement measures in the AC/DC transmission system at the receiving end after integrating the new converter, a theoretical derivation based on modulation theory and commutation principles was conducted to explore the formation mechanisms of characteristic and non-characteristic harmonic components in the DC voltage and AC current. The harmonics of LCC-HVDC and CLCC-HVDC were analyzed in detail using FFT method on measured data from the converter stations.