Frequency Spectral Analysis of 6-Pulse LCC-HVDC in Single Conductor Ground Return Configuration Using FFT

HVDC is one of the viable options for electrical power transmission and integration of renewable energy into the existing grid. To make an economic, controlled and efficient exchange of power HVDC uses current source converter (CSC) and voltage source converter (VSC) technologies. The 6-pulse LCC is the basic building block of CSC. The realization of flexible power flow control, asynchronous interconnection, and higher line loading is possible only because of HVDC transmission using LCC or VSC. However, the use of LCC or VSC causes the injection of harmonics in both the AC and DC sides of the system. This may further lead to higher losses and complexity in operation. Therefore, it is important to analyze and eliminate the dominant frequency components generated. This work performs the spectral analysis of line parameters on both AC and DC sides of each rectifier station to detect the dominant harmonic component present using FFT. The test system was developed using 6-pulse LCC-HVDC at sending station and constant load inversion mode at receiving station. The length of the HVDC transmission line is 300 km having distributed parameters supplying power to the constant load at receiving end. The MATLAB/ Simulink environment is used to develop the test system and digitalized at the sampling interval of 43$\mu$s.