Optimal SHE-PWM switching patterns for an HVDC system built with eight conventional three-phase VSC modules

This paper discusses optimal selective harmonic elimination (SHE) pulse-width modulation (PWM) patterns derived from a pre-calculated 9-level waveform. The patterns are suitable for a high-voltage direct-current (HVDC) power transmission system based on eight conventional three-phase voltage-source converter (VSC) modules. The switching frequency of each module is maintained very low and is used as a measure to derive the optimal patterns. Both the switching losses of each module and of the overall HVDC system are kept to a minimum level. The theoretical findings are verified through simulation studies using PSCAD/EMTDC and results are presented in the paper to confirm the effectiveness of the proposed approach.