A Novel Fundamental Frequency Modulation Strategy for Cascaded Multilevel STATCOM with Non-sinusoidal Load Currents

This paper proposes an improved method of fundamental frequency modulation for cascaded multi-level static compensators (STATCOMs). The non-sinusoidal nature of the current is one of the reasons for capacitor voltage imbalance in the direct current link of some of the compensators’ cells. As compared to conventional FFM techniques, the proposed method samples the capacitor voltage every quarter period and eliminates the voltage imbalance by using pulse patterns with specific DC capacitor voltage ripples. This method maintains the advantages of conventional FFM, such as low pulse frequency and high efficiency. In addition, it is applicable to STATCOMs with a relatively high number of cells per phase. The proposed method has been verified as effective in a model of a 35-MVA 12-chain STATCOM for an arc furnace whose actual currents were used as test signals.