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

This work proposes an improved modulation method at the fundamental frequency modulation for STATCOM modular multilevel static compensators. One of the reasons for the voltage unbalance across the capacitors in the DC link of the individual cells at the multi-level compensator is the non-sinusoidality of the currents. A distinctive feature of the proposed modulation method compared to traditional FFM technologies is the monitoring of the voltage across the capacitors every quarter of the period and the elimination of voltage unbalance through the use of switching patterns with different peak-to-peak voltage ripple of the dc capacitor. At the same time, the advantages of traditional FFMs are preserved - low switching frequency and high efficiency. In addition, this method is applicable for CMC with a sufficiently large number of cells in phase. The effectiveness of the proposed modulation method is confirmed by the simulation results of 35 MVA 12-chain STATCOM for an electric arc furnace (EAF), the real currents of which are accepted as test signals.