Improved Fundamental Frequency Switching Control Method for MMC Based STATCOM Considering Capacitor Voltage Ripple

In the present, the use of STATCOMs with modular multilevel topology has spread over the past decades, which consists of a flying capacitor in each power cell. In particular, the capacitor voltage ripple will cause the fundamental component of the output voltage to shift relative to the ideal situation. This paper presents an optimized staircase modulation scheme to find the switching angles in modular multilevel converter (MMC) based STATCOM, by introducing the practical compensation parameters into the transcendental equations to get more exact solutions than the conventional selective harmonic elimination (SHE) method. Digital simulation analysis shows the correctness and effectiveness of the proposed modulation scheme.