Minimum voltage control for reliability improvement in modular multilevel cascade converters-based STATCOM

This work proposes an adaptive dc-link voltage strategy applied to a double-star chopper cell-based static synchronous compensator (DSCC-STATCOM). The proposed technique aims to improve the converter reliability by controlling the cell reference voltage according to the minimum voltage required in each STATCOM operation condition. It is important to remark that the proposed strategy does not require any hardware modification. The technique is evaluated in terms of dynamics and reliability. For this purpose, two modulation strategies were analyzed: phase-shifted pulse-width modulation (PS-PWM) and nearest-level control with cell tolerance band algorithm (NLC-CTB). The results show that the proposed technique can reduce the switching losses and increase the system reliability. For the evaluated case study, the DSCC-STATCOM B-1 lifetime increases 16% and 23% for PS-PWM and NLC-CTB, respectively, when the minimum voltage control strategy is employed.