Operation of the Low-Capacitance Cascaded H-Bridge StatCom under Grid Voltage Swells

Grid voltage transients and, in particular, grid voltage swells pose control challenges for static compensators (StatComs). This article presents an efficient control strategy for changing the dc value of capacitor voltages, which is especially useful for operating a low-capacitance StatCom (LC-StatCom) under grid voltage swells. In the proposed strategy, the capacitor voltages are changed as a function of the grid voltage magnitude in each phase. This article details all the required control stages for implementing this control strategy. The effectiveness of this strategy to deal with grid voltage swells is compared with other strategies both in conventional StatComs and LC-StatComs using a simulated 36-MVA 11-level cascaded H-bridge converter in MATLAB Simulink. The comparison is based on current transient performance and an analytical model of switching losses. Finally, the feasibility of this strategy is confirmed by experiments on a 1 kVA prototype.