Improved n+l redundant fault-tolerant control strategy of cascaded H-bridge DSTATCOM

Based on the DC-side voltage equilibrium control method for the unity-power-factor 4-quadrant H-bridge rectifier, an improved n + 1 redundant fault-tolerant control strategy is proposed for the cascaded H-bridge DSTATCOM, which adjusts the DC-side voltage of the healthy cells in the faulty phase to ensure the normal operation of the faulty device. Its main feature is that, the DC-side voltage of faulty phase is raised according to the capacity requirement when fault occurs, which increases the utilization efficiency of DC-side voltage and decreases the switching loss, du/dt and fault rate when device is in normal operation. In order to preserve the good harmonic characteristics of CPS-SPWM output voltage after device fault, the CPS-SPWM pulse generation sequence of the healthy cells in the faulty phase is regulated by modulating the carrier wave frequency of faulty phase. Simulative and experimental results show that, when the quantity of faulty cell is not beyond redundancy, the device with the proposed control strategy can adjust the output power in time, without any influence on the compensation performance.