A Fault-Tolerant Control Method for the Quasi-Z-Source Hybrid Active Neutral-Point-Clamped Three-Level Inverter with Reduced Power Losses

Semiconductor device fault is one of the main fault types of power electronic converter, which leads to output current distortion and degrades the system performance. In this paper, an improved fault-tolerant control (FTC) method is proposed for the quasi-Z-source (QZS) hybrid active neutral-point-clamped (HANPC) three-level inverter. When the open-circuit fault (OCF) of semiconductor devices <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$S_{a2}$</tex> or <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$S_{a3}$</tex> occurs, the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$[\mathrm{O}_{-}]$</tex> or <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$[\mathbf{O}_{+}]$</tex> state cannot be obtained, and the modulation strategy can be changed to restore normal operation. Specifically, the space vector diagram (SVD) is divided into normal half-cycle and abnormal half-cycle. During the normal half period, the upper shoot-through (UST) and lower shoot-through (LST) states are utilized to achieve the boost function. Meanwhile, the full shoot-through (FST) state is employed in the abnormal half period. Based on the principle, Si IGBTs can maintain high-frequency switching action for only one-sixth of each switching cycle. Compared with the conventional FTC methods, the power losses by the FTC method are reduced by about 20% and 45% in non-boost and boost modes, respectively. Simulation results and power losses analysis are provided to verify the effectiveness of the proposed method.