Analysis of space vector diagram of a modular H-Bridge Converter with bypassed cells during fault condition

This paper proposes a new analysis for the fault tolerant operation of Modular H-Bridge Converter using space vector diagram. The converter can be operated during fault condition after bypassing of faulty cells. Geometrical analysis is included to create balanced line voltages from unbalanced pole voltages due to bypass of faulty cells. The space vector diagram of unbalanced pole voltages becomes an irregular six sided polygon and depending on the number of cells faulty, the space vector diagram alters its shape. Sine-triangle based implementation of the space vector diagram is used to derive a general expression for common mode voltage. The modulation index is maximized by addition of common mode voltage. The biggest circle inscribed the irregular six sided polygon gives an expression for the maximum modulation index. The modified reference waveform is used in Level Shifted Pulse Width Modulation (LSPWM) technique for the converter topology. Simulation and experimental results are included to validate the proposed strategy.