Comparison of two phase shift strategies for Fault-Tolerant Operation of H-Bridge Multilevel Inverters in Photovoltaic Systems

today, Modular Multilevel Converters become very popular in photovoltaic systems. Because MMCs need independent DC voltage source and photovoltaic systems also make independent DC voltage source. For this reason, MMCs and PV systems are used together. These inverters consume less energy than traditional inverters because of high efficiency. But they have less reliability. this paper compares two fault-tolerant strategies to evaluate them in cases of fault occurrence. These strategies provide balanced line-to-line voltage even in cases of several faulty cells. The proposed fault-tolerant strategies need no additional cell and operates only with shifting signal carrier. For this reason, these strategies are low costs in comparison of other fault-tolerant strategies. The proposed strategies make the most use of other healthy cells in faulty condition, to generate balanced line voltage. In this paper, first, a background about Cascaded H-bridge (CHB) multilevel inverters and a brief review of fault-tolerant strategies will be provided. Then two phase shift strategies will be discussed completely and Total Harmonic Distortion (THD) and maximum modulation indexes will be calculated. Finally, several simulation results for seven-level inverter are provided to compare the operation of these strategies.

Comparison of two phase shift strategies for Fault-Tolerant Operation of H-Bridge Multilevel Inverters in Photovoltaic Systems Keywords:

Modular Multilevel inverters , Cascaded H-bridge converter , Fault Tolerant Strategy , Phase-Shift PWM , Photovoltaic Systems