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Single-Phase Five-Level IT-Type NPC Inverter With Improved Efficiency and Reliability in Photovoltaic Systems

The reduction in the cost of photovoltaic (PV) energy is still required to be competitive as an alternative energy source. The efficiency and reliability of PV inverters are important aspects to be enhanced to reduce the cost of PV energy since it is closely related not only to the annual energy production but also to the reduction in operational and maintenance costs of PV systems. In this article, a single-phase IT-type NPC inverter with one-leg clamping pulse width modulation (OLC-PWM) is proposed for efficiency and reliability improvements. The proposed IT-type NPC inverter with OLC-PWM can improve the efficiency by taking the advantages of I-type and T-type NPC inverters regarding the power loss. Furthermore, its reliability has been improved compared with the conventional I-type and T-type NPC inverters. The IT-type NPC inverter also has an ability to balance the neutral-point voltage. The superiorities of the proposed IT-type NPC inverter in terms of reliability and efficiency are validated through the simulations and experiments by comparing the reliability and efficiency of the conventional I-type and T-type, asymmetric I-type and T-type, and IT-type NPC inverters.