A multi-string fault-tolerant multilevel inverter configuration for off-grid photovoltaic applications

This paper presents an Multilevel inverters (MLIs) are widely used in renewable energy systems due to their ability to produce high-quality output voltage with reduced harmonic distortion, lower dv/dt stress, and smaller filter requirements. However, conventional MLI topologies require a large number of power semiconductor devices and complex control strategies as the number of voltage levels increases. This increases system cost and the probability of device failure, thereby reducing overall reliability. To overcome these limitations, a single-phase fault-tolerant multilevel inverter configuration is proposed for multi-string photovoltaic (PV) applications. The proposed topology utilizes four isolated DC sources derived from multiple PV strings, each having a voltage magnitude of Vdc/4, which reduces device count while maintaining the required voltage level. The configuration improves system reliability by ensuring continuous operation under switch open-circuit faults and DC source failures. In addition, the inverter provides energy balancing capability among the PV strings during partial shading conditions, enhancing overall system performance. Mathematical analysis of the energy balancing mechanism is presented to validate the proposed approach. The effectiveness of the proposed inverter is verified through simulation studies using MATLAB/Simulink.

Keywords Multilevel Inverter (MLI), Fault-Tolerant Topology, Power Semiconductor Switches, Off-Grid PV System, Harmonic Reduction, Power Quality Improvement, Renewable Energy Conversion.