Using Harmonic Spectrum for DC-Source Fault Detection and Output Improvement at Cascaded Multilevel Inverter

Increasing of multilevel inverters application, may cause some problems such as harmonic pollution which needs a suitable solution. In this paper, a three-phase 7-level cascaded inverter is simulated and tested considering three separate isolated sources. Usually, this structure is used when electrical sources are renewable energies like photovoltaic and wind turbine systems. Due to the type of the faults, one of the sources is collapsed. In this case the levels of the inverter are decreased to level five. For the five-level cascaded multilevel inverter, other hardware filters and other switching angels must be used. To meet the paper goals, the SHPWM technique is used for choosing switching angels. In addition, the 5th and 7th harmonics are used to perceive if the system is in usual mode or system is faulted. The simulation and experimental results show the magnitude of each harmonic for 7-level and 5-level multilevel inverters. Using FFT function shows the magnitude of system voltage and harmonic spectrum at each time. In the instant of fault detection, the switching angel and modulation index are changed to improve the voltage magnitude and power quality to fix the output voltage in specified level.