Stability study of output voltages of stand alone single stage NPC seven levels inverter for PV system in South Algeria

In this paper, the instability of output voltage of three-phase single stage seven level neutral point clamped inverter for stand-alone PV system is treated. In order to obtain the inverter output voltage at constant value under variations of both PV array voltage and load, authors propose to introduce a clamping bridge circuitry and a linear regulator. The clamping bridge circuitry maintains all capacitors voltage of DC bus equal. The reference voltage vector of voltage source inverter is determined by using an algorithm realizing the correction of the root mean square output voltage amplitude. The simplified space vector pulse width modulation is applied to get a good output inverter waveform. A real data of global solar irradiance measured on horizontal plane and ambient temperature obtained by a radiometric station installed in Ghardaïa city in south Algeria are used. Simulation results show that the designed inverter produce a stable voltage all the day despite the variation of both solar irradiation and load. Total harmonic distortion obtained is in the limits of the international standards.