El Madjid BERKOUK, Hachemi CHEKIREB, Khoukha IMARAZENE

Selective harmonics elimination PWM with self-balancing DC-link in photovoltaic 7-level inverter

In this paper, a new DC-link balancing method for a 7-level inverter fed by a photovoltaic system is proposed. The proposed redundant state technique is associated with selective harmonics elimination (SHE)-PWM instead of space vector (SV)-PWM. The switching angles related to the SHE are computed via the resultant theory method. Moreover, the study of this inverter is carried out on its equivalent matrix model. On the basis of this model, the link between the capacitor voltage, switching states, and load current is established. This allows understanding the switching redundancieseffect on the DC capacitor voltage balance. An algorithm is then developed to select the appropriate switching state, since there are 300 switching states and 720 unbalanced cases of the voltage capacitor. The proposed balancing method is tested in the case where the input DC inverter is provided by a photovoltaic generator (PVG) system and feeding an induction motor. The obtained results show that the 6 DC PVG capacitor voltages are kept balanced while cancelling the most undesirable harmonics row (5th, 7th, and 11th) in the inverter output voltage. Thus, using this cascade, photovoltaic supplying DC power can be amplified into high quality AC power.

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