The switching strategies for multilevel
inverters have typically focused on
synthesizing a desired set of three phase
sinusoidal voltage/current waveforms using
several DC voltage/current levels. This results
in the DC bus terminals to become unbalanced and hence causing the net power drawn from the multiple DC bus terminals to be unmatched and time-variant. In this paper, two methods that are capable of balancing the DC voltage/current sources in a cascade multilevel inverter introduced. The simulation results verify how to implement this strategy in order to maintain equal charge/discharge rates from the DC sources in a cascade multilevel converter. Next we are going to present a unified power quality conditioner (UPQC) based on multilevel inverters, for which this method eliminates transformers that are being used in the conventional UPQC. The main purpose is to compensate for supply voltage and load current imperfections, such as sags, swells, interruptions, imbalance, flicker, harmonics and current unbalance. The result is excellent conditioning performance of the proposed UPQC for resolving the power quality problems.
Ebrahim Babaei, Ghasem Ahrabian, Ghasem Alizadeh and Seyed Hossein Hosseini
Faculty of Electrical and Computer Engineering, Tabriz University