Reactive Power Control by STATCOM Quasi Linear Asymmetrical Multilevel-Based Photovoltaic System

Abstract

Recently, there has been an increasing interest in adopting Multilevel Inverters in high and medium-power industrial applications due to several inherent benefits compared to conventional two-level inverters, including a decrease in voltage-related stress, reducing the rating of power electronics switches and power quality. Compared to the symmetrical multilevel inverter, the asymmetrical multilevel inverter is composed of multiple ratios of DC source having the same number of components and providing an additional voltage level, giving rise to nearly sine-shaped output voltage with low THD. In this paper, 19th level Quasi-Linear Asymmetrical Multilevel Inverter QL-AMLI is constructed; in addition, a modified staircase modulation based on the maximum power and frequency of the operated cells within the phase has been designed for controlling the AMLI. The QL-AMLI is shunt-connected to the AC transmission lines for dynamic compensation and fed from photovoltaic arrays. The system response is achieved by controlling the voltage of the AMLI, which is governed by the DC link voltage control and modulation index; hence, the polarity of the injection reactive component and its magnitude are controlled. MATLAB/Simulink is adopted to simulate the system, and the results show the system is well behaved and stable under different scenarios, where the voltage at the point of common coupling is stable and within acceptable limits. Moreover, low THD voltage is obtained from the QL-AMLI, and the inverter is controlled according to the required reactive power. The aspects mentioned earlier confirm that the system is stable and behaves accordingly under changes in the attached load.

Keywords

• Dynamic compensation
• Asymmetrical Multilevel Inverter
• Reactive power
• STATCOM