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Multilevel operation of a PV fed grid connected current fed inverter under equal and unequal DC link currents

In this paper, space vector pulse width modulation control of a five-level current-fed grid tied photovoltaic (PV) system is analyzed. This system comprises of two current-fed inverters (CFIs) connected in parallel on AC-side. Each CFI is energized from a PV array of equal power rating. Unequal DC-link currents are inevitable in the above system due to partial shading effects. Therefore, the state vectors in the space vector hexagon of the above system get deformed. Consequently, implementation of SVPWM is complex i.e., in terms of sector identification and nearest vector time calculation. To address these limitations, a new SVPWM technique is proposed for above mentioned system. In this approach, each CFI is modulated corresponding to its space vector hexagon. Further, switching sequence of one CFI is phase shifted by 180° compared to the other and vice-versa. As a result, this system generates five-levels in the output phase current with equal DC-link currents. In addition, predominant harmonic harmonic spectrum of the output phase current is double the switching frequency. This leads to reduces size of filter components. The proposed SVPWM technique is analyzed on a 9 kW system using MATLAB/Simulink for wide range of modulation index. A scaled down prototype is developed to validate the proposed SVPWM technique experimentally and results are presented.