Central seven-level current-fed inverter with module-integrated DC-DC converters for grid-connected PV plant

This paper proposes a system of current-fed converters for the integration of a large photovoltaic (PV) plant with a utility AC grid. The system comprises of a central seven-level current-fed inverter (CFI) and a large number of PV modules with module-integrated DC-DC converter. The seven-level CFI consists of three three-phase, three-level CFI units connected in parallel on the AC-side. Dual inductor current-fed push-pull topology is used for DC-DC converters which inject continuous current into the DC-bus of the CFI units. Seven-level output current waveform is obtained using space vector modulation (SVM) technique when DC-bus currents are equal. However, mismatch in module characteristics and non-uniform insolation levels cause unequal DC-bus currents leading to distortion of the output current waveform. This limitation is addressed by appropriate selection of the switching state vectors while employing SVM technique. The performance of the proposed power converters system is studied using MATLAB/Simulink.