A hybrid multilevel inverter topology with third harmonic injection for grid connected photovoltaic central inverters

A three phase hybrid multilevel inverter topology is proposed for grid integrated photovoltaic central inverter systems. This topology is a hybrid of cascaded H bridge topology (CHB) and neutral point clamped (NPC) topology. The inverter uses asymmetric structure of dc bus voltage to increase the number of levels of the inverter. Third harmonic injection is proposed in order to have better utilization of the dc bus and to obtain higher number of levels. Nearest voltage level control is adapted as modulation technique to have good dynamic performance with less computational burden. A 29-level MATLAB/Simulink model of the inverter is developed to verify the performance of the proposed topology. The simulation uses only two H-bridges per phase and one three phase NPC (three-level) inverter to obtain 29 levels in line-to-line voltage. The objective of the work is: Reduction of number of switching devices, system (converter and controller) cost, EMI problem, device losses, and increasing the dynamic performance and efficiency. The proposed topology and its control are simulated using MATLAB/SIMULINK and confirmed through prototype experimentation in the laboratory.