Comparative evaluation of multilevel DC link inverter using symmetrical and asymmetrical DC sources

This paper presents a comparative evaluation of multilevel DC link inverter of photovoltaic (PV) renewable energy system using either symmetrical or asymmetrical dc sources. The four units of dc source can have the same dc voltage level, ie 81.32 V, resulting in symmetrical dc sources. The asymmetrical dc sources consist of input dc voltages in binary sequence, 21.68 V, 43.37 V, 86.74 V and 173.48 V. The boost converters with maximum power point tracking (MPPT) capability which is regulated by perturb and observe (P&O) based control are connected between the PV panels and the four dc sources. The varying dc voltages from the PV panels are regulated to track the maximum power available regardless of the irradiance and temperature conditions. The symmetrical dc sources will facilitate the generation of 9 levels of staircase ac waveform rms of 230 V after the H-bridge inverter. Whereas, the asymmetrical dc sources are able to produce 31 levels of staircase ac waveform also with rated rms 230 V. Detailed analysis and comparison on the powers, ac output voltage, output current, total harmonic distortions, and MPPT achievement are described.