A photovoltaic (PV) transformer‐less grid‐connected cascaded diode‐clamped half‐bridge multilevel inverter (MLI) is presented in this paper. Compared with the conventional cascaded H‐bridge (CHB) multilevel inverter, the projected inverter permits connection of double the DC‐link voltage and hence enhances its rating. The most common problem the PV‐based transformer‐less grid‐connected CHB MLI system faces is the flow of leakage currents created by parasitic capacitances due to the disparity in common‐mode voltage. As per the German standards VDE‐V‐0126‐1‐1, the leakage current must be less than 30 mA. In the proposed inverter, due to the high‐frequency pulse width modulation of voltage, a peak leakage current flow of nearly 300 mA at switching frequency (2500 Hz) and about 150 mA at its subsequent harmonics is observed. Therefore, LC‐filters are employed in the proposed inverter to suppress the peak leakage currents to less than 3 mA. Also, the LC‐filters improve the total harmonic distortion (THD) profile of the injected grid current. Further, the proposed inverter is also designed to address the temporary faults. The proposed transformer‐less inverter is simulated using the MatLab/Simulink platform, and the results are experimentally validated by performing on a real‐time hardware‐in‐the‐loop using OPAL‐RT OP5700 digital simulator as plant and dSPACE 1202 as controller.
This paper proposes a high power factor converter based symmetrical topology entitled cascaded diode clamped half-bridge multi-level inverter for high voltage photovoltaic (PV) applications along with a hybrid multi-level pulse width modulation technique. Due to the restriction of peak inverse voltage (PIV) on switching devices, the PV array voltage is restricted. Also, operating at high current causes switching losses and degrades the efficiency, hence limiting its power enhancement. Unbalance in the capacitor voltages leads to high PIV across the devices, which is undesirable. The proposed topology allows connecting double times PV array voltage keeping the PIV and current alike cascaded H-bridge multi-level inverter, hence increasing the efficiency, and thereby reducing cost and space. It ensures a capacity enhancement in renewable energy systems linked to on/off-grid applications. The projected scheme allows even power distribution among the sources along with maximum and efficient energy conversion. The control scheme adopted has the ability to balance dc-link capacitor voltage in each half-bridge results in equal PIV and switching losses across all the devices. Simulations of PV connected modified topology is carried out and validated with experimental results. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
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