Implementation of Asymmetrical Cascaded H-Bridge Multilevel Inverter with Flyback Converter for Solar Photovoltaic System

Abstract

The growing interest in multilevel inverters for high-power applications is largely attributable to their ability to lower Total Harmonic Distortion (THD) in the output voltage and to the reduced blocking voltage requirement for the switching devices. Presently, these inverters consist of series configurations of fundamental building blocks, each supplied by dedicated, constant DC voltage sources. The inverters have been examined in both symmetric and asymmetric operation modes to generate an expanded palette of voltage levels. The present study extends this architecture by replacing the conventional DC voltage sources with photovoltaic (PV) cells, whose output voltages vary with solar irradiation. The work of Takahashi and Yoshiharu (2002) provides the guiding framework for employing Maximum Power Point Tracking (MPPT) to extract optimal voltage from the PV source. Given that the input to the multilevel inverter should ideally remain constant, a flyback forward converter is interposed between the PV array and the inverter to stabilize the input voltage while accommodating the non-constant solar output. The flyback converter delivers a set of multiple constant output voltages, which the multilevel inverter then expands to a total of 49 discrete voltage levels. The combined system is analyzed to quantify both the total power dissipation within the switching devices and the Peak Inverse Voltage (PIV) experienced. The theoretical predictions are validated through a comprehensive simulation conducted in MATLAB. Results have been confirmed via experiments using bench-scale prototype systems.