Multilevel Inverter Operation With Reduced Capacitor Inrush Currents for Solar Photo-Voltaic Applications

Power electronic converters facilitate the integration of renewable energy sources into both households and the electrical grid. Researchers are exploring the use of multilevel inverters, given their advantages, particularly in low-power applications. This study focuses on re-investigating recent nine-level switched-capacitor multilevel inverters for their 11-level operation, aiming to enhance their reliability, especially in high-temperature conditions. This expanded operational capability allows for the generation of more voltage levels compared to previous technology and reduces inrush currents in the capacitors. However, when operating at nine levels, there is an unavoidable issue of high inrush currents during steadystate operation, which result in the overheating of capacitors due to the inherent ESR (electrolytic series resistance). This, in turn, leads to early evaporation of the electrolyte, causing variations in capacitance and an ESR increase with time. In order to mitigate these undesirable inrush currents, researchers often rely on adding a low-value inductance in the capacitor’s charging circuit. Nevertheless, this solution comes with the trade-off of increased losses and a higher ringing effect of the switches In this chapter, a novel inverter modulation technique is employed to generate 11 voltage levels of the inverter’s output. This modulation utilizes the unused states within the inverter operation theory to ensure the capacitor’s consistent charging and discharging. Consequently, this approach significantly suppresses the steady-state inrush currents by many times and leads to enhancement of the inverter’s reliability and lifespan. These improvements make these inverters particularly appropriate for solar PV applications, even in challenging weather. Furthermore, this also leads in lower switch voltage and conduction stresses. To validate the effectiveness of the enhanced topology and modulation strategy, comprehensive experiments are conducted in simulation, hardware in loop and on experimental prototype.