41. A Supercapacitive Multilevel Voltage Source Inverter for Photovoltaic System

This paper presents a transformerless multilevel inverter topology with highly efficient capacitive storage replacing the lead-acid batteries which have been used so far as the separate dc voltage sources. ECS (Energy Capacitor System) storage has been utilized to construct a 4-level single phase inverter of 50 Hz, 900 VA. Despite the long history of lead-acid batteries as a device for dc power storage in PV systems, an attempt has been taken in this work to use supercapacitor bank as an alternate power storage device. Use of traditional electrochemical batteries degrades the overall efficiency of the multilevel inverter system since the batteries are associated with problems like: long charging time, limited Coulomb efficiency, limited cycle life and low depth of discharge. An efficient solution for the problems mentioned above can be to eliminate batteries completely from the system. The cascaded H-Bridge inverter has been chosen here to produce the approximate sinusoidal waveform by connecting the separate dc sources of each H-Bridge by proper switching. The inverter using ECS banks provides a more efficient power conversion scheme from DC energy stored in Supercapacitors charged by photovoltaic cells. A simple simulation has also been done for the 4-level inverter.