Supercapacitor Assisted Inverter for the purposes of Input Ripple Control

Abstract

This thesis describes the use of a series/parallel supercapacitor to actively control the input ripple of a DC-AC power inverter through the use of a new inverter topology. The topology is made up of two 'sub-inverters' placed in series, with a supercapacitor which is in parallel with one and series with the other. By varying the current draw of each sub-inverter both the current flow into the inverter and the current flow in and out of the supercapacitor can actively be manipulated by adjusting the ratio of the current drawn by each sub-inverter. When the sub-inverter in series with the supercapacitor draws more current than the one in parallel the supercapacitor bank begins charging and more power is drawn by the inverter than is output, conversely when the parallel sub-inverter draws more current than the series one then the supercapacitor bank discharges and the inverter outputs more power than its input. By manipulating the ratio of the current draws the inverter can draw more power than it outputs during low periods of the output cycle and store it, and then release this energy during high periods of the output cycle. This technique overcomes the inefficiencies of using a conventional parallel input capacitor arrangement as the capacitor is charged in series with a load, resulting in only a negligible amount of energy lost in the path resistance.