Full Bridge Based Level Doubling Network for Reduced Capacitance

Abstract

A capacitor-fed half-bridge can be used as a Level Doubling Network (LDN) and when connected to any multilevel inverter unit, it can double the number of levels. Closed loop voltage balancing techniques are not required for maintaining the desired capacitor voltage. The capacitor of the half bridge based LDN, has to be in charging operation for half-a-cycle and discharging for the rest half. This results in a large voltage ripple across the capacitor, during low frequency operation of the inverter. A large value of capacitance is required to suppress the ripple voltage. This paper presents a method to reduce the size of LDN capacitor keeping the voltage ripple within limits by extending the half-bridge LDN to full-bridge. Working principle of the proposed method is validated by simulation in MATLABI Simulink and experimentation on a laboratory prototype.