Nine Level Cascaded H Bridge Inverter (For High Performing UPS Applications)

Abstract

This paper proposes a nine level Cascaded H-Bridge Multi-Level Inverter, realized via Distortion Minimization PWM technology which is incorporated in an Uninterrupted Power Supply (UPS), operating in the low power end. The proposed UPS is capable of supplying four typical personal computers simultaneously. Due to the increased number of switching power poles used, switching frequency per device is reduced, minimizing the switching stress per device. Thus a prolonged lifetime of the inverter can be anticipated. Moreover, the suitability of Distortion minimization PWM for this inverter design is discussed compared to Selective Harmonic Elimination PWM (SHEPWM): one of the most popular PWM methods for multi-level inverters. Furthermore, in order to incorporate the designed inverter in a UPS application such that cost, weight and size are minimized while ensuring a good transient response at the failure of the mains supply, a novel approach named “Offline Synchronization”: an attempt to combine the advantages of both offline UPSs and Online UPSs is introduced.