New method for estimating flying capacitor voltages in stacked multicell and flying capacitor multicell converters

Abstract

Multicell converters are an interesting alternative for medium voltage and high power applications, because of the increased number of output voltage levels and apparent frequency. The two most significant types of multicell converter are the flying capacitor multicell (FCM) converter and its derivative, stacked multicell (SM) converter. Balancing flying capacitor voltages is an important constraint to the proper performance of FCM and SM converters. Thus, observation of the flying capacitor voltages used in active control is valuable, but using voltage sensors for observation increases cost and size of the converter. This paper deals with a new strategy to estimate the flying capacitor voltages of both FCM and SM converters. The proposed strategy is based on a discrete time model of the converter and uses only a load current sensor. The circuit was simulated using PSCAD/EMTDC software and simulation results were presented to validate the effectiveness of the proposed estimation strategy in observing the flying capacitor voltages. Simplicity is the most significant advantage of the proposed strategy, its performance being based on simple equations.