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A simple method to analyse for and compare the harmonic characteristics in the multi-level inverter is presented. Generally, the magnitude of harmonic components is determined differently according to the available multi-carrier PWM techniques, the modulation index and the switching frequency. Previous papers have analysed the harmonic characteristics from the viewpoint of the space voltage vector. Hence, the calculation of harmonic vectors becomes more difficult and complex at four-level or over five-level. However, the proposed method has reduced the amount of calculation and simplified the process of it, using the relation between the reference phase voltage and the output phase voltage to the load neutral point. It is applied to a five-level cascade inverter and the harmonic characteristics for each multi-carrier PWM technique are compared through simulation.
Date of Publication: 4 March 2005