Optimal surplus harmonic distribution in selected harmonic elimination PWM technique for multilevel inverters

A concept of optimal surplus harmonics distribution in the selective harmonic elimination PWM technique for multilevel inverters is introduced in this paper. There are several performance indexes that can be optimized in PWM inverters, e.g., distortion factor, current or voltage total harmonic distortion or efficiency. Minimization of magnetic noise is selected as an example here. Several methods of alleviating the magnetic noise problems in PWM inverters, like harmonic decentralization and random PWM modulation, have been given in literature but only for three-level (single-cell) inverters. Numerical difficulties associated with a solution of PWM harmonic elimination equations for multilevel systems are overcome by using a nonconstrained optimization. Simulation and experimental results are presented for a double-cell series-connected voltage source PWM inverter. The theoretical and experimental results are in a very good agreement