Reduced switching frequency computed PWM method for multilevel converter control

This paper presents two computed PWM methods for 11-level multilevel converters to eliminate the specified harmonics in the output voltage to decrease total harmonic distortion (THD). The first method uses the fundamental switching scheme to eliminate low order harmonics, and uses the active harmonic elimination method to eliminate higher order harmonics. The second method uses these schemes in the reverse order, the fundamental switching scheme to eliminate higher order harmonics, and the active harmonic elimination method to eliminate low order harmonics. The computational results show that the difference between the THD of the two methods is small, but the second method has lower switching frequency. An experimental 11-level H-bridge multilevel converter was used to implement the algorithm and to validate the two computed PWM methods. The experimental results show that the two methods can effectively eliminate the specific harmonics as expected, while the second method results in a significantly lower switching frequency.