Optimized hybrid modulation for harmonics mitigation in multilevel converters

Multilevel converters have emerged as a very important alternative in the area of high power medium-voltage applications. The multilevel inverter topology can overcome some of the limitations of the standard two-level inverter. Output voltage and power increase with the number of levels, while harmonics decrease as the number of levels increase. In addition, increasing output voltage does not require an increase in voltage rating of individual force commutated devices. Several multilevel voltage source inverters and modulation topologies exist. The cascaded-inverter with separated dc sources is discussed with simulation results to verify the proposed concept. An optimized hybrid modulation technique is presented. The basic idea is to combine the SHE PWM with quarter-wave symmetric stepped waveform. By using this method a three level inverter provides the performance of higher level inverters.