Advanced PWM for balancing DC-link voltages in seven-level CHB inverter based active filter

DC-link voltage balancing among different capacitors is a serious issue in case of multilevel inverter based shunt active power filter in medium-voltage and high-power distribution sector. Therefore, this paper presents an advanced pulse width modulation (PWM) technique for seven-level cascaded H-bridge inverter in order to maintain voltage balance among different dc-links. This modulation method is well capable of balanced charging and discharging of dc-link voltages without increasing circuit complexity. This method also can be well applicable when number of H-Bridges changes. This modulation technique is very effective in terms of voltage balancing as well as for maintaining voltage output THD at lower level. The proposed modulation technique along with synchronous reference frame theory is used in shunt type active power filtering application and found very effective during the operation of transient and steady-state condition. The proposed system is implemented in Simulink platform of MALTAB software and performance shows its effectiveness over conventional PWM techniques used for cascaded inverters.