DC link voltage balancing approach for cascaded H-bridge active rectifier based on selective harmonic elimination-pulse width modulation

This study presents an improved voltage balancing strategy which can be employed on multilevel cascaded H-bridge (CHB) rectifiers using low switching frequency. The proposed method balances the voltage of all DC links in a CHB rectifier to a predefined value, without increasing the number of switching transitions. The redundancy states which are available in the CHB rectifier to produce a voltage level are used to balance the DC links in each transition. Moreover, using the well-known selective harmonic elimination-pulse width modulation method, all current harmonic components up to 29th harmonic are eliminated in the three-phase CHB rectifier, whereas the average switching frequency of each switch is limited to 150 Hz. The effectiveness and validity of the proposed strategy is verified by several simulations and experiments that are carried out on a 7-level CHB rectifier.