Improvement of Input Current THD of Cascaded H-Bridge Multilevel Inverters Under Faulty Condition

This paper suggests a modified post-fault control method of Cascaded H-Bridge Multilevel Inverters (CHB-MLI). The proposed method focuses on improvement of the power quality by reduction in input current total harmonic distortion (THD) of the inverter under faulty condition. Initially, the algorithm of the proposed method is described to determine the optimal operation state which has less input current THD in comparison to the other possible post-fault states with the same output line to line voltages. This method yields the reduction in the input current THD in this case which the desired output line-line voltage is less than its maximum level. Then, the validity of the proposed method has been verified by the simulation of the symmetric 11-level CHB-MLI by MATLAB/SIMULINK. It is shown that by applying the proposed method in some faulty conditions, the THD of the input current has been reduced by 85%. Finally, it is concluded that the proposed method has been made less level of the input current THD in comparison with the existing control methods which results in reduction in electromagnetic interference (EMI), less transformer heat and improvement of the power quality.