Selective harmonic elimination for quasi seven-level operation of cascaded-type multilevel converters with unequal DC sources

Generally, selective harmonic elimination (SHE) complexity for multilevel converters increases with the increase in number of levels. In this paper, an approach for multilevel converters´ SHE is introduced. This approach is based on cancelling the 5^th and 7^th order harmonics irrelevant of the number of levels in three-phase cascaded-type multilevel converters with unequal DC sources, such that the solution for the angles required for the proposed SHE mimics that of the seven-level inverter SHE elimination (i.e. quasi seven-level operation of an m-level converter). The advantages of the proposed quasi seven-level SHE (Q7L-SHE) approach are the simplicity in format and independency of number of levels. The proposed approach can be extended for more of low order harmonic cancellation. Compared with the existing methods, the proposed method can be easily applied for a large number of switching angles, since it does not contain complex equations. A 17-level cascaded-type inverter with the unequal DC sources is considered as an example to validate the proposed concept. Simulation results using MATLAB/SIMULINK platform have been presented to elucidate the proposed concept.