  Conventionally, Selective Harmonic Elimination (SHE) method in 2-level
inverters, finds best switching angles to reach first voltage harmonic to
reference level and eliminate other harmonics, simultaneously. Considering
Induction Motor (IM) as the inverter load, and wide DC bus voltage variations,
the inverter must operate in both over-modulation and linear modulation region.
Main objective of the modified SHE is to reduce harmonic torques through
finding the best switching angles. In this paper, optimization is based on
optimizing phasor equations in which harmonic torques are calculated. The
procedure of this method is that, first, the ratio of the same torque harmonics
is estimated, secondly, by using that estimation, the ratio of voltage
harmonics that generates homogeneous torques is calculated. For the estimation
and the calculation of the ratios motor parameter, mechanical speed of the
rotor, the applied frequency, and the concept of slip are used. The advantage
of this approach is highlighted when mechanical load and DC bus voltage
variations are taken into consideration. Simulation results are presented under
a wide range of working conditions in an induction motor to demonstrate the
effectiveness of the proposed method.
