Engineering and Technology Journal

The traditional two or three levels inverter does not completely eliminate
the unwanted harmonics in the output waveform. Therefore, using the
multilevel inverter as an alternative to traditional PWM inverters is
investigated.
This paper describes the Optimized Harmonic Elimination Stepped Waveform
OHESW technique to improve the output waveform quality of multilevel
inverter fed induction motor. A new method is presented where switching
angles are computed such that a desired fundamental sinusoidal voltage is
produced while at the same time certain higher order harmonics are eliminated.
The proposed method also is used to minimize the Total Harmonic Distortion
THD of the synthesized multilevel waveform. The THD is investigated over a
wide range of possible output control voltages and number of voltage levels
used to synthesize the output waveform.
Simulation results of a cascade multilevel inverter under OHESW technique
with 5- up to 15-levels are used to eliminate the (3rd-13th) harmonics.
A prototype single-phase cascade 7- level inverter loaded by single-phase
induction motor is investigated.

This paper represents new method to determine the optimum switching angles for
Selective Harmonic Eliminated PWM (SHEPWM) inverter. Such switching angles are
defined by a set of nonlinear equations to be solved using the Resultant method. This is
done by first converting these equations that specify the harmonic elimination problem into
an equivalent set of polynomial equations. Then, using the mathematical theory of
Resultants, all solutions to this equivalent problem can be found without the need for any
initial guess. The complete solutions for unipolar SHEPWM switching pattern which
produce the fundamental while not generating specifically chosen harmonics are
investigated.