The power switching device can be easily
damaged when the two-level inverter implemented cause of the
limitation of the voltage vectors. Fig.8 has shown the simulation
result by using 3-level inverter Cascaded H-bridge multilevel
inverter with a proposed method for different operating speed.
The switching frequencies for 3-level CHMI are better than 2-
level conventional inverter. Besides that, by applying the lower
amplitude voltage can produce low dv/dt which can eliminate the
harmonic component. By using 3-level CHMI topology, more
voltage vector can be produced and by selecting appropriate
voltage vectors the performances of the induction motor can be
further improved. From the figure 8 (a-2), (b-2) and (c-2) clearly
shows the closed up for low, medium and high speed to make the
comparison. The voltage phase profile of CHMI is different
amplitude. This is because different voltage magnitude is applied
according the speed region of the motor. Whereas two-level
inverter has same voltage amplitude for different speed
operation.