5. CONCLUSIONThe switching time del

5. CONCLUSION
The switching time delay in a PWM inverter has effects on
inverter operation. It causes a decrease in the fundamental
component of load voltages and introduces low-order harmonics.
It is shown that, despite PWM methods that produce
sinusoidal outputs, free from any lower order harmonics, inverter
dead-time generates odd low order harmonics. This is
important in all cases in which the output voltage is set in
open-loop or it is evaluated on the basis of dc voltage and
switching pattern.
In this paper the dead-time effects on inverter output
variables has been analyzed in three-phase inverters with
output currents with relevant ripple. It has been shown that
due to multiple zero crossings of current, dead-time effect is
reduced, and there is different voltage harmonic spectrum
with respect to one which considers pure sinusoidal output
currents. A simplified theoretical approach is proposed to
evaluate the value of time interval when the zero crossings
occur, on which is based the theoretical analysis of the effect
of dead-time on output voltage distortion. Further on, this
analytical developments have been compared with numerical
results obtained by circuit simulations, showing a good
agreement. Experimental results are currently in progress.