3. EFFECTS OF THE OUTPUT CURRENT RIPPLE
If the output current is with ripple, the effect of dead-times
is reduced since during the zero crossings the average of
sign function of current is zero, so there is no effect on
specific pulses of pole voltage at zero crossings. More
specifically, it can be shown that dead-time doesn’t affect
the width of the pole voltage pulse if the current turns from
negative to positive during the voltage pulse. On Fig. 3 are
shown the phase currents without and with ripple and the
corresponding dead-time instantaneous voltage error (the
dashed line is the average), obtained by simulations. It can
Tc
td
ik > 0
ek ik < 0
upper
lower
Fig. 1 Switching patterns and output pole voltage
Fig. 2 Currents ik (top) and load voltage error u1 (bottom, normalized with
respect to ΔVd ) for three-phase inverters
208