Page 256 - Rashid, Power Electronics Handbook

14 Inverters 245

FIGURE 14.26 Gating pattern generator. Waveforms for third and ninth harmonic injection PWM (m a ¼ 0:8, m f ¼ 15): signals as described in
Figure 14.24.

current i . This is due to the fact that the fundamental ac line The duality issue among both the three-phase VSI and CSI
i
current expression is should be noted especially in terms of the line-load wave-
forms. The line-load voltage produced by a VSI is identical to
p 
4 3 the load line current produced by the CSI when both are
^ i ¼ i ð14:54Þ modulated using identical techniques. The next section will
oa1
p 2 i
show that this also holds for SHE-based techniques.
The ac line current contains the harmonics f , where
h
h ¼ 6 k 1 ðk ¼ 1; 2; 3; ...Þ, and they feature amplitudes
that are inversely proportional to their harmonic order (Fig. 14.4.3 Selective Harmonic Elimination in
14.27d). Thus, Three-Phase CSIs

p  The SHE-based modulating techniques in VSIs de®ne the
^ i ¼ 1 4 3 i ð14:55Þ gating signals such that a given number of harmonics are
oah
h p 2 i eliminated and the fundamental phase-voltage amplitude is