IGBT Modules - Technologies, Driver and Application (Second Edition) - page 494

482
To produce the graph in
a value of
3
2 has been used for k
f
. A far worseHDF
would result without this increase in frequency in theDPWM technique.
Fig. 13.20
HDF as a function of the modulation factor with otherwise unchanged
conditions but increased switching frequency f
SW
for theDPWM techniques
To evaluate the quality of the PWM technique a look at the losses of the power
semiconductors apart from the HDF has to be taken. In the CPWM technique all three
inverter phase currents commutate within one period of the fundamental frequency.
Therefore, the switching losses for thesePWM variants, based on theCPWMalgorithm,
are identical and independent of the current phase angle and, thus, independent of the
power factor cos
ϕ
. For the DPWM techniques, however, there is a dependency of the
switching losses on the phase angle of the current, as – depending on the selected
DPWM algorithm – the power semiconductors are not switched for a certain period. To
assess the loss behaviour of the individual variants the switching loss factor (SLF) is
introduced, which is defined as the relation of the losses with a certain modulation
variant to the losses occurringwith aCPWM technique.
CPWM
DPWM
P
P SLF
=
Eq. 13.30
According to the calculations of A.M. Hava et al.
he following relations result for the
variousDPWM techniques, defined section by section:
π
≤ϕ≤
π
π
≤ϕ≤
π
π
−≤ϕ≤
π
ϕ
+
ϕ ⋅
ϕ
=
2
6
6
6
6
2
4
sin 5.0
4
cos 3 1
4
sin 5.0
SLF
DPWMMIN
Eq. 13.31
DPWMMIN
DPWMMAX
SLF
SLF
=
Eq. 13.32
1...,484,485,486,487,488,489,490,491,492,493 495,496,497,498,499,500,501,502,503,504,...548