Application Note
38 of 53
V 1.0
2019-04-01
IM393 Application note
IM393 IPM Technical Description
Thermal design
7.2
Power losses
The total power losses in the IM393-XX are composed of conduction and switching losses in the IGBTs and
diodes. The loss during the turn-off steady state can be ignored, as it is very low and has little effect on
increasing the temperature in the device. The conduction loss depends on the DC electrical characteristics of
the device, i.e. saturation voltage. Therefore, it is a function of the conduction current and the device’s junction
temperature. The switching loss, however, is determined by dynamic characteristics such as turn-on/off time
and over-voltage/current. Hence, in order to obtain accurate switching losses, the DC-link voltage of the
system, the applied switching frequency, the power circuit layout, and the current and temperature should be
considered.
In this chapter, detailed equations are shown to calculate both losses of the IM393-XX based on a PWM-inverter
system for motor-control applications. They apply to the case in which three-phase continuous sinusoidal
PWMs are adopted. For other cases, like three-phase discontinuous PWMs, please refer to [4].
7.2.1
Conduction losses
The typical characteristics of forward-drop voltage are approximated by the following linear equation for the
IGBT and the diode, respectively.
i
R
V
V
i
R
V
V
D
D
DIODE
I
I
IGBT
⋅
+
=
⋅
+
=
(14)
•
V
I
= Threshold voltage of IGBT
•
V
D
= Threshold voltage of monolithic body diode
•
R
I
= On-state slope resistance of IGBT
•
R
D
= On-state slope resistance of monolithic body diode
Assuming that the switching frequency is high, the output current of the PWM-inverter can be assumed to be
sinusoidal. That is,
φ)
cos(θ
I
i
peak
−
=
(15)
Where, ϕ is the phase-angle difference between output voltage and current. Using the previous equations, the
conduction loss of one IGBT and its monolithic body diode can be obtained as follows.
sφ
MIco
R
3π
I
R
8
I
MIcosφ
V
8
I
V
2π
I
i)dθ
ξ(V
2π
1
P
I
2
peak
I
2
peak
I
peak
I
peak
π
0
IGBT
con.I
+
+
+
=
×
=
∫
(16)
MIcosφ
R
3π
I
R
8
I
MIcosφ
V
8
I
V
2π
I
i)dθ
ξ)(V
(1
2π
1
P
D
2
peak
D
2
peak
D
peak
D
peak
π
0
DIODE
con.D
−
+
−
=
×
−
=
∫
(17)
con.D
con.I
con
P
P
P
+
=
(18)
Where
ξ
is the duty cycle in the specified PWM method.
2
MIcosθ
1
ξ
+
=
(19)
Where, MI is the PWM modulation index defined as the peak phase voltage divided by half of the DC-link
voltage.
It should be noted that the total inverter conduction losses are six times that of the P
con
.