Specifications

41
Dec. 2012
Mitsubishi IPM-series Application Note
11. Average Power Loss Simplified Calculation
(1) VVVF Inverter
ع
Applicability Range
It is applicable to total power loss calculation for selection of IGBTs used in VVVF inverters.
It is not applicable in the thermal design of the device (limit design).
ع
Assumption Condition
٤
1
PWM modulation used to synthesize sinusoidal output currents in VVVF inverters
٤
2
PWM signal generated by comparing sinusoidal wave to triangular wave
٤
3
Duty cycle of PWM among the rank of )100/(%
2
D1
~
2
D1 +−
D : modulation rate
٤
4
Output current of I
CP
㨯sin x without ripple
٤
5
With inductive load rate of cosǰ
ع
Calculation Equation
Duty cycle of PWM is constantly changing and its value equal to time x
2
xsinD1 ×+
at the corresponding moment.
The output current corresponds to the output voltage change and this relationship is represented by power factor cosǰ.
Therefore, the duty cycle of PWM corresponding to output current at arbitrary phase x is
2
)xsin(D1
DutyPWM
xsinIcpcurrentOutput
θ+×+
=
×=
V
CE(sat)
and V
EC
at this moment are
)xsinIcp)(@sat(Vce)sat(Vce ×=
)xsin)Icp(Iecp)1(@(VecVec ×=×−=
Static power loss of IGBT is
Similarly, static power loss of FWDi is
On the other hand, dynamic power loss of IGBT is not dependent on the PWM duty and can be expressed as the
following formula.
As for dynamic power loss of free-wheeling diode, calculation is given by an example of ideal diode shown in Fig.11.1.
㫋㫉㫉
㪭㪺㪺
㪠㫉㫉
㪠㪼㪺
㪭㪼㪺
㫋
Fig.11.1 Dynamic Power Loss of FWDi
4
trrVccIrr
Psw
××
=
Average Power Loss Simplifi ed Calculation