Specifications

42
Dec. 2012
Mitsubishi IPM-series Application Note
Because reverse recovery of free-wheeling diodes occurs in half cycle of the output current, the dynamic power loss of
FWDi is
ع
Inverter Loss Calculation Notes
࡮Divide one cycle of output current into many equal intervals, then calculate actual "PWM duty", "Output current", and
"V
CE(sat)
, V
EC
, and Psw responding to the current" in each interval. The power loss during one cycle is the sum of each
interval.
࡮The PWM duty depends on the method of generating the signal.
࡮The output current waveform and the relationship between output current and PWM duty cycle are dependent on signal
generator, load and other factors. Therefore, calculation should always be done with actual waveforms.
࡮V
CE(sat)
uses the value of Tj=125°C.
࡮Psw uses the value under half bridge operating case at Tj=125°C.
ع Thermal Design Notes
٤
1
It is necessary to examine the worst switching condition.
٤
2
Consideration of temperature variation due to current cycle should be given in thermal design.
(Temperature variation rate is 30% to 35% for 60Hz case. When the output current of several Hz switches for a few
seconds, it almost has equal temperature to a direct current with the same peak value continuously flowing. )
٤
3
Temperature ripple caused by switching operation should be considered especially when switching frequency is much
lower than 10kHz.
Average Power Loss Simplifi ed Calculation