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Power losses and dissipation

AN4043

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Doc ID 022726 Rev 2

Power losses and dissipation

The total power losses in an inverter are comprised of conduction losses, switching losses,

and off-state losses and they are essentially generated by the power devices of the inverter

stage, such as the IGBTs and the freewheeling diodes. The conduction losses (PCOND) are

the on-state losses during the conduction phase. The switching losses (PSW) are the

dynamic losses encountered during turn-on and turn-off. The off-state losses, due to the

blocking voltage and leakage current, can be neglected.

Finally, the total power losses are given by:

Equation 14

Figure 26 shows a typical waveform of an inductive hard switching application such as a

motor drive, where the major sources of power losses are specified.

4.1

Conduction power losses

The conduction losses are caused by IGBT and freewheeling diode forward voltage drop at

rated current. They can be calculated using a linear approximation of the forward

characteristics for both the IGBT and diode, having a series connection of DC voltage

source representing the threshold voltage, VTO for IGBT, (and VFO for diode) and a collector

emitter on-state resistance, RCE, (and anode cathode on-state resistance, RAK), as shown

Figure 27.

cond

tot

≈

Figure 26.

Typical IGBT power losses

AM09357v1

10% I

10% V

10% I

sw(on)

sw(off)

CE(sat)

c(on)

c(off)

conduction

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