UM0969 datasheet(35/46 Pages) STMICROELECTRONICS

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UM0969

Power losses and dissipation

Doc ID 17665 Rev 2

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Power losses and dissipation

The power dissipation of the IPM, during normal working, is due to the conduction and

switching losses of IGBTs and diodes. The losses during the turn-off steady-state can be

ignored, because of their very small amount, and because of the minor effect of increasing

the temperature in the device.

The conduction losses depend on the static electrical characteristics of the device (i.e.

saturation voltage), therefore, they are a function of the conduction current and the device's

junction temperature.

On the other hand, the switching loss is determined by the dynamic characteristics, like turn-

on/off time and overvoltage/current. Therefore, in order to obtain an accurate estimation of

the switching losses, it is necessary to consider the DC-link voltage of the system, the

applied switching frequency, the sinusoidal carrier frequency, and the power circuit layout in

addition to the load current and junction temperature.

In this chapter, simple equations for calculating the average power dissipation of the

STGIPS10K60A are shown. The power loss calculation intends to provide users with a way

of selecting a matched power device, however, it is not expected to be used for thermal

dissipation design.

8.1

Assumptions

●

PWM controlled inverter with sinusoidal output

●

PWM signals are generated by the comparison between a sinusoidal waveform (at a

fsine frequency) and a triangular waveform (at a fsw frequency)

●

Duty amplitude of PWM signals varies between (1-ma)/2 and (1+ma)/2 where ma is the

PWM modulation index

●

Output current is sinusoidal (i=Ipeakcos(θ - φ)) and it does not include ripple

●

Power factor of load output current is cos(

φ); ideal inductive load is used for switching

8.2

Conduction loss

The typical characteristics of forward drop voltage (at Tjmax) are approximated by the

following linear equation for the IGBT and the diode, respectively.

Equation 10

●

Vto_I = threshold voltage of IGBT

●

Vto_D = threshold voltage of diode

●

Rce_I = on-state slope resistance of IGBT

●

Rd_D = on-state slope resistance of diode

cesat

⋅

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