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Posted on 08 March 2019

IGBT and Diode Switching Loss Calculation

 

 

 

 

 

 

 

In power electronics, both IGBT and diodes are operated as switches, taking on various static and dynamic states in cycles. In any of these states, one power dissipation or energy dissipation component is generated, heating the semiconductor and adding to the total power losses of the switch. Suitable power semiconductor rating and cooling measures must be taken to ensure that the maximum junction temperature specified by the manufacturer is complied with at any standard moment of converter operation. Exceptions to this are short-circuit turn-off and surge current loads where Tj(max) is usually exceeded. Such events may, however, happen very seldom only during the entire component lifetime. Following such cases, the components must be allowed sufficient time to cool down.

Individual power losses of power modules used as switches

Figure 1. Individual power losses of power modules used as switches

IGBT

Owing to the fact that forward blocking losses and driver losses account for a small share of the total power dissipation only, they can normally be neglected. In case of high blocking voltages (> 1kV) and/or high operating temperatures (≥ 150°C), blocking losses may gain importance and may even result in thermal runaway owing to the exponentially rising reverse currents. Often, control losses must only be taken into account for low-voltage MOSFET applications with very high frequencies.

On-state power dissipation (Pcond(T)) is dependent on:

  • Load current (over output characteristic VCE(sat) = f(IC , VGE))
  • Junction temperature
  • Duty cycles

At given control parameters (RG , VGG) and neglecting parasitic effects (LS , Cload), turn-on and turn-off losses (Pon , Poff) are dependent on:

  • Load current and the electric load type (ohmic, inductive, capacitive)
  • DC link voltage
  • Junction temperature
  • Switching frequency

Total losses are composed as follows:

P_{tot(T)} = P_{cond(T)} +P_{on} +P_{off}

Freewheeling diode

Since it only accounts for a minor share of the total power dissipation, reverse blocking power dissipation may also be neglected in this case. The same constraints apply as for IGBT. Schottky diodes might be an exception here owing to their high-temperature blocking currents. Turn-on power dissipation is caused by the forward recovery process. As for fast diodes, this share of the losses may be neglected as well.

On-state power dissipation (Pcond(D)) is dependent on:

  • Load current (over output characteristic VF = f(IF))
  • Junction temperature
  • Duty cycles

At given control parameters of the IGBT commutating with the diode, and neglecting parasitic effects (LS), turn-off losses (Prr) are dependent on:

  • Load current
  • DC link voltage
  • Junction temperature
  • Switching frequency

Total losses are composed as follows:

P_{tot(D)} = P_{cond(D)} +P_{rr}

The total losses of a module Ptot(M) are obtained by multiplying the individual losses with the number of switches n integrated in the module:

P_{tot(M)} = n\cdot (P_{tot(T)} +P_{tot(D)})

 

For more information, please read:

Driver Parameters and Switching Properties of IGBTs and MOSFETs

Switching Loss Reduction Networks - Snubber Circuits

Overvoltage Limitation for Power Transistors

Overload and Short Circuit Behavior of IGBTs and MOSFETs

 

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