# Subsystems & thermal Models

**URL:** <https://forum.plexim.com/t/subsystems-thermal-models/2894>\
**Category:** PLECS\
**Tags:** thermal-model\
**Created:** [March 2, 2026, 9:58am UTC](https://forum.plexim.com/t/subsystems-thermal-models/2894 "2026-03-02T09:58:32Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![Stefan](https://avatars.discourse-cdn.com/v4/letter/s/bbce88/32.png) [@Stefan](https://forum.plexim.com/u/Stefan)\
**Post date:** [March 2, 2026, 9:58am UTC](https://forum.plexim.com/t/subsystems-thermal-models/2894/1 "2026-03-02T09:58:32Z")

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Hello,

I’m using Plecs V5 standalone and I’m not sure how to change all thermal description for a half-bridge inside an subsystem by using a mask parameter of a subsystem.

So I have subsystem, where I can select a thermal description. But how to use this custom variable inside a MOSFET model. Is there any example?

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**Author:** ![Kris\_Eberle](https://dub1.discourse-cdn.com/flex006/user_avatar/forum.plexim.com/kris_eberle/32/6_2.png) [@Kris\_Eberle](https://forum.plexim.com/u/Kris_Eberle)\
**Post date:** [March 2, 2026, 11:19am UTC](https://forum.plexim.com/t/subsystems-thermal-models/2894/2 "2026-03-02T11:19:56Z")

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You simply need to select the “By reference” option in the Thermal description field of the semiconductor block(s) and assign the custom reference variable. Several of our demo models include an example of this, such as the “Double Fed Induction Generator Wind Turbine”.

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**Author:** ![Stefan](https://avatars.discourse-cdn.com/v4/letter/s/bbce88/32.png) [@Stefan](https://forum.plexim.com/u/Stefan)\
**Post date:** [March 2, 2026, 11:46am UTC](https://forum.plexim.com/t/subsystems-thermal-models/2894/3 "2026-03-02T11:46:06Z")

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> [@Kris\_Eberle](#):
>
> Double Fed Induction Generator Wind Turbine

Yes, this is how it worked for PLECs \< 5.

Using Plecs V5 I’m struggling as you can see in my attachment. Running a model created in PLECs 4 is running. But if you try to change anything you can not close the shown dialog box without a Custom variable.

 ![grafik](https://europe1.discourse-cdn.com/flex006/uploads/plecs/original/2X/6/68d39425e7ed99ed7a2ad10873e2ab22793c8500.png)

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**Author:** ![Kris\_Eberle](https://dub1.discourse-cdn.com/flex006/user_avatar/forum.plexim.com/kris_eberle/32/6_2.png) [@Kris\_Eberle](https://forum.plexim.com/u/Kris_Eberle)\
**Post date:** [March 2, 2026, 12:42pm UTC](https://forum.plexim.com/t/subsystems-thermal-models/2894/4 "2026-03-02T12:42:34Z")

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Yes, this is unfortunately a bug that has been fixed with PLECS 5.0.2!