# RT\_Box HIL simulation error

**URL:** <https://forum.plexim.com/t/rt-box-hil-simulation-error/2364>\
**Category:** RT Box\
**Tags:** rt-box\
**Created:** [July 23, 2025, 12:15pm UTC](https://forum.plexim.com/t/rt-box-hil-simulation-error/2364 "2025-07-23T12:15:05Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![Anup96](https://avatars.discourse-cdn.com/v4/letter/a/82dd89/32.png) [@Anup96](https://forum.plexim.com/u/Anup96)\
**Post date:** [July 23, 2025, 12:15pm UTC](https://forum.plexim.com/t/rt-box-hil-simulation-error/2364/1 "2025-07-23T12:15:05Z")

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Hi,  
I am trying to simulate a custom topology in rt Box. Since i am using custom topology i cant use nanostep model. I am using normal switch with digital input to sample PWM. I tested this with a simple model like boost converter and it works fine. But when i use topology with the number of switches to about 8 switches, It does not work. RT\_box shows the simulation error. Is there any way to simulate custom topologies in RT\_Box in HIL mode? I can share the file if that helps make it clearer.

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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:** [July 23, 2025, 8:41pm UTC](https://forum.plexim.com/t/rt-box-hil-simulation-error/2364/2 "2025-07-23T20:41:54Z")

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Yes, please share your model file so we can provide clear feedback!

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<div class="post-metadata">

**Author:** ![Anup96](https://avatars.discourse-cdn.com/v4/letter/a/82dd89/32.png) [@Anup96](https://forum.plexim.com/u/Anup96)\
**Post date:** [July 24, 2025, 9:35am UTC](https://forum.plexim.com/t/rt-box-hil-simulation-error/2364/3 "2025-07-24T09:35:37Z")

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Hi Kris,  
Here is the model file. it’s for a five level inverter.

> **(attachments)**
>
> [five\_level model.plecs](https://forum.plexim.com/uploads/short-url/AcGOaHBNaTgaO8H2154t9uLft3L.plecs) (75.2 KB)

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<div class="post-metadata">

**Author:** ![Bryan\_Lieblick](https://dub1.discourse-cdn.com/flex006/user_avatar/forum.plexim.com/bryan_lieblick/32/10_2.png) [@Bryan\_Lieblick](https://forum.plexim.com/u/Bryan_Lieblick)\
**Post date:** [July 28, 2025, 5:55pm UTC](https://forum.plexim.com/t/rt-box-hil-simulation-error/2364/4 "2025-07-28T17:55:05Z")

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> Is there any way to simulate custom topologies in RT\_Box in HIL mode? I

To an extent, yes, but not for this particular topology. To have performant real-time models one needs to develop an equivalent sub-cycle average or Nanostep based implementation of the topology.

One can also use discrete components as you are attempting but you will quickly notice one of two limitations: 1) for high numbers of switching elements the number of switching combinations grows exponentially, creating very slow code generation and real-time model execution or 2) the model runs in real-time, but the accuracy is quite poor because the sensed switching signals and circuit topology are constant within an RT Box step, requiring the ratio of the switching period (Tsw) to RT Box step size (Ts\_rtbox) to be extremely high (Tsw/Ts\_rtbox \> 100 to 1000).

In short, this topology is not a good fit for the RT Box.