Frequently Asked Question

How to connect grounds in multi-core models?
Last Updated a year ago

1. How do grounds work in Typhoon HIL Schematic Editor?

During the modeling process sometimes you may want to connect blocks to a ground component. The figure below shows an example of this, where the neutral points of Transformers Tr1 and Tr2 and Voltage sources Vs1 and Vs2 are all connected to the ground.


If you try to compile this model you will get an error message similar to this one:

Core coupling: Core Coupling 1 sides are connected.   
Please, make the needed corrections and restart the compilation.
Compilation process interrupted.

The reason for this message is how the ground component is modeled in Typhoon Software. The two nodes that are connected to ground components are resolved as one node during the compilation process, generating a short circuit between them. In principle the model above is equivalent to this one:


As shown, a Core Coupling is used with the intention to divide the circuit into 2 decoupled sub-circuits, but the green and red sides of the coupling remain connected through the ground components.

If this is your first time working with circuit partitioning or you have questions about the process, we warmly suggest you go through the circuit partitioning quick start guide. If you are not sure if the core coupling is needed in your circuit you can go directly to this link.

2. When should I (or shouldn't I) use a ground in my model?

Before adding ground elements in your model please consider the following:

  1. Typhoon models do not need a reference point as some other simulation softwares do. You can compile and run your model without any ground element inside it. The voltage measurement component has two terminals (positive and negative) and it is not referencing to any "neutral" point in the model.
  2. In most balanced 3-phase models using a ground component will not make any significant difference in model results.
  3. Adding ground components to your model creates additional connections, which can increase the FPGA matrix memory and processing power utilization.
  4. The Electric tag component is a generalization of the ground component. While with the ground component you are forcing the compiler to connect all the nodes, with the electric tag component you can create several subsets of connected nodes by specifying tag names.
  5. Often it is enough to connect neutral points of components inside one core. This can be done easily by specifying the scope of the Ground component to be core. 

    Alternatively, connecting neutral points in another core separately can be done with electric tags. This is illustrated in the figure below.image
  6. In case you want to measure phase voltage in a 3-phase system, you can make an "artificial" neutral point using a shunt resistor. For example if the voltage level is 10kV, you can set Rshunt = 1e6Ω which will consume only 100W of power. The described concept is illustrated in the figure bellow. Also, it is worth mentioning that you can use our microgrid component: Three-Phase Meter which has prebuild option of creating artificial neutral point.

3. What if grounds from different cores unavoidably have to be connected?

In some applications, it is crucial to connect grounds/neutral points between two or more FPGA cores. Typical use cases are power electronics applications with significant zero component in 3-phase system. The general rule in these kinds of situations is to use core coupling with one phase more than the original number of phases. To be more precise following has to be done:

    1. Single Phase Core Coupling has to be replaced with Three Phase Core Coupling,
    2. Three Phase Core Coupling has to be replaced with Four Phase Core Coupling, and
    3. Four Phase Core Coupling has to be replaced with Five Phase Core Coupling

Below are the illustrated cases (a) and (b):



The Important thing to note is that an increasing number of phases in core couplings enlarge model complexity which can result in the need for a larger simulations step, or in extreme cases, even the inability to fit the model on HIL device. For these reasons, it is encouraged to avoid connecting grounds from multiple FPGA cores if possible.

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