Sub-components and inheritance of the Engee physical Modeling language

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In this article we will look at how using the physical modeling language Engee it is possible to build more complex models by assembling from sub-components. This mechanism allows you to organize a hierarchy of elements, make models reusable and more compact.

Component inheritance

Sometimes a new component is very similar to an existing one, and there is no point in rewriting everything anew. To do this, the physical modeling language Engee uses the construction @extend, which allows you to inherit variables and equations from another physical component.

@extend Branch
@extend Branch(i = 0)

All parameters/variables/sub-components with access=Public from Branch will be automatically visible in the inherited component.

Apply @extend it is possible only once inside one component.

Sub-components

Sub-components are ordinary physical components that we embed inside other physical components. They are created using the construction @components.

@components begin
    diode     = EngeePhysicalFoundation.Electrical.Elements.PieceWiseLinearDiode(v_forward = 0.6, R_on = 0.3, G_off = 1e-8)
    capacitor = EngeePhysicalFoundation.Electrical.Elements.Capacitor(C = 1e-4)
end

Here, two sub-components have been added to the new component: a diode and a capacitor. In the arguments of the sub-component constructor, you can immediately set the parameters (v_forward, R_on, C etc.).

Example of passing values

You can use the parameters of the main component as the parameter values of the sub-components, and you do not need to specify the units of measurement.

@engeemodel A begin
    @variables begin
        a = 1
        b[:] = [1, 2]
    end
    @parameters begin
        c = 3
        d[:] = [3, 4]
    end
    @equations begin
        a^2 ~ 2
        b[1] * b[2] ~ 5
        b[1]^2 ~ 12
    end
end

@engeemodel B begin
    @components begin
        a1 = A(a = 2, b = [3, 4.0], c = 1, d = [5, 6])
        a2 = A(a = e, b = f*2, c = sin(e), d = f .+ 2)
    end
    @parameters begin
        e = 3
        f[:] = [3,4]
    end
end

In this example:

For a1 values are passed directly: numbers and arrays;
For a2 the parameters of the component are used B: e, f;
When passing values, you can use expressions: f*2, sin(e), f .+ 2;
You don’t need to specify units of measurement — Engee automatically uses units from the parameter declaration in the component A.

Arrays of sub-components

Sub-components can be set not only one at a time, but also in arrays.

@engeemodel ArrayExample begin
    @components begin
        res = [EngeePhysicalFoundation.Electrical.Elements.Resistor() for i in 1:5]
        cap = [EngeePhysicalFoundation.Electrical.Elements.Capacitor() for i in 1:3]
    end
end

Features:

The sub-components are accessed as regular Julia arrays. Example: connect(diode[1].p, capacitor[3].p).
The names of the elements for external use will be of the form diode_1, diode_2, … and capacitor_1, capacitor_2, …

This is convenient if you need to connect a group of identical elements at once (for example, several diodes or capacitors).

Connections of sub-components

Function connect(…) solves two problems:

Connects sub-components with each other;
Connects the port of the sub-component to the port of the main component.

@engeemodel RC begin
    @nodes begin
        p = EngeePhysicalFoundation.Electrical.Pin
        n = EngeePhysicalFoundation.Electrical.Pin
    end

    @components begin
        r = EngeePhysicalFoundation.Electrical.Elements.Resistor(R = 1000)
        c = EngeePhysicalFoundation.Electrical.Elements.Capacitor(C = 1e-6)
    end

    @equations begin
        connect(r.n, c.p)  # (1) we connect the sub-components together
        connect(p, r.p)    # (2) Connect the r.p port to the external p port
        connect(c.n, n)    # (2) Connect the c.n port to the external port n
    end
end