.Spot.UsersGuide.Introduction.Interfaces

Interfaces

Information

Interfaces and Ports

Most connector-types exist as pair. Exceptions are the connectors for position and frequency (see Base.Interfaces)
We use consistently the indices _p for 'positive' and _n for 'negative' connectors, for all types, electrical, mechanical and thermal.
Both connector types are physically identical. The only difference is the icon, filled for _p, empty for _n.

This choice allows a graphical definition of the positive direction in two-terminal components, from _p to _n.
The sign of internal flow-variables is defined with respect to this direction.
For one-terminal components an internal positive flow corresponds to an in-flow at _p and an out-flow at _n terminals.

Instances of electrical connectors are named 'term' for terminal, except in special cases.
Instances of mechanical connectors are named 'flange' both for rotational and translational connectors.

We distinguish the following electrical connectors *)

  standard connectors 'Electric':  scalar variables v, i,                 square icon
  standard connectors 'ElectricV': vector-pin, pin variables v, i,        square rotated45 icon
  reference connectors 'ACabc':    theta[2], vector-variables v[3], i[3], circular icon
  reference connectors 'ACdqo':    theta[2], vector-variables v[3], i[3], circular icon

Standard electric connectors are used for one-phase and DC systems.

Reference connectors are needed for three-phase systems, representing a particularly important special case. They contain theta additionally to the variables v and i:

  theta[1]:         relative angle (used in initial equations)
  theta[2]:         reference-angle (used in dynamical equations)
   with
  theta[1]+theta[2] = theta_root

Each connected network-part contains a root-node, providing a frequency omega_root and by integration an angle theta_root. Only sources (voltage, power, generator, inverter) represent potential roots.
The system parameter ref then allows running a model in an inertial or a synchronous reference frame.

  theta = {theta_root, 0}     if ref = "inertial"
  theta = {0, theta_root}     if ref = "synchron"

As theta is transmitted through all connections, a connected network part uses a common reference.
The electric variables v and i refer to a coordinate system with angular orientation theta[2]. (see also Transforms).

Basic one-, two-, and three-ports are defined, also using the indexing _p and _n.

  two-ports 'Port_p_n': no conservation of flow-variable (current)
  two-ports 'Port_pn':  conservation of flow variable (current_p + current_n = 0)

Special ports are defined for 3-phase Y- or Delta-topology, and also for switchable Y_Delta-topology.

_____
*) The reason for this choice is the following:
For three-phase systems it is useful to consider both voltage and current as abstract signal-vectors, which may be represented in different reference frames, related by appropriate transforms. It is natural and meaningful to transform vectors, whereas it is unnatural to transform 'pins', 'contacts' and the like.

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