Foil 14.4 : VHDL-AMS conservative systems and terminals

conservative electrical systems are obeying to laws of Kirchhoff
the description of conservative systems uses the theory of graphs
in VHDL-AMS we use branch quantities that are decomposed in two members, the across quantities that represent voltages and through quantities that represent the currents

For example, a resistance is a path governed by the law of Ohm that connects the tension levels of its terminals (across quantity) and specifies the current that crosses it (through quantity).

resistance is a two-terminal path to be declared with two terminals
resistance terminals are types of simple nature
simple nature depends on the domain (electrical, thermal, hydraulic...).

Voltage & current:
In the following example we declare two subtypes: voltage and current with their respective tolerances and a simple nature electrical.
Then we declare two terminals of this nature, and a quantity v across the terminals and a current i through the same terminals t1 to t2.

subtype voltage is real tolerance - " tol_voltage" ;

subtype current is real tolerance - " tol_current" ;

nature electrical is voltage across current through;

terminal t1, t2: electrical;

quantity v across i through t1 to t2;

v is the difference of potential between terminals, that is the typical voltage and has for code of tolerance "tol_voltage" and i represents current through the path and its tolerance is "tol_current"

the two terminals are called plus and minus, the way of the path is plus to minus, that is the positive flow of the current

Natures & arrays:
In the following example, one declares an array of nature type and a subnature of this vector type:

nature electrical_vector is array(natural range <>) of electrical;

subnature el_vect4 is electrical_vector(0 to 3);

terminal t3, t4: el_vect4;

quantity vpp across ipp through t3 to t4;

quantity vps across ips through t1 to t4;

the tolerance group of a path is determined by its subtype
it is possible to redefine it in the subnature of the declaration or in the declaration of the path

tolerances of vlow1 and ilow1 are defined by the declaration subnature, it is "tol_lowvoltage" for voltage and "tol_lowcurrent" for current

the predefined attributes 'across and 'through allows to extract the nature corresponding to the object. Given the above declarations, tx'across is voltage and tx'through is current

Terminal attributes:

entity simple is

port (terminal terin, terout:electrical);

end simple;

if a path is declared with only one terminal, than the other one (default terminal) is ground terminal
the ground is considered as minus terminal

Conservative systems and terminals