How to Implement Kirchoff Rules

Question

1.What data structure to use for electric circuit representation

for Kirchoff Rules computation purposes
how to differentiate between different types of electric components
how to 'recognize' wire inter-connections between them

2.how to implement Kirchoff Rules

how to obtain current and voltage loops
how to store and evaluate Kirchoff equations

[original question text] Specifically, how would the program recognize something is in series and parallel and how will it differentiate between a battery, resistor, capacitor, inductors, etc..

pretty broad question ... did a reedit so check it out if I did not broke the meaning of what you want also you should add to the question what kind of circuits you want to use (AC,DC,analog,digital,passive,active,NF,VF,VVN ...). — Spektre, Mar 21 '14 at 18:44

duffymo · Answer 1 · 2014-03-21T19:31:52.893

Java's an object-oriented language. Start thinking about how you'd model your system as objects.

You have a few object candidates already:

Battery
Resistor
Capacitor
Inductor

These would have input and output nodes. The output from one is the input to the next.

What about transistors? You'll have more than one input. What then? Those are non-linear. How do you model those?

You'll build in the proper behavior for each one and wire them together.

You'll have some kind of transient forcing function here. Input current or voltage waveforms. Output is current and voltage at each node versus time.

This is the electrical engineer's equivalent of finite element analysis.

These are really transient ODE, right? How do you plan to solve them? Numerical integration?

score 2 · Answer 2 · edited May 23 '17 at 11:58

agree with duffymo's answer just some things to add (I am C++ friendly so I stick to it)

first some data to represent components

    struct pin
     {
     char name[];  // name id for pin ("C","B","E"...

     int part_ix,pin_ix;  // connected to patrs[part_ix].pins[pin_ix]

     double i,u;  // actual: current,voltage
     int direction; // in,out,bidirectional
     };

    struct part
     {
     char name[];  // name id for part ("resistor","diode",...
     pin pins[n];  // n pins of the part (resistor has 2 , transistor has 3, ...) 
     // here add all values you need for simulation like:
     double R,H21E,...
     // or even better do a matrix for it so when you multiply it by input currents and voltages
     // of every pin you get the correct currents and voltages
     double m[n][n+n];
     };

also you can add list of pins connections instead of part_ix,pin_ix to save some processing time.

circuit
```
part parts[];
```
simple dynamic list of components the interconnections are inside it
loops

you have to extract closed circuit loop from interconnections for current equations and get nodes that connect current loops for voltage equations. This would lead you to system of equations. Nodes have more that 2 connections and closed current loops are just sequence of connections leads back to itself. Look here:
- https://stackoverflow.com/a/21884021/2521214
it is one of my answers where part of the code finds closed loops
evaluation

can use gauss elimination for that. Problematic are non linear components like diodes, transistors ... so may be you will need to add more matrices (approximate to polynomial with bigger degree) then you will need to multiply by all currents and voltages powered by (0,1,2,3,...). I think ^3 will be enough for most components and do not forget that some non linear component also need to remember their states (or last current,voltage,... ...).

Also sometimes is better to use symbolic expressions instead of matrix approach but for that you will need expression evaluation engine. I use this approach a lot for self resizing geometry in CAD/CAM meshes.

How to Implement Kirchoff Rules

2 Answers2

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