# Simulink Power Library custom block multi switch

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Jannis Maq on 25 May 2016
Answered: Joel Van Sickel on 17 Sep 2020
Hello,
I'm trying to build a multi switch which connects several terminals. Therefore I'm building a custom block. The model where the switch is to be integrated is build with the Power Library. First I tried to build a simple switch. But this isn't as simple as it sounds... The first big problem is: When I declare the nodes like this:
nodes
U0 = foundation.electrical.electrical; % +:top
U1 = foundation.electrical.electrical; % -:bottom
end
then I cant connect the custom block with components of the Power Library. I havent found anything about the domain of these components. Any suggestions here?
The second problem is, that I have no clue how to make the current go through (in closed position of the switch). First I delcared variable i as a through variable.
branches
i : U0.i -> U1.i; % Through variable i from node p to node n
end
But then it's getting tricky. Because something like
equations
U0.i == U1.i;
end
is not working, I declared a very small resistance and calculated the voltage across the terminals
equations
v == U0.v-U1.v;
i == (v)/R;
end
But this isn't working. Does anyone know how to make a nice switch?
PS: Here is the whole custom block code
component switch1
% switch
nodes
U0 = foundation.electrical.electrical; % +:top
U1 = foundation.electrical.electrical; % -:bottom
end
parameters
R = { 1e-10, 'Ohm' };
end
variables
i = { 0, 'A' }; % Current
v = {value = { 0, 'V' }, priority = priority.high}; % Voltage drop
end
function setup
end
branches
i : U0.i -> U1.i; % Through variable i from node p to node n
end
equations
v == U0.v-U1.v;
i == (v)/R;
end
end

Joel Van Sickel on 17 Sep 2020
Here is the code which is available from the switch block in simscape foundations:
component controlled_switch
% Switch
% The block represents a switch controlled by an external physical
% signal. If the external physical signal PS is greater than the threshold,
% then the switch is closed, otherwise the switch is open.
%
% The closed resistance is defined by parameter R_closed, and the open
% conductance is defined by parameter G_open. Both parameters must be
% greater than zero.
% Copyright 2005-2018 The MathWorks, Inc.
inputs
vT = { 0.0, '1' }; % PS:bottom
end
nodes
p = foundation.electrical.electrical; % :top
n = foundation.electrical.electrical; % :bottom
end
parameters
R_closed = { 0.01, 'Ohm' }; % Closed resistance R_closed
G_open = { 1e-8, '1/Ohm' }; % Open conductance G_open
Threshold = { 0.5, '1' }; % Threshold
end
variables
i = { 0, 'A' }; % Current
v = { 0, 'V' }; % Voltage
end
branches
i : p.i -> n.i;
end
equations
assert(R_closed>0)
assert(G_open>0)
v == p.v - n.v;
if vT > Threshold % Switch is closed
v == i*R_closed;
else % Switch is open
v == i/G_open;
end
end
end
Regards,
Joel