simscape motor speed is not stable system

1
votes

I'm trying to build dc motor in simscape

I used the command ssc_dcmotor to get the example

I added controlled voltage source instead of voltage source and s-ps converter and made input port ... i replaced scope with output port

I made this to get linear model of speed of dc motor using [A, B, C, D]=linmod('dcmotor')

When I get eig(A) I see poles at zero which means system is not stable

What is the bug in my understanding here?

1
matlabsimulinksimscape

1 Answers

2
votes

The state of the system returned by linmod includes the states of all it's blocks (even if these states are empty or constant). Try executing

sstr= linmod('dcmotor1');
disp(sstr.StateName);

and you will see

[1x50 char]
[1x50 char]
'dcmotor1/DC Motor/Inertia'
'dcmotor1/DC Motor/Rotor Inductance'
'dcmotor1/Sensing/Ideal Rotational Motion Sensor'
'dcmotor1/DC Motor/Friction'
'dcmotor1/DC Motor/Rotor Resistance'
[1x50 char]
[1x50 char]

Obviously, we don't need the states of DC Motor/Friction, Rotor Resistance, Ideal Rotational Motion Sensor and their equations of the form dx/dt= 0. However, it is easy to remove the unused states (The Control System Toolbox is needed):

sys= ss(A,B,C,D);     % create the state space model
sys= minreal(sys)     % remove the unnecessary states
pole(sys)             % now we can calculate the poles