not converging

Steve — Sat, 01 Sep 2007 01:10:33 -0400

Hello,

I have a relatively complex Simulink model. I decided to
control the outputs using a simple proportional gain. When
I set the gain to zero, I get the same results as I did
before adding the gains. However, when I set the gain to
where I need it to be (15,000), then I get "not converging"
error. In both cases, (as well as gains up to about 40), I
used ODE15s with a min step of 1 and a max step of 10, and
an error tolerance of 1e-09. I'm curious as to why the
gain would cause the system to not converge?

I thought that maybe at the first time step, the error was
large due to my initial conditions, which made my
proportional control react heavily due to the gain, which
blew the hole system up. But when I set my initial
conditions equal to the setpoint that I'm trying to control
the outputs to, the same thing happened.

Why is this, and is there a way around it besides reducing
my minimum step size or relaxing my tolerance?

Thanks,
Steve

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not converging