problem with Circuit Breaker and induction Motor

dear sir,

I have to model a drive system with 2 Induction motors. one motor is running up to 3 sec of simulation time and after that I have to switch on another motor. means after 3 sec. I have to give supply to second Induction motor by the same inverter, which is for using for giving supply to first induction motor. for this model, I used a circuit breaker, i put time as [3 5], because I have to switch ON second motor at 3 sec, and run up to 5 sec. here, I connected circuit breaker in between Induction motor and Inverter. for first induction motor, I didn't use any circuit breaker, that is connect directly.

now i faced problem after time 3 sec. the singularity or NAN problem coming in case of discrete simulation type, the model is running with out any problem in continuous mode of simulation. but its take to much time to run. so i have to run this model in discrete model, here I put Ts=5e-6 in power gui. my version is 2008 a. I used induction motor from simulink library, I didn't use any modeling. and I used IGBT/Diode based inverter. so please help me, I have to run model in discrete mode without any problem. so How can I overcome this problem?

[Walter Roberson]

Is your second motor turning on "instantly" when you run in discrete mode? If so, then would be a discontinuity in the voltages and current and power, which could generate the kind of singularity you see.

I do not have experience with Simulink, so I do not know what the usual or recommended solution would be. My instinct would be put the power through a ramp function or smoothing filter of some kind.

Answer 1

[Sabin]

Without a model would be impossible to point out to an exact root cause. However, as the continuous time simulation works fine, and it fails in discrete time I believe either the discretization method or the sample time are the culprit leading to numerical instability. Parameterization of the system may also be problematic as the system may be stiff which will cause solver problems.