Flying start of an induction motor

Hi,
I have a question about starting an induction motor that is rotating already, an application like fans. I know that a method used is feeding motor with 10-30% of nominal voltage and change frequency from highest possible frequency toward lower frequencies; whenever highest current is sensed, that frequency is which breakdown torque is generated. By adding a percentage of slip frequency, we can get the rotating speed. Out of curiosity, I ran a simulation. I did not observe current peak around rotating frequency. However, I saw minimum current which indicates synchronous frequency. isn't it better to search for minimum current instead maximum current? Why didn't maximum current show up in the simulation?
Please find the picture of simulation result attached. respectively from top to bottom are current, voltage frequency and rotating frequency (I kept it constant).

I would be grateful if you share your comments.

I am curious, how did you simulate slip?

I did not consider load. just some friction. Te-Tl=Jdw/dt+Dw, where J is inertia, w is angular speed , D is friction and Te and Tl are electrical and load torque, respectively. I calculate Te using an electrical model of an induction motor ( I simulate it in ABC-frame). using Co-energy formula should be p/4*I'*dLdtheta*I; where p is pole number, L is inductance matrix and it size is (6*6), and I is current vector (stator and rotor) size is (6*1). then I calculated speed using above formula.
The book titled "Analysis of Electrical Machinery and Drive System" written by Paul Krause is a good reference. I have checked simulation for various other cases, seems correct.

Why don't people look for minimum current instead maximum current? according to simulation, it seems there is a problem with that!

kappa_am said:

Hi,
Out of curiosity, I ran a simulation. I did not observe current peak around rotating frequency. However, I saw minimum current which indicates synchronous frequency. isn't it better to search for minimum current instead maximum current? Why didn't maximum current show up in the simulation?
View attachment 146832

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I think your simulation is correct. I wrote earlier on another thread, that there is a current increase, but decreasing current makes more sense. There is also practical reasoning for this besides simulation. Induction motor starting current on direct-on-line start is 5-7 times nominal current as long as nominal frequency is reached and slip is small. Then current decreases. This also gives the reason why 10-30% is reasonable voltage while scanning the frequency. Too high voltage would cause too high current for the inverter. On the other hand, current during scanning should be well above the no load current of the motor.