Asynchronous machine incorrect speed plot

Question

Julio Incerti de Figueiredo 2021-3-10

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https://ww2.mathworks.cn/matlabcentral/answers/768057-asynchronous-machine-incorrect-speed-plot

回答： Graham Dudgeon 2021-4-27

asynchronous_machine_speed_problem.png

I have made a simple model for an Induction Motor. I've used its constants (stator's and rotor's impedance and resistance etc) that I've found at its datasheet. I was expecting to find its Nominal Speed (around 4400 rpm with 2 pairs of poles at 150Hz), but instead I find this strange plot. At the beginning, it seems like the speed is indeed around 4400, but it starts decreasing until it hits 0 and I cant understand why.

During the simulation shown at the photo I was using Rotor Type: Squirrel Cage, Reference Frame: Rotor and Mechanical Power (at "Load Flow") = 6000W

Steps that didn't solve the problem:

-Change the voltage between 51V, 51*sqrt(2)V and 51*sqrt(2)/sqrt(3)V

-Change the slip between 0.0267, 0 and 1

-Change the reference frame between Rotor, Stationary and Synchronous

-Add an input at Tm

-Change the solver information between ode15, ode23 and ode45

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Mike Sasena 2021-4-27

Hi Julio,

It might help to update the tags in your question. The motor model you're showing is not part of Powertrain Blockset's library, but appears to be a Simscape model instead (this one?). I've added the Simscape Electrical tag so that team can better find your question and provide some guidance.

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Answer 1

Graham Dudgeon 2021-4-27

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https://ww2.mathworks.cn/matlabcentral/answers/768057-asynchronous-machine-incorrect-speed-plot#answer_686395

Hi Julio,

The speed reduces as you have a friction factor of 0.05479 on your motor shaft that is not compensated for by an input torque. Connect a constant block to 'Tm' and set the value to -150*2*pi*(1-0.0267)*0.05479/2.