I have an inverter fed induction motor, to control the speed i wanted to first measure the slip of the induction motor from dc current supplied to the inverter.
i have an access to three phase induction motor, CRO, TI Inverter board, Regulate dpower supply.
Under constant flux operation of an induction motor:
Torque is proportional to slip frequency and hence to slip speed.
Now torque is equal to total power developed divided by angular frequency of rotation. If you assume slip is very small, then angular frequency is approximately proportional to set speed (synchronous speed).
Total power developed is equal to total power input minus losses. Losses to be approximated from efficiency.
Total power input is equal to DC input voltage multiplied by DC input current to inverter. If DC input voltage is constant, then power input is proportional to DC input current.
Hence, you can design a slip estimator based on the above calculation using the DC input current of inverter feeding an induction motor under constant flux. In fact some such estimators were published around mid 1980's, but lost their popularity due to their poor performance compared to better techniques using motor instantaneous voltage and instantaneous current based computation.
Thank you Mr.sujit biswas
I will try to implement some modelling with hardware and revert you back.
Good to hear from you
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