I am facing some problems in performing clarke-park transform for an induction motor(4 pole stator, squirrel cage IM). The motor is run with three sine wave inputs, 120 degrees phase shifted with each other. I am measuring the rotor position from the encoder and using twice of this value as theta for the park transform(position in radians). But since the rotor speed is slightly less than the synchronous speed, the transform is displaying a sinusoidal waveform. The frequency of Id-q sine wave increases with increase in the input frequency. For 10Hz input sine wave I am getting 0.01Hz sine Id-Iq values. I also tried by integrating the speed(rad/s) to get theta, but the result was the same.
Instead of using the rotor position value, if I use a constant of 2*pift for theta, I get a proper constant dq values. But when I would be performing control, I wont have the frequency data available with me and it would be difficult to get a constant dq values. I had used the same formulas for the PM synchronous motors and it gave constant Id, Iq values.
Could you please suggest any way of solving this problem. Thanks