Torque control of an Induction motor using field oriented control

I am trying to simulate torque control of an induction motor using the matlab example of field oriented controller for ASM. While in speed control mode, the outer speed control works fine along with the inner current control of i_qs_e, thereby, tracking the set speed reference. But while in torque control mode, I am using the inner current loop by computing the reference value of i_qs_e from the torque setpoint using the expression,

i_qs_e* = 2/3 * 2/(p*2) (1+s_r) / (Lm * i_mr) * T_ref

- all values are in per units

where,

p - no of pole pairs

s_r - rotor leakage co-efficient = Llr/Lm

i_mr - magnetizing current

T_ref - reference torque in per units

However, the motor is not able to track the reference torque even though the inner current loop is working fine i,e, error in i_qs_e is converging to zero in very small time after the system starts.

The above image shows that the electromagnetic torque(BLUE-0.82) is not able to track the reference torque(YELLOW-around 0.2). Load torque is set to be zero(RED). The underlyin gimage shows the dynamic value of i_qs_e* and the error of the current loop on i_qs_e. Please help if you can!

Answer 1

[Prasad Parameswaran]

Without the model it is difficult to troubleshoot the issue. Since the current and torque are directly proportional, torque should track the reference as the error tends to zero. Initial trouble shooting steps can be:

• Torque is measured correctly.
• Error calculations and its implementations are proper.
• Controller gains and their implementations are proper.