TMS320F28069M: ACIM operation using lab12b : cannot reach target speed

Have you used lab2b to identify the motor parameters, as well as lab12a to identify the system inertia and friction? Lab2b will provide the correct value for USER_MOTOR_MAGNETIZING_CURRENT.

Also, have you verified the current and voltage feedback loop is correct for your custom hardware? That is one critical question you'll need to answer moving forward.

Sean

yes ı have followed the identification procedure and checked hardware. It works fine with motors up to 20A nominal current. But for more that 20A motors I see that it cannot reach target speed. When ı look at params in watch window I see that current and speed is measured correctly. but somehow itcannot reach target speed when i load it. In no load there is no problem to reach target. ısee that there is no problem to reach Id ref current, on the other hand it cannot reach to Iq ref at loaded condition.

with a different inverter ı bought from the market ı can drive the motor at loaded condition with a smaller current.

Of course I modified original instaspin software to suit my application needs. which point do you advise me to look for finding a bug or error that results from my modifications?

I have found one thing. I think the problem arises from the value of rotor resistance. Those higher current motors have lower resistance than others. In identification procedure detected rotor resistance is 0.35ohm. In normal operation with lab12b, if I use 0.35 ohm value motor draws so much current and cannot reach target speed.

But if change rotor resistance parameter to 0.25ohm, it draws 20% less current and can reach target speed. Possibly, due to the wrong estimation of rotor resistance in identification, this problem arises. Does it seem reasonable? But I could not understand the effect of rotor resistance in closed loop operation with an encoder feedback, why does it affect motor operation so much?

Sometimes for the small motor with high current/speed ratings, you will also have very low inductance, making the motor difficult to identify. Please try with lab2c if this is the case, as this lab is meant for motors with low inductance.

Sean

Thank you for your reply. Actually the motor is a 11kW ACIM. It is not a small motor, also it is a standard 4-pole 50Hz induction motor. Its rated speed is 1470 rpm. Its resistance is low but inductance is around 3mH.
Anyway, I have found that filter capacitor at resistive voltage divider part is a bit high than it should be. When I have corrected the capacitance value identification is better and it works better.

But the question I have is that: How does the rotor resistance value affect motor operation like that? In smaller motors, rotor resistance is higher (i.e. around 1 ohm) and at that smaller motors 0,1 ohm difference in rotor resistance does not affect the operation so much. On the other hand at a motor with rotor resistance 0.25 ohm, 0.1 ohm error is important and it results a reduced performance (higher motor current, reduced maximum reachable speed etc.) Could you please explain that?

Best regards