Initial transients in speed torque characteristics of three phase induction motor

I am trying to observe the starting torque of three phase induction motor. I have used the inbuilt model of three phase asynchronous motor available in simulink. However, the plot below has heavy starting transients. Is there a way to reduce the transients?

Answer 1

[SOUMNATH PAUL]

Hi Vineeth,

To my understanding you are trying to mitigate the heavy transients in the initial space of the Torque-speed plot.

For inspiration, you can go through the model mentioned in the link below for direct torque control of an inductive motor drive:

https://in.mathworks.com/help/sps/ug/power-motordrive-IM-DTC-HYST.html%22

Above example model can be simulated and the speed-torque characteristics for specific time intervals can be visualized.

Here are some additional suggestions that may help you to reduce the starting transients:

1. You can gradually ramp up the motor speed instead of starting it abruptly.
2. Make sure the parameters accurately represent the characteristics of the motor you are simulating.

Hope it helps!

Regards,

Soumnath

[VINEET]

Thank you Soumnath.

The link shared by you considers DTC control which i understand. However my issues was, without introducing any power electronics, if i give a three-phase supply to the motor, it gives the above characteristics. My concern is whether i need to define some initial conditions for the motor to overcome the initital transients?

[SOUMNATH PAUL]

Hi Vineeth,

Certainly, if you're observing heavy starting transients in your three-phase induction motor simulation in Simulink and you want to reduce these without involving any power electronics like Direct Torque Control (DTC), you might consider the following approaches:

1. Soft Starting: Instead of applying the full voltage to the motor instantly, you can use a soft starting technique where the voltage is gradually increased. This can be done in Simulink by using a ramp function to slowly increase the voltage applied to the motor over time.
2. Parameter Tuning: Ensure that the motor parameters in your Simulink model accurately reflect the physical motor you're trying to simulate. Incorrect parameters can result in unrealistic behavior including exaggerated transients.
3. Initial Conditions: Setting initial conditions can help in some cases. For example, you can set the initial rotor speed to a small value to avoid the abrupt change from standstill to motion. However, this would not represent a real-world scenario where the motor starts from rest.
4. Mechanical Damping: Check if there's an option to increase mechanical damping in the motor model. Higher damping can reduce the oscillations during startup.
5. Load Characteristics: Adjust the characteristics of the load attached to the motor. A sudden application of load can cause high transients. If possible, simulate a more gradual application of the load torque.
6. Simulation Settings: Review the simulation settings in Simulink. Sometimes, the solver settings and step size can affect the smoothness of the simulation. Try using a stiff solver if not already doing so, as it might handle the transients better.

Some transients are natural during the startup of an induction motor due to the inrush current and the sudden application of electromagnetic torque. Completely eliminating these transients is not always possible or realistic, but the goal is to reduce them to a more realistic level.