The fluctuations in input caused the output range of Simulink's 2D lookup table module to far exceed the set value.

I am currently calculating the motor's efficiency based on its rotational speed and torque. The first two graphs show the torque and rotational speed respectively, the third one is the motor's efficiency characteristic curve, and the fourth one is the motor efficiency I have output. I have a question: why is the output efficiency far greater than 100% when both the torque and rotational speed are within the normal range? I don't understand where the problem lies. There is no number greater than 100% in my motor efficiency characteristic curve.

Answer 1

[Fangjun Jiang]

The most common cause for this is the combination of out-of-range input values and the "linear" extrapolation method.

The extream "greater than 100%" efficiency output seems to be corresponding to the time when the motor rpm is zero.

The table data shows columns for motor rpm at 499, 500, 999, 1e3. The columns for motor rpm at 499 and 999 seem to be un-necessary.

Anyway, try this, in the "Algorithm" tab of the lookup table block dialog, change "Extrapolation method" from "Linear" to "Clip".

[Fangjun Jiang]

By the way, the table data should provide a column corresponding to motor rpm equals 0.

[靖璋]

• Thank you for your response, Mr. Jiang. I tried changing the extrapolation method from "linear" to "clip", but the output is still much larger than the table output I provided. However, interestingly, when I replaced the torque input that fluctuates very frequently with a constant value, the output became very normal. I'm not sure if the problem lies here?
• Thank you again for your response! By the way, this is my first time posting a question in the MATLAB community. I didn't expect to receive such a serious answer and I'm very happy.

[Fangjun Jiang]

The table data might be problematic.

1. Break points 499 and 999 seem to be unnecessary for motor rpm since 500 and 1e3 are there.
2. It does not make sense for the first 14 break points for motor torque to cover the value from -446.65 to -442.42, since the range of the motor torque seem to be from -400 to 400.