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MCAT:unable to measure motor parameters

Question asked by xiangjun.rong Employee on May 14, 2018
Latest reply on Jun 28, 2018 by Pavel Sustek

We are trying to run a 1.2 kW 24 V BLCD motor with Freemaster and MCAT with sensorless FOC, but we are unable to measure the motor parameters. We keep getting "Wrong characteristic data" fault.


Our HW is based on NXP TWR58F220 CPU board and TWRMCLV3PH motor control board. The largest difference are bigger FET's on the power stage to allow motor currents of up to 100 A. Of course the phase current measurements have been scaled accordingly. We are using KV56 CPU, which is basically the same CPU as the KV58. The FET driver is MC33937, which it the same as in the development kit. The FETs are Infineon IPB020N08N5ATMA1.


We have been able to run the BLDC motor that comes with the TWRMCLV3PH (Linix 45ZWN24-40, 24 V, 40 W) with our own HW. We have also been able to tune and run a 180 W BLCD motor, but we can't tune or run the 1.2 kW BLDC.


Power stage characterization:
We've made the power stage calibration for our own HW with the 40 W Linix motor. It seems that it is not possible to the calibration with the 180 W motor, because it has much lower phase stator resistance than what the MCAT allows to use. Minimum allowed Rs for MCAT is 0.3 Ohm, but the 180 W motor has Rs of 0.084 Ohm according to the motor's datasheet.


After the calibration with the 40 W motor, we are able to run the motor measurement for the 180 W motor, and for example the Rs value is measured to be 0.07 Ohm, which seems to be close to the motor's specification. The measurement is done with "Is DC" set to 1.2 A and "Is AC" set to 0.6 A.
After the measurement, we are able run the motor.


If we try the same setup with the 1.2 kW motor, we get "Wrong characteristic data" fault. Manufacturer does not specify the Rs value for the 1.2 kW motor, but obviously it is much smaller than with the 180 W motor.


1. Are we doing the power stage characterization correctly when using small motor instead of a larger one? Why does MCAT limit the Calib Rs value to minimum of 0.3 Ohm?


2. Why can't MCAT measure parameters for the large BLDC? Could it be caused by the very small Rs, that MCAT has trouble to measure? We have tried different Is current values without success.


We are not very familiar with these kinds of motors, so we are a bit lost with the big amount of parameters. We are happy to provide additional information if needed.