Output phase current being limited to 200A

Question

Hi folksWe have a 3-shunt sensor-less FOC solution for running a PMSM motor generated from STM32 Motor Control Workbench (ver 5.4.4). The max readable current is upwards of 500A. However, we find that the phase current gets limited to 200A peak. When the peak phase current exceeds 200A, the motor stops but remains in the Run state and outputs a DC current of 50A, which is incidentally equal to the current value specified in the starting parameters.We find that we are able to get higher phase currents by entering an incorrect shunt value in the workbench. This way, we were able to reach a peak of almost 300A. Entering a higher/lower shunt value increases/decreases the actual peak phase current proportionally. In short, the current is always being limited to 200A as read by the software.We are not able to figure out the reason for this behavior. What are the factors/parameters that limit the peak phase current?Also, why does the motor stop but remain in Run state under this condition?Would appreciate any help on this.Thanks & Cheers

Laurent Ca... · Accepted Answer

Dear @PAlva.1​ We have never been confronted with this limitation because the management of such a high current is not at all part of our usual work.We are very sorry about this.It turns out that the current is indeed limited in the "Amplifying Network Gain" panel for some unknown reason but there is no impact on the generation of the project. Indeed you can put 2, 10, 50 or 200A and this will generate the same project. The "Imax" of this panel simply makes it possible to verify that the amplification network is well dimensioned and that the input voltage of the ADC will be in the range of 0V to 3.3V.We will create an internal ticket on the MC Workbench in order not to limit the maximum current in the “Amplifying Network Gain�? panel.But in fact, as @cedric H​  has suggested to you in his answer, this value is given for information and is has no impact on the amplifying parameters you can freely set.Therefor, he “true�? maximum current is that indicated in the nominal current of the motor board: this value is used in the code to set the high and low limits of the PIDs of the current controller. Therefore, if you have a motor rated current over 200A, the firmware should not limit the current to 200A.Just a remark: a limiting factor could be the maximum modulation index (MMI) because if it is too low the firmware may not allow going beyond 200A.In conclusion, first check the rated current of the motor and MMI.Best regardsLaurent Ca...

cedric H · Answer

Hello PAlva.1It is pretty tough to guess what's going wrong in your system, but first, I would suggest to check, or double check the amplification parameters of your project. Do you use your own inverter board or ST boards supported by the SDK ? RegardsCedric

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