Learning Forum

[Ruchika Singh]

Hi,

I am trying to simulate a PMSM motor with currents. I give my current excitation for 3 phases as below:

Phase A: Ipeak*sin(((pi*(Mechanical_speed/1rpm*NumPoles)/60)*time)-120deg)

Phase B: Ipeak*sin(((pi*(Mechanical_speed/1rpm*NumPoles)/60)*time)-0deg)

Phase C: Ipeak*sin(((pi*(Mechanical_speed/1rpm*NumPoles)/60)*time)+120deg)

1. In the beginning I dont give any alignment angle in the rotation of rotor and the induced voltgae and the currents align but not perfectly. Is there a need to have alignement angle always as I believe I dont need here as I get the max torque?
2. Then I take the alignment angle from no load analysis, where the Phase A flux linkage has negative maximum and at the same time the back-emf for phase A is zero. But after putting the alignment angle, I dont get the max. torque and something seems incorrect as induced voltage (voltage on load) can never be less than the back-emf. I am not sure what I am doing wrong?
3. Also, since induced voltage is back-emf + voltage due to flux linking the coils, will the induced voltage and three phase currents will always be in perfect alignment?

I am a little confused. Some help in this regard is very much appreciated. Thank you very much.

Best regards,

Ruchika

 

[GLUO]

Hi,

1. Is there a need to have alignement angle always as I believe I dont need here as I get the max torque? Yes, if you would like to get max torque. Initial angle and currrent phase affect the torque when mechanical transient is not considered.
2. Please elaborat the motion setup.
3. No

GL

 

[Ruchika Singh]

Hi GL,

Thank you for your reply. 

2. I run the model at no load (0 current) and then check the flux linkage and induced voltage. According to the Ansys document, the alignment angle is the angle at which, the Phase A flux linkage has max lower value as well as the induced voltage for Phase A crosses 0. I do the same, and put this angle in the rotation mechanical angle for the load analysis but I dont get the max torque. I am not sure what seems to be the problem? 

1. Also, as I mentioned that when I dont put any angle, I get the max torque. I am not sure, if I needed any angle here?, also because of the reason in point 2.

3. Also, if the induced voltage and currents at no load will not be in perfect alignment, then what is the indicator that the obtained results are correct? Can you please elaborate this a little bit more.

 

Thank you very much.

 

Best Regards,

Ruchika

[Ruchika Singh]

Hi,

 

An additional information to the above is that my motor is a spoke type motor. Looking forward to the feedback. Thank you very much.

 

Best Regards,

Ruchika

[GLUO]

Hi,

2. I run the model at no load (0 current) and then check the flux linkage and induced voltage. According to the Ansys document, the alignment angle is the angle at which, the Phase A flux linkage has max lower value as well as the induced voltage for Phase A crosses 0. I do the same, and put this angle in the rotation mechanical angle for the load analysis but I dont get the max torque. I am not sure what seems to be the problem? 

This is the method to align the rotor pole to the stator pole, it only gives the initial angle that aligns the poles to use DQ transoform. You need to find the Max torque angle/phase after that.

1. Also, as I mentioned that when I dont put any angle, I get the max torque. I am not sure, if I needed any angle here?, also because of the reason in point 2.

You could possibly get the Max torque angle with 0 initial angle defined in the motion setup, depending on how you draw the rotor and how the windings are arranged.

3. Also, if the induced voltage and currents at no load will not be in perfect alignment, then what is the indicator that the obtained results are correct? Can you please elaborate this a little bit more.

I am not sure what do you mean by correct result. To get max torque, we usually set the speed at 0, then run with sine current to find at which time point the torque reaches the max value, and use the phase at that time point as the initial current phase. 

GL

 

[Ruchika Singh]

Hello,

 

Thank you for your reply. 

2. I run the model at no load (0 current) and then check the flux linkage and induced voltage. According to the Ansys document, the alignment angle is the angle at which, the Phase A flux linkage has max lower value as well as the induced voltage for Phase A crosses 0. I do the same, and put this angle in the rotation mechanical angle for the load analysis but I dont get the max torque. I am not sure what seems to be the problem? 

This is the method to align the rotor pole to the stator pole, it only gives the initial angle that aligns the poles to use DQ transoform. You need to find the Max torque angle/phase after that. - Aligning rotor pole with stator pole, does that mean aligning phase A axis with d-axis?

I am not sure what do you mean by correct result. To get max torque, we usually set the speed at 0, then run with sine current to find at which time point the torque reaches the max value, and use the phase at that time point as the initial current phase. - I dont fully understant this method. Could you please elaborate? 

 

Thank you very much.

 

Best Regards,

Ruchika

 

[GLUO]

Aligning rotor pole with stator pole, does that mean aligning phase A axis with d-axis?

Yes

Could you please elaborate? 

When you run with sine current and fixed rotor, rotor MMF is stationary and stator MMF is rotating. So you are actually sweeping different angles. In this case, the rotor stator MMF angle when torque reaches max value is the angle you need to keep the torque at the its max value.

GL