q- d- currents of PMSM drive in Delta configuration

I measure the line-currents of a Delta-wired 3 phase PMSM (SimScape).

Then, I apply the Park transform to transform abc to dq0.

Now, the output of the Park transform is different from the d- and q- currents that I see in the SimScape result explorer.

When I switch to Wye-configuration. The values are as expected, but the torque is higher than what I would expect from torque = K_t * i_q.

Notice how the idq0Scope (after Park transform) gives different values. (d/q; 10/0 vs 5/-2.887A)

Can anyone explain this difference?

Current controller:

Answer 1

[Mohsen Aleenejad]

Hi Tom,

Could you please tell me if these numbers are the exact values you observe? If not could you please provide the exact values?

Thank you

Mohsen

[Mohsen Aleenejad]

I mean (d/q; 10/0 vs 5/-3A)

[Tom Lankhorst]

What I get after Park-transforming the line-currents to the drive is:

Q = 10A

D = 0 A

(This is because I'm controlling those currents to these values).

What the Drive reports is:

Q = 5A

D = -2.887A

At electrical position 2.93 rad.

When I multiply these values by sqrt(3) and take the geometric sum I get 10A...

I have configured the drive and the Park transforms to define the rotor angle between the a-phase magnetic axis and the q-axis.

[Mohsen Aleenejad]

Yes, as I was suspicious there is a 30 degree phase shift between your measurements and the Simscape explorer results. The amplitude of the line current in delta configuration is equal to 1/sqrt(3) of the phase with a 30 degree phase shift. So you should modify the theta to get the exactly equal results with the Simscape results explorer:

10/sqrt(3) x -1/2= 2.887

10/sqrt(3) x sqrt(3)/2= 5

-1/2= sin (-30)

sqrt(3)/2= cos(-30)

1/sqrt(3): amplitude scale

I hope this helps.

Good Luck

Mohsen

[Tom Lankhorst]

Thanks for your insight Mohsen.

I scaled the 'measured' current by 1/sqrt(3) then subtracted pi/6 from theta... and it works.

Only the output torque is exactly 1.5 times as high as I would expect from the torque constant.

[Mohsen Aleenejad]

I'm happy that could help. Regarding the torque, if I recall correctly, there is a 2/3 constant in the equation, probabley the difference is coming from there and you need to consider it somewhere.