Phase voltage accuracy for PMSM motors

[jmailloux]

Hello,

Not sure how important model accuracy is to you, but I believe the phase voltages being calculated for PMSM motors is incorrect. One relatively easy way to see this is to calculate output power of the motor (torque omega), and then calculate input power to the motor (3 vrms irms). The input power is less than the output power. isupusup is more reasonable. It is higher than the output power.

[wallscheid]

Hey Jerry,

3 V_rms I_rms is the apparent input power of the drive and not only the active input power. The latter would be equal to the sum of the motor (ohmic) losses + the the mechanical output power in steady state (note: we do not model inverter losses or other losses except for the ohmic losses within the motor). And of course you can calculate the active input power via i_dc*u_dc but again, that would be identical to the mechanical output power plus motor losses in steady state.

We have also cross-checked our code and did not found any error in the power balance during a quick simulation. We would therefore ask you to post a minimal example, so that we can understand where you think the power balance of the simulation does not add up.

[bhk11]

Hi Jerry, attached you can find our minimal example for the calculation. Please keep in mind that the additional losses in the motor during transients (d i /d t ≠ 0) are not calculated in this example.

test_power.zip

[jmailloux]

Hi. Thanks for getting back to me so fast. I couldn't run your example because I am having trouble installing gem-control. Here is my example. I calculated power (called it motor_input_power) the same way you did (using Vd, Vq, Id, Iq), and that looks reasonable. So I don't understand why apparent_power would be less than that. I believe the current numbers are accurate because Kt is in line with what I expect. Ke is not so I suspect either ua, ub, uc are incorrect, or they aren't what I think they are (I assume they are phase to neutral voltages). power_example.py.zip

[bhk11]

Hi Jerry I looked through your code. We usually use the DC-link voltage as nominal value for our drive system to give a short hint to your comment in the code. With this voltage, I get also the values which, I expect in the phase voltages. For example: If I apply the action np.array([-1,1,1]) to the gem environment, I receive the phase voltages shown in tab. I. of https://ieeexplore.ieee.org/document/10214121 . So, the phase voltages are measured between phase and 0 V potential of the inverter not the neutral point of the machine.

[bhk11]

As there is no further response to this topic, I am closing the issue.