Relationship between back EMF (Ke) and maximum achievable speed

Is there a standard relationship between DC bus voltage and the maximum achivable speed, from which we can calculate the maximum achvable speed of a PMSM motor given the DC bus voltage?

Looking at this thread:

https://e2e.ti.com/support/motor-drivers-group/motor-drivers/f/motor-drivers-forum/1271711/mcf8315a-speed-control-issue

Is the formula given there a valid equation for a general FOC controller?

Eletrical frequency = (DC bus / sqrt(3))/Ke ?

We are trying to run the Motor driver from a C2000 LaunchPad (LAUNCHXL-F28379D + BOOSTXL-3PHGANINV)

https://www.mathworks.com/help/mcb/gs/matlab-project-foc-pmsm-qep.html

Answer 1

[akshatsood]

Hi @Arun,

The relationship between DC bus voltage and the maximum achievable speed of a Permanent Magnet Synchronous Motor (PMSM) can be influenced by several factors, including the motor’s back EMF constant (), the control strategy, and the voltage limit imposed by the inverter.

Formula for Maximum Electrical Frequency

The formula mentioned in the thread:

is a simplified representation that can be used to estimate the maximum electrical frequency of a PMSM when using a Field-Oriented Control (FOC).

Practical Implementation

When using a C2000 LaunchPad with a BOOSTXL-3PHGANINV and implementing an FOC strategy (as described in the MathWorks example), you should:

• Ensure the motor parameters, especially (), are accurately measured or provided by the manufacturer.
• Consider the maximum voltage that the inverter can apply, which is limited by the DC bus voltage.
• Implement the FOC algorithm to maintain efficiency and stability at high speeds.

Conclusion

While the formula provides a useful estimate, the actual maximum speed achievable in practice may vary due to additional factors like load conditions, motor efficiency, and thermal limits. Testing and tuning your specific setup will be essential to achieving optimal performance.

I hope this helps.

[Arun]

Thanks you for your detailed answer, Just for clarity , the back emf constant(Ke) in the formula that you have posted, what is the unit of this that is normally used, generally some OEMs givethe back emf with reference to a certain speed ...