Controller design and technology-why not both sinewave and squarewave?

[kebekua]

Hi board,

I got a question for members who are versed in controller design and technology.

Squarewave controllers are more efficient at high speed. Sinewave must use field weakening to achieve the same speed with a given voltage and motor, and therefore are less efficient at high speed.

Why is it not possible to use sinewave at low speed, then switch to squarewave instead of using flux weakening?


Thanks in advance for your answers

 

[Alan B]

Could do that, not clear it is useful. Square waves include harmonics that waste some energy, so efficiency is not optimized.

There are other techniques that may work better.

Using SVM (space vector modulation) sine wave drive you gain 15% speed (voltage) without field weakening.

https://www.electronicproducts.com/Electromechanical_Components/Motors_and_controls_Space-vector_modulation_vs_sinusoidal_commutation.aspx

 

[Toorbough ULL-Zeveigh]

We use all three forms of excitation in our algorithm. Trap at startup and then sine with FOC.

That is awesome to hear.  Should enable ~5% more torque around startup at the cost of a tiny bit of efficiency and increased torque ripple (which would also be significantly less noticeable with 5p than 3p). Then cruise efficiency is unaffected by induced harmonic content from trap drive, but you still get the torque advantage when starting. Cool 

What are we paying $645-$745 more for? i think it's important to state the justification for the price premium.

Trapezoid Excitation: A five phase motor architecture can be driven with a trapezoid which covers full 180 degree electrical cycle whereas a three phase trapezoid can only cover 120 degrees.

 

[kebekua]

thanks!

 

[zro-1]

OK, dumb question: How does a FOC (field oriented controller) compare to what's been described above?

 

[Alan B]

FOC is one way to do Sinewave, it measures the voltages and currents and uses matrix calculations to find the position of the rotor precisely and control the currents in relation to its position.