PU or SI for Motor Control Applications

Louis Zhu

In motor control applications, input data for the computation of PWM duty ratios are normalized. If the data are normalized upfront, PU approach is used; if the data are normalized at the end, SI approach is used. I saw that PU approach has been used in many TI reference applications, and I am used to it. However, many of my colleagues are not. To decide which unit system to be used for my team projects, I'd like to ask the experts in the forum, which unit system is more preferable for motor control applications?

over 4 years ago

0 Ramesh Ramamoorthy over 4 years ago

TI__Mastermind 27240 points

It is convenience based. If the processor is fixed point, it was easier than using pu. With floating point, both are good. PU may save few cpu cycles at best, depending when implementation.

0 Louis Zhu over 4 years ago in reply to Ramesh Ramamoorthy

Expert 1675 points

All the feedback signals (currents, voltages, etc.) are obtained via ADC (or other conversion devices, e.g. RDC for position and speed), and the ADC results with certain resolution must be converted to either PU or SI regardless of the processor types. From that perspective, which unit is preferable?

0 Ramesh Ramamoorthy over 4 years ago in reply to Louis Zhu

TI__Mastermind 27240 points

Correction to my earlier post, it is easier to use pu with fixed point.

Well, my choice will be pu, again, it will upto the designers.

Even with pu, you have to do conversions based on SI ahead of time.

0 Ramesh Ramamoorthy over 4 years ago in reply to Ramesh Ramamoorthy

TI__Mastermind 27240 points

If the concern is resolved, let us know so we can close the thread.

0 Ramesh Ramamoorthy over 4 years ago in reply to Ramesh Ramamoorthy

TI__Mastermind 27240 points

Since there is no response, we assume the query is resolved and closing the thread. If not, you can reopen the thread by posting within 30 days, or else open a new thread.

Motor drivers

Motor drivers forum

PU or SI for Motor Control Applications