FOC of PMSM - speed response

jason manbodh

Other Parts Discussed in Thread: TMS320F28035, DRV8312

Goodnight, I am running the PM_SENSORLESS code on the DRV 8312-C2 kit with TMS320F28035 and debuging with CCS v6.

I am using the motor that was shipped with the DRV8312 kit.

I am at build 6 where im observing the estimated speed response (produced using the rotor position from SMO) and the actual speed (produced using the rotor position generated by an encoder).

When the motor reaches rated speed, both responses produce oscillations. I dont understand the cause of this. I've attached a screenshot showing this phenomenon. NB: rated speed = 3000 rpm.

Any feedback will be appreciated.

thank you

-Jason

over 9 years ago

0 Wilson Zuo over 9 years ago

TI__Mastermind 26065 points

Hi Jason

We will move your post to C2000 forum for more experts there.

Best regards,

0 ChrisClearman over 9 years ago

TI__Guru** 119680 points

does your motor actually have an encoder? the one in the kit does not

is the rotor actually oscillating like shown in the graphs? if so, the estimator/encoder is doing its job and you need to tune the controller to stabilize the system

0 jason manbodh over 9 years ago in reply to ChrisClearman

Intellectual 470 points

I am using a shaft encoder i got in school. The rotor seems to be rotating smoothly. I will try tuning the controller and see if that works.

0 ChrisClearman over 9 years ago in reply to jason manbodh

TI__Guru** 119680 points

are you overflowing a variable? Looks like maybe you are going over 1pu of speed so it is wrapping around to -1pu?

Is the motor actually running at ~1pu during this time or is it oscillating wildly?

0 jason manbodh over 9 years ago in reply to ChrisClearman

Intellectual 470 points

I am not sure how to check if a variable is overflowing. When i set the speedref variable in the watch window to 1.0 pu, the speed builds up until what appears to be 1pu, then oscillates wildly between 1.0 and -1.0.

I've attached a magnified view of the plot at 1.0pu.

0 ChrisClearman over 9 years ago in reply to jason manbodh

TI__Guru** 119680 points

what is your speed ref in pu or Hz?
what does 1 pu represent in Hz?

0 jason manbodh over 9 years ago in reply to ChrisClearman

Intellectual 470 points

it represents 3000rpm
3000/60 = 50Hz

0 ChrisClearman over 9 years ago in reply to jason manbodh

TI__Guru** 119680 points

50 Hz @ 3 KRPM would be a 2 pole machine
the motor that comes with this kit is 8 poles

Is your
#define BASE_FREQ 200

still 200 Hz?

3 KRPM with 8 poles = 200 Hz, right where you are having the issue

change
#define BASE_FREQ 400

so that your per unit of 1.0 now represents 400 Hz

0 jason manbodh over 9 years ago in reply to ChrisClearman

Intellectual 470 points

The following is how the base rpm is calculated in the code.
BASE_FREQ = 200
POLES = 8
this gives baseRPM = 3000rpm

speed1.BaseRpm = 120*(BASE_FREQ/POLES);

when i used #define BASE_FREQ 400, the motor stalls at approximately 2750 rpm.
Therefore the problem still persist.

0 ChrisClearman over 9 years ago in reply to jason manbodh

TI__Guru** 119680 points

the motor actually goes significantly faster than 3 KRPM with no load and 24V, so I can't see what the problem would be.

I would try running it with just the encoder for feedback and not using the observer

0 jason manbodh over 9 years ago in reply to ChrisClearman

Intellectual 470 points

Thank you

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FOC of PMSM - speed response