Speed Loop FOC

DIJO PAULSON

Intellectual 710 points

Other Parts Discussed in Thread: TXB0106

Hi,

I am using TMDSHVMTRPFCKIT and FOC Sensored algorithm on PMSM.

At build level 4 I start my motor (lsw=1) at low speed

SpeedRef = 0.3 pu

Iq=0.1pu

Id = 0

Vdc = <100V

Then I close my speed loop, lsw =2

With a small jerk the motor continues to spin in the same direction by taking feedback from the Encoder.

The pid_spd.Fbk approaches to 0.3 pu. Current Iq reduces in magnitude

When I increase the DC bus voltage further (>100V) at one point the motor the stalls with a high jerk.

I assume that the rotor has lost its synchronization with the stator field.

Now when I look at the graph window the qep.ElecTheta has changed its direction and rests at 0.

The current waveforms (clark.As & clark.Bs) has increased to 0.9 pu.

I can't figure out why this phenomenon is happening. Please help

Regards,

Dijo Paulson

over 9 years ago

0 Ramesh Ramamoorthy over 9 years ago

TI__Mastermind 27240 points

It looks like the QEP feedback is having some problems/ malfunction when the inverter is switching at that voltage. I recommend running the motor in open loop and verify if the QEP operation is good. Also, verify if the pull up resistors R20-R22 in the QEP fbk input stage is 47K instead of 4K7. If not, change it to 47K.

0 DIJO PAULSON over 9 years ago in reply to Ramesh Ramamoorthy

Intellectual 710 points

Hi,
The resistors R19-R22 have value 472 written on them. So it is 4.7k right?
Are you sure that changing it to 47k would work ?
What actually happen if I change the value from 4.7k to 47k ?

0 DIJO PAULSON over 9 years ago in reply to DIJO PAULSON

Intellectual 710 points

Please do reply

0 Ramesh Ramamoorthy over 9 years ago in reply to DIJO PAULSON

TI__Mastermind 27240 points

Did you test after replacing with 47K? It is the recommended pull up value.

0 Reshma Ravi over 8 years ago in reply to Ramesh Ramamoorthy

Prodigy 110 points

Hi Ramesh,

I am trying to take forward the project, previously done by Mr. Dijo Paulson. The same problem was encountered when speed loop was closed (lsw = 2). Then the resistors R20 -R22 in the QEP feedback input stage was replaced with 47K (these were originally 4.7K). Now, the motor works under the closed speed loop till variac voltage of 130 V and above 130 V, the motor stalls abruptly. Previously when the resistors (R20 - R22) were 4.7K, the motor worked till variac voltage of 100 V and above 100 V it stalls. Kindly help in understanding the changes that happens when the resistors are replaced with 47K and also why is the motor stalls above 130 V of variac even after replacing the resistors.

Please do support with your valuable suggestions.

Best Regards,
Reshma Ravi

0 Ramesh Ramamoorthy over 8 years ago in reply to Reshma Ravi

TI__Mastermind 27240 points

Hello,

The RC filter is to snub any ground jitters from passing through the level translator buffer TXB0106. In fact, TXB0106 suggests to use a value higher than 50K if at all it is used. I would consider increasing the pull up to say 56K. If you still end up seeing issues, consider increasing C25-C27 from 1nF to 2nF (up to 10nF). Hopefully it should fix.

rgds,
ramesh

0 Reshma Ravi over 8 years ago in reply to Ramesh Ramamoorthy

Prodigy 110 points

Hi Ramesh,

The issue is solved. Thanks a lot.

Best Regards
Reshma Ravi

0 Ramesh Ramamoorthy over 8 years ago in reply to Reshma Ravi

TI__Mastermind 27240 points

Glad to know, would you pls post the values of R and C that fixed it, for the benefit of others visiting this forum.

rgds,

ramesh

0 Reshma Ravi over 8 years ago in reply to Ramesh Ramamoorthy

Prodigy 110 points

The issue was fixed when R20 - R22 was changed to 56K and C25 - C27 was changed to 2.2nF.

Regards
Reshma Ravi

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Speed Loop FOC