Control.com - Nerds in Control

I am using a Eurotherm 690 + drive in sensorless vector control mode to control a small motor. The motor controls extremely well across its entire range. However there is one small problem when I increase the speed from standstill the motor "jumps/judders" as it passes through the 5 Hz. point after & before that point it is perfect. If I reduce the speed below 5 Hz then back up again the "jump / judder" is not there. It only happens when starting from Zero speed. I am quite sure that it is a drive setting that is the cause. If you have any suggestions please let me know.

Thankyou.

Try changing the skip frequency such that it min 4.7Hz and max 5.5 Hz to skip this possible mechanical resonant frequency

The 690 in Sensorless mode reverts back to V/Hz at the lower frequencies. (Something they left out of the manual.

Mark,

I won't discount using the skip freq. as one poster states (that may be the fix, you may try opening the skip freq. a little more than +/- 0.5 Hz, say +/- 1Hz). But I want to ask a few obvious questions... did you make sure that all the motor name plate data is correctly entered into the drive? Did you perform a full rotating auto-tune with the correct speed parameters setup (max speed etc.)? In sensor-less vector mode? If so, then try the skip freq... you may have to link that block into the speed setpoint though... using the keypad or CELite, etc. If none of these work feel free to re-post or call SSD's tech support, they have been very useful in past applications that I have worked in using their drives. You may give some simple details about the application.

Now to Ronny_resistor... I think you lost your -cap-. How can you state such absurd things? That is the whole point in sensor-less vector is to be able to control open-loop lower than the slip speed (which you can't do in V/Hz)... If what you state is true (which it isn't), they or any other drive company that did this wouldn't be able to control at all below slip speed... I'm very disappointed in you posting such a farce. If you are going to state such things, please give details on where you find such information. Sensor-less vector algorithms are not complex and the drives that I work with don't toggle them on and off thru the speed range, it’s basic algebra, you know -vector- diagrams.