VFD not decelerating as expected. 4

[itsmoked]

I'm using a MA7200 to run a lathe motor. The original motor was a 3hp. This one is a 5hp VFD motor. I have everything working fine except the deceleration is anemic.

I've set accel and decel to 1 second. The motor ramps to 1720 in one second but refuses to decel in less than about 4 seconds. I have a mondo load resistor that doesn't rise above room temperature (which is saying a lot since it's ^*#@^%! 45F).

Running it in sensorless vector.

I've tried "Full Range" DC injection braking with only trivial improvement.

When STOP is commanded the current changes from about 5A at full speed with no load, to 7A on its leisurely stroll to zero.

Conversely when I switch instantly from full speed forward to full speed reverse the VFD dumps 30A into the motor and has it running full speed reverse in about a second.

I'm sure it's one of those cases where some quasi-related parameter is limiting the maximum stop current but I can't find it after more than an hour of weeding thru the manual and trying everything even remotely suspicious.

BTW: Never once have I had a single fault so it's not like it physically can't decelerate as fast as I'm asking it to.

Here's the: Manual

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Skogsgurra]

I downloaded the manual. Tip: very good if you want to sleep - which is what I wanted.

I cannot find any explanation for the acronym ASR, but I think that Automatic Speed Regulator is a safe guess. I would have used ASC (Automatic Spped Controller - that is what I am used to).

Page 3-27 says:
(43) ASR Proportion Gain 1 (Cn-47)
(44) ASR Integral Gain 1 (Cn-48)
•Set the proportion gain and integral time of the speed control (ASR)
(45) ASR Proportion Gain 2 (Cn-49)
(46) ASR Integral Gain 2 (Cn-50)
•Use these constants to set different proportional gain and integral time settings for
high-speed operation.

My comments: Cn-49 and Cn-50 are used when you go faster than base speed. As long as your drive works below and up to 60 Hz, you do not need them.


Cn-47 is the proportional gain of the speed controller. Increase to get "crisper" control. Try also with Cn-48 (integration time) and see if that helps after you have found an optimal setting of Cn-47.

Appendix 9 and 10 are good reading.

Hope this helps. Next step would be me coming over to have a go at it. How far is San Jose from Schenectady? No, just kidding, but an interesting thought.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[rhatcher]

It looks like Skogsgurra is all over this. I agree with his definition of ASR.

 

[itsmoked]

Skogs, rhatcher; Excellent. So it does have a PID for it's speed. The dorks just don't admit it.

You're in Schenectady Skogs? What? There's a slide-rule convention there?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Skogsgurra]

There is no PID in the speed controller. Just a PI controller. You never have any small time constant to compensate with a D in a cascade arrangement with speed loop and a "subordinated" torque loop.
If you look at the block diagram on page 3-60, you will see it clearly.

The autotuning sets the P and I in the speed controller and since P can be set much higher (needs to be) when there's inertia added, you may need to adjust it manually to get a good transient and load step response.

Yes, me and my colleague are going to Schenectady to do some work for that "bank with an electrical workshop". It is a very natural thing to do when one considers that they have taken my initials. But, of course, we are flattered to be invited. It's a pity it's so far from S.F. Would really like to go there again.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[itsmoked]

I see.

Can't wait to try out the PI.

Thanks.

A bank with an electrical shop... Guess I've heard everything now.

Keith Cress
kcress -

http://www.flaminsystems.com