Powerflex 70 Output & Commanded frequency

[andypot]

The question here is:
What type of VFD control does your application require???!
If you need Speed Control only use V/Hz control and your Reference Command will "go straight" to the Speed Regulator/Frequency Output.
If your application needs Torque Control with Speed Regulation, choose the Flux Vector Control Mode, however" you will generate the corresponding "difference" between speed reference and output frequency due to the required torque settings.

I think your answer is slightly confusing. The question should be what type of load are you trying to control?

V/Hz control is the simplest and most basic type of control, Flux Vector is a more advanced form of control and will improve the performance of the drive with better dynamic response. However, it still relies on the basic volts/Hertz core for controlling the motor.

If you are trying to control a simple centrifugal fan then V/Hz in most cases would be the ideal option however this will be open loop with no encoder feedback. In V/Hz mode the drive has no idea what speed the motor is running it just outputs the required frequency and hopes for the best.

As there is an encoder fitted it would suggest that closed loop control is required therefore Flux Vector is the way to go BUT you must ensure that parameter 88 is set to Speed Reg.

With Flux Vector control in Speed Regulation mode the motor should run straight up to the Speed Reference and stay there if the drive is set up correctly.

So the question is what type of load are you trying to control?

I would suggest as you don't seem to be getting very far I would start again with this drive, backup it up, if you haven't got Drive Executive then back it up to the HIM (that way you can always get back to where you are now).

When you have your backup set the drive back to defaults and using the Start-up Wizard go through all the commissioning steps, this should only take a few minutes. If conditions on your plant allow it may be worth initially setting the drive up to allow control from the HIM, that way you can play with it and verify that it is working correctly before connecting to the PLC.

Make sure you do an Auto tune, preferably a Rotate Tune. if in Flux Vector Mode.

If you continue to have problems please answer the following questions:

1. What load are you trying to control, is it variable torque, ie like a centrifugal fan where the faster the fan runs the greater the required torque or more constant torque which is something like a hoist or lift where you will need lots of torque at low speed.

2. Is this a high inertia application, another indicator that you need Flux Vector Control.

3. Where is the encoder fitted, on the motor (or somewhere else but running at motor speed) or is it the other side of a gearbox.

 

[kekrahulik]

I've never had a problem running FVC mode. The drive runs EXACTLY the speed I command it to run if P88=speed reg. Are you sure that the drive is following your speed command? If you change your speed command, does the drive increase/decrease speed (maybe not the right speed, but do you see a change?). If it doesn't check your speed select bits in your output command word (bits 12-14??). The drive may be following speed select B and not speed select A. Check the values of P90 and P91(speed select B). Set both to 22 (port 5).

Possibly an encoder issue? Try running V/hz and set P80 (feedback) to open loop.

This may not be your issue, but it may help you with this or future PF70 applications:

By default, SpeedRef = [CommandFreq/MaximumFreq] X 32767. You currently have P55=120(max freq), P82=100(max speed), P83=20(overspeed). So your PLC speed command (0-32767) gets scaled (0-120hz), but the drive will only allow itself to go 0-100Hz. To me, that's very confusing from the PLC side because your effective speed command is 0-27305. If you send any value larger than this, the drive will not increase speed because it has hit max speed (P82).

This is what I do:
1. Set P196=1 (allows access to other params)
2. Set P298=1 This makes your PLC speed command scale from 0-max speed (P82). So now SpeedRef = [CommandFreq/MaximumSpeed] X 32767.
3. I leave P55=120 (default)
4. P82=60 (or whatever max speed you need - in your case 100)
5. P83=10 (Default) This value shouldn't need to be more than 10. This value doesn't matter until you tell the drive to go near full speed. When doing so, the drive's speed regulation may see that you are commanding full speed, but feedback shows that the motor isn't quite reaching full speed. So the drive needs permission to add a little onto your speed command so it can actually achieve your desired speed. If you set this value to zero, you will likely fault the drive whne you try going full speed.

Anyway, by setting P298=1, your PLC program can now scale 0-100% speed as 0-32767 which will command the drive to go 0-Max Speed. This gives you full resolution of your speed command.