PowerFlex 755 stop and hold

[VulcPAC]

Hi everyone:

Is there a way to stop a PowerFlex 755 in a fast ramp and then hold the motor for a few seconds? I need this to avoid the load to rotate with the inercia after the inverter releases the motor.
I tried "Ramp to Hold" but I cannot control a delay time, it remains with the VFD active and 0 speed until the next start. For now, I dont have wire stop to Di to use as a "stop mode B", only a stop command via Ehtenet/ip.

The other question, in case that I need a very fast stop, if I use "Current limit Stop", do I neccesary need a dynamic brake resistor? Can I use "current limit stop" and bus regulator with "Adjust freq"? Is a powerflex 755, 400V, 2,2 kw, motor with gear box and a unwind roll as the load. For now, I dont have the data of weight and inertia, is not a huge mass, I am just controlling the torque or speed with a diameter sensor with an equation in Logix.

Thanks!

 

[VulcPAC]

I found this in the reference manual:

Ramp mode can also include a timed hold brake. Once the drive has reached zero output hertz on a Ramp-to-Stop and both parameters 395 [DC Brake Time] and P394 [DC Brake Level] are not zero, the drive applies DC to the motor producing current at the DC Brake Level for the DC Brake Time:

But my doubt is if I can use DC to brake withot having a braking resistor.

Thanks

 

[alan_505]

The DC hold injects DC into the motor windings, so best not to use it for long periods as it can cause motor winding temperature rise.
The braking resistor is used to limit the DC bus voltage during rapid stops as the motor will act as a generator putting energy back into the VSD, the brake resistor is turned on to shunt some of this energy into the resistor when the DC bus goes over a certain value.

 

[VulcPAC]

The DC hold injects DC into the motor windings, so best not to use it for long periods as it can cause motor winding temperature rise.
.

Hi. What do you mean with "long periods of time"? For example, in a 2,2 kw VFD, inject DC with the default value of 8.7 Amps diring 3 seconds after the stop, could be considered a long period of time?

Thanks

 

[alan_505]

No I would consider that a short period of time, 30 seconds would be a long time.

 

[kekrahulik]

Maybe I'm not seeing the whole picture but if you have EthernetIP...
1. You can set the Accel Rate as a datalink which will allow the program to set a rapid decel when desired or a softer decel when not desired.
2. When you want to stop fast, change the speed setpoint to 0.0 and the accel rate to a fast decel. The drive will decel fast to zero speed and hold it there.
3. After the drive has held at zero speed for the desired time, then issue the stop command.

 

[VulcPAC]

Thanks to all, I will consider that options and try.