Hello All.

This question is for anyone that has had issues with regen power from a motor driving a draft fan application.

My question is as follows:

- My customer has a 110kW 500-600 VAC G130 drive installed at their facility.
- The power system nominally operates at 600V. The motor is a high efficiency motor which is
alsorated for 110kW at 575V 60Hz.
- The current problem they are having is that the motor appears to be regenerating back onto the
drive.
- The ramp up is 60s and ramp downis set for 120s. The UV and OV DC controllers are turned on. - The drive has been configured in V/Hz Linear Characteristic mode.

In the Masterdrivefirmware you used to be allowed to set your Max Regen Pwr Limit to whatever setting you needed regardless of the drive's control mode. In the SINAMICS it appears that when the drive is configured in V/Hz, parameter p1530 (Power limit motoring / P_max mot) is not available to change. If the drive were configured for Sensorless Vectoror Close loop Vector, the parameter becomes accessible.

My question is what is the value of the Power limit motoring / P_max mot (p1530) when operating the drive in V/Hz?

I am considering having the customer re-configure the drive for Vector. A brake chopper would be overkill for this application since the fan inertia is relatively low.

I am looking forward to anyone's thoughts on this subject.

Thank you.

Hi zlatan

I am new to this forum however I clearly understand your problem. When AC drives operate in V/F control mode we all assume at zero frequency the out put voltage will be zero. It is not. There will be a magnetizing current in the motor and for that there will be a certain percentage of output voltage.

I hope you understand ramp up time and ramp down time. Ramp down time plays big roll during regeneration. Let’s say your fan has higher inertia and you took the fan to maximum speed you can run and at that speed you stopped. What will happen the energy stored in motor some how has to be taken out from the fan .In that situation regeneration comes in to action. So the energy stored in the fan will be transferred to DC link and from there it will transfer to the power system or grid via regulators.

If we have low ramp down time and the energy stored in the fan is high then all the energy has to be transferred in short time. If the drive try to do in short time , there will be increase in the DC link voltage(spike) and it will exceed the maximum rating of the DC link voltage as a result drive will be faulted. So this problem can be solved by increasing the ramp down time. When you increase the ramp down time drive will have enough time to transfer the energy back to system and there won’t be any voltage spike in the DC link voltage of the drive.

The reason why re-generation occurs even we stop the drive by putting out put frequency zero there will be torque in the rotor due inertia force and magnetizing current in the stator will produce magnetic filed and motor will act as a generator.

If you find your fan has higher inertia and re-generation energy can’t be handle by the drive then best option use costal stop function. During the costal stop there want be any output voltage on the phases and it simply pull out firing pulses from IGBT.

Then the energy stored in the motor will reduced by the friction forces in the fan and it will take long time to come to zero speed.

However it depends on your application too. If you don’t worry about stopping time and starting time then coastal stop will resolve your problem.

cheers

steve

Hi zlatan

Default value is ( if complete calculation mode is selected ) -0.01 kW (default value always very low) and if we are using pure V/F control then recommended maximum set point would be the same as rated motoring power.(motor rated power).

But for vector control motoring power can go up to 300% of rated power and regeneration power also the same.

Normally it is not ignored. Still you can modify P1531 by changing P340 to no calculation mode or any other mode except complete calculation mode.

p1240 = 1, 3:
When the DC link voltage limit, specified for the Motor Module is reached, the following applies:
- the Vdc_max controller limits the regenerative energy in order that the DC link voltage is kept below the maximum DC link voltage when braking.
- the ramp-down times are automatically increased.
p1240 = 2, 3:
When the switch-in threshold of the Vdc_min controller is reached (p1245), the following applies:
- the Vdc_min controller limits the energy taken from the DC link in order to keep the DC link voltage above the minimum DC link voltage when accelerating.
- the motor is braked in order to use its kinetic energy to buffer the DC link.
p1240 = 4, 5, 6:
When the threshold in r1242 or r1246 is reached, the DC link voltage monitoring initiates a fault (F07403 or F07404) with a response and therefore reduces additional negative effects on the DC link voltage.