PowerFlex Drives: Common Mode Noise Reduction

Summary

PowerFlex Drives: Common Mode Noise Reduction

Question

• What solutions are available to reduce the affects of Common Mode Noise?
• What can be done to help reduce Common Mode Current from affecting other devices?
• How can I reduce common mode noise that is generated when a PowerFlex drive is running?
• Is the 1321-M009 in accordance with NFPA79?
• What is an alternative to the 1321 Common Mode Choke which require the cables to be wrapped around the cores?

Environment

• PowerFlex 4-Class Drive
• PowerFlex 520-Series Drive
• PowerFlex 7-Class Drive
• PowerFlex 750-Series Drive

Answer

For installations that encounter problems due to high frequency common mode noise current, a common mode choke can be connected to the drive end of the motor cable, as close as possible to the drive’s output terminals. When installed at the drive output the common mode choke helps to guard against interference with other electrical equipment (Programmable Controllers, sensors, analog circuits, etc.).

The common mode choke reduces the rise time of the high frequency noise by a factor of 10-20, and the amplitude by a factor of 5. In addition, lowering the Pulse Width Modulation (PWM) carrier frequency of the drive also helps; in fact it reduces the effects and lowers the risk of common mode noise interference. Ensure the power jumpers on the drive are set appropriately. Refer to the drive’s respective power jumper installation manual for location and proper setting.

The 1321-M Common Mode Chokes can be installed with PowerFlex drives rated 200 VAC thru 600 VAC:

• 1321-M001 – For Communication Cables, Analog Signal Cables, etc.
• 1321-M009 – For drives 9 Amps continuous and under.
• 1321-M048 – For drives 48 Amps continuous and under.
• 1321-M180 – For drives 180 Amps continuous and under.
• 1321-M670 – For drives 670 Amps continuous and under.

For more information on the 1321 Common Mode Chokes Please see: 1321 Power Conditioning Products Technical Data, Publication 1321-TD001

The pre-wired 1321-M009 is in accordance with NFPA79 by Clause 12.9.2, which specifically permits the use of AWM under one of several conditions; including:

1. Where part of an assembly that has been identified for the intended use, and
2. Where the AWM has been identified for use with approved equipment and is used in accordance with the equipment manufacturer’s instructions

Below some indications to be followed to mitigate common mode current.

PowerFlex 70/700/753/755 Drive

The following can be done to mitigate common mode current:

• Parameter 151 [PWM Frequency] set to 2 kHz for PowerFlex 70/700
• Parameter 38 [PWM Frequency] set to 2 kHz for PowerFlex 753/755 .
• Refer to PowerFlex 70 Power Jumpers Installation Instructions publication 20A-IN010 for power jumper location.
  Refer to PowerFlex 700 Power Jumpers Installation Instructions publication 20B-IN021 for power jumper location.
• Refer to PowerFlex 750 Series Power Jumpers Installation Instructions publication 750-IN011 for power jumper location.
• Install a common mode choke on the output of the drive.
• Install a load reactor.

PowerFlex 4/40 Drive

• Parameter A091 [PWM Frequency] set to 2 kHz.

There are two common mode chokes that can be used with the PowerFlex 4/40 (choose the one that fits the output current rating of the drive):

• The 1321-M009 is a 9 Amp device. It is supplied with a terminal block for ease of customer wiring. The 1321-M001 is the core used in the 1321-M009, it has no wires and no terminal block.
• The 1321-M048 is a 48 Amp device.

The PowerFlex 4/40 drives do not incorporate common mode capacitors internal of the drive. The optional EMC Line Filters (22-RFxxx-xx) incorporate common mode capacitors internal of the filter. If Common mode capacitors are required, the solution would be to add the EMC Line Filter.

An alternative to the 1321 Common Mode Chokes that require wire to be wrapped around the core is the 1321-M055. For more information, see 1321-M055 Common Mode Choke, publication 1321-IN002.

---

Source: Rockwell Automation’s Technote database.