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Controlling Danfoss frequency drives

Danfoss frequency drives supports Modbus protocol. To enable it, the parameter 08-30 should be set to [2].

Other communication parameters are in the same 8th group:

  • 8-31 Bus address, [1..247]
  • 8-32 Baud rate, [0..4] (2400..38400 respectively)
  • 8-33 Parity and stop bit [0..3] ( Even, 1 stop; Odd, 1 stop ;No parity, 1 stop; No parity, 2)

After changing protocol type, it neccessary to re-power the drive. Also, with changing protocol 8-30 [0] FC to Modbus [2] the baud reat will be automatically changed too (9600 for FC51 and 19200 for Modbus).

The drive can only be controll via Modbus when it is switched from Hand to Auto mode.

There might be a case, when actual frequency differs from the setpoint by a certain level. This is possible when there are many source frequency inputs enabled (485, analog input, digital input) and they summed together.

The drive is controled and monitored via:

  • CTW control word - start, stop, configuration etc. accessible bitwise on C0..C15 addresses with Read coils or HR49999 with holding register read
  • REF Bus reference register - frequency setpoint HR50009
  • STW status word - accessible bitwise on C32..C47 addresses with Read coils or HR50199 with holding register read
  • MAV actual frequency HR50209.

More details on working with Danfoss FC drives are described in document MG.02.A4.02 VLT® Micro Drive FC 51 Operating Instructions. Below is a table with parameters. The parameter numbers specified in these tables must be specified in the register settings with an offset of -1. For example, the Bus reference register (REF) in the documentation has the address 50000, but in the WebHMI you set it as HR49999.

To access any paramter you can use the formula: (Pr.Num. * 10 - 1). E.g. 8-31 (bus address) will equal 831*10 - 1 = 8309.

Below are the register settings for controlling the VLT Micro drive FC51 frequency converter - start / stop, change of direction of rotation, speed reference.

In the frequency converter, the frequency values are presented as follows: the frequency 50 Hz (100% of the scale) corresponds to the number 16384. Negative values are also a number in binary complementary form (two's complement). Therefore, to correctly display the frequency and its task for the registers, it is necessary to use the multiplier 50/16384 = 0.0030517578125, and specify the appropriate format in the register properties.

There is a video (in Russian language) with live demo of controlling Danfoss FCS 51, and cooling controller Danfoss AK-CC 550 as well. webhmi_fc51_aka550.jpg