Integrating Danfoss VLT Frequency Converters into SIMATIC PCS 7: APL FbDrive and MotSpdL Implementation

To integrate Danfoss variable frequency drives (such as VLT FC 202 or FC 302 with MCA 101 PROFIBUS or MCA 120 PROFINET) into SIMATIC PCS 7, configure the drive in HW Config using Standard Telegram 1 (or Telegram 20) and connect it in CFC using the standard APL channel block FbDrive (FB1881) paired with MotSpdL (FB1856). In HW Config, install the Danfoss GSD/GSDML file and assign matching input/output addresses. In CFC, connect the drive's first process data word (PZD1 / LAddr) to FbDrive; the PCS 7 driver generator automatically interconnects module diagnostics during compilation, providing speed setpoint control, status monitoring, and faceplate visualization.

Fieldbus Architecture for Third-Party Variable Frequency Drives

In industrial facilities automated with SIMATIC PCS 7, third-party variable speed drives—such as Danfoss VLT AQUA Drive (FC 202) or AutomationDrive (FC 302)—frequently control centrifugal pumps, mixers, and conveyor belts. To incorporate these drives into the high-availability DCS environment, communications are established over PROFIBUS DP (using Danfoss MCA 101 interface cards) or PROFINET IO (using Danfoss MCA 120 interface cards).

Rather than writing custom communication ladders or STL pointers, PCS 7 engineers utilize standard Advanced Process Library (APL) technological blocks designed to interface PROFIdrive-compliant equipment directly.

Danfoss MCA 101/120 Communication Profiles: Standard Telegram 1 vs 20

The Siemens APL channel block FbDrive (FB1881) is strictly engineered to evaluate standardized PROFIdrive telegram types:

Standard Telegram 1: Transfers 2 Process Data Words (PZD) input and 2 PZD output (4 bytes each):
Setpoint Telegram (AS to Drive): PZD1 = Control Word (STW1), PZD2 = Speed Reference (NSOLL_A).
Actual Telegram (Drive to AS): PZD1 = Status Word (ZSW1), PZD2 = Actual Speed (NIST_A).
Standard Telegram 20: Standard VIK-NAMUR telegram, transmitting 2 PZD output and 6 PZD input (including fault codes and motor current).

In the Danfoss drive parameter setup, configure parameter 8-10 (Control Word Profile) to PROFIdrive standard to ensure bit-level compatibility with Siemens command words.

APL Driver Concept: Pairing FbDrive (FB1881) with MotSpdL (FB1856)

APL enforces an object-oriented two-tier block hierarchy for speed-controlled motors:

Channel Block (FbDrive): Interfaces directly with physical fieldbus I/O addresses. It scales raw frequency integers (0–16384 hex 4000H = 100% nominal speed) into percentage or engineering units, extracts drive trip codes, and generates diagnostic quality codes.
Technological Block (MotSpdL): Implements operating modes (Manual, Automatic, Local), ramp rate limits, interlock evaluation (Intlock, Protect, Permit), operator faceplates, and trending.

MotSpdL interconnects directly to FbDrive: control commands feed FbDrive.SP_Out and FbDrive.Fwd, while drive feedback routes to MotSpdL.Rbk and MotSpdL.FbkRun.

Automated Driver Generation and Address Interconnection Rules

During CFC compilation with the option 'Generate module drivers' enabled:

The PCS 7 Driver Generator inspects the logical base address connected to FbDrive.PZDIn1 (or LAddr).
It identifies the Danfoss GSD slave from HW Config, verifies DP master diagnostics, and automatically instantiates helper blocks (MOD_PAL0 / MOD_D1) in chart @(1).
These diagnostic blocks continuously poll the health of the Danfoss communication card, setting FbDrive.Bad = 1 if the PROFIBUS connector is pulled or if the drive loses line power.

Danfoss Integration Specification and Telegram Parameter Matrix

The following table summarizes communication mapping between Danfoss VLT drives and PCS 7 APL blocks:

Telegram WordDanfoss Drive FunctionPROFIdrive DesignationFbDrive ParameterConnected MotSpdL ParameterOutput PZD 1Drive Start/Stop / Reset CommandControl Word 1 (STW1)CtrlWordMotSpdL.Start / MotSpdL.StopOutput PZD 2Speed Reference Setpoint (0-16384)Speed Setpoint (NSOLL_A)SP_Li (via MotSpdL)MotSpdL.SP_OutInput PZD 1Drive Running / Ready / FaultStatus Word 1 (ZSW1)Status1MotSpdL.FbkRun / MotSpdL.TripInput PZD 2Speed Actual Value (0-16384)Actual Speed (NIST_A)ActSpdMotSpdL.Rbk (Readback)Diagnostic DataPROFIBUS Diagnostic DP-V1Extended DiagnosticsDiagWordEvaluated by MOD_PAL0 / FbDrive

Step-by-Step CFC Configuration and Engineering Workflow

Follow this sequence to commission a Danfoss drive in PCS 7:

Install Danfoss GSD File: Download the official GSD/GSDML file from Danfoss for MCA 101/120. In HW Config, install via Options -> Install GSD Files.
Add Slave to HW Config: Drag the Danfoss drive onto the PROFIBUS DP master line. Insert Standard Telegram 1 into slot 1. Assign matching start addresses (e.g. Input IW 512, Output QW 512) in Process Image Partition 1 (TPA 1).
Configure Drive Parameters: On the drive LCP keypad, set parameter 8-10 = PROFIdrive, 8-01 = Digital and control word, and verify bus baud rate.
Place Blocks in CFC: Insert FbDrive (FB1881) and MotSpdL (FB1856) into a cyclic interrupt chart (OB35).
Interconnect Channel Block: Connect physical input IW 512 to FbDrive.PZDIn1. Interconnect FbDrive and MotSpdL control/feedback pins.
Compile Charts and OS: Compile CFC charts with Generate module drivers. Compile WinCC OS.
Runtime Operation: Open WinCC Runtime; test starting, stopping, speed ramping, and faceplate alarms.

Verification

Verify drive integration through these diagnostic tests:

CFC Test Mode Online Check: Confirm FbDrive.Bad = 0 and ActSpd reflects zero when stopped.
Start and Speed Reference Test: In manual mode on the MotSpdL faceplate, click Start and set 50% speed. Verify motor accelerates to half speed.
Readback Verification: Verify MotSpdL.Rbk reads 50.0% matching the physical shaft tachometer.
Bus Interruption Test: Unplug the PROFIBUS DP connector. Verify FbDrive.Bad transitions to 1, generating a drive communication fault alarm in WinCC.

Limitations and Operational Precautions

Observe the following operational constraints:

Telegram 1 Limitations: Standard Telegram 1 only passes 2 words each way; it does not transmit motor current (Amperes) or power (kW). If current monitoring is required, configure Standard Telegram 20 or use acyclic DP-V1 reading via RDREC.
Control Word Profile Selection: If parameter 8-10 on the Danfoss drive is accidentally left in 'FC Profile' mode, bit mapping differs and the drive will refuse to start via FbDrive.
Commercial Accuracy Disclaimer: Software order numbers (MLFBs), package structures, and hardware capacity prerequisites vary across PCS 7 versions and hardware platforms. System integrators must confirm exact software entitlements and licensing requirements against the official Siemens Catalog CA 01 and obtain an authorized Siemens distributor quotation prior to purchasing.

Engineer FAQ

Do I need to interconnect all PZD words manually in CFC for FbDrive?

No. Interconnecting the first process input address (PZDIn1) is sufficient; the PCS 7 Driver Generator handles module diagnostic linkage automatically during chart compilation.

Is a separate Siemens library license required for third-party drives?

Using native APL blocks FbDrive and MotSpdL requires no extra software licenses; however, Siemens Industry Services sells optional dedicated third-party drive libraries with custom faceplates.