SINAMICS V20 Speed Control with S7-1200 via USS Protocol
The solution enables data exchange between the PLC and the SINAMICS V20 drive using the universal serial interface protocol (USS), allowing centralised control of drive operation and status feedback.
A single controller can operate multiple drives through the same communication structure.
Application Objective
The example shows how to:
- Control drive start, stop, direction, and speed setpoint from the PLC
- Continuously read operational status and actual speed values
- Access inverter parameters for configuration and diagnostics
- Visualize operation through an HMI interface
System Architecture
Typical configuration includes:
- SIMATIC S7-1200 CPU
- CM1241 RS485 communication module
- SINAMICS V20 inverter
- KTP HMI panel for monitoring and control
Communication is implemented via an RS485 bus using USS telegrams between the controller and the drive.
Communication Concept – USS Protocol
The USS protocol enables cyclic and acyclic communication:
- Cyclic exchange transfers control words and speed references to the drive.
- Acyclic communication allows reading/writing parameters on demand.
Dedicated instructions such as USS_PORT, USS_DRV, USS_RPM, and USS_WPM manage communication and parameter handling inside the PLC program.
Drive Control Functions
The PLC can control key drive signals including:
- RUN command to enable operation
- OFF2 / OFF3 stop functions
- Direction control
- Speed setpoint is defined as a percentage of the rated frequency
The drive continuously returns operational feedback such as running status, faults, and actual speed.
HMI Integration
An operator panel allows:
- Start/stop and speed adjustment
- Reading and writing inverter parameters
- Monitoring real-time drive status
- Viewing diagnostic and communication errors
This simplifies commissioning and testing of the communication setup.
Engineering Workflow
Implementation typically involves:
1️⃣ Configuring RS485 communication module in TIA Portal.
2️⃣ Setting USS parameters such as baud rate and address.
3️⃣ Loading Siemens function blocks for cyclic and parameter communication.
4️⃣ Creating HMI screens for operation and diagnostics.
Key Benefits
✔ Simple integration of low-voltage drives with PLC automation
✔ Cost-effective multi-drive control over serial communication
✔ Enables centralized monitoring and diagnostics
✔ Scalable system capable of handling multiple inverters
✔ Ideal for retrofits and small-to-medium automation systems
Typical Use Cases
This solution is commonly used in:
- Conveyor systems
- Pump and fan control
- Packaging machines
- Small production lines
- Retrofit modernization projects
