As factories' requirements for automation system reliability continue to increase, production interruptions caused by automation system failures may cause great losses to factories. Therefore, fault tolerance is a very basic requirement for automation systems. To address this issue, we have further improved the reliability of application networks based on the Siemens platform. The commonly used simple chain network structure is shown in the figure below.

To increase system reliability, the connections between nodes in industrial communication networks are often designed as redundant physical connections, which requires the use of the Media Redundancy Protocol (MRP). Ring networks are a common network topology used to achieve media redundancy in industry.

Compared with traditional networks, the advantages of media redundancy protocols are as follows:

1. Because the damage of a single device does not affect network communication, the redundant structure can significantly increase the reliability of the system and equipment.

2. Since damage to a single device will not cause the entire system to shut down, there is no time pressure for maintenance work.

3. When a network failure occurs, the fault can be located and solved in time through rapid network diagnosis.

4. It can reduce the losses caused by downtime due to failure.

An example of an MRP ring with 4 nodes is shown in the figure below. It consists of an MRP manager and 3 MRP clients. The manager can be a PLC or a switch. Each node in the ring needs to have an integrated dual-port switch, with two ports connected to the previous node and the next node respectively.

The ring manager's job is to monitor the network for errors. It sends test frames simultaneously from port 1 and port 2. The test frames are passed in both directions, entering the other port of the ring manager.

Under normal circumstances, the ring network administrator will block the network data flow of one port, so that the physical ring network becomes a linear network at the logical level to prevent loops.

For MRP, the maximum time required from ring network interruption to redundant path establishment is 200ms. For slave stations with network monitoring watchdog function, the watchdog monitoring time needs to be set to greater than 200ms, otherwise the slave station may shut down due to communication interruption.

The following details how to configure a ring network containing G120/S120 inverters in PCS7 software.

G120/S120 inverters with firmware version V4.5 and above support MRP. The following example shows how to configure a ring network including G120/S120 inverters in PCS7 software.

The main equipment list and topology diagram of the network topology of the Weihai Longgang Paper Transmission Project are as follows:

Equipment Name Model Application Quantity

PLC412-5H PN/DP Administrator

Switch Sanwang IES618 data exchange ordinary switch one

S120CU320-2PN Several clients

G120CU250S-2PN Several clients

A PCDELL host computer

The main configuration steps are as follows:

(1) Do not connect the network into a closed loop before the configuration is completed. Otherwise, frame loops will form and cause network failures.

(2) Assign IP addresses and device names to all node devices.

(3) Add PLC and G120 inverter to connect to the PN network, with PLC as the administrator and CU as the client.

(5) After completing other required configuration steps, you can compile and download the configuration to the PLC.

(6) Connect the network into a closed loop.

You can view the current network status by viewing the topology view online.

Normal communication is as follows:

Disconnect the network cable of any inverter control unit, and the inverter does not display any fault. Disconnect the 24V power supply of any inverter control unit (power off the network port), which does not affect the communication of other inverters. The current network operation status can be obtained by viewing the topology view online. The communication is shown in the figure below.

The ring network is restored and communication is normal.

The above tests can fully illustrate the role of MRP ring network:

When the MRP ring network is not formed, if the network connection is interrupted, the G120 inverter will report F1910 fault and stop running.

After forming the MRP ring network, the inverter has two network connection paths. When one path is disconnected, communication can be established from the other path, and the inverter will not report a communication interruption fault.