Abstract: Taking the steel rolling system improvement as an example，the design of 12-pulse parallel electric

control system of SIEMENS SINAMICS DCM 6RA80 in the steel rolling system was described in detail，as well as

the calculation and selection of main components，such as rectifier transformer，rectifier device and smoothing

reactor. The parallel communication between the master and slave devices，the peer to peer communication between the master and the excitation device，the functions of the current balance，overvoltage protection and overcurrent protection of the master and slave devices in the rectifier system were stressed，and the necessity of various protection functions was described in detail.

      Key words: 12-pulse parallel；parallel communication；system protection