The main control units of the CSC-861 series distributed automation comprise main control units of five models of CSC-861C, CSC-861D and CSC-861F, which are the core equipment of communication control layer in the photovoltaic monitoring system and integrate functions of monitoring slave station, terminalequipment management and communication management. The main control unit is the information center of the monitoring system, at the nexus level. It is connected into various inverters and intelligent protection and control devices through PROFIBUS-DP, LonWorks, RS-485, Ethernet and other field bus access, and is connected to the master station system upward through protocols such as IEC 61850, IEC 60870-5-104 and MODBUS/TCP. The master control unit also has the functions of programmable logic control, redundancy and parallel nodes, which ensures the reliable and stable operation of the system.