Research On PLC-based SCADA System For Seafloor Junction Box

Considering domestic and international ocean observatory technology development,the importance of research on the Junction Box in seafloor observatory networks has become increasingly prominent.Long-term stability and reliability of the Junction Box is essential to various subsea observatory instruments.In this thesis,a supervisory control and data acquisition system inside the Junction Box,which is based on the programmable-logic-controller(PLC),is developed The system provides operation reliability check on all nodes in the observatory network while guaranteeing power connection and fault protection on the load side.The general framework of this thesis is as following:A multi-node supervisory data acquisition and control network for seafloor observatory networks is designed.With S7-300 series PLC being taken as the control core of a single Junction Box node,the system realized centralized control and management from shore station computer to all Junction Box nodes.The control system is composed of a host computer on the shore,lower machine systems in the Junction Boxes and other network devices,realizing remote communication via Industrial Ethernet protocols.As to hardware design of lower machine system,the PLC hardware modules are selected and configured;meanwhile peripheral circuits such as environmental state detection circuit,junction and protection circuit and grounding resistance detection circuit are designed.With collaborative work of PLC and the peripheral circuits,data acquisition in multi-point detection of leakage,temperature and humidity inside the Junction Box,isolated sampling and monitoring of load voltage and current,and ground resistance real-time online monitoring are achieved.Meanwhile the realization of load power connection both on the MV 375V and LV 48 V system and fault detection with high-speed response are also discussed in this thesis.As to the system software,a structured design approach in programming using both Ladder(LAD)and the Statement List(STL)is adopted in PLC system,and a monitoring and management HMI of Junction Box nodes based on WinCC is designed.With the combination of PLC software and HMI runtime,functions like monitoring,data acquisition and power management of the Junction Boxes,fault alarm,historical data storage and querying,remote browsing are implemented.After experimental joint commissioning and running tests,a secondary development of WinCC and the database is made to enrich the system features.In the research,some modular experiments for both the hardware and software in key aspects of this system,as well as the joint commissioning and running tests are conducted to verify the practicality and reliability of the PLC-based data acquisition and control system.Finally,a summary and outlook of the research is given in this thesis.