Study On Underwater Junction Box Prototype System Technology Of Seafloor Observatory Network

Underwater junction technology of seafloor observatory network has become the forefront subject of the ocean science and technology. Underwater junction technology connects several seafloor observation instruments underwater, and implements centralize control and management for electric energy and information of various seafloor observation instruments. Junction box is a kind of equipment which applies underwater junction technology to control and manage electric energy and information. Conventional ocean observation technology is restricted by long-term electric energy supply and realtime information transmission. Seafloor observatory network based on underwater junction technology provides continuous electric energy supply and realtime high-bandwidth data transfer, and implements long-term continuous realtime in-situ observation for seafloor.This dissertation is supported by the Second Stage of the National985Project for the Mechatronic System Innovation Platform of Zhejiang University (Project title: Seafloor Observatory Network Test Platform). By means of theoretical analysis and experimental test, underwater junction box prototype system technology of seafloor observatory network is studied in this dissertation, and the Zhejiang University Experimental Research Observatory (ZERO) system has been built basically. The main contributions of this work are as follows:1. A modularization framework of junction box prototype system is proposed. Three waterproof pressure-resistant housings including communication control housing, high voltage converter housing and low voltage converter housing, were chosen as mechanical and electronic integration encapsulation structure of the junction box prototype system. Intensity design calculation and stability verifying for the pressure-resistant housing of junction box were fulfilled based on the first intensity theory. ANSYS software was chosen to complete simulation analysis for the pressure-resistant housing and end cap. Accordingly, the junction box can work reliably in the deepsea high-pressure environment. Two O ring were used to implement reliable axial seal. A method combining oil-filled housing heat dissipation and end cap heat dissipation was chosen to assure steady work of the junction box system.2. A sort of system architecture of seafloor observatory network was presented, which is composed of the control center layer, the backbone network layer, and the subnet layer. Referring to OSI/RM model, a kind of communication protocol layered model based on TCP/IP of the backbone network was designed. Considering the real-time request of the information transmission, the optic Ethernet technology based on TCP/IP, the Modbus protocol, the RS485protocol, and the application layer user-defined protocol were chosen to implement data collection and corresponding communication control for seafloor observatory network. Combinatorial timing method including the SNTP server timing and the command frame timing were chosen to implement accurate system time synchronism.3. Based on comparative analysis of direct current and alternating current high-voltage power transmission, metal conductor loop mode was chosen for high-voltage direct current power transmission of ZERO system. PWM control, two-transistor forward conversion, and input-side voltage sharing output-side current sharing of input-series output-parallel (ISOP) combinatorial system were analyzed. By arraying power MOSFET parts in series on the input-side and in parallel on the output-side, a new method based on PWM current feedback control and two-transistor forward circuit was proposed to transform2kV high-voltage DC to400V middle-voltage DC for the2kV/400V DC/DC converter of junction box.4. The electric power management system based on single chip processor MSP430F149of junction box was designed. Hall electric current sensor was chosen to measure electric current for seafloor observation instruments. Resistance voltage divider was chosen to measure electric voltage. Thermal resistor was chosen to measure internal temperature of junction box. By remote on-off control of the relay, the electric energy distribution control was implemented for seafloor observation instruments.5. High-pressure chamber and pool experiments for ZERO junction box system were performed in the laboratory, and the experiments results manifest that the underwater junction box prototype system can be used in the high-pressure seafloor environment. Accordingly, the underwater junction technology developed is effective and reliable.It's certain that the results of present research provide important theoretical research basis and key technology support for the building of Chinese practical seafloor observatory network. The underwater junction box prototype system has the advantage that it can also be used in applications such as marine environmental monitoring, tsunami disaster monitoring, seafloor resource exploration.