Research On The Key Technologies Of Power Junction For Cabled Ocean Observatories System Based On Tree Topology

Long-term, continuous, real-time and in situ observation is becoming an urgent requirement of many scientists. While the traditional ocean observation approaches which are mostly through ship based cruise, underwater robotics and off-line equipments are unable to satisfy the increasingly requirements, cabled ocean observatories system that enables large amount of power and broad bandwidth to seafloor becomes an innovation approach. During the last decade, cabled ocean observatories systems have been or being developed in north American, Europe and Japan, but it is almost a vacant field in China, which will dramatically restrict the domestic ocean science research, so developing cabled ocean observatories system will have great scientific significance and broad application prospect. In this thesis, some key technologies and difficulties faced in building cabled system such as power structure and method, power conversion and distribution, heat dissipation, fault detection and isolation, reliability analysis are discussed, respectively.Power structure and method for cabled ocean observatories system affect the structure design of the observation node. The observation requirements and environments are discussed, as well as the technique, power requirements, cost for deployment and maintenance. Negative high voltage, direct current, monopole and single line are adopted for power delivery, and tree topology power structure is used. The power system stability analysis starts from the scenario of a single node structure with long-cable. Results show that the parasitical inductance, capacitance and resistance of the cable impact the maximum power capacity and dynamical stability. The analysis method for multi-node system is also simply introduced.According to the application requirements of the primary Junction Box (JBox), module stacking method based on common duty ratio control strategy is introduced to build its power conversion system. Voltage and current sharing characteristics of three topologies, including input series output series (ISOS), input series output parallel (ISOP) by paralleling capacitors and ISOP by sharing output filters, are theoretically analyzed based on common duty ratio control strategy, as well as the impact factors are discussed together. Basic tests are carried out to validate the analysis. Two prototypes with one is2kV@2kW converter and the other is10k V@10kW are realized based on the three introduced topologies. At the same time, according to the heat dissipation mechanism of the power conversion system, filling oil in vessel and fixing pressure-release facility are introduced to cool the power conversion system. Experiments validates that the methods for building the conversion system are applicable, as well as the heat dissipation method.Secondary JBox is the key facility of secondary node for cabled observatories system and the low voltage power conversion and distribution is the heart of its power system. As it is the terminal junction facility, its design should concern users’ requirements and features and require strong reliability against faults. An isolated modular power system is presented after analyzing the merit and demerit of three traditional DC power distribution systems and a prototype are realized. Moreover, dissipating heat via the arc wall of pressure vessel is introduced for its heat dissipation, and an adaptable outer profile structure for it is designed.For poor maintainable of underwater power system, reliability is an important performance index. According to the power tree topology for cabled system, its basic reliability, task reliability and fault tree analysis are discussed based on the theory of reliability block diagram (RBD) and fault tree analysis (FTA). The corresponding models of single node system are built as well. Moreover, a simply simulative method based on fault tree model is presented and used on the topology selection of the low voltage power conversion system. To enhance the reliability of this power system, technologies on fault detection and isolation against cable delivery faults and power faults of JBox are studied, respectively. Due to the deficiency of communication, different voltage levels and polar are used to transmit commands when faults occur at power cable. Corresponding circuits for cable fault detecting and isolating are designed and simply validated. As for the faults occur at JBox, the potential faults are discussed, and corresponding methods are introduced and applied on the JBox prototype.Finally, according to the mentioned theories and technologies, two different cabled observatories system prototypes based on2kV and10kV powered methods were built, and they were tested in tank in laboratory, in shallow water in East China Sea and in deep water in USA. The laboratory tests validated the introduced technologies on power delivery, power conversion, heat dissipation, fault detection and isolation at JBox were feasible. The shallow water experiments validated that the corresponding technologies were able to use in real sea. The successful operation of connecting the prototype to MARS in USA validated the corresponding technologies satisfied the requirements of building a cabled network underwater and also validated its long-term operative reliability.The successful development and sea trails show that the discussed technologies such as power structure, power conversion, heat dissipation, fault detection and isolation have good practicability and reliability. The study achievements can provide theoretical and technical basis for further research in building the practical cabled ocean observatories system.