The Research On Underwater High Reliability Medium Voltage DC/DC Converter

With the continuous improvements of ocean observation equipments and technology,the undersea observatory has become a hotspot of current research and development because it can achieve all-weather,long-term,in-situ,continuous,real-time and high-precision observation of the ocean.The junction box power conversion system is the core component of the scientific node in the undersea observatory.As the key link of the junction box power conversion system,the underwater medium-voltage DC converter convert the MV or HV inputed by the undersea cable to ± 375 VDC and supply it to the secondary conjunction box,thereby providing multi-channel interfaces to various submarine loads.It mainly requires accurate voltage conversion,high reliability,high integration,and long lifespan in application.Compared with the United States,Japan,and other countries,China’s undersea observatory power supply project started late,and the underwater power conversion technology is still in the preliminary exploration stage.It is urgent to carry out research and device development work on underwater highly reliable medium voltage DC conversion.Furthermore,the existing undersea observatory power supply project still continues the technology of more than ten years ago,and it is difficult to make further breakthroughs in power expansion,reliability improvement and operation monitoring.With the development of new power devices and DC conversion topology at home and abroad,the research and development of a new generation of underwater highly reliable power conversion technology is rapidly advancing.Therefore,it is of great significance to carry out research on the MVDC of the conjunction box.Although some progress has been made in fault location and isolation of the undersea observatory at home and abroad,the fault handling and protection mechanism of the power supply system of the undersea observatory still cannot keep up with the development of the current undersea observatory,and urgent research is needed.The main research work is summarized as follows:(1)Compared with the traditional phase-shifted full-bridge DC/DC converter,the Vvoltage-fed Quasi-Z-Ssource Full-Bridge DC/DC Converter(VQZFB)is introduced due to the quasi-Z source impedance network has the characteristics of wide voltage regulation range,flexible control variances,and allows straight-through.It has advantages in underwater DC conversion applications.First,the working principle and operating characteristics of the voltage-fed quasi-Z source full-bridge DC/DC converter are analyzed.The universal ?-? modulation method of VQZFB is studied,and small signal model of VQZFB is established.Then the advantages and disadvantages of VQZFB and phase-shifted full-bridge converters are analyzed and compared in detail in terms of the voltage regulation range,DC voltage utilization rate,and so on;(2)Based on the voltage-fed quasi-Z-source full-bridge DC/DC converter,through the input series output and parallel combination,the VQZFB combined converter topology suitable for underwater MVDC conversion is proposed,and the reliable operation mechanism of the converter is analyzed,then a small signal model is established;Based on the analysis of the ISOP combined converter power balance constraints,a two-variances cooperative control method is proposed.By controlling the phase shift angle and the shoot through angle of VQZFB,the IVS & OCS of the converter are adjusted,thereby achieving Flexible and precise control of the VQZFB combined converter;the design basis of the main circuit parameters of the VQZFB combined converter is given;finally,simulation analysis and experimental verification are carried out;(3)This paper discusses the possible faults in the undersea oboservatory power supply system based on its networking mode,thus a top-down protection scheme for the undersea oboservatory power supply system is designed according to different equipment levels and fault types.The protection mechanism can judge and isolate the fault according to the fault location and type,so as to save the resources and protect the undersea oboservatory efficiently and reliably,and realize the high reliability and long-term economic benefits of the undersea oboservatory.