This paper presents a hybrid modular dc solid state transformer (HMDCSST) composed of a series resonant-dual active bridge (SR-DAB) and a phase shift-dual active bridge (PS-DAB), aiming at improving the transfer efficiency as well as maintaining the control flexibility. The key problems in terms of modeling and control strategy are discussed in the paper. The generalized average and small signal models of the HMDCSST are derived and confirmed by simulation, in which two LC filters are also considered to reduce the ripple components of the input and output currents. Based on the models, the control strategies to achieve flexible control of the output voltage and power are designed. Moreover, as a key problem for HMDCSST, the design principle of the number for each type of DAB is discussed to meet the demands of the grid. Finally, a three-module prototype of HMDCSST consisting of one PS-DAB and two SR-DAB modules was built-up and tested, and the results proved that HMDCSST has higher efficiency than the traditional DCSST based on PS-DABs purely, without sacrificing the output voltage and power regulating capability in the meanwhile.
The key issue for the oil filter product sand operating status of the transformer oil filter, and in-depth research, based on the research and development of the transformer oil filtering device charged. Charged transformer oil filtering device structure includes an external oil circulation system, internal purification systems and automatic control and protection system of three parts. The device has also explained the conventional oil filter and oil filter charged two modes, when conventional oil filter modes election, workflow is identical with ordinary oil filter; If you choose to live oil filtering mode, you need to set the control variable range and start monitoring and adjustment, transformer oil filtering method has been put live field application, its efficiency and reliability of the actual verification.
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