A Dual Buck-Boost AC/DC Converter for DC Nano–Grid with Three Terminal Outputs
Abstract
Due to the widely used DC characterized loads and more distributed power generation sources, the DC Nano-grid becomes more and more popular and it is seen as an alternative to the AC-grid. For safety considerations, the DC Nano-grid should provide reliable grounding for the residential loads like the low voltage AC power system. There are three typical grounding configurations for a DC Nano-grid, including the united grounding, the unidirectional grounding and the virtual isolated grounding. Each grounding configuration has its own specifications to AC/DC converters. In this letter, a dual Buck-Boost AC/DC converter for use in the united grounding configuration based DC Nano-grid with three terminal outputs is proposed. The working principle of this converter is presented in details through analyzing the equivalent circuits. Experiments are carried out to verify the theoretical analysis.
EXISTING SYSTEM:
Recently, research on DC Nano-grid gets of more and more concern , especially for the control of AC/DC topologies, which are the connections between the DC Nano-grid and the traditional AC power system. It should be pointed out , when designing the AC/ DC convert for DC Nano-grids, the grounding configuration needs to be addressed, since it determines the costs, the flexibility of the installation and also the efficiency of DC Nano-grid system. his letter analyzes first three grounding configurations of the DC Nano-grid. Then, a dual Buck-Boost AC/DC converter is proposed, which will facilitate the applications of the DC Nano-grid with three terminal outputs. Also, theoretical analysis of the proposed converter will be given as well as experimental verifications are carried out. Finally, conclusions are drawn.
PROPOSED SYSTEM:
Traditionally, the DC Nano-grid is connected into the AC power system with bi-directional AC-DC converters, which allows extra DC power to be injected back into the AC power system. In some areas, due to the high population density, the distributed power can generally not meet the demand of the local loads, so the connection between the AC power system and the DC Nano-grid can be simplified to be a power factor correction circuit. In, AC/DC converters were reviewed and compared. However, suitable AC/DC converters for the united grounding configuration based DC Nano-grid application were not introduced. In this paper, a new AC/DC converter is proposed The advantage of the united grounding configuration is that the DC Nano-grid can easily be installed into the original low voltage AC power grid to form a hybrid power system. The disadvantage is that due to the low voltage devices, most of the original low voltage AC power systems cannot adopt this configuration and share the same ground line directly with a DC Nano-grid, if no special or complicated AC/DC converters are adopted. At the same time, the DC Nano-grid has to adopt a bipolar voltage structure with three terminal outputs.
CONCLUSIONS
In residential applications, the DC Nano-grid should provide ground line for safety. The grounding configuration determines the different requirements on the AC/DC converters. In this letter, three types of the grounding configurations for the DC Nano-grid are summarized. It can be concluded, 1. The united grounding configuration is the most attractive since the DC Nano-grid can be directly connected with the low AC power system using the same ground line, which will strongly address the high efficiency character of the DC Nano-grid. This grounding configuration makes it easy to construct a DC Nano-grid based on the original low voltage AC power system and contributes to the application of the DC Nano-grid. However, suitable AC/DC converters are currently lacking of this grounding configuration. 2. The unidirectional grounding configuration is widely introduced in current DC Nano-grids. It is suitable for construction a new DC Nano-grid alone. 3. Compared with the united and unidirectional grounding configurations, the flexibility of the virtual isolated grounding configuration is good, but it results in reduced efficiency, more materials, and thereby higher costs. Based on the analysis on the grounding, a dual Buck-Boost AC/DC converter is proposed for the united grounding configuration based DC Nano-grid. The principle of the proposed converter is illustrated using equivalent circuits. Experiments are in good agreement with the theoretical analysis. The proposed AC/DC converter will help to exploit the application of the DC Nano-grid with three terminal outputs. ACKNOWLEDGMENT This work was partially supported by the Project of Shanghai Pujiang Program under Award 14PJ1404200, the Shuguang Project of Shanghai Municipal Education Commission under Award 14SG43, and the Project of National Science foundation of China (NSFC) under awards 51577114 and 51561165013
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