| With the development of economy, fuel and environment crisis become increasingly outstanding. More and more attention has been paid for renewable energy which could be the substitute of fossil energy. Microgrid is a kind of efficient organization forms because of its ability to integrate distributed generation, loads and energy storage. It could operate stable when connected with utility grid. So the study of microgrid has very important academic value and realistic meaning. With the development DC distributed generation (such as solar cells, fuel cells, wind turbines, etc) and DC load in microgrid, and DC power transmission for commercial, industrial and resident DC load has a unique advantage, so the DC microgrid gradually getting people’s attention in recent years.This paper studies the control scheme of bidirectional DC/DC converter of energy storage system in DC microgrid. A hierarchical control strategy for energy storage system in DC microgrid is proposed. A control system of automatic charging/discharging of energy storage system is designed. Finally, the analysis is verified by MATLAB and dSPACE. The details are as follows:(1) This paper introduces the development of DC microgrid, and the configuration of laboratory-scale DC microgrid is presented. The operating characteristics of two different modes of DC microgrid are analyzed, the model and controller of PV module and battery are designed. Based on the mathematical model of PV module and battery, the control circuit of DC/DC boost converter and battery bi-directional DC/DC converter are designed respectively.(2) This paper proposed a hierarchical control strategy for reliable and effective operations of a standalone DC microgrid. The features of proposed hierarchical controlled DC microgrid can be summarized as:1) maximal usage of renewable energy and reliability enhancement is achieved by HLI control;2) real-time voltage regulation capability for power modules and prioritizations for charging/discharging of the BESS with different SOCs are considered in HLⅡ control;3) emergency conditions are managed by the HLⅢ control.(3) Based on proposed hierarchical control strategy for energy storage system in DC microgrid, a control scheme of bidirectional DC/DC converter and an automatic charging/discharging energy storage system are designed. According to the range, where the DC bus voltage belongs to, the operating mode of the energy storage system can be automatically judged and the switching over among operating modes can be automatically performed as occasion requires, thus the energy storage system can be freely switched among charging, discharge and idle modes, and the damage of the battery caused by the frequent switching over between charging and discharging modes due to ordinary fluctuation of DC bus voltage can be avoided.(4) The model for control system and main circuit of bidirectional DC/DC converter of single battery energy storage system are built in Matlab/Simulink and different cases in charging mode and discharging mode are simulated analyzed. The feasibility of the proposed control strategy is valid by results of experiments.(5) Experimental platform of bidirectional DC/DC converter based on dSPACE is built. The signal acquisition circuit, driving circuit and software protection module are designed. Real-time control is realized in the Control Desk. The experimental results show that, DC voltage can be maintained stable when converter operates in different modes, and bidirectional power flow smoothly is achieved. |
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