Stability Research For DC Micro-grid Based On The Load Cutting And Output Change

Under the multiple pressures of the environmental protection, energy crisis and the economic development, micro-grid technology attracts considerable attention from all walks of life. Since the AC power transmission and distribution technology is relatively mature, AC micro-grid technology gets rapid development. However, with the wide application of DC micro source and DC load, the DC micro-grid has shown a huge advantage in the aspects of improving the power transform efficiency, reducing power transform links, lowering the power loss,improving power quality and so on.The DC micro-grid is a large dynamic system, and the energy balance of the system is easily influenced by the outside dynamic factors, such as changing of the micro power output or the load, system failures and so on. Meanwhile, each module of the DC micro-grid connects in the DC bus through converters, so there is a mutual influence between the converters, what aggravates the system coupling degree and the difficulty of control system. Furthermore, stable operation of the DC micro-grid is under the threat of the above-mentioned dynamic factors and interaction. But so far, there is less study on stability for DC micro-grid by international and domestic academics, and some module of the DC micro-grid is put as research object in the most of currently researches, with no detailed analysis aiming at the energy flow state at the time of instability. According to the above problem, the entire DC micro-grid was treated as the research object. Through theoretical analysis and simulation, this paper studied the influence of load changing and micro power output changing to the system stability. The details are as follows:(1) The DC micro-grid simulation platform is established. The paper analyzed photovoltaic power generation system, battery energy storage system, the equivalent model of the distribution network as well as line impedance, mathematical model of which is set up. The simulation model of the DC micro-grid is established based on MATLAB/Simulink platform, what lays the foundation of follow-up study.(2) Considering the dynamic characteristics of micro-grid and the mutual influence between the converters, coordinated control strategy and five working modes is put forward. Based on MATLAB/Simulink platform, simulation was carried out about the typical operating modes, andproved the correctness and rationality of the coordinated control strategy and five kinds of operating modes.(3) The paper has researched how load changing influenced the stability of the DC micro-grid. In the first place, an example was given about the loss of system stability when the load was put into suddenly. Afterwards, this article come to the table operation condition and the stability criterion by the theory analysis, and in the end studied the influence about the outside conditions and system parameters to the system stability domain.(4) In a similar way, the phenomenon about DC micro-grid losing stability when micro power output changed was studied, that can provide a reference for the choice and coordination of the DC micro-grid parameters.