Research On Voltage Stability Control Method Of DC Micro-grid Based On Ultracapacitor

DC micro-grid is a kind of power network in order to adapt to the rapid development of distributed generation technology, which has more advantages compared with the AC micro-grid. In a DC micro-grid, power generation equipment is usually a new energy power supply represented by photovoltaic which generally has the characteristics of randomness and volatility. Ultracapacitor with high power density, long life and other characteristics, accessed in the DC micro-grid can not only stabilize the generation and load fluctuation, but also maintain voltage quality of the system at a normal level.Firstly, the paper introduces the structure of the DC micro-grid with both ends of the supply, and analyzes the model of the PV array,the ultracapacitor and the bidirectional DC/DC converter whose parameters are determined. The main energy management strategy and the four operating modes are also formulated,.Secondly, as for the realization of MPPT, the incremental conductance method is used to seek the voltage corresponding to the maximum power point, and PI control method is used to track this voltage; and a double loop PI control method is adopted for the rectifier. In view of the ultracapacitor energy storage system's linear controller, based on the traditional small signal model, the PI control system of bidirectional DC/DC converter working in Boost and Buck modes are designed.Then, according to the bidirectional DC/DC converter's Boost mode, the paper analyzes the principles of variable structure sliding mode control based on exponential reaching-law, for the Buck mode, does the principles of variable structure sliding mode control based on hysteresis adjustment, and two double loop sliding mode variable structure controllers combined with PI control are proposed. In addition, the principle of the location of ultracapacitor energy storage system and its influence to the system voltage quality are also discussed.In the end, the structure of the DC micro-grid with both ends of the supply is made in the MATLAB/Simulink environment, and the simulations of these two kinds of control methods are carried out, and the simulation results are compared, which show that the sliding mode variable structure control method has a better effect on anti- jamming and dynamic performance than PI control, and is more suitable for the DC micro grid system. At the same time, it also makes a simulation verification of the position of the ultracapacitor, which shows the correctness of the layout principle and has the guiding significance to the actual arrangement of the ultracapacitor.