Distributed Operation Control Strategy Of Converters In DC Micro-grid

With the extensive application of renewable energy, DC micro-grid has attracted more and more attention with its advantages of lower cost and improved efficiency. To ensure the reasonable load distribution and maintain the stability of the DC voltage are the two main control objectives of DC micro-grid. In order to achieve the above two objectives, the coordination control of multiple micro sources is needed. The real time coordinated operation control scheme of the DC micro-grid, typically adopts the Master slave control centralized control, the point-to-point control and hierarchical control. However, there are some defects in these three methods. The Master-slave control method has great dependence on the main controller. The point-to-point control method(the droop control), the traditional droop control method is easily influenced by the line impedance. The load distribution is unable to satisfy the power and voltage requirements. The hierarchical control method, the distributed power and the upper controller need communication line, once the communication failure, micro grid will not be a normal work, reducing the system reliability. It is necessary to find out a high reliability, lower influence by the line impedance, greater extensibility coordinated control strategy of the multiple converters. In this paper, based on the analysis of the current coordination control method of the micro grid converter, the main work and the main research results are as follows.(1) The topological structure and control method of DC/DC converter, AC/DC converter are introduced, and the related models description are also given.(2) The related basic concepts of graph theory and matrix theory are introduced.Some existing research work and important lemma in the distribution control field are given.(3) In the case of multi power-multi load DC micro-grid system, the effect of line impedance on load distribution and DC voltage is derived when the traditional droop control is used. On the basis of this, a distributed control method for DC micro-grid is proposed. The proposed control method, overcoming the defects of the traditional droop control, can ensure the reasonable distribution of load between converters and maintain the average voltage of equal to the rated value. Comparing the master-slave control method, the central controller is replaced by multi slave controllers. Because there is no central controller, the reliability of the system and the ability of adjustment system are increased. Comparing the hierarchical control method, the proposed control method adapts bidirectional ring network which can maintain converter of plug and play and expansion of DC micro grid isstrengthened.(4)Finally, with an actual multi power-multi load DC micro-grid system, the validity and effectiveness of the proposed strategy is verified by the MATLAB simulation results.