The Control Optimization Strategy For Microgrid Considering Dynamic Characteristic

With the increasingly electric energy consumption and the seriously environmental crisis, the microgrid which use the flexible, reliable, environmental and economic renewable energy power generation has become a hot research issue all around the world, and greatly contribute to the future smart grid construction. Microgrid can operate in grid-connected and islanded operation mode, but it may cause small disturbance and lead to transient oscillation during the process of switching because of its low inertia feature. This paper researches the control strategies, dynamic performance and stability for microgrid in different operation mode, which has important theory and practical significance. The main research results are as follows:(1) From the control methods of distributed generation and control strategies for microgrid, this paper researched the basic principles and function of three typical control methods of distributed generation, as PQ, V/f and droop control. Build the separated model in MATLAB/Simulink platform to compare the output power changes of DG, and stability of voltage and frequency under different control methods. By contrast we find the droop control can applied between grid-connected and islanded mode flexibly, and easily realize the "plug and play" function of distributed generation and loads, which has gradually been in a hot research.(2) In order to improve the dynamic performance of microgrid, this paper adopted state-space linearization method to derive a complete small-signal state-space model of inverter. The presently researches ignored the influence of network and load characteristics, so this paper put forward a more accurate microgrid small-signal model and take the coupling effect between multi inverters into consideration. Through eigenvalue analysis of state matrix, we can obtain the main control parameters of inverters and their optimum ranges which are of great significance to the microgrid stability and dynamic performance. To prove the proposed model a microgrid based on droop control is built in MATLAB/Simulink, the simulation results demonstrate the effectiveness of the proposed small-signal model and root locus analysis, which can be the reference for smooth operation and parameter design of droop control in low voltage microgrids.(3) Finally, in view of the traditional centralized peer-to-peer operation of microgrid is difficult to achieve the dispatching plan of DG, this paper proposed a hierarchical coordinated control structure of microgrid based on droop control, to realize the coordinated control of different DGs, which has the theory and practical value to a certain extent.