Modeling And Control Of Microgrid Based On Renewable Energy

Micro-grid is a small power distribution system can realize self control, protection and management, which is composed by distributed generations, energy storages, loads, the monitoring units and protector, etc. Micro-grid posses high flexibility, which can give full play to the value and efficiency of the distributed energy sources such as renewable energy and reduce the high permeability of the influence of the distributed power access to power grid. Micro-grid is the direction of the development of electric power system in the future. In the paper, a low voltage micro-grid system model which contains a variety of distributed power and energy storage is built by overall modeling several main distributed power generations and its grid converter, studied and analysis the operating characteristics of island and grid-connected modes based on master-slave control strategy.Comprehensive analysis of the research background and significance of micro-grid and its research status at home and abroad, the micro-grid operation control modes and the key problems of the research of micro-grid. Model of prime mover of fixed pitch permanent magnet direct-drive wind turbine which is based on constant tip speed ratio control is established. Then, Elaborated several common battery equivalent circuit and according to the working principle and structure of photovoltaic array, models of battery and photovoltaic are set up, which are validated by PSCAD and can well present the output characteristics of solar photovoltaic cells.According to the mathematical of the grid converter, the structure diagram of current inner loop controller is deduced, combined with outer power loop, which could realize the constant power control of the grid-connected system. According to the measured value of the ac bus frequency and voltage and droop characteristics, a kind of V/f control strategy based on droop characteristics is proposed, which can determine the output of active and reactive power and provide reference for current loop, finally realize the constant pressure constant voltage and frequency control. The control of the energy storage unit and the MPPT control of photovoltaic generation systems are studied in this paper. A variable universe fuzzy control algorithm for global MPPT based on multiple peak characteristic curve is proposed, which is based on the principle of interpolation of variable universe fuzzy control algorithm with photovoltaic maximum power tracking theory. The simulation results show that the proposed algorithm can quickly respond to the external environment changes, search the global optimal point accurately, has good dynamic characteristics and steady-state accuracy.Put the DGs into the low voltage power distribution system and form a micro-grid contains a variety of distributed power supply system. Respectively simulated micro-grid system to the external environment changes when the grid system steady state operation, the transient states between island and grid-connected operation and island mode, the results show that master-slave control strategy can effectively maintain a balance of power system and is enough to make the system voltage and frequency in micro-grid operation mode switch are quickly restored to the steady-state value, better meet the requirements of micro-grid operation, Verify the correctness and effectiveness of the control strategy.