| With the increased prominence of environmental issues and the electricity demand growing, wind power, photovoltaic and other distributed power generations, which is less investment, flexible and environment-friendly, have been got great attention. However, due to the influence of wind speed, light intensity, temperature and other natural conditions, a large number of distributed generators connected to the grid produce many adverse effects to the stable operation of power system and power quality. In order to make use of DG more rationally and efficiently, the scholars have put forward the concept of the microgrid. Micro-grid connects to the grid through a common connection point, and adopts coordinated control strategy. The micro-grid can operation in grid-connected mode, when the grid happens a fault, the microgrid can disconnect from the grid and switch to islanded mode for continue operation and supply electricity to the users.This paper studies the converter control strategies, and uses different control strategies for different type of DGs。A AC microgrid simulation model, which is consist of wind power generation, photovoltaic system and battery, is built through MATLAB/Simulink software. The microgrid operation condition in two modes and its switching progress is simulated and analyzed to verify the feasibility of the control strategies. The power flow between microgrid and big grid is analyzed when the DG output power changes. And the role of the battery energy storage system in islanded mode and grid-connected mode is also studied.The details are as follows:(1) The basic components and principles of three DGs, photovoltaic power generation system, wind power generation system and battery energy storage device, are analyzed. Especially, the bidirectional DC/DC converter and its control strategy, which are used in the battery energy storage device, are illustrated. The simulation model of the three DGs is established in the MATLAB/Simulink software and operates them respectively. The results show that, the photovoltaic system and wind power generation system output voltage waveform quality is good and when the external environment condition changes, they can achieve maximum power tracking. Battery energy storage device can keep the DC voltage constant, so it is suitable to be a micro-grid energy storage device to study the operating characteristics of the microgrid.(2)Base on the topology of the DG inverter, this paper analyzed the PQ and V/f control strategy that used in the voltage source inverter. Their control systems are designed and the control model is built and operated, the result verified the feasibility and effectiveness of the control strategy.(3) A wind-PV-battery AC microgrid simulation model is built. In this system, different control strategies are used in different type of DGs. The battery energy storage device uses the V/f control strategy in order to maintain the voltage and frequency stability of the microgrid in islanded mode, wind power units and photovoltaic power generation unit use PQ control strategy to obtain maximum utilization of renewable energy. Through studding the simulation cases of microgrid operation situation in grid-connected mode and islanded mode and the switching progress between two modes. The simulation results show that the microgrid which uses the proposed control strategy can operate stably.(4) the feasibility of using multi-agent system in the micro-grid is analyzed, and energy management system based on MAS technology is studied when the microgrid operate in islanded mode. The coordinate control strategy among DGs is also considered, which could save the battery energy, and reduces the power consumption of the battery during operation. So the battery can reserve sufficient energy to deal with the unexpected events in the subsequent. This can not only maintain the reliability of the microgrid, but also helps help to extend the battery life. |
PDF Full Text Request