Optimal Power Flow For A Micro-grid Considering Plug-in Electric Vehicles

In recent years, in order to cope with the dual pressures of environment and energy, it’s realized that the energy conservation for sustainable development has an important significance by governments. Relying on the characteristics such as eco-friendly, low-carbon, low noise, electric vehicles(EVs) is seen as an effective measures to reduce oil dependence and environmental pollution, control greenhouse gas emissions. With the increase of electric vehicles’ users, a large number of electric vehicles will charge in grid in the future. However, as the discrepancy of each electric vehicle user’s habits, it will make the start charging time and frequency has great randomness and unpredictability, and electric vehicles charging frequently have directly impact on power quality, it will increase the difficult to control power system optimal operation and new demands of operation and planning is proposed to the power system.However, electric vehicles charging in micro-grid instead of grid directly, which micro-grid is a single controllable independent power system as an interruptible load access to grid and consist of distributed generation, load, energy storage devices and control apparatus, the way will make electric vehicles greatly reduced direct impact on the power system to better serve the bulk grid and micro-grid. Therefore, how to make the micro-grid system more stable and economical operation becomes an important issue to be taken into account necessarily. This article will focus on optimal power flow for a micro-grid considering plug-in electric vehicles and obtain the optimal operation scheme of micro-grid which combines the economy, safety and power quality of micro-grid together perfectly by regarding electric vehicle as a mobile energy storage device with others distributed energy resources in micro-grid together to participate optimal dispatch. The research results can be applied to micro-grid energy management system, and will achieve real-time dynamic economic dispatch of distributed energy resources.Firstly, by analyzing the characteristics of the vehicles’ day trip chains, the probability distribution is used to fitting the daily driving distance and start charging time of electric vehicles, the Monte Carlo method is used to compute charging load.Secondly, it presents the corresponding mathematical model based on operating characteristics of each distributed energy resources, and then considering the economic and environmental benefits of micro-grid, created a mathematical model of optimal power flow for micro-grid based on spot power prices, and solved by aimproved particle swarm algorithm(PSO) based on Newton-Raphson optimal power flow method. Finally, the program of improved PSO optimal power flow algorithm is developed in Matlab environment. Through analyzing the economy of an area under different conditions, the correctness and validity of the method is proven. The results show that the electric vehicles involved in optimal dispatch can effectively avoid the "peak plus peak" phenomenon, increase economic efficiency and environmental benefits of micro-grid operation.