Design and Implementation of a Control Strategy for Microgrid Containing Renewable Energy Generations and Electric Vehicles

Hindawi Publishing Corporation Mathematical Problems in Engineering Volume 2013, Article ID 686508, 15 pages http://dx.doi.org/10.1155/2013/686508 Research Article Design and Implementation of a Control Strategy for Microgrid Containing Renewable Energy Generations and Electric Vehicles Mingchao Xia, Xuanhu He, and Xiaoqing Zhang School of Electrical Engineering, Beijing Jiaotong University, No. 3 Shang Yuan Cun, Hai Dian District, Beijing 100044, China Correspondence should be addressed to Mingchao Xia; Received 13 December 2012; Accepted 12 May 2013 Academic Editor: Massimo Scalia Copyright © 2013 Mingchao Xia et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Large amount of such renewable energy generations as wind/photovoltaic generations directly connected to grid acting as distributed generations will cause control, protection, security, and safety problems. Microgrid, which has advantages in usage and control of distributed generations, is a promising approach to coordinate the conflict between distributed generations and the grid. Regarded as mobile power storages, batteries of electric vehicles can depress the fluctuation of power through the point of common coupling of microgrid. This paper presents a control strategy for microgrid containing renewable energy generations and electric vehicles. The control strategy uses current control for renewable energy generations under parallel-to-grid mode, and uses master-slave control under islanding mode. Simulations and laboratory experiments prove that the control strategy works well for microgrid containing renewable energy generations and electric vehicles and provides maximum power output of renewable energy and a stable and sustainable running under islanding mode. 1. Introduction As long as the growing demands for green, clean, and highquality energy supplies, renewable energy generations such as solar and wind power acting as distributed generations (DGs) are gaining more and more attentions. Discussions about grid of the future on 2012 International Council on Large Electric Systems (CIGRE2012) pointed that new technologies, new participants, and new market environments are leading the traditional value chain of “fossil energy sourcegrid transmission end user” to a new value chain adopting renewable energy generations and distributed generations, power storages, and electric vehicles (EVs) [1]. To some extent, DGs can improve power quality, power reliability, economy, and flexibility along with impacts to grid caused by its fluctuant power output. The key factor of using DGs lies on how to coordinate DGs with main grid to stable and reliable running. Concept of microgrid or minigrid—a small grid that integrates DGs and loads to form a controllable grid which can provide power supply both under parallel-to-grid and islanding mode—was proposed and adopted by many countries and power companies. Control strategies of microgrid containing control of grid and control of DGs must coordinate DGs with main grid under parallel-to-grid mode and coordinate different DGs with loads under islanding mode. Commonly used control methods of microgrid include peel-to-peel control, masterslave control, and multiagent control, while control methods of DGs include current control method, voltage control method, and droop control method. The main concern of control method under parallel-to-grid mode is how to depress the fluctuations of power outputs of DGs while using the maximum amount of DG energy such as wind power or solar power. The main concern of control method under islanding mode is how to coordinate power outputs of different DGs with loads to keep stable voltage and frequency level for constant running. Electric vehicles regarded as a new traffic method have been paid more common attention. While commonly treated as loads, batteries of electric vehicles can provide power support when necessary—which is called vehicle-to-grid (V2G) mode [2]. V2G mode of electric vehicles can reduce the need of common power storages in microgrid by depressing fluctuation of power and providing emergency power supply. 2 Compared with common battery storage, batteries of electric vehicles can be regarded as mobile power storage devices: mobility of vehicles cause the capacity change of charging and discharging along with the unpredictability of charging or discharging status; transport demand, charging methods (charge/replace), and charging speed (fast/slow) of vehicles cause differences in control and external characteristics. To coordinate DGs and grid, considering the instability and unpredictability of DGs and EVs, a control strategy for microgrid containing renewable energy generations and electric vehicles was presented in this paper. Control methods of microgrid were analyzed and studied to propose a comprehensive control strategy for microgrid with DGs and EVs. The control strategy uses MPPT current control for renewable energy generations under parallel-to-grid mode and uses master-slave control which elects battery storages as master while other DGs and EVs as slaves under islanding mode. A common structure microgrid with DGs, battery storage, and EVs was built both in simulation and laboratory experiment. Simulations and laboratory experiments prove that the control strategy works well for microgrid containing renewable energy and EVs and provides maximum power output of renewable energy and a stable and sustainable running under islanding mode. 2. Distributed Generations and Microgrid Generally, distributed generations (DGs) refer to such environment friendly or renewable power generation devices as photovoltaic, wind power, fuel cells or microgas turbine which are located near loads and capacity of tens of kilowatts to several megawatts. DGs can improve power quality and power reliability with the following characteristics [3]. (1) Power Generation near loads without step-up and stepdown transformer and load distance transmission will reduce construction and maintenance cost, reduce power loss of transmission and improve efficiency. (2) Immune to faults in transmission, and transformation system which will improve power reliability and power quality. (3) Immune to the interferes of regional voltage and frequency fluctuations, preventing regional failure develop to blackouts. Commonly adopted DGs are microgas turbine, fuel cell, wind power, photovoltaic, and power storage devices. Microgas turbine burns gas, methane, or gasoline with total efficiency up to 75% under thermoelectricity cogeneration mode which is a promising commercial DG [4]. Fuel cell transforms the fuel chemical energy into the electrical energy through the electrode reaction with little emission, which has higher efficiency than traditional power plant [5]. Nevertheless, gas turbine a (...truncated)