1.Introduction

Micro-grid is known as a set of loads and energy distributed generation resources which located in small-scale areas and in low voltage levels. Regarding the connection of these small networks to the main grid, they can be operated either separately or cooperatively [1-4]. The use of these networks leads to providing energy in small areas. Main characteristic of the small networks includes multiple connected loads, various energy resources, the capability of connection or disconnection to the network, the ability to control power production, power consumption in the small networks and levels of energy storage systems usage. Small networks can be used as a combination of power production units, such as photovoltaic, wind, diesel generator with storage systems. These grids convey power from manufacturers to consumers by using two-way-transmitting pass that leads to energy efficiency increase [5, 6]. According to changes of generated power and load in micro-grids, frequency control is one of the most important issues, which emphasizes the coordination of generated power and load consuming. One of the ways in frequency controlling is using the output of diesel generator that can control generated power variations in other units such as photovoltaic systems [7, 8]. Due to the high expenses in construction of transmission lines in remote areas, it is not economically affordable. Furthermore, concerning the potential of renewable energy resources like photovoltaic and wind in these areas, it is possible to use the distributed power generation units which depend on the meteorological conditions of wind speed, temperature and solar irradiance [9, 10]. Technical characteristics of a micro-grid, makes it appropriate for power supplying for remote rural areas. By designing a local small unit, it is possible to provide power of a small residential area with high reliability and security using strict monitoring and control [11, 12]. For optimum operation of system, VPP requires the same information to define the amount of produced energy by wind or photovoltaic resource, fuel cell and battery charge-discharge storage, considering the following observations:
-Wind power generation is strongly dependent on weather and production capacity for a period of 24 hours can be estimated exactly.
-Photovoltaic power production is also predictable.
-Fuel cell output for a long period is limited, but total produced energy is determined according to the amount of hydrogen fuel.
-Discharge of the storage system depends on the maximum discharge capacity and the amount of the available stored energy.