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In this paper, modeling and decentralize control principles of a MicroGrid (MG) whom equipped with three Distributed Generation (DG) systems (consist of: Solar Cell System (SCS), MicroTurbine System (MTS) and Wind Energy Conversion System (WECS)) is simulated. Three arrangement of load changing have investigated for the system. In first one the system doesn’t have transfer of power between MG and grid. In other two arrangements system have transfer of power between MG and utility grid. Of course in third case transfer of power between DG resources is considerable. Case study system is equipped by energy storage devices (battery bank) for each DG’s separately by means of increasing the MG reliability. For WECS and SCS, MPPT control and for MTS, voltage and frequency (V&F) controller has designed. The purpose of this paper is load respond in MG and storage process of surplus energy by consider of load changing. MATLAB/Simulink and its libraries (mainly the Sim Power Systems toolbox) were employed in order to develop a simulation platform suitable for identifying MG control requirements. This paper reported a control and op- eration of MG in network tension by applying a three phase fault.

Microgrid concept widely developed in countries such as USA, Canada, Japan and UK. It has been investigated and implemented [1,2]. The increase in researches due to benefits of this type of networks including provide the reliability and security of network and loads, high efficiency, environmentally friendly and self-healing [

Basic structure of a typical MG is shown and discussed in [

Here is assumed that distributed generation sources have the ability to respond the loads. After disappearing network fault, synchronization operation performed and isolated network connected to Utility Power Source again [

In reference [

Note that the decentralized control means that on each DG resources has been an independent controller and each of this resources performed control operations independently. May be the type of applied controller is different and even similar. Fault events that may lead to islanding of a distribution system are discussed in [

In

1) Input-Side Controller: which should be possible to take the maximum power from the input source. Naturally, the protection of input side converter must be in considered.

2) Grid-Side Controller: that can follow these tasks: a) Input active power control derived for network; b) Control of the reactive power transferred between network and micro-grid; c) DC link voltage control; d) Synchronization of network; e) Assurance of power quality injected to the network. Generally the network controller position is VSI, which both amplitude and phase of the output voltage are controlled. All items listed above are the basic features for the grid-side controller that these converters should have. Studied network in this paper consists of two distributed generation sources, which is briefly explains their structure.

3) Microgrids Internal Structure: According to given system studied in this article is including distribution generating resources of PV and MT. The structure of this two system and their relevant controlling parts are shown below. It is noteworthy that PV and Fuel Cell (FC) systems have similar hardware structures [10,11].

3.1) Photovoltaic and FC systems: As previously noted the PV and FC hardware structure is similar. Although voltage or current by FC and PV is low, but by binding a set of them together can increase the production levels and also can increase or decrease the voltage level by using DC-DC converters such as boost converter for increasing the voltage level.

Non-linear relationship between obtain from the below equation [

Which in it is short circuit current, is reverse saturation current, is series resistance and is constant factor which is depends on the type of materials used in cell.

In this paper a silicon solar panel, () has been used. Sample model is constructed by Iranian Optical Fiber Fabrication Company (OFFC) that related table of its coefficients and parameters comes to

According to related values Equation (1) is written as follows:

Non-linear characteristics of and are shown in

By changing temperature, the coefficients will changes [

For displaying MPPT technique in we act the way [

This equation shows MPPT technique which in it called voltage factor that for OFFC its value considered 0.71. This method for maximum power estimating is simple and fast.

Equivalent circuit to cell block shown in

For VMPPT its related equivalent circuit shown in

Now we want to see the performance of this system in

connected to the grid-connected mode and with applying a controller in AC part according to what is seen in

Vector control in a rotating reference frame with the line voltage vector is used. The purpose in this controller is regulation of DC voltage and reactive power control. Using the Park conversions, voltage equations can be controlled to reference frame d-q. The idea of control is taken from [

is active part of current and is reactive section on current. In order to obtain a transformation from active power, the value of current reference (reactive part) considered as zero. PLL used in figure is to synchronize converter frequency with main grid. It is assumed that the harmonics produced by switching is zero.

Recently microturbines have been much attention because of their small size, relative low cost, repair and cheap maintenance and relatively simple control. Different dynamic models have been discussed for micro-turbines by Rowen, Hannet, Saha and Nern for combustion gas turbine [15-17]. In 1993 mathematical method of gas turbine by Rowen was developed [

acceleration control block, fuel system control and temperature control. Single-shaft turbine model is considered. Power producer with a Permanent Magnet Synchronous Generator (PMSG) has two poles and smooth poles rotor. Because of high speed shaft, generators of an AC voltage source will be a high frequency (frequency angular higher than 100,000 rad/sec) [

1) Module 1: mechanical system of turbine and fuel.

2) Module 2: PMSG and AC/DC rectifier and energy storage devices.

3) Module 3: AC/DC voltage source inverter, PWM controller.

Mechanical Model and MT Control Functions:

Based on Rowen and Hannet model, we examine the MT model. Dynamic equations of MTS in [

According to the principle of energy conversion and ignore the inverter losses, total of instantaneous powers in output of AC terminal must be equal to the instant powers in dc terminal like.

Which and are dc link voltage and current.

VSI simplified model shows in

Diagram block of V&F controlling model presented in

Now MT model of distributed generation in gridconnected mode is shown in

LCL Filters in this paper is designed by the idea in [21,22].

Conceptual and technical solution of MG is presented in [23,24].

Electrical wind generators are the equipment who converts wind to electrical energy. Different types of generators are used in wind turbines. For example small sized wind turbines are equipped by DC generators with capacity up to 90 kw (from 10 to 90).

In wind turbines modern systems three phase AC generators are customs [

General kind of AC generators who are used in modern wind turbines are:

1) Squirrel Cage Induction Generator (SCIG)

2) Wired Rotor Induction Generator (WRIG)

3) DoubleFed Induction Generator (DFIG)

4) Synchronous Generators with output excitation (SG)

5) Permanent Magnet Synchronous Generator (PMSG)

Synchronous Generator is a kind of generators who are used in some researches [26,27]. These generators could connect to wind turbine without any gearbox. These benefits are attractive by consider of maintenance and limited shelf life. Synchronous generators could to excite by electric or with permanent magnet rotor. By considering the above reasons, used generator in this paper is kind of PMSG.

This system is modeled by equations of wind turbine as could be seen in Equations below. In this paper a variable speed wind turbine is used. Wind speed 12 m/sec is considered. The parameters value of PMSG is shown in

Equations for wind turbine are shown in below [

Output mechanical power in watt is shown in Equation (6). In this equation, air density in (kg/m^{3}), C_{p}, performance coefficient, wind speed in m/sec, , tip speed ratio, , pitch angle, , turbine swept area.

In Equation (7), the coefficients to are: and [

In Equation (8), is rotor radius in meter; w, angular speed in rad/sec the output torque of wind turbine is input of used PMSG.

In order to acquiring the output maximum power in WECS, we use the MPPT algorithm

Inverter’s in each DG’s are modeled base on SANTERNO products [

In this algorithm, the initial value adjusted for DC references voltage. Correspondingly, voltage and current will be measured. After the measurement, DC output power (Po) would be calculated. In next step, the reference voltage ought to be altered as much as dc variations. By this way:

Then dc power will calculated with . If, the system output isn’t in maximum point, so accordingly the reference voltage have to rise a quantum of and power should compare with earlier amount. This process continued till receiving to maximum point. Now if, the reference voltage should decrease.

Value and parameters of boost model is shown in

In

In

As you see in

As we said, output power of WT is 7100 watt that is shown in

Produced torque of WT in system run time is 184 N.m.

DC link Voltage in battery bank terminal is shown in

produced power and connected load to the system. This signal is input of three phase inverter. In