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In this paper, a model of a variable speed wind turbine using a permanent magnet synchronous generator (PMSG) is presented and the control schemes are proposed. The model presents the aerodynamic part of the wind turbine, the mechanic and the electric parts. Simulations have been conducted with Matlab/Simulink to validate the model and the proposed control schemes.

Renewable energy was strongly encouraged. It doesn’t produce emissions either provided by the sun, wind, wa- terfalls or plant growth. They participate in the fight against the greenhouse effect and CO_{2} emissions in the at- mosphere, facilitate rational management of local resources, and also create jobs. Solar (solar photovoltaic, solar thermal), hydro, wind, biomass, geothermal energy are inexhaustible resource of energy versus “energy stock” from fossil fuels deposits such us scarce oil, carbon, natural gas.

In this paper, study focuses on wind energy conversion systems. Indeed, wind energy has become a major pro- ducer of renewable electric energy.

A wind turbine generator system (WTGS) transforms the wind energy into electrical energy. In fact, wind turbines generate mechanical forces such as windmills of the past. Through their blades, wind turbine captures the wind kinetic energy and transforms it into mechanical one.

Then this later was transformed into electric energy by a generator.

There are many types of generator available for wind energy conversion; as example induction generator in all its forms like wound rotor asynchronous generator, dual stator induction generator, MADA, etc. The permanent magnet synchronous generator is selected for many reasons. A permanent magnet synchronous generator is cha- racterized by the absence of gearbox and reduced active weight, besides having a high power density and a high efficiency (disappearing of the copper losses in rotor).

Generally the wind turbine generator based on rotational speed can be splited into two types: fixed and varia- ble speed WTGS. Fixed speed turbines are easier to interface with the electrical grid. However, variable speed turbines are able to extract more energy from the wind and are the design preferred by the wind industry.

This paper interested to a variable speed WTGS. It has higher efficiency, especially at low wind speeds and also its power variations are lower than fixed speed turbines.

The paper analyzes a complete model of a variable wind turbine equipped with a permanent magnet synchron- ous generator it also proposes a vector control strategy to control the wind turbine generator. This strategy in- cludes a speed controller and two current controllers.

The wind conversion system model and the control schemes were verified using Matlab/Simulink. Simulations results are selected, dicussed and come to prove the obtained performances of the used controllers.

The wind energy captured by the blades was transformed by the wind turbine into mechanic energy.

The model studied is illustrated by

The wind speed model requires wind climate and geographical data of the concerned site and the period of the concerned year by the study. The wind model is given by a Fourier series representation of the wind which has as a signal consisting of a superposition of several harmonics. It is given by:

where

The aerodynamic energy of the wind can be represented as [

where

Using the wind aerodynamic energy, aerodynamic power can be produced by the turbine. It can be expressed by [

Simplified scheme of wind turbine

where

where

where

However, the power coefficient is maximal when

Power coefficient curve family versus and

Power coefficient with different values of (with)

To have best results, next simulations are carried with

The aerodynamic torque is determined by [

The aerodynamic turbine power curves family with varying the turbine rotor speed for different value of wind speed illustrated in

With varying the turbine rotor speed for different wind values, the curves family of the aerodynamic torque speed is given by

The fundamental dynamic equation is described with the following equation [

where

Then, the wind turbine generator drive that represents the mechanical bloc can be given by:

Curve family of turbine power versus and

Curve family of aeodynamic torque versus and

The PMSG model can be written, in the d-q synchronously rotating reference frame, by the following equation system [

where

In the d-q synchronously rotating reference frame, the electromagnetic torque is represented by [

Vector control strategy is used to have more preferment results, to control the wind turbine.

As given in Equation (11) we have a problem of coupling between d- and q-axis, represented by the terms

Vector control strategy is based on the field orientation,

Two inputs

where

According to (16) and (17), two separate first-order models in the d-q axis [

Therefore, we obtain two similar PI regulators witch used in two independent current loops that one of them controls the q-axis component and the second controls d-component as described in

Control schemes

Using the mechanical equation of wind turbine (10) the transfer function of the wind speed is written by:

Therefore, based on the last model the wind speed regulator is designed by a PI controller.

Then, the speed controller output presents

Simulations are carried out, in order to prove the wind turbine model and the effectiveness of the proposed con- trol strategy. The block simulated is represented by

The complete WECS bloc given by

Simulations are carried with the following model:

Simulation results demonstrate the performances of the wind turbine model and the vector control strategy. In fact, the output mechanical rotational speed

Complete model of the wind energy conversion system

Wind speed profile

Wind turbine reference rotationnal speed

Wind turbine actual rotationnal speed

Current component

Current component

Electromagnetic torque

Voltage component

Voltage component

Coefficient power C_{p}

Wind turbine power P_{t}

Tip speed ratio

Coefficient power C_{p}

In this paper, the different bloc of the wind energy conversion system was studied and modeled. In fact, the model of the wind turbine has been presented, the permanent magnet synchronous generator using in variable speed wind turbine has been modeled, controlled and simulated. Using Matlab/Simulink, simulation results were carried when the proposed WECS model was confirmed and the performances of vector control strategy are substantiating.

We faced a number of problems, when making the different component model of the wind energy conversion system. First, the performances of the WECS are relied to the choice of pitch angle. Then, the aerodynamic power is related to the wind speed. And as assumed by simulation results, the coefficient power isn’t in its maximum, the speed ratio isn’t in the optimum one and the turbine power isn’t maximal. So, as results, trying to overcome these problems, we propose for the continuation of this chain of conversion energy controlling the pitch angle, studying and research of the maximum power point tracking to have more preferment results.