The aim of this research is to model an autonomous control wind turbine driven permanent magnetic synchronous generator (PMSG) which feeds alternating current (AC) power to the utility grid. Furthermore, this research also demonstrates the effects and the efficiency of PMSG wind turbine which is integrated by autonomous controllers. In order for well autonomous control, two voltage source inverters are used to control wind turbine connecting with the grid. The generator-side inverter is used to adjust the synchronous generator as well as separating the generator from the grid when necessary. The grid-side inverter controls the power flow between the direct current (DC) bus and the AC side. Both of them are oriented control by space vector pulse width modulation (PWM) with back-to-back frequency inverter. Moreover, the proportional-integral (PI) controller is enhanced to control both of the inverters and the pitch angle of the wind turbine. Maximum power point tracking (MPPT) is integrated in generator-side inverter to track the maximum power, when wind speed changes. The simulation results in Matlab Simulink 2012b showing the model have good dynamic and static performance. The maximum power can be tracked and the generator wind turbine can be operated with high efficiency.
Renewable energy such as wind power is an important solution to reducing carbon emissions. Nowadays, with the rapid development of wind power technology, wind power can be converted into a useful form of energy, such as using wind turbines—the device that converts kinetic energy from the wind—to make electrical power. In fact, since wind power, as an alternative to fossil fuels, produces no greenhouse gas emissions during operation, it makes a huge difference to our environmental impact. Despite very significant advancements and influence to the environment, wind power costs continue to be greater than the existing low-carbon alternative such as natural gas. Therefore, much research remains to be done in order to improve wind turbines’ behaviour and to make them cost-efficient to compete with the traditional energy such as natural gas.
There are many kinds of variable speed generators used for wind turbine. According to the reference [
According to the continuous development of wind power technology, the efficiency of inverter device, facing some tough issues, plays an important role in the improvement of wind power generation system performance. They need to be enhanced by novel controller [
This study will model the whole wind turbine system including physical part of permanent magnet synchronous generator and control strategies for generator side and grid side as well as the pitch angle controller to depict the effects and the efficiency of PMSG by autonomous controllers. The model system and control strategies contain a PMSG wind turbine model, a pitch angle control model, generator-side inverter control model, and grid-side inverter control model. The generator-side inverter and grid-side inverter controller adopt the back to back space vector PWM to enhance the performance of MPPT as well as decoupling control of the active and reactive power by adjusting the current of
The basic of PMSG wind turbine structure shown on Figure
General wind turbine PMSG system with control schemes (a) and (b).
The generator is connected to a three-phase inverter which rectifies the current from the generator to charge a DC-link
The wind turbine is used for the conversion of wind kinetic energy to mechanical work. On the basis of relationships for the calculation, it is possible to express the value
Here,
The power coefficient
with
The relationship between the wind speed and the rotor speed is defined as tip speed ration
From the value of the rotational motion performance, it is possible to determine the value of the torque
These formulas are evident that the instantaneous values of the performance, respectively, of the mechanical torque, are dependent on the wind speed very much. On the basis of these equations, it is possible to build the model, which structure is shown in Figure
Figure
The curve of power wind turbine coefficient.
Figure
The curve to illustrate the relationship between power and wind speed.
Model of the aerodynamic of wind turbine in Matlab Simulink 2010b.
In Figure
The generator model is implemented entirely in
The
The equation of the electromagnetic torque in the rotor is
There,
Figure
The generator-side inverter is controlled to catch maximum power from available wind power. According to (
There,
From (
with
The generator-side inverter control schematic is illustrated in Figure
Scheme of generator-side inverter controller.
The goal of the grid-side inverter is keeping the stability of the DC-line voltage [
Here,
Scheme of grid-side inverter controller.
The system of aerodynamic control plays an important role in regulating the mechanical power. Pitch angle controller is based on the principle which is changing the blades angle at the revolutions over the maximal generator speed as well as protecting the generator before overloading at high wind speeds. The optimal angle for the wind speed below the nominal value is approximately zero and then it increases with the wind speed growing. It has considerable impact on the performance coefficient and on the value of the turbine torque in [
In this controller, illustrated in Figure
Model of pitch angle controller in Matlab Simulink 2010b.
In the generator-side inverter, MPPT produces the
Wind turbine generator power curve at various wind speeds.
The tip speed ratio is kept at constant value for all maximum power points, while the relationship between the wind speed and the wind turbine generator speed is explained as follows:
with
The MPPT control strategy is based on monitoring the wind turbine generator output power using measurements of the wind turbine generator output voltage and current as well as directly modelling the dc/dc converter duty cycle, which is followed by the comparison of among output power values.
In order to verify the model of the whole autonomous control system design, Matlab 2010b is used to simulate this system design in Figure
Simulation model of autonomous control PMSG wind turbine.
Model of wind turbine is in wind turbine; models of control system of generator-side inverter and grid-side inverter are included in Subsystem 1 and Subsystem 2. The MPPT controller and PI controller are also included in Subsystem 1 and Subsystem 2. The pitch angle controller is completely modelled in wind turbine. In this simulation, the wind turbine PMSG model obtains the wind speed and provides an optimal reference speed to control the system. The simulation results are shown in Figures
DC-link voltage, load voltage, and inverter voltage.
Three-phase voltage and current of the grid.
Active and reactive power.
The main system parameters are listed in Table
The parameters of autonomous control PMSG wind turbine.
PMSG | Rated voltage of stator: 5 KV |
Rated frequency of stator: 50 Hz | |
Rated rotor torque: 450 N·m | |
Stator phase resistance: 0.01 Ω | |
Armature inductance: 0.03 H | |
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Number of poles: 56 | |
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Wind turbine | Rated power: 2 MW |
Blades radius: 35 m | |
Optimum tip-speed ratio: 8 | |
Optimum power coefficient: 0.4 | |
Air density: 1.225 kg/m3 | |
Cut-in wind speed: 3 m/s | |
Rated wind speed: 12 m/s | |
Cut-out wind speed: 25 m/s | |
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Others | Grid line voltage: 900 V |
DC-link voltage: 1200 V | |
DC-link capacitor: 15000 |
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Transformer output voltage: 12 KV | |
Frequency: 50 Hz |
Figure
Figure
The voltage phase per unit (pu) of PMSG is decreased after the beginning stage; however, it keeps constant value at that later time.
Figure
Figure
By the autonomous control, including pitch angle controller, generator-side inverter, and grid-side inverter, the wind turbine is able to achieve the highest efficiency. Through the MPPT strategy as well as pitch angle controller, it can catch the maximum wind energy and operate at optimal speed ratio.
This study analyzes the control strategies as well as models and designs and simulates the whole autonomous system of PMSG wind turbine feeding AC power to the utility grid in Matlab Simulink 2010b. The simulation results show that the combination of pitch angle controller, generator-side inverter controller, and grid-side inverter controller has good dynamic and static performance. The maximum power can be tracked and the generator wind turbine can be operated in high efficiency. DC-link voltage is kept at stable level for decoupling control of active and reactive power. Hence, the output will get the optimum power supply for the grid.
The authors declare that they have no conflict of interests regarding the publication of this paper.