Electrical and Electronics Engineering (Power Systems)
Abstract: With the increasing penetration of wind power into electrical power DIFG (double fed induction Generator) has been widely used in the variable speed frequency wind energy generation system. A novel two stage buck converter and boost converter are used in conventional P&O method with MPPT controller(maximum power point tracking) this study provides a review of past and present MPPT controllers used for extracting maximum power from the WECS(wind energy conversion system). This paper seeks for analysis of MPPT controller by using perturbs and observes method in wind farm. The simulation result is accomplished in MATLAB\SIMULINK\SIMPOWER SYSTEM.
Introduction: Wind farm has been used as long as humans have put sails into the wind .the wind powered machines used to Grind grain ,Pump water through wind pumps and wind mills where developed in 9th century . Laterally increases of usage of electrical power throughout world development of electrical power, wind power found new application in lighting buildings remote from centrally generated power. According to statistics of in 2018, global wind power capacity grew 9.6% to 591 GW and yearly wind energy production grew 10%, reaching 4.8% of worldwide electric power usage.
Wind power is use of wind it is also called kinetic energy, mechanical energy converters into electrical power to generate power. Wind is sustainable energy and renewable energy and has less impact on environmental compare to burning foil fuel, oilfield etc… Wind farm consist of independent turbine which are connected to electrical power transmissions network.
Onshore wind power economy is cheaper comparable to other electrical source like solar, hydro, Cole, nuclear plant it is also have an impact on the landscape, as typically they need to be spread over more land than other power stations. Offshore wind is stable and muscular than on land and offshore farms have a small amount of visual impact, but construction and maintenance costs are higher. Power-management techniques such as having dispatch able power sources, excess capacity, geographically distributed turbines, exporting and importing power to neighboring areas, energy storage, or reducing demand when wind production is low, etc.. are used to overcome problems in many cases. In some cases weather forecast also permit the electrical power to be ready for the predictable variations in production that occur. Community wind energy – projects are locally owned by farmers, investors, businesses, schools, utilities, or other public or private entities who utilize wind energy to support and reduce energy costs to the local community.
Wind Energy Systems:
Wind energy is created by the atmosphere is heated unevenly by the sun, some patches of air rise, other air rushes in to replace them- thus wind blow. A wind turbine extracts energy from moving air by slowing the wind down, and transferring this energy into a spinning shaft, which usually turns a generator to produce electricity. The power in the wind that’s available for harvest depends on both the wind speed and the area that’s swept by the turbine blades.
It consist of 2 axis, In horizontal axis turbine it is possible to capture large amount of energy compare to vertical axis ,but the design of horizontal axis the tower is higher and more blades are needed . In vertical axis turbine there is no cyclic load on the blade and no yaw system is required thus it easy to design. Maintenance is easier in vertical axis turbine whereas horizontal axis turbine offers better performance. Blades and rotor are converters which help to convert wind energy to mechanical energy, thus it generates electrical power. The hub brakes, gearbox, generator with electrical controls is accommodated in a box called nacelle.
A yaw control mechanism is also provided to adjust the nacelle around a vertical axis to keep it wind facing. A servomechanism operated by a wind direction sensor controls the nacelle so that the turbine blades are always oriented in the direction perpendicular to wind to have the maximum wind stream area. The pitch of the blade (0o to 30o) is controlled automatically so as to provide the feathering action. The speed of wind turbine shaft and power are adjusted to squeal with generator speed and its electrical output. To obtain the optimum performance pitch control mechanism are adjusted.
Wind energy turn into Mechanical energy by an aerodynamic, since rotor speeds are low, a gear system is necessary to match the synchronous speed of the generator .Due to fluctuations in wind speed, it not possible to obtain a power supply of a fixed frequency from wind farm. To overcome this problem, the output of 3 phase generator is rectified and converted into AC with the help of a PWM inverter operating at 50 or 60 Hz. In this paper we will study about the working principle of Double fed induction Generator it also covers the operation of three-phase wound-rotor induction machines used as three-phase synchronous machines and doubly-fed induction motors.
Working Principle of DFIG:
3 -phase wounded rotor induction machine can be set as double fed induction generator, these machine works with synchronous speed ,the speed at which motor shaft rotates. DFIG consist of a 3phase wound rotor and 3phase wound stator. The rotor is fed with a 3 phase AC signal which induces an ac current in the rotor winding. As the wind turbine rotate, they exert mechanical force on the Rotor, causing it to rotate. As the rotates the magnetic field produced due to the ac current also rotates at a speed proportional to the frequency of the ac signal applied to the rotor winding. Rotating magnetic flux passes through the stator winding which cause induction of ac current in the stator winding. Thus the speed of rotational of the stator magnetic field depends on the rotor speed as well as the frequency of the ac current fed to the rotor windings. Frequency of the ac signal generated across the stator should be constant irrespective of the rotor speed variations. To achieve this, the frequency of a signal applied to the rotor windings need to be adjusted. Prime mover makes the rotor of the generator rotate, the static magnetic field created by the dc current fed into the generator as the rotor, rotates with equal speed. Magnetic flux passes through the stator winding as the rotor winding rotates magnetic field produces and inducing in alternating voltage across stator winding. The convection from prime mover the electrical power is available in stator winding.
Block Diagram of Double Fed Induction Generator
DFIG and wind modal in Synchrous dq ref frame of variable of dfig equation are given below:
From the ws=synchronous speed, wr=rotor angular frequency, P= no of poles, wsl= slip frequency
3 MPPT Controllers:
Maximum power point tracking (MPPT) OR in some cases just Power Point Tracking (PPT) is a techniques majorly used with wind energy and PV solar system to maximize power extraction under all conditions. MPPT consists of non- identical techniques like :tip speed ratio (TSP)control, optimal torque (OT) , Power signal Feedback (PSF)control, Perturbation and observation (P&O) control and some of Advance methods are :Artificial intelligence control, hybrid methods, fuzzy logic control method. Neural network techniques are used to estimate the actual machine speed and Torque of wind farm, the control structure, Wilcoxon radial basis function network (WRBFN) and modified particle swarm optimization (MPSO) are presently used in MPPT algorithm in this paper we study about mainly preferable for conventional P&O MPPT control method.
Conventional P&O MPPT Control Method:
The MPPT controller is P&O technique adjust the voltage by the small amount of wind and measurement power, when its direction is adjusted utilization of power is no longer increased. In this method perturbing the Rotor speed and observing the change in power. The output voltage and current are proportional to the speed and torque in Double fed induction generator (DFIG). The perturbing output voltage of generator give rise to vary rotor speed .perturbing the voltage will perform to adjust the Duty cycle (PWM signal) in the Buck and Boost converters as show in below fig2
Flow chart of P&O algorithm operates by varying the duty cycle of the Buck, converter and Boost converter, thus varying output voltage of wind generator and observer the result of output power Increases or Decreases in next Duty cycle. If Duty cycle increases then power also increases the direction of perturbation signal will be same as previous cycle. If Duty cycle Decreases automatically power also Decreases such that direction of perturbation signal is in opposite direction compare to previous cycle.
Buck Converter-It is DC-DC power converter it is also called step-down converter in this input voltage supply is step down to its output load. It consist at least two semi conductors like diode, transistor etc…It also has storage capacitor, instructors. In this paper we use MOSFET in mat lab /simulation. It consist of Insulated-Gate Bipolar Transistor switch, diode Resistance (R), Inductor (L), Input capacitor (Ci), Output capacitor (Co), Load resistance (RL).
Boost converter- It is DC-DC power converter it is also called step-up converter in this input voltage supply is step up to its output load. It consist at least two semi conductors like diode, transistor etc…It also has storage capacitor, instructors. Boost converters are suitable for any DC source like rectifier, Batteries, DC generators. In this paper we use MOSFET in mat lab /simulation. It consist of Insulated-Gate Bipolar Transistor switch, diode Resistance (R), Inductor (L), Input capacitor (Ci) ,Output capacitor (Co) ,Load resistance (RL).
At variable speed of DFIG to track maximum amount of power from wind, MPPT techniques are used by controller of P&O method. In this processes buck converter tracking is less then boost. Boost converter tracking maximum amount of power. Simulation result is accomplished in MATLAB\SIMULINK\SIMPOWER SYSTEM.
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