AN OVERVIEW : ON WIND ENERGY SYSTEM & VARIOUS CONTRL STRATEGIES

1. AN OVERVIEW : ON WIND ENERGY SYSTEM & VARIOUS CONTRL STRATEGIES

2. INTRODUCTION OF WECS • Fastest growing segment among other renewable energy sources . • Wind energy is clean, geographically available, low cost, and useful in rural areas.

3. COMPONENTS OF WECS

4. CLASSIFICATION OF WECS

5. COMPARISION Horizontal axis wind turbine Vertical axis wind turbine • Comprises Two Or More Blades That Are Designed To Best Aerodynamics • Includes A Yaw Mechanism That Turns The Rotor Blades To Face Wind Directions • Due To High Efficiency & easy maintenance, This Is Most Popular • Consists Blades Located Vertically • Able To Capture Wind Independently From Wind Directions. • Due To Less Efficiency, Complicated Maintenance, And Large Land Occupation, The Use Of This Converter Has Falling Down During Last Decades

6. OPERATING AND DESIGN PRINCIPLES OF WIND TURBINE • A wind turbine obtains its power input by converting the force of the wind into a torque (turning force) acting on the rotor blades. • The amount of energy which the wind transfers to the rotor depends on the density of the air, the rotor area, and the wind speed. • The kinetic energy of a moving body is proportional to its mass (or weight). The kinetic energy in the wind thus depends on the density of the air, i.e. its mass per unit of volume. In other words, the "heavier" the air, the more energy is received by the turbine.

7. The rotor area determines how much energy a wind turbine is able to harvest from the wind. • Since the rotor area increases with the square of the rotor diameter, a turbine which is twice as large will receive 22 = 2 x 2 = four times as much energy • To be considered a good location for wind energy, an area needs to have average annual wind speeds of at least 12 miles per hour.

8. DESIGN OF WECS • A WECS captures wind energy and then uses a generator to convert it to electrical energy • The design of a WECS is an integral part of how efficient it will be. • When designing a WECS, one must decide on the size of the turbine, and the size of the generator

9. Wind Turbines LARGE TURBINES: • Able to deliver electricity at lower cost than smaller turbines, because foundation costs, planning costs, etc. are independent of size. • In areas where it is difficult to find sites, one large turbine on a tall tower uses the wind extremely efficiently.

10. SMALL TURBINES: • Local electrical grids may not be able to handle the large electrical output from a large turbine, so smaller turbines may be more suitable. • High costs for foundations for large turbines may not be economical in some areas. • Landscape considerations

11. WIND TURBINES: NUMBER OF BLADES*Most common design is the three-bladed turbine. The most important reason is the stability of the turbine. A rotor with an odd number of rotor blades (and at least three blades) can be considered to be similar to a disc when calculating the dynamic properties of the machine.*A rotor with an even number of blades will give stability problems for a machine with a stiff structure. The reason is that at the very moment when the uppermost blade bends backwards, because it gets the maximum power from the wind, the lowermost blade passes into the wind shade in front of the tower.

12. Wind Turbine Generators • Wind power generators convert wind energy (mechanical energy) to electrical energy. • The generator is attached at one end to the wind turbine, which provides the mechanical energy. • At the other end, the generator is connected to the electrical grid. • The generator needs to have a cooling system to make sure there is no overheating.

13. SMALL GENERATORS: • Require less force to turn than a larger ones, but give much lower power output. • Less efficient i.e.. If you fit a large wind turbine rotor with a small generator it will be producing electricity during many hours of the year, but it will capture only a small part of the energy content of the wind at high wind speeds. • LARGE GENERATORS: • Very efficient at high wind speeds, but unable to turn at low wind speeds. i.e.. If the generator has larger coils, and/or a stronger internal magnet, it will require more force (mechanical) to start in motion.

14. WIND TURBINE MODELING Tls Kr

15. The aerodynamic power Pa captured by the wind turbine is given by π λ is defined as the ratio of the tip speed of the turbine blades to wind speed, and is given λ=R The rotor power (aerodynamic power) is also defined by P C Therefore the rotor torque is given by The rotor dynamics with generator inertia is given by Gear box ratio is given by The generator power is given by

16. CONTROL METHODS • HARD CONTROL • SOFT CONTROL

17. HARD CONTROL • PID CONTROL • OPTIMAL CONTROL • ADAPTIVE CONTROL • ROBUST CONTROL • SLIDING MODE CONTROL

18. PID CONTROL • TO REGULATE POWER FLOW TO THE GRID WITH MINIMAL REACTIVE POWER DRAWN FROM THE GENERATOR. • CONTROLLING THE FIRING ANGLE WITH PI CONTROLLER. • PI GAINS ARE CALCULATED OPTIMALLY BASED ON THE NONLINEAR DYNAMICS OF SYSTEM FOR TWO SAMPLE RATES OF TWO CONTROLLERS. • COMPARING THE EFFECTS OF SINGLE RATE & MULTIRATE SAMPLING ON THE SYSTEM PERFORMANCE.

19. PID CONTROL

20. Performance of optimal multi-rate PI controller • PI gains for convertor & inverter firing angle loops are calculated by minimizing the squared error b/w the dc link current & its reference value • The actual optimization is stiff & is done by a direct search polytope algorithm • RESULTS • Multi-rate is better than single rate • At sampling period ratio 2,controller have a good performance(good overshoot & settling time).

21. ADAPTIVE CONTROL • Aim: To capture max. power from the wind • A MPPT algorithm is used for this purpose • The algorithm consists of two loops. (a) change detection loop(CDL) & (b) an operating point adjusting loop(OPAL).

23. Proposed algorithm’s adjustment process

24. ADVANTAGE • The algorithm is able to determine the optimum operation point within a reasonable range • Suitable for any wind turbine • Easily customized • Able to improve its performance over time

25. SLIDING MODE CONTROL

26. ADVANTAGES • Sliding mode control strategy ensures stability in all operating region • This is a ideal feedback control solution despite model uncertainties • Sliding mode control method presents attractive features such as robustness to parametric uncertainties of the turbine & the generator as well as to electric grid disturbances

27. Simplicity • Provide a suitable compromise b/w conversion efficiency and drive train mechanical stresses

28. OPTIMAL CONTROL • Optimal Control Strategy Used In Order To Capture The Maximum Power From Wind , • For A Fixed Pitch WECS Using Permanent-magnet Synchronous Generator (PMSG),A MPPT Algorithm Combined The Derivative Of PMSG Stator Frequency And The Predicted Maximum Output DC Power Versus DC Voltage Characteristic Curve Of The WECS To Drive The System Operate At Maximum Power Points. • In This Control Scheme No Need To Use The Anemometer Sensor To Measure Wind Speed • This control scheme showed the satisfactory performance in comparison with some other methods that utilized the sensor

29. LQG CONTROLLER STRUCTURE OBSERVER PLANT MODEL K

30. Based on the linear state space model of a wind turbine system, an optimal state feedback controller- Linear Quadratic Regular (LQR) is used for a wind energy system • LQR guarantees optimal behaviors for some criterion functions ,takes into account scholastics properties as turbulence part of wind speed • LQR uses a observer for state vector estimator to minimize objective function J. J= • The objective function include tracking optimal point & minimization of torque variations • LQR controller provided better performance than conventional control methods

31. ADVANTAGES • This control scheme is able to keep the WECS at maximum efficiency points • Provide solutions to the control problem of WECSs in the below-rated speed (partial load) operating region using both linear models with traditional PI controllers and nonlinear models with MPPT • This control method can be used for optimization of energy with mechanical load variations • For large WECS with more requirements such as global stability, mechanical damage, output power standards, etc. , frequency separation control is used for handling such multi-objective optimization problems

32. FUZZY CONTROL • Fuzzy controller is mainly used in nonlinear system which can not be accurately modeled and has more inputs, uncertain factors and inaccurate property. • controller offers a good tracking behaviour and robustness to parameter variations

33. FUZZY CONTROLLER DESIGN OF VARIABLE SPEED GENERATOR SYSTEM • The Choice of Linguistic Variable and Determination of Membership Function under low Wind Speed • The Determination of Fuzzy Rules under low Wind Speed

34. Choosing the error E and the derivative of the error ECof blade tip speed ratio and the wound voltage U of electricmachine stator as the linguistic variables. E1 and E1C areinputs of the fuzzy controller, U is the output • The linguisticvalues of E1 are:[NB NM NS NZ PZ PS PM PB], whichmeans negative big, negative middle, negative small, negativezero, positive zero, positive small, positive middle, andpositive big respectively; The linguistic values of E1C and Uboth are: NB, NM, NS, ZR, PS, PM and PB.

35. The defuzzification use center of gravity method • When the error is big, the controlling variable (the voltage) should be chosen to remove the error. When the error is small, the controlling variable should be chosen to prevent the overshoot and maintain the stability of the system

36. When the error is big, the controlling variable (the voltage) should be chosen to remove the error. When the error is small, the controlling variable should be chosen to prevent the overshoot and maintain the stability of the system

37. ADVANTAGES • The variable speed generator system can obtain smooth and steady output power and generator rotation speed if no interference under low wind speed. • The rotation speed of wind turbine can trace the optimum power coefficient curve and therefore the wind turbine gets the biggest energy. • Disturbance can be restrained effectively by using fuzzy controller over the classical PID controller. • The output power and generator rotation speed have little fluctuation.

38. CONCLUSION • The overview, in terms of contributions of the hard and soft control techniques to WECSs, indicates that the sliding mode control method, due to its useful features of fast convergence and robustness to system’s uncertainties, dominated the applications to the field • The application of soft control techniques to WECSs has dramatically grown up in the recent years due to their attractive features of nonlinear identification and control , human knowledge and reasoning in the form of membership functions and rules (fuzzy logic) .

39. FUTURE DIRECTIONS Some of the areas identified for future investigations in the area of WECSs are; • More accurate, physics-based dynamic (both lumped and distributed- parameter) models for both existing and future WECSs. • Advanced algorithms for optimal, model predictive, robust, adaptive, networked, and resilient control systems with industry-standard embedded platforms for the integrated WECSs. • Advanced algorithms based on soft computing techniques including neural networks, fuzzy logic, genetic logic, genetic programming, swarm intelligence, probabilistic reasoning and others.

40. More sophisticated WECSs software packages for modeling, analysis, design, development, testing and validation with capabilities of modularity and integration with power grids and Internet connectivity. • Finally, all the research and development work stated above needs to focus on the critical issues reduced cost, feasibility, compliance with industry-standardization, physical and cyber security.

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