ICSGET-2024 SUBMISSION NO 96 Manohar G.pptx

Doubly Fed Induction Generator: Grid Integration and Performance Analysis

1. International Conference on Sustainable Green Energy Technologies, 2024(ICSGET-2024) Vardhaman College of Engineering Hyderabad Doubly Fed Induction Generator: Grid Integration and Performance Analysis Presented by G.Manohar Assoc.Professor in EEE Dept. CVRCE Submission No. 96

2. Absract : Renewable energy sources are emerging to replace conventional energy sources in the energy mix as a result of the growing demand for power and the constraints of existing energy sources. Wind energy promises attractive features such as bulk power production and reduced maintenance costs . With technological advancements, wind energy has become a promising secondary energy source, resulting in the proliferation of wind farms around the globe to bolster traditional energy systems . This has led to a rapid increase in the incorporation of wind power into the power grid, emphasizing the need to understand its effects on the system's parameters. A range of generators, including DFIG, SG, and SCIG, are used to generate wind power. Due to the benefits of separate control over true and wattless power, variable speed operation and maximum power tracking, a DFIG-based wind turbine became a favorite choice for power utilities.

3. Outline Introduction Working of DFIG Equivalent circuit and modelling Wind Energy Conversion System Objectives Control of DFIG Grid Integration of DFIG Simulation and results. Conclusions References

4. Introduction Renewable energy sources are sustainable, reliable, environmentally friendly, and require less maintenance Solar energy and wind energy are major sources of energy in renewable energy sources. Wind energy offers the advantages of bulk power generation and cost-effectiveness Doubly Fed Induction Generator(DFIG) is one of the promising wind generators and nearly 50% of the bulk power wind generators are DFIG Type only. DFIG offers several advantages such as Capital cost of the system is low compared to SCIG of the same rating Its ability to maximize the output over a wind speed range in both sub-synchronous and super-synchronous speeds. Power electronic converters are connected in the rotor side and hence have to support only slip power. Power electronic converters are cheap. Independent control of active and reactive powers. However, they suffer from the drawbacks of DFIGs are sensitive to GRID disturbances such as grid faults and low voltage dips Maintenance of slip rings is difficult and laborious

5. Working of DFIG Stator of DFIG is directly connected to grid and rotor is connected through power electronic converters namely Rotor Side Converter(RSC) and Grid side Converter(GSC) Since DFIG is driven by variable speed wind turbine the frequency of the power developed varies. To keep the frequency constant back-to-back converters are used.

6. Equivalent Circuit and modelling of DFIG

7. Voltage equations of stator and rotor in d – q reference frame = + - = + = + - = + + Where flux linkages are given by = = = = , , and stator and rotor voltages in d-q reference frame , , and are stator rotor currents in d-q reference frame  

8. Active Power P S is given by P S = Reactive Power Q S is given by ( - )  

9. Wind Energy Conversion System(WECS) Wind energy conversion system(WECS) converts kinetic energy of the wind into mechanical energy , by means of turbine blades. The mechanical power developed by wind turbine depends on wind velocity, air density and is given by = ( , β ) where is the mechanical power developed is the density of the air in Kg/ (1.225 Kg/ ) area swept by the wind turbine blades Velocity of the wind in m/s power coefficient which depends on tip speed ratio(  ) and blade Pitch angle( β )  = is rotational speed of the wind turbine r is the radius of the wind turbine  

10. Wind Energy Conversion Systems(WECS) WECS can be broadly classified into two types Fixed speed wind turbine systems Variable speed wind turbine systems Fixed-speed wind turbine systems The fixed-speed wind turbine has the advantage of being simple, robust and reliable, and easy to maintain. Traditionally, the constant speed wind turbines were coupled to squirrel cage induction generator (SCIG) or wound-field synchronous generator. In the fixed speed wind turbines, the generator is directly connected to the grid. Operate at a constant rotor speed regardless of wind speed variations. Require a gearbox to match the turbine speed to the generator speed.

11. Fig: Fixed speed wind turbine with squirrel cage induction generator Disadvantages: Less efficient as they cannot adapt to varying wind speeds, leading to suboptimal energy capture. Higher mechanical stress due to the fixed speed operation, which can reduce the lifespan of the components. Poor power quality due to fluctuations in wind speed, causing voltage and frequency variations. Limited capability to control reactive power, making grid integration more challenging.

12. Variable-speed wind turbine systems Operate at varying rotor speeds to adapt to changing wind speeds, optimizing energy capture. Typically use doubly-fed induction generators (DFIG) or permanent magnet synchronous generators (PMSG). Incorporate power electronic converters to control the rotor speed and ensure optimal performance. May or may not use a gearbox depending on the design (direct-drive systems avoid gearboxes) Advantages: Higher energy efficiency as they can optimize rotor speed for different wind conditions. Reduced mechanical stress due to smoother operation, leading to potentially longer component lifespan. Better power quality with more stable voltage and frequency control. Improved grid integration capabilities with the ability to control reactive power and provide ancillary services.

13. Disadvantages: More complex design with additional components like power electronic converters, leading to higher initial costs. More sophisticated maintenance requirements due to the complexity of the system. Increased capital investment required for the advanced technology and control systems. Fig: Variable Speed Wind Energy Conversion system employing DFIG.

14. PMSM SCIG DFIG Converter Rating Full Scale Full Scale Partial Scale Generator Cost Expensive Cheap Cheap Converter Cost Expensive Expensive Cheap Grid Fault Robustness Strong Strong Week Control Complexity Mid Complex Complex Table: Characteristics summary of Variable Speed Wind Turbine Configurations.

15. Grid codes Conventional power plants can support voltage and frequency during and immediately after the grid faults. Due to the penetration of bulk amount of renewable energy into the grid, transmission and distribution operators has imposed new Grid codes Grid codes are specific rules imposed by transmission and distribution operators to generating stations regarding few technical characteristics like voltage ,frequency reactive power etc Fig: Typical LVRT requirement of Germany PSO E.ON

16. Control of DFIG Vector control method is employed for controlling DFIG. This control method ensures to decoupling between active and reactive power through the use of park transformation. Stator flux vector is aligned with d axis and by making reference frame speed ω equal to stator flux speed ωe , we obtain = 0 = constant True power and wattless powers of DFIG are given by   = = - ( - )  

17. Where Φsd is d axis stator flux, Lm is mutual inductance ird is d axis rotor current irq is q axis rotor current PS is true power of the DFIG QS is wattless power of DFIG For Rotor side converter(RSC) active power reference and measured are compared and the error is processed through PI controller then idr reference is generated and this is compared with idr measured and finally Vdr (rotor voltage in d axis) is generated. Simlarly reactive power reference and measured are compared and the error is processed through PI controller then iqr reference is generated and this is compared with iqr measured and finally Vqr (rotor voltage in q axis) is generated

18. Fig: Rotor side Controller (RSC) Block Diagram For Rotor side converter(RSC) active power reference and measured are compared and the error is processed through PI controller then idr reference is generated and this is compared with idr measured and finally Vdr (rotor voltage in d axis) is generated.Simlarly reactive power reference and measured are compared and the error is processed through PI controller then iqr reference is generated and this is compared with iqr measured and finally Vqr (rotor voltage in q axis) is generated

19. Fig: Grid S ide Controller (GSC) Block Diagram For Grid side converter(RSC) Dc link voltage reference and measured are compared and the error is processed through PI controller then finally Vds ( Staor voltage in d axis) is generated.Simlarly Iqs reference is compared with the measured value of iqs and the error is processed through PI controller and finally Vqs ( Staor Voltage in q axis ) is generated and fed to DFIG

20. Grid integration of DFIG Integration of bulk amount of renewable energy sources to the utility grid was started nearly two decades ago. It is required to sense the grid frequency and voltage in order to connect a DFIG to the grid. This is achieved by connecting Phase Locked Loop(PLL). PLL continuously track the frequency and voltage of the grid and these signals were sent to control mechanism of DFIG. DFIGs when integrated to grid, influences the system stability, transmitted power and power quality.

21. System stability Since the DFIG is coupled to variable speed turbines, they have the capability to adjust reactive power and ability to control both active and reactive powers independently. This can be accomplished by power electronic converters. Since reactive power can controlled, it is possible to enhance the voltage stability of the grid. In case of grid disturbances, DFIG act like an ancillary source of wattless power and hence enhances the grid voltage stability. The DFIGs can enhance frequency stability(±1% during steady state operation) along with voltage stability(±10% during steady state operation) A properly designed controller can regulate the frequency in transient conditions such as loss of network generation.

22. Wind power transmission Power transmission from large size DFIGs into power system always a challenging job since wind is uncontrollable in nature. In case of large offshore plants, the power transmission is accomplished by incorporating common collection bus exclusively controlled by STATCOM. To the onshore grid, the power is transmitted using HVDC cables.

23. Power Quality When bulk wind power is injected into the grid, it may cause voltage flicker and deviations in frequency. Frequent switching of power switches in Power converters of DFIG is the major cause for voltage flicker. Voltage flicker also depends on average wind velocity, impedance angle of the grid and short circuit capacity of the grid. Deterministic method using transfer function is one of the methods to estimate the frequency deviation.

24. Simulation and results: A 9 MW,575V capacity DFIG pumping power to a 120KV grid through 20 km and 10Km transmission lines and power transformers is simulated using MATLAB Simulink. Output of DFIG 575KV is stepped up using power transformer to 25KV and then transmitted through 10Km line. The 25KV is stepped up to 125KV using power transformer of rating 2500MVA. A 500 KW load is connected at the output of DFIG and a 2MVA plant is connected after 10 km transmission line. Different types of faults are created near 2 MVA plant and the tripping times are measured. A 9 cycle fault is created at t=5 sec.

25. Active power of DFIG in steady state

26. Reactive power of DFIG in steady state

27. DC Link Voltage Vdc Steady state DC link voltage is 1200V.At 5s a step in wind speed is programmed from 8 m/s to 14m/ s.A small transient voltage of 2V is occurred and settled to 1200V at 20s.

28. Objectives To study the different Wind Energy Conversion Systems in the current literature. To simulate the DFIG model in MATLAB Simulink and study its performance in steady state. To simulate the DFIG model under different fault conditions and implement the protection for wind turbine.

29. S.No Type of fault Trip time in Sec 1 L-G 5.221 2 L-L 5.111 3 L-L-G 5.108 4 L-L-L 5.01 5 L-L-L-G 5.01 Table 1. Trip time of DFIG under different fault conditions.

30. Conclusion: Causes and probable solutions of low voltage ride through of doubly fed induction generator are discussed thoroughly. Doubly fed induction generator connected to grid was simulated in MATLAB Simulink using controllers conventional PI controller, artificial neural network controller and Random Forest optimization controller. It was found that the performance of the DFIG is superior in RFO controller compared to ANN and conventional PI controllers. Useful power and wattless power supplied by the DFIG is higher in RFO controller.

31. References   [1] Ezzat, Marwa, Mohamed Benbouzid , S. M. Muyeen , and Lennart Harnefors . "Low-voltage ride-through techniques for DFIG-based wind turbines: state-of-the-art review and future trends." In  IECON 2013-39th Annual Conference of the IEEE Industrial Electronics Society , pp. 7681-7686. IEEE, 2013. [2] K. Jadhav, H. T., and Ranjit Roy. "A comprehensive review on the grid integration of doubly fed induction generator."  International Journal of Electrical Power & Energy Systems  49 (2013): 8-18. [3] Tourou , Pavlos , and Constantinos Sourkounis . "Review of control strategies for DFIG-based wind turbines under unsymmetrical grid faults." In  2014 Ninth international conference on ecological vehicles and renewable energies (EVER) , pp. 1-9. IEEE, 2014. [4] Muisyo , Irene Ndunge , Christopher Maina Muriithi , and Stanley Irungu Kamau. "Enhancing low voltage ride through capability of grid connected DFIG based WECS using WCA-PSO tuned STATCOM controller."  Heliyon  8, no. 8 (2022): e09999. [5] Anita, Balasubramaniam Babypriya — Rajapalan , and B. Babypriya . "Modelling, simulation and analysis of doubly fed induction generator for wind turbines."  Journal of electrical engineering  60, no. 2 (2009): 79-85. [6] C. Marques, G. D., and Duarte M. Sousa. "Understanding the doubly fed induction generator during voltage dips." IEEE Transactions on Energy Conversion 27, no. 2 (2012): 421-431. [7] Manohar, G., and S. Venkateshwarlu . "Analysis of Grid-connected Doubly Fed Induction Generator based Wind Turbine.” CVR Journal of Science and Technology 10 (2016): 59-64. [8] Schulz, Detlef. “Grid integration of wind energy systems.” Power electronics in smart electrical energy networks (2008): 327-374. [9] Zhang, Shao. Investigations of the grid-connected wind power system: low voltage ride through and power quality issues. Diss. Nanyang Technological University, 2011. [10] Roy, Kallol , Kamal Krishna Mandal, and Atis Chandra Mandal. "Ant-Lion Optimizer algorithm and recurrent neural network for energy management of micro grid connected system." Energy 167 (2019): 402-416

32. [11] Sekhar, Velappagari , and K. Ravi. "RETRACTED: Low-voltage ride-through capability enhancement of wind energy conversion system using an ant-lion recurrent neural network controller." Measurement and Control 52.7-8 (2019): 1048-1062. [12] https://www.business-standard.com/article/economy-policy/why-india-s-offshore-wind-energy-potential-remains-untapped-121112900180_1.html [13] https://www.javatpoint.com/machine-learning-random-forest-algorithm [14] Mohan, Ned, Tore M. Undeland , and William P. Robbins. Power electronics: converters, applications, and design. John wiley & sons, 2003. [15] Shi, L., N. Chen, and Q. Lu. "Dynamic characteristic analysis of doubly-fed induction generator low voltage ride-through." Energy Procedia 16 (2012): 1526-1534.

33. Thank You