STUDY OF WIND TURBINE DRIVEN DFIG USING AC/DC/AC CONVERTER A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS OF THE DEGEREE OF Bachelor of Technology In Electrical Engineering By ASHISH KUMAR AGRAWAL (10502066) BHASKAR MUNSHI (10502049) SRIKANT KAYAL (10502054) Under the guidance of Prof. K. B. Mohanty Department of Electrical Engineering National Institute of Technology Rourkela National Institute of Technology Rourkela CERTIFICATE This is to certify that the thesis entitled, “Study Of Wind Turbine Driven Induction Generator Using AC/DC/AC converter” submitted by Ashish Kumar Agrawal, Bhaskar Munshi and Srikant Kayal in partial fulfillment of the requirements for the award of Bachelor of Technology Degree in Electrical Engineering at the National Institute of Technology, Rourkela (Deemed University) is an authentic work carried out by them under my supervision. And to the best of my knowledge, the matter embodied in the thesis has not been submitted to any other University/Institute for the award of any Degree or Diploma. Date : Prof. K. B. Mohanty Dept. of Electrical Engg. National Institute of technology Place : Rourkela-769008 2 National Institute of Technology Rourkela CERTIFICATE This is to certify that the thesis entitled, “Study Of Wind Turbine Driven Induction Generator Using AC/DC/AC converter” submitted by Ashish Kumar Agrawal, Bhaskar Munshi and Srikant Kayal in partial fulfillment of the requirements for the award of Bachelor of Technology Degree in Electrical Engineering at the National Institute of Technology, Rourkela (Deemed University) is an authentic work carried out by them under my supervision. And to the best of my knowledge, the matter embodied in the thesis has not been submitted to any other University/Institute for the award of any Degree or Diploma. Date : Prof. K. B. Mohanty Dept. of Electrical Engg. National Institute of technology Place : Rourkela-769008 3 ACKNOWLEDGEMENT We would like to articulate our deep gratitude to our project guide Prof. K. B. Mohanty who has always been source of motivation and firm support for carrying out the project. We express our gratitude to Prof. B. D. Subudhi, Professor and Head of the Department, ELECTRICAL Engineering for his invaluable suggestions and constant encouragement all through the thesis work. We would also like to convey our sincerest gratitude and indebtedness to all other faculty members and staff of Department of Electrical Engineering, NIT Rourkela, who bestowed their great effort and guidance at appropriate times without which it would have been very difficult on our project work. An assemblage of this nature could never have been attempted with our reference to and inspiration from the works of others whose details are mentioned in references section. We acknowledge our indebtedness to all of them. Further, we would like to express our feeling towards our parents and God who directly or indirectly encouraged and motivated us during this dissertation 4 ABSTRACT In recent years, wind energy has become one of the most important and promising sources of renewable energy, which demands additional transmission capacity and better means of maintaining system reliability. The evolution of technology related to wind systems industry leaded to the development of a generation of variable speed wind turbines that present many advantages compared to the fixed speed wind turbines. These wind energy conversion systems are connected to the grid through Voltage Source Converters (VSC) to make variable speed operation possible. The studied system here is a variable speed wind generation system based on Doubly Fed Induction Generator (DFIG). The stator of the generator is directly connected to the grid while the rotor is connected through a back-to-back converter which is dimensioned to stand only a fraction of the generator rated power. To harness the wind power efficiently the most reliable system in the present era is grid connected doubly fed induction generator. The DFIG brings the advantage of utilizing the turns ratio of the machine, so the converter does not need to be rated for the machine’s full rated power. The rotor side converter (RSC) usually provides active and reactive power control of the machine while the grid-side converter (GSC) keeps the voltage of the DC-link constant. The additional freedom of reactive power generation by the GSC is usually not used due to the fact that it is more preferable to do so using the RSC. However, within the available current capacity the GSC can be controlled to participate in reactive power generation in steady state as well as during low voltage periods. The GSC can supply the required reactive current very quickly while the RSC passes the current through the machine resulting in a delay. Both converters can be temporarily overloaded, so the DFIG is able to provide a considerable contribution to grid voltage support during short circuit periods. This report deals with the introduction of DFIG, AC/DC/AC converter control and finally the SIMULINK/MATLAB simulation for isolated Induction generator as well as for grid connected Doubly Fed Induction Generator and corresponding results and waveforms are displayed. 5 NOMENCLATURE Pm Mechanical power captured by the wind turbine and transmitted to the rotor Ps Stator electrical power output Pr Rotor electrical power output Pgc Cgrid electrical power output Qs Stator reactive power output Qr Rotor reactive power output Qgc Cgrid reactive power output Tm Mechanical torque applied to rotor Tem Electromagnetic torque applied to the rotor by the generator Wr Rotational speed of rotors p derivative symbol Vqs ,Vds are the three-Phase supply voltages in d-q reference frame, respectively iqs ,ids are the three-Phase stator currents in d-q reference frame, respectively λqs ,λds are the three-Phase stator flux linkages in d-q reference frame, respectively Vqr ,Vdr are the three-Phase rotor voltages in d-q reference frame, respectively iqr ,idr are the three-Phase rotor voltages in d-q reference frame, respectively λqr ,λdr are the three-Phase rotor voltages in d-q reference frame, respectively Rs ,Rr are the stator and rotor resistances of machine per phase, respectively Lls ,Llr are the leakage inductances of stator and rotor windings, respectively θ s ,θ r are the stator and rotor flux angle, respectively Te ,Tm are the electromagnetic and mechanical torques, respectively Ps ,Qs are the stator-side active and reactive powers, respectively 6 Pr ,Qr are the rotor-side active and reactive powers, respectively RON ,ROFF are the IGBT ON and OFF resistances, respectively D, J are the moment of inertia and damping coefficient, respectively P are the Number of poles M1,M2 are the stator and rotor modulation depths, respectively Vtri is the triangular Voltage Signal R,L are the resistance and inductance of input filter, respectively V1, I1 are the input filter line voltage and current, respectively E is the DC-link voltage s is the Laplacian Operator C is the DC-Link capacitance PDC is the DC-link active power J Combined rotor and wind turbine inertia coefficient Ws Rotational speed of the magnetic flux in the air-gap of the generator, this speed is named synchronous speed. It is proportional to the frequency of the grid voltage and to the number of generator poles .   7 List of Diagrams s.no Name of the diagram and graph Page No. 1  Doubly fed induction generator (DFIG) with  16 converter control  2  Power flow in DFIG 17 3  Back to Back AC/DC/AC converter 23 4  Turbine power characteristics 26 5  Rotor converter control block Diagram 28 6  V‐I characteristics of turbine 29 7  Grid side converter control block Diagram 31 8  Pitch angle control block Diagram 32 9  Simulink diag. for wind turbine driven  isolated  34 squirrel cage induction generator.    10  Wind turbine simulink block diagram 35 11  Simulink diag. for DFIG 41 12  Wind turbine data acquisition block diagram  43 13  Grid data acquisition block 44   8 CONTENTS                                               Page No Acknowledgement   04 Abstract   05 Nomenclature  O6 Chapter 1 Introduction     11 Chapter 2 Doubly Fed Induction Generator  15 2.1 operating principle DFIG     17               2.2 Dynamic simulation of DFIG  20 Chapter 3 Back to Back AC/DC/AC Converter 22 modeling  Chapter 4 Converter control system 25 4.1 Rotor side converter system 26 4.2 grid side converter system 31 4.3 pitch angle control system 32 Chapter 5 Wind turbine driven Isolated Induction 33 Generator model Simulation in SIMULINK 5.2 Output characteristics 36 5.3 Operation of protection 38 system         9 Chapter 6 Operational Characteristics of a Doubly- 39 Fed Induction Generator (DFIG) Driven by a Wind Turbine 6.1 SIMULINK DIAGRAM 40 6.2 Wind Turbine Protection Block 42 6.3 Wind Turbine Data Acquisition 43 6.4 Grid Data Acquisition 44 6.5 Generator Data 46 6.6 Control parameter 46 Chapter 7 SIMULATION RESULTS 48 7.1 Turbine response to a change in 49 wind speed 7.2 Simulation of wind turbine and grid 53 parameters when the mode of operation is set to Control Parameters 7.3 Simulation of a voltage sag on the 57 120-kV system 7.4 Simulation of a fault on the 25-kV 60 system Chapter 8 CONCLUSION 63 REFERENCES 65                                                                                                      10