Fault-Tolerant Control of a Blade-pitch Wind Turbine With Inverter-fed Generator

Fault-Tolerant Control of a Blade-pitch Wind Turbine With Inverter-fed Generator V. Lešić 1, M. Vašak 1, N. Perić 1, T. Wolbank 2 and G. Joksimović 3 1 Faculty of Electrical Engineering and Computing, University of Zagreb 2 Faculty of Electrical Engineering and Information Technology, Vienna University of Technology 3 Faculty of Electrical Engineering, University of Montenegro e-mail: mario.vasak@fer.hr

2 Presentation Outline Wind energy The problem we tackle Wind turbine classical control system Fault-tolerant control extension Simulation results Conclusion

3 Wind energy The fastest-growing renewable energy source Expensive energy Main focus today is to: increase energy production reduce structural loads, extend lifecycle of wind turbine increase power quality and improve power system integration increase availability of wind turbines Wind turbines are located on remote locations High-cost repairs and maintenance

4 The problem we tackle Besides gearbox and power converter faults, electromechanical faults are the most common faults in wind turbine systems In case of generator fault wind turbine shut-down Lots of monitoring and control equipment is already installed

4 The problem we tackle Besides gearbox and power converter faults, electromechanical faults are the most common faults in wind turbine systems In case of generator fault wind turbine shut-down Lots of monitoring and control equipment is already installed We show how to:

4 The problem we tackle Besides gearbox and power converter faults, electromechanical faults are the most common faults in wind turbine systems In case of generator fault wind turbine shut-down Lots of monitoring and control equipment is already installed We show how to: stop or postpone the generator fault development once the fault is characterized - fault-tolerant control achieve maximum energy production under emergency circumstances

5 Wind turbine control system ω TORQUE controller T gref GENERATOR & INVERTER T g WIND WIND TURBINE ω ω ref + - ω SPEED controller β ref PITCH servo & controller β Torque control loop (variable-speed) T gref = K λ ω 2 g Speed control loop (variable-pitch) Proportional-integral(-derivative) gain scheduling

6 Fault-tolerant control Stator winding inter-turn isolation fault Rotor bar fault (squirrel-cage induction machine) Both can be well characterized with machine flux path areas a c' θ 2 b' T g_nonf T gf θ 1 b θ 2 c Generator torque (Nm) T g_nonf T gf Δθ θ off θ 1 θ 2 θ on π θ 1 Flux linkage angle (rad) a'

Fault-tolerant control Stator winding inter-turn isolation fault Rotor bar fault (squirrel-cage induction machine) Both can be well characterized with machine flux path areas a c' θ 2 b' T g_nonf T gf θ 1 b θ 2 c Generator torque (Nm) T g_nonf T gf Δθ θ off θ 1 θ 2 θ on π θ 1 Flux linkage angle (rad) 6 a' We propose: Fast loop: keeping torque below safety value on the faulty part of the flux path and its proper control elsewhere Slow loop: keeping the power production optimal under fault by selecting the optimal average torque

7 Fault-tolerant control(2) Maximizing the power production under emergency circumstances 250 T gn Generator torque (knm) 200 150 100 50 T av T gf Faulty machine T gopt Healthy machine 0 0 ω* 10 20 ω 30 g g1 Speed (rpm)

Fault-tolerant control(3) Interventions in conventional control system ω TORQUE controller T gref ' ω g T gref FAULT-TOLERANT control θ GENERATOR & INVERTER T g WIND WIND TURBINE ω ω ref + - SPEED β ref PITCH servo controller & controller β ω

Fault-tolerant control(3) Interventions in conventional control system ω TORQUE controller T gref ' ω g T gref FAULT-TOLERANT control θ GENERATOR & INVERTER T g WIND WIND TURBINE ω ω ref + - SPEED β ref PITCH servo controller & controller β ω θ T gref ' ω g SLOW loop T g_nonf θ start θ end FAST loop T gref T gf θ 1,θ 2 T gf Fault detection and characterization ω ref

9 Simulation results Healthy and faulty wind turbine through the entire wind speed operating area 20 Wind speed (m/s) 10 800 400 0 0 50 100 150 200 250 300 350 400 healthy faulty Power (kw) 20 10 0 0 50 100 150 200 250 300 350 400 healthy faulty Pitch angle (degrees) 0 0 50 100 150 200 250 300 350 400

10 Simulation results(2) Stator winding inter-turn isolation fault 250 Generator torque (knm) 125 120 115 Generator torque (knm) 200 150 100 20 25 30 35 40 45 50 250 34.8 34.9 35 35.1 35.2 Rotor speed (rpm) 22.62 22.6 30 200 150 100 34.8 34.85 34.9 34.95 35 35.05 35.1 35.15 35.2 Rotor speed (rpm) 34.8 34.9 35 35.1 35.2 28 26 24 20 25 30 35 40 45 50

11 Simulation results(3) Rotor bar defect 250 Generator torque (knm) 200 Generator torque (knm) 150 125 120 100 35 40 45 50 55 60 250 115 35 36 37 38 39 40 41 42 43 44 45 Wind turbine rotor speed (rpm) 22.8 200 150 22.7 22.6 22.5 22.4 35 36 37 38 39 40 41 42 43 44 45 29.5 29 28.5 28 27.5 100 35 36 37 38 39 40 41 42 43 44 45 Wind turbine rotor speed (rpm) 27 35 40 45 50 55 60

12 Conclusions Proper reacting to diagnosed wind turbine faults and postponing their further development can save lots of money

12 Conclusions Proper reacting to diagnosed wind turbine faults and postponing their further development can save lots of money We propose a fault-tolerant control for generator electromechanical faults diagnosed fault is fully respected in operation power delivery under fault is deteriorated as less as possible compared to healthy machine conditions

12 Conclusions Proper reacting to diagnosed wind turbine faults and postponing their further development can save lots of money We propose a fault-tolerant control for generator electromechanical faults diagnosed fault is fully respected in operation power delivery under fault is deteriorated as less as possible compared to healthy machine conditions Simple extension of conventional wind turbine control system

12 Conclusions Proper reacting to diagnosed wind turbine faults and postponing their further development can save lots of money We propose a fault-tolerant control for generator electromechanical faults diagnosed fault is fully respected in operation power delivery under fault is deteriorated as less as possible compared to healthy machine conditions Simple extension of conventional wind turbine control system Can be applied to different types of machines Many issues are open with this strategy, like e.g. investigation of structural wind turbine oscillations induced by torque modulation

13 Acknowledgment The work has been supported by FP7 SEE-ERA.NET PLUS under contract No. ERA 80/1 (MONGS Monitoring of Wind Turbine Generator Systems) more info at http://www.ieam.tuwien.ac.at/forschung/mongs/