1. 1. Introduction 2. E-On Guidelines 3. Modelling 4. Controller Design 5. Simulation Results 6. Conclusion Voltage Regulator for Reactive Power Control on Synchronous Generators in Wind Energy Power Plants NORPIE / 2004 Nordic Workshop on Power and Industrial Electronics 14-16 June, 2004 Trondheim, Norway FACULTY OF ELECTRICAL ENGINEERING DEPARTMENT OF ELECTRICAL MACHINES AND DRIVES Voltage Regulator for Reactive Power Control on Synchronous Generators in Wind Energy Power Plants Balduino Rabelo Wilfried Hofmann Andreas Basteck Martin Tilscher NORPIE‘04 - Nordic Workshop on Power and Industrial Electronics 14-16 June, 2004 Trondheim, Norway VOITH TURBO CONTROLABLE DRIVES

2. 1. Introduction 2. E-On Guidelines 3. Modelling 4. Controller Design 5. Simulation Results 6. Conclusion Voltage Regulator for Reactive Power Control on Synchronous Generators in Wind Energy Power Plants NORPIE / 2004 Nordic Workshop on Power and Industrial Electronics 14-16 June, 2004 Trondheim, Norway 1. Introduction 2. E-On Guidelines 3. Machine Modelling 4. Controller Design 5. Simulation Results 6. Conclusion Topics

3. 1. Introduction 2. E-On Guidelines 3. Modelling 4. Controller Design 5. Simulation Results 6. Conclusion Voltage Regulator for Reactive Power Control on Synchronous Generators in Wind Energy Power Plants NORPIE / 2004 Nordic Workshop on Power and Industrial Electronics 14-16 June, 2004 Trondheim, Norway In a project with the Voith Co. the AEM Co. and the TU Dresden preliminary studies of a windmill using a hydrodynamic torque converter (VORECON) were carried out. The TU Chemnitz accomplished the following tasks: Modelling and simulation of a synchronous generator Emulation of the E-On cases for power plant connection to the electrical grid 1. Synchronisation and connection with the mains supply 2. Reactive power exchange with the net 3. Load drop 4. Active power limiting with frequency variation 5. Short-circuit behaviour Motivation

4. 1. Introduction 2. E-On Guidelines 3. Modelling 4. Controller Design 5. Simulation Results 6. Conclusion Voltage Regulator for Reactive Power Control on Synchronous Generators in Wind Energy Power Plants NORPIE / 2004 Nordic Workshop on Power and Industrial Electronics 14-16 June, 2004 Trondheim, Norway Why? Further expansion of wind energy. 2010 - 20,000 MW 2020 – 40,000 MW European interconnected system can bare a maximum drop of 3,000MW Wind generators will have to support the grid in case of faults Who? Wind farms with more than 100 MW connected to the high voltage and extra- high voltage grids. How? 2 - Reduce the active power and frequency fluctuation. 10% Pc/min 1 - Support the grid in case of 15% to 60 % voltage drops for not more than 3s 3 - Limit the cut-in in 1.2 of the rated power Pc at the connection point 4 - Control the reactive power in a desired range Verification of compliance with the new norms Guideline from manufacturers and measuring institutes Ergänzende Netzanschlussregein für Windenergieanlagen, 1.8.2003, E-on Netz Ltd. Guidelines for net connection from E-On

5. 1. Introduction 2. E-On Guidelines 3. Modelling 4. Controller Design 5. Simulation Results 6. Conclusion Voltage Regulator for Reactive Power Control on Synchronous Generators in Wind Energy Power Plants NORPIE / 2004 Nordic Workshop on Power and Industrial Electronics 14-16 June, 2004 Trondheim, Norway Active Power Limiting Curve

6. 1. Introduction 2. E-On Guidelines 3. Modelling 4. Controller Design 5. Simulation Results 6. Conclusion Voltage Regulator for Reactive Power Control on Synchronous Generators in Wind Energy Power Plants NORPIE / 2004 Nordic Workshop on Power and Industrial Electronics 14-16 June, 2004 Trondheim, Norway Enlarged Range Reactive Power Control Range t < 30min

7. 1. Introduction 2. E-On Guidelines 3. Modelling 4. Controller Design 5. Simulation Results 6. Conclusion Voltage Regulator for Reactive Power Control on Synchronous Generators in Wind Energy Power Plants NORPIE / 2004 Nordic Workshop on Power and Industrial Electronics 14-16 June, 2004 Trondheim, Norway Voltage Drop Profile

8. 1. Introduction 2. E-On Guidelines 3. Modelling 4. Controller Design 5. Simulation Results 6. Conclusion Voltage Regulator for Reactive Power Control on Synchronous Generators in Wind Energy Power Plants NORPIE / 2004 Nordic Workshop on Power and Industrial Electronics 14-16 June, 2004 Trondheim, Norway Hydrodynamic Torque Converter VORECON

9. 1. Introduction 2. E-On Guidelines 3. Modelling 4. Controller Design 5. Simulation Results 6. Conclusion Voltage Regulator for Reactive Power Control on Synchronous Generators in Wind Energy Power Plants NORPIE / 2004 Nordic Workshop on Power and Industrial Electronics 14-16 June, 2004 Trondheim, Norway Dynamical Model of the VORECON Rotor HubGear BoxVorecon - Voith Coupling Brake Interface TU Chemnitz Torque

10. 1. Introduction 2. E-On Guidelines 3. Modelling 4. Controller Design 5. Simulation Results 6. Conclusion Voltage Regulator for Reactive Power Control on Synchronous Generators in Wind Energy Power Plants NORPIE / 2004 Nordic Workshop on Power and Industrial Electronics 14-16 June, 2004 Trondheim, Norway The voltage equation of a synchronous machine where the underline defines a complex vector Description in a rotating reference frame   q d rr Basic Equations

11. 1. Introduction 2. E-On Guidelines 3. Modelling 4. Controller Design 5. Simulation Results 6. Conclusion Voltage Regulator for Reactive Power Control on Synchronous Generators in Wind Energy Power Plants NORPIE / 2004 Nordic Workshop on Power and Industrial Electronics 14-16 June, 2004 Trondheim, Norway The electromechanical torque expression The dynamical interactions between the stator, damping and field circuits are given the following operators The fluxes can be obtained by the expressions Torque and Flux Linkage Equations

12. 1. Introduction 2. E-On Guidelines 3. Modelling 4. Controller Design 5. Simulation Results 6. Conclusion Voltage Regulator for Reactive Power Control on Synchronous Generators in Wind Energy Power Plants NORPIE / 2004 Nordic Workshop on Power and Industrial Electronics 14-16 June, 2004 Trondheim, Norway Block Diagram of the Synchronous Generator

13. 1. Introduction 2. E-On Guidelines 3. Modelling 4. Controller Design 5. Simulation Results 6. Conclusion Voltage Regulator for Reactive Power Control on Synchronous Generators in Wind Energy Power Plants NORPIE / 2004 Nordic Workshop on Power and Industrial Electronics 14-16 June, 2004 Trondheim, Norway Control Variables Wind Turbine Vorecon Synchronous Generator Pitch Angle  Guide Vane Position H Field Voltage u f The system has 3 control variables: - pitch angle and the guide vane position control the main power flow - field voltage controls the magnetising of the synchronous generator and the reactive power flow. This latter can also influence the stability of the system.

14. 1. Introduction 2. E-On Guidelines 3. Modelling 4. Controller Design 5. Simulation Results 6. Conclusion Voltage Regulator for Reactive Power Control on Synchronous Generators in Wind Energy Power Plants NORPIE / 2004 Nordic Workshop on Power and Industrial Electronics 14-16 June, 2004 Trondheim, Norway Induced Voltage Controller The induced voltage controller U Pol uses the field voltage u f to regulate the flux In high-powered generators these self-excited control schemes present a faster inner field current control not shown here Considering the speed constant the induced voltage dynamics depends only on the flux

15. 1. Introduction 2. E-On Guidelines 3. Modelling 4. Controller Design 5. Simulation Results 6. Conclusion Voltage Regulator for Reactive Power Control on Synchronous Generators in Wind Energy Power Plants NORPIE / 2004 Nordic Workshop on Power and Industrial Electronics 14-16 June, 2004 Trondheim, Norway The field controller has to accomplish the following tasks: regulate the induced voltage at the machine terminals during synchronisation control the power factor or the reactive power flow during normal operation guarantee the dynamical stability during undesired transient conditions An outer power factor control loop influences the induced voltage in normal operating conditions, as well as compensates the voltage drop over the stator windings during loading Controller Tasks and Structure

16. 1. Introduction 2. E-On Guidelines 3. Modelling 4. Controller Design 5. Simulation Results 6. Conclusion Voltage Regulator for Reactive Power Control on Synchronous Generators in Wind Energy Power Plants NORPIE / 2004 Nordic Workshop on Power and Industrial Electronics 14-16 June, 2004 Trondheim, Norway Controller Optimisation The induced voltage controller posses 2 basic PI structures for synchronisation and for normal operation that were optimised by module (BO) and by symmetrical optimum (SO) rules, respectively.

17. 1. Introduction 2. E-On Guidelines 3. Modelling 4. Controller Design 5. Simulation Results 6. Conclusion Voltage Regulator for Reactive Power Control on Synchronous Generators in Wind Energy Power Plants NORPIE / 2004 Nordic Workshop on Power and Industrial Electronics 14-16 June, 2004 Trondheim, Norway Synchronisation Starting Currents Connecting the machine to the mains with an angle error from less than 10 degrees gives transient currents which peak values lie under 40 % of rated value vanishing in less than one second, as shown in the left figure. With a neglectiable angle error the start-up currents are much smaller, as can be observed in the right figure. t(s) stator phase currents t(s)

18. 1. Introduction 2. E-On Guidelines 3. Modelling 4. Controller Design 5. Simulation Results 6. Conclusion Voltage Regulator for Reactive Power Control on Synchronous Generators in Wind Energy Power Plants NORPIE / 2004 Nordic Workshop on Power and Industrial Electronics 14-16 June, 2004 Trondheim, Norway Torque Step from No-load to Rated Value An extreme power step is simulated where the input torque is increased from no-load condition to rated torque. The generator is kept in synchronism and the currents reach the rated value after the transient period. t(s) generator torque stator phase currents

19. 1. Introduction 2. E-On Guidelines 3. Modelling 4. Controller Design 5. Simulation Results 6. Conclusion Voltage Regulator for Reactive Power Control on Synchronous Generators in Wind Energy Power Plants NORPIE / 2004 Nordic Workshop on Power and Industrial Electronics 14-16 June, 2004 Trondheim, Norway Coupling with the Reactive Power Control After a negative mechanical torque step over-shoots on the electromechanical torque occur during the transient period. The well-damped power factor controller reduced the over-shoots due to the coupling with the active power canal and let the actual value reach the reference smoothly after some seconds. t(s) generator torque power factor

20. 1. Introduction 2. E-On Guidelines 3. Modelling 4. Controller Design 5. Simulation Results 6. Conclusion Voltage Regulator for Reactive Power Control on Synchronous Generators in Wind Energy Power Plants NORPIE / 2004 Nordic Workshop on Power and Industrial Electronics 14-16 June, 2004 Trondheim, Norway Power Factor Control The power factor controller presents good responses over the desired range. Higher damping is observed on the capacitive range, as expected. actual ref inductive capacitive power factor

21. 1. Introduction 2. E-On Guidelines 3. Modelling 4. Controller Design 5. Simulation Results 6. Conclusion Voltage Regulator for Reactive Power Control on Synchronous Generators in Wind Energy Power Plants NORPIE / 2004 Nordic Workshop on Power and Industrial Electronics 14-16 June, 2004 Trondheim, Norway Power Factor Step The power factor step presents a retarded response due to the coupling with the active power channel. The increase on the torque caused by the reference power factor step is less damped than the reaction caused again on the power factor. Such extremes reactive power steps must be avoided in the normal operation of the generator in order to avoid the observed torque steps. t(s) power factor generator torque

22. 1. Introduction 2. E-On Guidelines 3. Modelling 4. Controller Design 5. Simulation Results 6. Conclusion Voltage Regulator for Reactive Power Control on Synchronous Generators in Wind Energy Power Plants NORPIE / 2004 Nordic Workshop on Power and Industrial Electronics 14-16 June, 2004 Trondheim, Norway The 3-phase voltage drop profile from E-ON have a similar effect of a 3-phase short-circuit on the machine. After the well-known transient periods further oscillations appear on the torque and on the currents due to the slow increase of the mains voltage. Voltage Drop t(s) generator torque stator phase currents net voltages

23. 1. Introduction 2. E-On Guidelines 3. Modelling 4. Controller Design 5. Simulation Results 6. Conclusion Voltage Regulator for Reactive Power Control on Synchronous Generators in Wind Energy Power Plants NORPIE / 2004 Nordic Workshop on Power and Industrial Electronics 14-16 June, 2004 Trondheim, Norway The oscillations observed previously on the torque and on the currents are also observed on the speed. The power angle crosses the stability limit for a short period of time. The machine is kept in synchronism due to the reached dynamical stability enabled by the power factor controller. However, the required field voltages to magnetise the machine in such cases are higher than the maximum allowed.  break down  Rated Power Angle and Speed t(s)  n  rpm) pole pitch angle rotor speed

24. 1. Introduction 2. E-On Guidelines 3. Modelling 4. Controller Design 5. Simulation Results 6. Conclusion Voltage Regulator for Reactive Power Control on Synchronous Generators in Wind Energy Power Plants NORPIE / 2004 Nordic Workshop on Power and Industrial Electronics 14-16 June, 2004 Trondheim, Norway Load Drop A 100 % load drop was simulated in order to verify the possible overvoltage effects on the machine terminals. The induced voltage increases after at the load drop moment but the field controller actuates faster and limits the increase ratio letting the intern voltage in acceptable levels until switching off or reloading. stator phase currents induced voltage t(s)

25. 1. Introduction 2. E-On Guidelines 3. Modelling 4. Controller Design 5. Simulation Results 6. Conclusion Voltage Regulator for Reactive Power Control on Synchronous Generators in Wind Energy Power Plants NORPIE / 2004 Nordic Workshop on Power and Industrial Electronics 14-16 June, 2004 Trondheim, Norway A synchronous machine classical model was used to simulate different situations before and after synchronisation with the electrical grid. A voltage regulator for the field excitation of the synchronous generator was designed. This controller has to guarantee stable operation of the generator under various conditions including faults. Simulation results show the good performance of the controller. With the already existing controller the machine is kept stable during extreme conditions like torque steps and reactive power variations. Faulty conditions were also simulated. Further studies will investigate the effects of faulty conditions on the mechanical drive train caused by high electromechanical torque and its harmonics and of the distribution line and the transformer on the performance of the machine under voltage drops. Summary and Future Works