Mitigation & Protection of Sub-Synchronous Controller Interactions (SSCI) in DFIG Wind Turbine Systems

Transcription

1 Mitigation & Protection of Sub-Synchronous Controller Interactions (SSCI) in DFIG Wind Turbine Systems Krish Narendra, P.hD. CTO ERL Protection, Automation, Control & Smart Grid ERLPhase Power Technologies Ltd. All Rights Reserved. 14 April 2015, Hannover, Germanay

2 Outline What is DFIG? What is Sub Synchronous Controller Interaction (SSCI)? Why does the Wind System Controller interact with the system? How does the Wind System Controller interact with the system? Why it is important to Mitigate & Protect against SSCI? What is S-PRO Relay? How to mitigate the SSCI Using S-PRO Relay? How to protect from SSC Using S-PRO Relay? What are the consequences if we don t mitigate or protect? Conclusions

3 What is DFIG? Doubly Fed Induction Generator Double Fed : There will be excitation (voltage & current) on both STATOR & ROTOR windings This is different from normal induction machine, where the STATOR is excited and the ROTOR is normally short circuited or through a variable resistance

4 DFIG should produce CONSTANT POWER to the electrical grid to which it is connected?? ROTOR excitation is applied here STATOR excitation is applied here Wind Turbine

5 Electrical Equivalent Circuit of DFIG S = Slip = w1 wm w1 : w1 = synchronous speed, wm = rotor mechanical speed Pr = -s Ps; Pr = rotor power, s= slip, Ps= stator power fr = s f1; fr = rotor frequency, s = slip, f1 = stator or network frequency

6 DFIG constant power how to achieve? SHOULD KEEP THE RATIO OF STATOR VOLTAGE / FREQUENCY A CONSTANT V/ f = constant = flux

7 What is SSCI (sub synchronous controller Interaction)? Sub Synchronous Controller Interaction (SSCI)

8 How does the controller interact with the system?

9 Ohms Ohms How Does Turbine Side Dynamic Resistance Varies with Frequency? Turbine Side Scans, R & X, 100% Dispatch Resistance Reactance -4-6 Frequency (Hz) Turbine Side Scans, R & X, 30% Dispatch Resistance Reactance Frequency (Hz) 9

10 Ohms Z1 (ohms) How does the controller interact with the system..? Frequency Scan - CTG Frequency (Hz) CTG008-current_injection CTG008-Harmonic_Scan Turbine Side Scans, R & X, 100% Dispatch Resistance Reactance -4-6 Frequency (Hz)

11 Xcel Energy (USA) Utility Event System Single Line Diagram- 2008

12 Utility Event: What Happened? 1- Breaker 1 & 2 opened for regular system switching procedure 2- CT1,CT2, and W start feeding radially through series capacitor 345 kv To the System Line kv 15 MW (20% of total generation) 45 MVA 3- Tripped the CT generator unit 12

13 Utility Event - TESLA DFR Capture 9 Hz & 13 Hz dominant sub harmonics High speed recording of 3 phase generator currents captured by the DFR 13

14 Utility Event Slow Speed Event Analysis Slow speed (swing ) recording of one of the phases 14

15 What are the consequences? Damage to the wind turbine Damage to the series compensation system Damage to the electronics convertor Possible saturation of the transformers at low frequency sub harmonics

16 How to mitigate SSCI Use advanced Micro Processor Based Protection Relay Use high speed detection sub harmonic currents / voltages using advanced microprocessor based system Improve existing controller performance more positive damping at critical sub harmonic frequencies Faster command to by pass the series compensation system

17 Microprocessor Based Sub harmonic Protection Relay (S-PRO)

18 AC Voltages SSCI - Sub harmonic calculations using dual processor implementations in S-PRO AC line currents FPGA Processor -1 (Field Programmable Gate Arrays) Anti Aliasing Filter High Speed Recursive Fourier Transform (RFT) Using 2 ms Sliding Window from high speed samples (5760 / s on 60 Hz or 4800/ s on 50 Hz) A/D Conversion DSP Processor -2 Sub Harmonic Detection Logic ( 5 45 Hz) Band Pass Filtering (5 45 Hz) Evaluation of sub harmonic logic using MAX (f5 f45) principle. Trip / Alarm based on user configuration

19 Microprocessor Sub Harmonic Detection Logic Diagram

20 Microprocessor Sub Harmonic Detection Trip or Alarm: = max (f2, f3, f4, f5, f6, f7) > Lset 20

21 Mitigation: By Passing of Series Capacitor Using S-PRO Relay Use existing PLCC to send close command to bypass circuit Wind generators Series Capacitor Other Generators (Combustion, Steam etc.) Direct Connection from Relay output contact to the bypass circuit IEC GOOSE message through FO

22 Mitigation: Change Wind Controller gain using S-PRO Relay Logic Wind generators User defined Relay logic to vary the gain of the controller to damp the oscillations Other Generators (Combustion, Steam etc.) Series Capacitor

23 Mitigation: Transfer Trip Wind Generator using S-PRO Relay Logic Wind generators Send transfer trip command through output contact or GOOSE message to remove Wind Generator System from the grid Other Generators (Combustion, Steam etc.) Series Capacitor

24 Protection : Trip Wind Generator / Other Generators using S-PRO Relay Logic Wind generators Other Generators (Combustion, Steam etc.) Series Capacitor

25 Xcel Energy (USA) SSCI EVENT 2008 Playback on S-PRO Relay

26 Xcel Energy (USA) SSCI EVENT 2008 Playback on S-PRO Relay

27 ERCOT TEXAS (USA) SSCI EVENT 2009 Playback on S-PRO Relay

28 ERCOT TEXAS (USA) SSCI EVENT 2009 Playback on S-PRO Relay

29 Conclusions With the increase use of wind generators (DFIGs) feeding HV and EHV utility networks with series compensation, it is necessary to ensure that sub harmonic oscillations are monitored, and that the electrical grid is protected from any resulting detrimental effects. Micro Processor Based S-PRO Relay can reliably mitigate / protect from sub harmonics ( 5 55 Hz with 60 Hz system) generated due to following phenomena with dual processor ( < 250 ms) : SSR sub synchronous resonance (Generators, HVDC, FACTS, PV - Convertor etc..) SSI sub synchronous interactions SSCI sub synchronous controller instability/interactions- New phenomena in Wind Turbines controller interactions in Type 3 DFIG system. SSTI sub synchronous torsional interactions IGE- Induction generator effect SSFR sub synchronous ferro resonance (in distribution system transformers)

30 THANK YOU!! erlphase.com