Stability analysis on WECC Systems with Wind Penetration and Composite Load Model

1. Stability analysis on WECC Systems with Wind Penetration and Composite Load Model Hyungdon Joo and Melissa Yuan Mentor Yidan Lu Professor Kevin Tomsovic Young Scholars Program Young Scholars Presentation 17 July 2014 Knoxville, Tennessee

2. Overview • Topic and Purpose of Research • Introduction • What is the WECC? • Generic wind model for Type 3 WTG • Composite Load Model • Contingencies/NERC/WECC Standards • Methodology of Research • TSAT stability analysis • Results • Contingency simulation for case studies • Conclusions and Summary • Future Work

3. Topic and Purpose of Research Topic: • Analyzing the stability of WECC network given integration of wind power • Specific attention given to Pacific DC intertie • Application of new composite load model in the study of grid stability • Analyzing the combined effect of wind integration and motor penetration on system stability. Purpose: • To update the operating limit of the Pacific DC Intertie with new generation and load patterns. • More economic in improving existing components than building new components • To observe the influence of wind turbine and motor load • Damping • Transmission fault clearing

4. What is the WECC? • Western Electricity Coordinating Council (WECC) • Canada: Alberta and British Columbia • United States: Washington, Oregon, California, Idaho,  Nevada, Utah, Arizona, Colorado, Wyoming, Montana, South Dakota, New Mexico, Texas • Mexico: northern area, Baja California • Pacific Intertie (3 AC line and 1 DC line) • Path 65(DC) Path 66 (AC) • 3.1GW of DC and 3 GW of AC • Oregon • Los Angeles

5. Generic Wind Model for Type 3 WTG • Four separate models • Pitch control Model • Calculates optimal blade pitch from shaft speed and power input • Pitch Control and Compensator are Non-windup Integrators • Turbine Model • Simplified modeling of turbine aerodynamics and shaft dynamics • Calculates shaft speed given blade pitch Blade Pitch Limited by Integrators Aerodynamic Model Shaft Dynamics Model

6. Generic Wind Model for Type 3 WTG (cont’d) • Generator Model • No Mechanical-state variables (in Turbine Model) • Calculates power injected into network in response to power commands from Converter control model Power Injected into network Power Commands from Coverter Type 3 WTG Generator Model

7. Generic Wind Model for Type 3 WTG (cont’d) • Converter Control Model • Controls Real and Reactive Power output • Reactive power control • Faster due to power electronic converter • Three control modes • Reactive Power Command output • Active (torque) power control • Slower due to physical components • Anti-windup limits on power • Real Power Command output 1.Plant-side Voltage Regulation 2.Constant Power Factor Angle 3.Constant Reactive Power Power Outputs Realistic Limits on Power

8. Composite Load Model • 60% of load is represented by 3-phase and 1-phase motors and 30% by constant power load, 10% represented by frequency depended load. • Bus 150, 3118MW of load consists of 20% 1-phase motor and 80% constant power load

9. Composite Load Model (cont’d) • Distribution Equivalent Data • Transformer tap control and substation feeders • Equivalent load modeled at High voltage transmission bus • Additions to Conventional model – bulk-power delivery transformer, a feeder equivalent, and end use loads at different types • More realistic for Transient Stability Studies

10. Introduction to Contingencies Normal Rating (A/R) refers to the applicable normal and emergency facility thermal rating Planned or controlled interruption may occur in certain areas without impacting the overall security of the interconnected transmission systems.

11. Methodology of Research • Conversion of PSSE wind model data to TSAT data format

12. TSAT Stability Analysis • Case I is control with no wind penetration or composite load • Doubly-Fed Induction Generator (DFIG) Model is used for 11 wind turbines in Case II and Case IV. • Composite Load Model with representation of compressor stalling applied in Case III and Case IV.

13. TSAT Stability Analysis • Pacific HVDC is represented by constant load in NW and injection in CA. • 247 non-fault AC contingencies are analyzed in 20 seconds of transient period and 5 seconds of post-transient period. • 8 critical contingencies around pacific intertie are identified post transient voltage check.

14. Case I: Base Case Contingency Simulation on WECC system without wind penetration nor composite load model

15. Case I: Post-transient Voltage Analysis • Case I Post-transient Voltage Violation after Pacific Intertie Outage

16. Case II: Wind penetration

17. Case III: Motor penetration Case III transient Voltage Response at Limiting Transfer Capacity Case III transient Voltage Violation in response to North California Outage Fig . 8 Case III Transient Voltage Violation in Response to North California Outage Fig . 8 Case III Transient Voltage Violation in Response to North California Outage

18. Case IV: Wind and motor penetration below 59.6Hz more than 6 cycles Fault cleared, frequency above 59.6 Hz Freq. Response to Northwest Outage in Case II and IV at Limiting Transfer Capcity Freq. Standard Violation in Response to Northwest Outage in Case II and IV

19. Conclusions and Summary • One of the three AC branches near the Pacific Intertie, 111-173 was weakest part of WECC in base case. • Nearby wind turbines weakened the stability of Northwest with a limiting contingency (branch outage 66-78). • Air conditioning compressor stalling caused low voltage issues in California during transient period. • Wind Turbines restored transfer capacity reduced by stalling motors by allowing more dynamic VAR around Pacific Intertie.

20. Future Work • Applying dynamic High Voltage DC (HVDC) model in 200-bus WECC system. • Including monopole DC contingency in N-1 transfer capacity analysis for all test systems. • Developing wide area control schemes to restore transfer capacity to compensate for compressor stalling of air conditioning units.

21. References • WECC Wind Power Plant Dynamic Modeling Guidelines - August 2010 draft • Hiskens, Ian A. Dynamics of Type-3 Wind Turbine Generator Models. • WECC New Load Model – December 2010 • WECC/NERC Planning and Operating Criteria. Section XI • 2012 Spring System Operating Limit Study Report

22. Acknowledgements Thank you to Mentor Yidan Lu and Professor Kevin Tomsovic

23. Questions?