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 2

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 3

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 4

5. Generic Wind Model for Type 3 WTG 5 Blade Pitch Limited by Integrators Aerodynamic ModelShaft Dynamics Model 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

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 6 Power Commands from Coverter Power Injected into network 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 7 3.Constant Reactive Power 2.Constant Power Factor Angle 1.Plant-side Voltage Regulation Realistic Limits on Power Power Outputs

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 8

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 9

10. Introduction to Contingencies 10 CategoryContingencies System Limits or Impacts Initial Event(s) and Contingency Element(s) Elements Out of Service Thermal Limits Voltage Limits System Stable Loss of Demand or Curtailed Firm Transfers Cascading Outages c A-No Contingencies All Facilities in Service None Normal Rating a YesNo B- Event resulting in the loss of a single element SLG or 3 phase fault with normal clearing or loss an element without fault SingleA/R YesNo b No Single pole block with normal clearing SingleA/R YesNo b No a)Normal Rating (A/R) refers to the applicable normal and emergency facility thermal rating b)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 11

12. TSAT Stability Analysis 12 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. Case NumberBus NumberWind PenetrationLoad Model Case I 181 bus0%Constant Power Case II 197 bus12% ( NW and CA)Constant Power Case III 181 bus0%Composite Load Model Case IV 197 bus12% (NW and CA)Composite Load Model

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. 13 Transient VoltageTransient Frequency Post-transient Voltage Minimum 0.75 at load buses or 0.7 at non-load buses Minimum 0.8 for maximum 20 cycles at load buses Minimum 0.96 for 500kV bus voltage following disturbance Minimum 59.6Hz for maximum 6 cycles at load buses Minimum 0.95 at any bus after critical contingencies

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

15. Case I: Post-transient Voltage Analysis Case I Post-transient Voltage Violation after Pacific Intertie Outage 15 Case Limiting Transfer Capacity Limiting Factor Limiting Contingency Minimum Violation Value I4695.93MW Post-transient Voltage dip Branch outage 111-173 0.949Pu on Bus 172 II4643.99MW Frequency Drop Branch outage 66-78 59.230Hz on Bus 65 III4311.07MW Non-load Voltage Drop on Bus 134 Branch outage 119-134 0.6950Pu on Bus 134 IV4643.99MW Frequency Drop Branch outage 66-78 59.230Hz on Bus 65

16. Case II: Wind penetration 16 Case Limiting Transfer Capacity Limiting Factor Limiting Contingency Minimum Violation Value I4695.93MW Post-transient Voltage dip Branch outage 111-173 0.949Pu on Bus 172 II4643.99MW Frequency Drop Branch outage 66-78 59.230Hz on Bus 65 III4311.07MW Non-load Voltage Drop on Bus 134 Branch outage 119-134 0.6950Pu on Bus 134 IV4643.99MW Frequency Drop Branch outage 66-78 59.230Hz on Bus 65

17. Case III: Motor penetration 17 Fig. 8 Case III Transient Voltage Violation in Response to North California Outage Case III transient Voltage Response at Limiting Transfer Capacity Case III transient Voltage Violation in response to North California Outage Case Limiting Transfer Capacity Limiting FactorLimiting Contingency Minimum Violation Value I4695.93MW Post-transient Voltage dip Branch outage 111- 173 0.949Pu on Bus 172 II4643.99MWFrequency DropBranch outage 66-7859.230Hz on Bus 65 III4311.07MW Non-load Voltage Drop on Bus 134 Branch outage 119- 134 0.6950Pu on Bus 134 IV4643.99MWFrequency DropBranch outage 66-7859.230Hz on Bus 65

18. Case IV: Wind and motor penetration 18 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 Fault cleared, frequency above 59.6 Hz below 59.6Hz more than 6 cycles Case Limiting Transfer Capacity Limiting FactorLimiting Contingency Minimum Violation Value I4695.93MW Post-transient Voltage dip Branch outage 111- 173 0.949Pu on Bus 172 II4643.99MWFrequency DropBranch outage 66-7859.230Hz on Bus 65 III4311.07MW Non-load Voltage Drop on Bus 134 Branch outage 119- 134 0.6950Pu on Bus 134 IV4643.99MWFrequency DropBranch outage 66-7859.230Hz on Bus 65

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. 19 Case Limiting Transfer Capacity Limiting Factor Limiting Contingency Minimum Violation Value I4695.93MW Post-transient Voltage dip Branch outage 111-173 0.949Pu on Bus 172 II4643.99MW Frequency Drop Branch outage 66-78 59.230Hz on Bus 65 III4311.07MW Non-load Voltage Drop on Bus 134 Branch outage 119-134 0.6950Pu on Bus 134 IV4643.99MW Frequency Drop Branch outage 66-78 59.230Hz on Bus 65

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. 20

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 21

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

23. Questions? 23