1. High Voltage Power Electronics Technologies for Integrating Renewable Resources into the Grid RenewElec Workshop Carnegie Mellon University October 22, 2010 – Pittsburgh, PA Dr. Gregory F. Reed & Brandon M. Grainger Power & Energy Initiative University of Pittsburgh, Swanson School of Engineering Electrical & Computer Engineering Department

2. Background Background Technology and Infrastructure Challenges Technology and Infrastructure Challenges Power Electronic Technologies Power Electronic Technologies HVDC Systems HVDC Systems FACTS Devices FACTS Devices Summary Summary Overview 2

3. Background 3

4. Background 4 Challenges with Renewable Integration Integration of conventional generation resources (coal, petroleum, and natural gas) and renewable sources (solar and wind) present technological obstacles to the current system and practices Focus of Work: Characterize common obstacles and present solutions that derive from the interconnection of transmission technologies for better renewable integration FACTS Compensation Devices for AC Infrastructure Expansion Conventional and Voltage-Source Converter Based HVDC Transmission Technology Important Factor: Multiple hybrid configurations can be considered for more economic and reliable grid interconnection

5. Texas / ERCOT Example 5 Texas as a Model: Trends to Observe Generation portfolio consists of traditional fossil generation sources such as coal, petroleum, and natural gas. It also boasts a strong supply of renewable generation, most notably, wind power; and clean nuclear energy Stands as the U.S. leader in wind generation capacity with 7.892 GW installed CREZ Project will add 10 GW more wind power…… 2,300 miles of new 345-kV transmission with shunt and series dynamic compensation

6. 6 Geographic Intensity of Highest Penetration Potential Renewable Resources Wind Speed Across the USSolar Intensity Across the US

7. Technological and Infrastructure Challenges 7

8. 8 Issues that are Turbine (Rotating Machine) Related Turbine Tripping Loss in generators can lead to major cascading issues Subsynchronous Resonance (SSR) Contributor to turbine shaft damage, SSR results from turbine tensional vibration that is amplified by series capacitors. Reactive Power Consumption Induction generators require substantial amounts of reactive power during operation. This power is pulled from the grid and can cause depressed voltage conditions and stability problems. Transmission Infrastructure Issues Power System Dynamic Performance Moving New/Distant Resource Portfolios to Load Centers Operations in New Market and Regulatory Conditions Challenges and Issues

9. 9 Issues Related to Dispatch of Generation Resources Voltage Instability Large differences between the output voltage of the generating utility and grid operating voltage at the point of common coupling can lead to instability on the grid. Changes in wind speed can contribute to this issue Voltage Flicker Wind and solar power generators are non-dispatchable (fuel source is inherently variable by nature) often resulting in fluctuations in output voltage.

10. Power Electronics Available for Improved Integrated Generation Management (IGM) 10

11. Power Electronics for IGM 11 Inspiring Quote: “Up until now we’ve just been connecting wind farms to the grid. What we need to be doing is integrating them. Power electronics will enable us to do this by controlling the power flows. It’s a solution that’s starting to be used, but NOWHERE, near to the extent that will be needed in the future.” (Wind Directions, 2008)

12. Power System Basics Generation Mechanical-to- Electrical Energy Conversion Transmission Distribution Electrical Power Used and Electrical-to-Mechanical Energy Conversion Power Generation, Transmission and Distribution FACTS / HVDC – High Capacity Power Electronics are applied here for improved operation, reliability, etc. 12

13. 13 Evaluation of AC & HVDC for Future Generation Options Many of today’s interconnections make use of high voltage AC transmission to integrate many alternative energies to the electric network. But is it the most optimal, reliable, and secure option for future infrastructure expansion in all cases? Renewable resources located further from load centers There is a distance at which HVDC becomes economically more attractive compared to AC. Why? AC cable transmission suffers from excessive reactive current drawn by cable charging capacitances. Reactive shunt compensation required to absorb excessive reactive power and avoid overvoltage conditions Power Electronics for IGM

14. HVDC HVDC Transmission and HVDC BTB-Link AC Network (A) AC Network (B) Converter Station A Converter Station B DC Transmission Lines ~ or ~ DC-Link 14

15. 15 Planning Considerations Planners should consider the HVDC backbone systems and AC systems with FACTS compensation to achieve the needed capacity and system security. Two Types of HVDC Technologies Current-Source Converters (Thyristor Based) Voltage-Source Converters (Advanced Semiconductor Based) HVDC

16. 16 Summary Comparison of HVDC Technologies: HVDC

17. 17 Advantages of HVDC Systems: More power can be transmitted more efficiently over long distances by applying HVDC HVDC lines can carry 2 to 5 times the capacity of an AC line of similar voltage Interconnection of two AC systems, where AC lines would not be possible due to stability problems or both systems having different nominal frequencies HVDC transmission is necessary for underwater power transfer if the cables are longer than 50km Power flow can be controlled rapidly and accurately HVDC

18. 18 FACTS: Flexible AC Transmission Systems Greater demands are being placed on the transmission network and will continue. At the same time, its becoming more difficult to acquire new rights of way for new transmission infrastructure/lines. FACTS open the door for new opportunities in controlling power, enhancing the usable capacity of present and future transmission; improving system performance, reliability and security; and validating the use of power electronics to enhance power systems operation and dynamic performance. FACTS

19. 19 FACTS: Flexible AC Transmission Systems Function: Shunt and Series Compensation Static Var Compensator (SVC) and Voltage Sourced Converter (VSC-based) STATCOM Fast VARsBetter, Faster VARs Slow VARs FACTS

20. 20 Advantage of FACTS Devices Efficient Installations: 12 to 18 month timeframe Increased System Capacity: Maximum operational efficiency of existing transmission lines and other equipment Enhanced System Reliability: Provide greater voltage stability and power flow control, which improves system reliability and security Improved System Controllability: Intelligence built into the grid, ability to instantaneously respond to disturbances & redirect power flows Investment: Less expensive than new transmission lines FACTS

21. Power Electronics Technologies Voltage Control Power System Stability FSC / TCSC S/S UPFC Power Generation Load Increased Transmission Capacity Inter-area Control Inter-tie Reliability Power Flow Control System Reliability Improved Power Quality Enhanced Import Capability Inter-connected ITC/RTO System Inter-connected Power System HVDC / BTB STATCOM / SVC S/S STATCOM / SVC Load Wind Farm Interconnections Voltage Support BTB DC SVC / STATCOM 21 A View of the Smart Grid

22. Summary and Conclusions Needs are developing in the electric power sector for improved integrated generation management (IGM) with respect to the increase in green energy resource penetration. Many of the challenges faced for IGM and the new green resource portfolios that are emerging are within the power transmission delivery sector. There is a strong need for applying advanced transmission technologies to assure safe, reliable, and efficient electricity delivery. Future applications and development requirements for power electronics and control technologies in a diversified generation environment, with respect to power system dynamic performance, are needed. In general, the case is made for employing more power electronics control technologies throughout transmission and distribution systems for strategically interconnecting green energy resources. Combinations of FACTS and HVDC transmission technologies can provide optimal solutions and enhanced investment for utilities and generation providers alike – we need continued development and deployment !! 22