High Voltage Power Electronics Technologies for Integrating Renewable Resources into the Grid

RenewElec WorkshopCarnegie Mellon UniversityOctober 22, 2010 – Pittsburgh, PA

Dr. Gregory F. Reed & Brandon M. Grainger

Power & Energy InitiativeUniversity of Pittsburgh, Swanson School of EngineeringElectrical & Computer Engineering Department

• BackgroundBackground

• Technology and Infrastructure ChallengesTechnology and Infrastructure Challenges

• Power Electronic TechnologiesPower Electronic Technologies

• HVDC SystemsHVDC Systems

• FACTS DevicesFACTS Devices

• SummarySummary

OverviewOverview

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BackgroundBackground

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BackgroundBackground

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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

Texas / ERCOT ExampleTexas / ERCOT Example

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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 capacitywith 7.892 GW installed

CREZ Project will add 10 GW more wind power……

2,300 miles of new 345-kVtransmission with shunt andseries dynamic compensation

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Geographic Intensity of Highest Penetration Potential

Renewable ResourcesRenewable Resources

Wind Speed Across the US Solar Intensity Across the US

Technological and Infrastructure ChallengesTechnological and Infrastructure Challenges

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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 ConsumptionInduction 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 IssuesChallenges and Issues

Challenges and IssuesChallenges and Issues

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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.

Power Electronics Available for ImprovedPower Electronics Available for ImprovedIntegrated Generation Management (IGM)Integrated Generation Management (IGM)

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Power Electronics for IGMPower Electronics for IGM

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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)

Power System BasicsPower System Basics

GenerationMechanical-to-

Electrical EnergyConversion

TransmissionDistribution

Electrical Power Usedand Electrical-to-Mechanical

Energy Conversion

Power Generation, Transmission and Distribution

FACTS / HVDC – High Capacity Power Electronicsare applied here for improved operation, reliability, etc.

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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 centersThere 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 IGMPower Electronics for IGM

HVDCHVDC

HVDC Transmission and HVDC BTB-Link

ACNetwork(A)

ACNetwork (B)

ConverterStation A

Converter Station B

DC Transmission

Lines

~ or ~

DC-Link

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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)

HVDCHVDC

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Summary Comparison of HVDC Technologies:

HVDCHVDC

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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

HVDCHVDC

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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.

FACTSFACTS

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FACTS: Flexible AC Transmission Systems Function: Shunt and Series Compensation Static Var Compensator (SVC) and Voltage Sourced Converter (VSC-based) STATCOM

Conventional

MechanicallySwitched

SVC

ThyristorControlled

STATCOM

Converter

Fast VARs Better, Faster VARsSlow VARs

FACTSFACTS

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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

FACTSFACTS

Power Electronics TechnologiesPower Electronics Technologies

Voltage ControlPower System Stability

FSC / TCSC

S/S

UPFC

Power Generation

Load

IncreasedTransmission Capacity

Inter-area ControlInter-tie Reliability

Power Flow ControlSystem Reliability

ImprovedPower Quality

EnhancedImport Capability

Inter-connectedITC/RTO System

Inter-connectedPower System

HVDC / BTB

HVDC / BTB

STATCOM / SVC

S/S

S/S

STATCOM / SVCLoad

Load

Wind FarmInterconnections

VoltageSupport

BTB DC

SVC /STATCOM

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A View of the Smart Grid

Summary and ConclusionsSummary 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 !!

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