thomas j. overbye university of illinois at urbana
TRANSCRIPT
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Transient Stability Aspects of Renewable Generation Integration
Thomas J. Overbye University of Illinois at Urbana-Champaign
[email protected] September 13, 2016
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Overview
• Interconnected electric grids are going to play a key role in the development of our sustainable energy future – In the US about 40% of our energy transported as
electricity, a value that should be increasing as transportation becomes more electrified
– Most non-carbon energy is first converted into electricity
– Off-grid options are unlikely to supply a significant percent of our energy needs
• Presentation covers implications of large-scale renewable integration on electric grid dynamics
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Where We Got Our Energy in 2015 3
Petroleum, 36.2
Coal, 16
Natural Gas, 29
Nuclear, 8.6Hydro, 2.5
Biomass, 4.8 Wind, 1.9
About 81% Fossil Fuels (86% in 1990 and 2000)
In 2015 we got about 1.9% of our energy from wind and 0.6% from solar (PV and solar thermal), 0.2% from geothermal
Source: EIA Monthly Energy Review, July 2016
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Renewable Energy Consumption 4
Source: EIA Monthly Energy Review, July 2016
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Growth in US Wind Power Capacity 5
Source: AWEA Wind Power Outlook 2 Qtr, 2016
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Wind Capacity Installations by State 6
Source: AWEA Wind Power Outlook 2 Qtr, 2016
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Natural Gas and Electricity 7
Marginal cost for natural gas fired electricity price in $/MWh is about 7-10 times gas price
Source: http://www.eia.gov/dnav/ng/hist/rngwhhdW.htm
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US Transmission Grid 8
Voltages up to 765 kV; Highly inter- connected but with some what limited long distance power transfer capabilities
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What Makes the Grid Unique
• Each electric interconnect is one large circuit • Fast system propagation of disturbances throughout
an interconnect. • There is no mechanism to efficiently store electric
energy: generation must equal load – only several seconds of kinetic energy stored – no equivalent of busy signal, or holding pattern
• With few exceptions, there is mechanism to directly control power flow in grid – flow is dictated by impedance of lines; “loop flow” is a
significant problem on some systems
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Power System Time Frames
Lightning Propagation
Switching Surges
Stator Transients and Subsynchronous Resonance
Transient Stability
Governor and Load Frequency Control
Boiler and Long-Term Dynamics; power flow
10-7 10-5 10-3 0.1 10 103 105
Time (Seconds)
Image: Sauer, P.W., M. A. Pai, Power System Dynamics and Stability, Stripes Publishing, 2007
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The Grid Needs to Be Resilient to Lots of Disturbances
• Lightning strike sequence of events: 1) lightning strikes line causing a fault, 2) circuit breakers deenergize line in a few cycles, clearing fault, 3) circuit breakers reclose within several seconds restoring line.
• But ice, tornados and hurricanes can bring large-scale damage.
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Frequency Response for Generation Loss
• In response to rapid loss of generation, in the initial seconds the system frequency will decrease as energy stored in the rotating masses is transformed into electric energy – Solar PV has no inertia, and for most new wind turbines
the inertia is not seen by the system • Within seconds governors respond, increasing power
output of controllable generation – Solar PV and wind are usually operated at maximum
power so they have no reserves to contribute
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But It Can Fail Dramatically 13
August 14, 2003 Blackout
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Power Grid Disturbance Example 14
Time in Seconds
Figures show the frequency change as a result of the sudden loss of a large amount of generation in the Southern WECC
Frequency Contour
20191817161514131211109876543210
6059.9959.9859.9759.9659.9559.9459.9359.9259.9159.959.8959.8859.8759.8659.8559.8459.8359.8259.8159.859.7959.7859.7759.7659.7559.7459.73
Green is bus quite close to location of generator trip while blue and red are Alberta buses. Black is BPA.
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Disturbance Animation 15
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Renewable Generation Implications
• Over last several decades the grid has been stabilized by the inertia provide by large generators, mostly coal and nuclear
• The integration of large amounts (e.g., 50%) of wind and solar PV requires enhanced controls to handle the potential for larger frequency excursions
• More dispersed renewable resources are less likely to suddenly fail, but can be subject to more prolonged, correlated changes – Cloud bank moving in over a region that contains lots
of solar PV – Rapid decrease in wind over large region
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Impact of Generator Inertia and Governor Response for Small Case
• Figure shows inertia determines initial frequency drop rate, and governor speed the recovery
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The least frequency deviation occurs with high inertia and fast governors
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Power System Dynamics Motivation: August 14th 2003 Blackout
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Image source: August 14 2003 Blackout Final Report, Figure 6.26
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Control Implications
• Possible solutions include – Operating renewable generation at values below
maximum power output to provide reserves; this helps with governor response but not inertia
– More controllable load; if response is fast (less than about 2 seconds) this can help with inertia response
– Modified wind controls to mimic inertia – Markets that correctly price value provided by inertia
• Frequency provides a useful control signal – Universally available; because of propagation delays
communication based control may be faster
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Valuing Inertia and Locational Impacts
• Electric grids need inertia to withstand disturbances • An open research issue is how to correctly value this
inertia • Another related issue is how much location matters
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Time (Seconds)20191817161514131211109876543210
Freq
uenc
y (H
z)
60.0460.02
6059.9859.9659.9459.9259.9
59.8859.8659.8459.8259.8
59.7859.7659.7459.7259.7
59.6859.66
Frequency, Bus 54490gfedcb Frequency, Bus 51667gfedcb Frequency, Bus 40687gfedcbFrequency, Bus 30018gfedcb Frequency, Bus 24086gfedcb Frequency, Bus 14931gfedcbFrequency, Bus 11217gfedcb Frequency, Bus 62994gfedcb Frequency, Bus 70627gfedcbFrequency, Bus 18443gfedcb
Time (Seconds)20191817161514131211109876543210
Freq
uenc
y (H
z)
60.0460.02
6059.9859.9659.9459.9259.9
59.8859.8659.8459.8259.8
59.7859.7659.7459.7259.7
59.6859.66
Frequency, Bus 54490gfedcb Frequency, Bus 51667gfedcb Frequency, Bus 40687gfedcbFrequency, Bus 30018gfedcb Frequency, Bus 24086gfedcb Frequency, Bus 14931gfedcbFrequency, Bus 11217gfedcb Frequency, Bus 62994gfedcb Frequency, Bus 70627gfedcbFrequency, Bus 18443gfedcb
100% in Subregion 10% in Subregion
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A Driver of Research: Synthetic Models
• Access to actual grid models is limited because of confidentiality concerns
• New research is ongoing in the development of synthetic models – Mimic actual grid
• Being used in ISEE for coupled infrastructure research
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Thank You! 22