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Modeling and Simulation of a Renewable and Resilient Electric Power Grid. Tom Overbye Fox Family Professor of Electrical and Computer Engineering University of Illinois at Urbana-Champaign overbye@illinois.edu. September 14, 2010.
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Modeling and Simulation of a Renewable and Resilient Electric Power Grid Tom Overbye Fox Family Professor of Electrical and Computer Engineering University of Illinois at Urbana-Champaign overbye@illinois.edu September 14, 2010
Power Grid Resiliency: The Ride May Take Some Unexpected Turns Source: Kingda Ka roller coaster, Six Flags New Jersey, http://en.wikipedia.org/wiki/File:Kingda_Ka.jpg
The Current Power Grid: Not Quite as Dumb as Some Think • In 2000 the National Academy of Engineering name electrification as the top engineering technology for the 20th century. Source: GE SmartGrid 2009 Superbowl ad; www.youtube.com ISO New England Control Center
An Important Consideration as We Move Forward With its user-friendly,plug-and-play designthe humble outlet hasmade the electricgrid easily accessibleto billions. Yet it is reallya simple gateway tothe world’s most complexmachine. As we moveforward with the SmartGrid it is important to not lose this simplicity.
Towards a Resilient Electric Grid • A resilient electric grid should have the ability to gradually degrade under increasing system stress, and then to return to its pre-fault condition when the stress is removed.” • A resilient power grid should not experience a sudden, catastrophic system collapse, but rather should be able to adapt to “keep the all the lights on” under small to moderate system disturbances, and to keep at least some level of system service even in the event of severe system disturbances.
The Power Grid is Already Fairly Resilient • 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, storms and hurricanes can bring large-scale damage. Photo sources: www.solarnavigator.net/geography/geography_images/Lightning_strikes_hill_january_2007.jpg, http://mgx.com/blogs/tag/public-utility/
Different Degrees of Resiliency • Individual users just want reliable, inexpensive electricity – the lights stay on (or the machine drive doesn’t trip) • Most outages are local and short • Talk focuses mostly on resiliency with respect to the game changers • Category 5 hurricane up the East Coast, large ice storm, volcano, geomagnetic storm, attack • Potential outages lasting well beyond two or three days
What Makes the Grid Unique • 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
Making a More Resilient Power Grid • The question isn’t whether we can make a more resilient power grid. The answer is “of course.” • The real question is how can we economically make a more resilient power grid without introducing new, hidden problems, yet still addressing the game changer scenarios. • A key driver is a decrease in control on the generation side as we move to more variable, less controllable renewable generation.
The Power Grid Fights Back Against Rapid Change • The interconnected power grid is complex and one “solution” often causes new problems: • High speed exciters reduced damping • Line compensation subsynchronous resonance • Long distance power transfer voltage instability • A more recent example is deregulation (restructuring) something that caught on quickly in the mid 1990’s but soon ran into the problem of “price spikes.”
California 2000/1 Energy Crisis The 2000/1 California Energy Crisis illustrated how “astute” traders could game large electricity markets
General Resiliency Comments • Generation: Closer is better, but economies of scale/fuel/environmental concerns often push it away from the load. • Fuel: Domestic sources with local storage are best, but coal has high CO2 emissions, nuclear has waste issues, natural gas has price volatility, and most renewables are intermittent. • T&D: More is better, but costs/NIMBY limit investment.
Natural Gas Prices: A Key Grid Barometer Low natural gasprices allow for increased naturalgas generation, which is 1) very controllable, and 2) has half the CO2emissions of coal. Source: research.stlouisfed.org/fred2/series/GASPRICE Source:www.eia.doe.gov/cneaf/electricity/epm/flash/april2010.pdf, Table 4.1
Large Grids and Islands • Large grids have some strong advantages, but in game changer scenarios we need the ability to effectively operate islands • Adaptive islanding during a disturbance is best • Black starting following a disturbance otherwise • This required that there be sufficient dispersed black start capability and control infrastructure • System protection also needs to be configurable enough to allow island operation. • Operating without some high voltage transformers
Details and Experience Matter! • In trying to predict whether a new “solution” will turn into a future problem, the esoteric details of the approach can be quite important • How fast does a control respond, what inputs are required for a response, how susceptible is it to human “interference”, what are its voltage and frequency characteristics, how much fault current does it provide?
Fast Load Controls • Any fast control (on the order of seconds) requires local or at most distribution level control • Local frequency and voltage magnitude are easy to measure but their meanings are quite different • Frequency is global to the system and relatively fixed; control response is straightforward (e.g., f < threshold decrease load) • Voltage is very local (feeder specific with LTC control); control response is difficult to determine.
What Could Have Been Done?Sammis-Star Flow Sensitivities DOE/NERC report said about 1500 MW of load shed wouldhave been needed
The Anatomy of LMP-Based Demand Response • In determining whether LMP-based demand response could have fixed either the June 1998 or August 14, 2003 events details matter • A state estimator solution is needed at the ISO • State estimator is used by security constrained OPF to determine LMPs • LMPs must be quickly conveyed to the load, which in turn must be able to react. • Fast changing system conditions can invalidate the results.
Active N-1 Reliability • Traditional n-1 reliability assessment requires that the system be able to withstand any credible contingency with little active control; this often requires significantly constrained system operation. We’ll call this “passive” n-1. • A potential approach, using true Smart Grid concepts, coupled with storage and controllable load, is to move to “active” n-1 • Goal is to increase transmission capacity.
Passive N-1 (Pre-Contingency) • With the passive N-1 approach the three transmission lines connecting the wind power to the urban load center cannot be fully used since in the event one line is outaged, the remaining two lines must not become overloaded
Active N-1 (Pre-Contingency) • Active N-1 allows full use of the wind capacity because in the unlikely event the contingency occurs, the excess wind capacity can be rapidly transferred to the storage and controllable load
Active N-1 (with Contingency) • Note that if the line outage contingency were to actually occur, the excess wind capacity could be transferred (at least temporarily) to the controllable load/storage. Transmission capacity is still fully used.
Pluggable Hybrid Electric Vehicles (PHEVs) • The real driver for widespread implementation of controllable electric load could well bePHEVs. • Recharging PHEVs when their drives return home at 5pm would be a really bad idea, so some type of load control is a must. • With V2G car could provide large amounts of power to grid in emergency
An Example: Community Energy Storage • AEP is investigating local, 240v storage located at distribution transformers, shared among several houses Devices along feeders could be networked. • Cost forecast overthe next five yearsshould come downto $500/kWh (25Kfor 50 kWh of storage) Source: www.aeptechcentral.com/ces/cespresentations.htm
Are We Really Building the Smartest Grid? • One doesn’t have to scratch too deep in the power industry to find lots of concerns about the direction of the “smart grid.” • As has been mentioned, the vast majority of the money is focused on meters. A small percentage was spend on transmission, and essentially nothing on innovative tools for system analysis.
