Convergence of Electric Vehicles and the Smart Grid
- Written by Russell Lefevre
Achieving targets for introduction of hybrid electric vehicles and electric vehicles (EVs) will depend not only on advancements in car technologies but also grid readiness. Key issues at the Smart Grid/electric vehicle interface are being aired in a wide range of IEEE publications.
Electric vehicle (EV) introductions by major automakers convey confidence in the long-term viability of EVs, and President Obama has set ambitious targets for adoption of plug-in hybrids (PHEVs). But given the fact that that cars and light trucks tend to stay in use for a decade, it will be tough for the President’s administration to meet its goal of one million PHEVs on U.S. roads by 2015.
One way to advance that goal is to provide incentives to replace traditional cars with EVs and PHEVs faster than the historical norm. Another way to accelerate the adoption process is to leverage the power grid with what is being called "Electrification Ecosystems".
That vision was spelled out in a technology roadmap released in 2009 by The Electrification Coalition, a consortium of 21 business leaders. It calls for a federal initiative to establish Electrification Ecosystems in cities or regions well-suited for deploying grid-enabled vehicles in high concentrations. In addition to creating economies of scale, these ecosystems will provide valuable experience that can be incorporated into business models for supplying, selling and servicing EVs and PHEVs.
IEEE has been active across a range of technologies that are relevant to introduction of electric and hybrid-electric vehicles, including batteries, battery management systems and grid technologies. In addition, key issues at the Smart Grid/electric vehicle interface are being aired in a wide range of IEEE publications.
The batteries used in EVs have traditionally been heavy, expensive and somewhat short-lived, providing cars with barely adequate driving ranges. Research and development on battery technology is a priority effort worldwide. A useful summary of the state-of-the-art can be found in "Recent Developments on Electric Vehicles," by K.W.E. Cheng, in the 2009 Conference on Power Electronics Systems and Applications. Cheng discusses not only batteries but also the charger and battery management system.
A test of 160 lithium ion phosphate batteries conducted by the National Renewable Energy Laboratory is the basis of a paper by F.P. Tredeau and Z,M. Salameh, entitled "Evaluation of Lithium Iron Phosphate Batteries for Electric Vehicles Application," which was delivered at the IEEE Vehicle Power and Propulsion conference in Dearborn, MI It found that lithium polymer cells show very good performance and may become the preferred battery type as manufacturing improves.
A battery management system (BMS) controls charging and discharging and assures reliable, safe operation. One critical design element is a model of the hardware, software and algorithms that determine BMS operation. A new modeling approach is described in "Algorithms for Advanced Battery Management Systems," by N.A. Chaturvedi, et al. in the June 2010 IEEE Control Systems Magazine.
Advances in power electronics have helped reduce the cost and improve the efficiency of electric vehicles. "Power Electronics and Motor Drives in Electric, Hybrid Electric, and Plug-In Hybrid Electric Vehicles," published by A. Emadi, et al. in the IEEE Transactions on Industrial Electronics in June 2008, shows how the integration of intensive power electronics solutions within advanced vehicular power systems can achieve that goal.
The analysis of how EVs and PHEVs will affect the grid is likely to play an important role in managing the evolution from today’s power grid to a Smart Grid capable of dealing with the challenges.
Peter Fairley's "Speed Bumps Ahead for Electric-Vehicle Charging," published by IEEE Spectrum online, provides some cautionary notes and words of advice. California citizens buy nearly a quarter of the hybrids sold in the United States, and there could be 5,500 of them on California roads by the end of this year. The state's utilities bet that most hybrid drivers will want to charge their cars at 240 volts, using AC Level 2 chargers. Each draws up to 6.6 kilowatts, and so activating just one of them is like powering up three houses simultaneously, all with their air conditioning, lights and laundry machines running.
Another such warning is found in "Impacts of Plug-in Vehicles and Distributed Storage on Electric Power Delivery Networks," by P. Evans et al., which was another contribution to the 2009 Vehicle Power and Propulsion Conference. Citing a study funded by the Department of Energy’s National Renewable Energy Laboratory, Evans and his coauthors describe tests that found PHEV battery charging can have a negative local impact. Once the situation is identified, however, they concluded that it can be readily addressed and managed.
"A Review of Plug-In Vehicles and Vehicle-to-Grid Capability" by B. Kramer, et al., in the Proceedings of the 34th Annual Conference of IEEE Industrial Electronics, explores the concept of bi-directional power flow. EVs must be capable of taking power during charging and providing power while discharging from and to the grid and this is an important consideration for power electronics.
"Challenges of PHEV Penetration to the Residential Distribution Network," by S. Shao et al., appeared in the Proceedings of the Power and Energy Society General Meeting, 2009. It identifies enabling technologies that have been acknowledged as being integral to the Smart Grid. These include bi-directional charging units and bi-directional meters, communication between the vehicle and the energy management center, intelligent, on-board power management units and intelligent energy management centers.
An extremely important consideration is the impact of wide spread deployment of GEVs on the grid. Many have analyzed the issues and have concluded that until deployment becomes very large the generation and transmission functions will be able to handle the increased load. However, a number of researchers have found that the distribution function may have significant problems. Saifur Rahman and has colleagues at Virginia Tech have analyzed the issue and have noted these problems. See, for example, "Analysis of the Impact of PHEVs on the Electric Power Distribution Network" . This article notes that for some scenarios where two GEVs are charging at the same time on the same distribution network the addition of a hair dryer on the same network will seriously stress it. Results of this type are very scenario dependent. Rahman notes methods to reduce the stress but the problem is one to be concerned with.
The robustness and sophistication of interface between EVs and the Smart Grid is likely to have a significant impact on the future on both of these convergent technologies. Through its work in standards, conferences and publishing, IEEE has played an important role in identifying problems and providing solutions. The publications mentioned in this article represent only a few of many examples. For more extensive and detailed information, interested parties are encouraged to contact the author.