A different spin on an EV batter

Article Abstract:

When Richard F. Post, senior scientist of the Lawrence Livermore National Laboratory, speaks of electric vehicle (EV) batteries, he is probably referring to batteries of the electromechanical kind, called flywheels. A flywheel is a massive steel rotor that spins at hundreds of radians per second (rad/s); the type Post works with are small, rotate at a velocity of 10,000 rad/s and are designed from a lightweight, ultrastrong material. Electromechanical batteries (EMB) can store more energy per unit mass than a more massive unit because stored energy increases only linearly with the mass of a flywheel but goes up as the square of its rotational speed. EMBs with a specific energy of about 150 Wh/kg are possible by employing composite materials based on graphite fibers. What really makes EMBs stand out, however, are their specific power. EMB's are capable of delivering up to 5,000 to 10,000 W/kg, whereas the better electrochemical devices deliver 200 to 400 W/kg and internal combustion engines test at 600 to 800 W/kg.

Research, Industrial research, United States. Department of Energy. Lawrence Livermore National Laboratory, Research and Development, Lawrence Livermore National Laboratory

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The great battery barrier

Article Abstract:

The biggest obstacle to the development of a marketable electric vehicle (EV) is the lack of an effective and commercially available power source. The current EV power supply, a lead/acid battery, is far from ideal. The problem is that, unlike conventional vehicles, EVs cannot go far on a single charge, and it take hours to recharge their batteries. The batteries also have a limited lifespan. Some researchers believe that the impossibility of maximizing a battery's energy and power ratings lends itself to the use of a pair, rather than a single, battery, with the main battery's being optimized for range, while the small one is optimized for hill climbing and acceleration. Another belief is that EV battery lifespan will depend on the technology; while some batteries, such as zinc/nickel oxide, approximate a constant energy throughput, others, like lead/acid, benefit from shallower cycles and last longer. Battery cost, alternative sources of power and the future of EV batteries are discussed.

Power resources, Technology

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Pursuing efficiency: given the limitations of EV batteries, success will depend on making the vehicles themselves highly efficient

Article Abstract:

The most important technical factor for an electric vehicle (EV) today is efficiency, and the only way to extend the range of an EV is to squeeze as much juice out of the energy the EV can store. One way to accomplish this is to reduce aerodynamic drag by limiting the vehicle's maximum speed and cross-sectional area. Another way is to reduce a tire's rolling resistance by making the tire firmer, so that it flattens less where it contacts the road. A third solution would be to minimize the losses in the vehicles' semiconductor devices by designing the controller so it drives the motor with a high-frequency square wave and to pulse-width-modulate the square wave sinusoidally. The semiconductor device of choice for doing this is the insulated-gate bipolar transistor, which combines the low on-state loss of a bipolar junction transistor with a higher switching speed. Additional ways to increase EV efficiency are discussed.

Efficiency, Methods

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