Feature: Transportation
Ultracapacitors: new source of energy for transportation
applications By Rodrigue Mao, Head of Product Management, Distrelec
M
odern public transport, such as trams and trains, are increasingly equipped with functionalites
such as onboard information and Wi-Fi connectivity – which require power. But providing power for transportation
applications presents many technical challenges, not least the operating environment which requires engines and motors to start in low-temperature conditions. Batteries have long been the power
source of choice for engine startup. Although conventional lead-acid batteries once were the only type available, recent innovations comprising different architectures and chemistries have significantly improved their power density and reduced their weight.
Diversity of mass transportation systems Our society is increasingly aware of its energy usage and carbon emissions when travelling from A to B. New metropolitan
32 June 2022
www.electronicsworld.co.uk
light rail, bus and mass-transit networks as well as existing railway infrastructure are making significant investments as consumers look for alternatives to the congested and polluting roads. Most major cities have either implemented or are planning new public transport systems to ease congestion and reduce pollution. Designing energy-efficient, sleek and
quick public transportation vehicles requires balancing the traction- and energy-storage components’ overall weight and load-carrying capacity. Batteries provide excellent source of
energy portability; however, for modern, demanding transportation applications, they don’t always meet all requirements. Accommodating peak current loads requires more capacity than normal running load conditions, which adds to weight and charging times. Banks of batteries are bulky and need considerable charging time, impacting operational availability. Also, batteries are constrained by ambient temperatures, particularly low and high extremes. Some battery technologies even slowly discharge in situ due to their internal equivalent series
resistance (ESR) – a factor that also limits the maximum current they can deliver and one leads to heating within the battery. Another aspect of batteries is their life
cycle. During their active life, they also require checking and routine maintenance. Tey typically have a finite in-service life, aſter which their capability to store a full charge and deliver a full load trends significantly lower. A further consideration when working
with batteries is their unsuitability for low temperature applications. Tey lose their capacity as temperature decreases and simply can’t be used in extreme cold conditions. For an electrically-powered bus or tram,
battery capacity determines the operating range. Tat range can be extended with regenerative braking concepts, by harvesting energy from the drive motors when the vehicle is decelerating. A substantial amount of energy can be recovered this way, and relatively quickly. To take full advantage of this method however also requires a method of storing that energy quickly. Recent innovations in capacitor
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