The Discharge profile of Battery in Electric Vehicle is of variable nature. During this drive-cycle, there is a peak current periods happening for short times during acceleration and braking, steady current is drawn during cruising. It is observed that the ratio of the peak current to average current can is over 10:1.
In brief Energy requirement of Electric Vehicle is split in two categories …
1. Power Density (for peak current requirement)
2. Energy Density (for normal steady current)
The Present Electric Vehicles are powered by Lithium Ion Batteries. The energy efficiency of these batteries depends on their Equivalent Series Resistance (ESR), and this ESR varies over time based on the operating conditions.
• The ESR of these Batteries if cycled at higher C rate tends to increase by around 12% after around 300 cycles.
Batteries in EV is required to address both Power density and Energy density requirement. This involvement of battery in addressing Power density needs of EV adversely affects performance and life of batteries.
Lithium Ion Battery performance/service life is highly Temperature dependent. This behavior is the biggest challenge for Lithium Ion batteries in the Electric Vehicle application especially in environments with Indian weather conditions. In Electric Vehicle application It is observed that working temperature above 35 degree C affects Lithium Ion battery pack performance which leaves permanent impact if subjected to prolonged continuous exposure of more than two months.
In cold conditions available power of these batteries reduces which leads to a weak user experience during winter season.
Based on the Ragone plot shown as below, there is a trade-off between the specific-power and specific-energy within the presently available technologies.
Furthermore, it is possible to optimize a given battery chemistry for better specific-energy or for better specific-power. The extracted energy from a Li-Ion battery is a function of the discharge current and the energy efficiency drops for higher currents.
From the above Ragone Plot, it is observed that amongst available technologies, single handedly none of them individually can suffice requirements of Electric Vehicle.
Also, from above Ragone Plot, Supercapacitor dominantly excels on Power density in comparison with Lithium Ion Battery.
A combination of Lithium Ion Battery and Supercapacitor resulting in “HYBRID POWER-PACK” is the best viable and sustainable approach/solution for addressing Energy requirements of Electric Vehicle.
Features combination improved efficiency and reliability comparison with existing standalone battery pack. SPEL Hybrid Power-pack is designed to handle and provide desired maximal power independent of battery ageing effect, in various temperature conditions., slowing down battery ageing process and extending usable life of Lithium battery pack.
Also, energy recovered during regenerative braking can be harvested in same HESS. Regenerative braking takes most of the load off mechanical brakes, reducing brake maintenance and replacement expenses, which makes system more efficient.