Project idea and background
The idea of the project is to apply combined energy storage system for electric or hybrid electric vehicle. This storage system is to comprise galvanic battery, a pack of ultracapacitors and special converters to manage energy flows within the system. Ultracaps will mitigate surge currents from the battery and capture braking energy and thus improve vehicle’s fuel efficiency and prolong battery’s service life. The research goal is to find optimal ratio of battery and ultracapacitor parameters, taking into account vehicle’s mass and urban driving patterns. Circuitry solutions to control charge/discharge processes are also to be developed.
Lithium-ion battery is a prevailing type for energy storage in electric and hybrid electric vehicles. Meanwhile, no galvanic batteries, and these in particular, can maintain the big charging currents during regenerative braking, and they quickly degrade due to surge discharge currents. To overcome this problem, manufacturers install batteries of big capacities. They are heavy, and still their performances are still not sufficient to utilize all braking energy. This considerably impairs the efficiency and performance of electric vehicle.
An idea to apply ultracapacitor as energy buffer or peak power source is not new, but there are no commercial vehicles with such energy storage available on the market. There is no final solution regarding optimal parameters of ultracapacitors and Li-ion battery depending on the driving cycle and vehicle performances.
So, the project implies modelling and simulations of the powertrain in order to estimate dependencies of output vehicle’s performances from the parameters of the battery and ultracapacitor. The state-of-charge control strategies are also to be improved. It is necessary to develop special algorithms of management of energy flows between the energy storage, electric motor and the vehicle.4
Project outcomes, expected results and their benefits
The project outcomes are:
· A technique for calculation of optimal parameters of Li-ion battery and ultracapacitor depending on the vehicle’s parameters;
· Circuitry solutions for the power converter;
· State-of-charge control algorithm;
Application of project results will reduce the cost of the vehicle due to lighter battery and improve vehicle’s energy (fuel) efficiency because of better utilization of kinetic energy in braking.
Project results may find their application in all kinds of road transport, especially for the heavy-duty urban vehicles like buses and semi-trucks. Such battery packs can also be applied for hybrid wind or solar energy storage systems.