The Developments of Electric Power Supply Sources for Electric Cars

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Fedorets S.G., Fedorov S.I., Bozhok I.M., Mazan N.M.
(Ukrainian Research and Scientific Institute of Machine-Building Technologies, Dniper, Ukraine; Department of Electrical Engineering, Dnipro University of Technology, Dniper, Ukraine)

Abstract

The article deals with the problem of electric power generation sources, in particular, contemporary electric car batteries.

The requirements to the mentioned electric power accumulators are given. The drawbacks and advantages of the existing car batteries are reported. The current article also reviews the contemporary technologies to ensure longer drives without additional electric charge. The fast-charging methods via supercapacitor are proposed for the electric car battery.

The Developments of Electric Power Supply Sources for Electric Cars

The development experience in the sphere of transport means and alternative energy systems points to the necessity of incorporating contemporary electric power generating sources within them. Considering the scales and perspectives of the electric-car building, the application of the innovational techniques in this sphere is beyond any doubt.

Generally, the electric cars are more ecologically friendly than those which work on diesel fuel or gas. However, the application of the former does not exclude the harmful effect produced on the environment, mainly at their manufacture and disposal. The most hazardous here are electric car batteries. The studies performed by Mazda have shown that the electric cars with larger capacities of their batteries have greater adverse effect on the environment than even the cars with diesel engines or petrol engines. The electric cars of Mazda are equipped with low-capacity batteries (35.5 kWh). Based on the dedicated research, Christian Schultze claims in his interview to Automotive News that this is the way how Mazda takes care of the environment and that production and disposal of the car batteries with large capacities (even after 100 000 miles of the car mileage) release as much CO₂ as hatchback Mazda 3 does during its complete service life. Electric car batteries of 95 kWh (Tesla Model 8 and Model X) release more CO₂ than cars with diesel engines or petrol engines. The situation grows worse if the car owner makes the early substitute of the car battery. Nissan LEAF with the car battery of 30 kWh is 30% more environmentally friendly than Peugeot 208 with 1.6 BlueHDi, according to the experts of International Council on Clean Transportation,

Anika Regett, FfE researcher, admits that ecologically the electric car is left behind the conventional one when the production cycle. However, the electric vehicle consumes less energy per a kilometre of its travel and at the 50 000 km it turns to be more environmentally friendly than the petrol car.

The production and operation of the electric cars are expected to be improved in terms of the climate protection. According to Svenja Schlze, the current German Minister for Economic Cooperation and Development, who served as the Minister for the Environment, Nature Conservation and Nuclear Safety, the electric cars are 16% ecologically cleaner than those with diesel engines and 27% more eco-friendly than petrol cars. By 2025, this gap will have become wider. The average estimation of the CO₂ emissions is forecasted as given: the car with the petrol engine – 168 g of CO₂ per vehicle-km of travel, the car with the diesel engine – 148 g of CO₂ per vehicle-km of travel, electric car– 101 g of CO₂ per vehicle-km of travel.

In the sphere of passenger cars, there are no better alternatives than the electric cars for the climate protection, according to Peter Kasten, Institute Freiberg.

Per data provided by Fondation pour la Nature et pour l’Homme, Le Fonds vert pour le climat and their partners of WWF, Renault and the manufacturers of electric car batteries, the electrical cars with smaller batteries emit green-house gasses three times less than diesel cars under the urban conditions.

In the electric power supply systems for electric cars, there have been widely applied acid tractor, starter and lithium-ion energy devices. They are operated under various conditions and this demands meeting certain requirements as follows:

– stable voltage under load;

– inconsiderable values of losses at increased consumption;

– performance stability at the temperatures below zero;

– low self-discharge rate in order to provide longer in time capacity of electric power sources;

– long performance at the great amounts of charge-discharge cycles;

– acceptable mass and size parameters;

– steadiness and simplicity of the construction.

For end consumers, the significant issue is long-time failure-free performance of an electric power source without additional charging during its operation. Chemical sources of power supply are actually capable of ensuring only a short distance for one-charge electric car running.

Therefore, car manufacturers are actively working at developing new techniques which can provide longer distance running without additional charging for a long time. For instance, one of the ideas is to employ the robot swift replacement of electric car batteries, but it demands sophisticated and complicated equipment of charging stations.

The other idea is to employ supercapacitor modules instead of batteries. The point is that the supercapacitor possesses the property of better capacity as compared against the common capacitor, but it is left behind in this characteristic as compared with the contemporary battery. However, the supercapacitor is more dependable and simpler, it is not affected by wear in contrast to the battery which performance is based on the chemical reaction. The supercapacitor withstands charge-discharge cycles in the number of hundreds of thousands and its life expectancy is more than 15-20 years. Such systems have been tested and found its application in the city transport means (the developments of the Chinese companies: Sinautec, Shanghai Aowei Technology, Beiqi Foton Motors; the developments of the American companies: Sinautec Automobile Technologies, Foton America Bus etc.). One of such designs, for instance, Ultracap Bus, is recharged at the bus stops.

The above-described technology is suitable for electric buses moving in the cites since their bus stops are located within several kilometres from one another. However, it is useless for the electric cars assigned for longer travels. One of the simplest engineering solutions for prolonging the electric car travelling distance is to enlarge the battery capacity which leads to considerable increase in its size, mass and cost. If we increase the amount of the flammable substances within the battery, it will result in the higher risk of electric hazards and fire problems when the car accidents. The shirt circuit at large capacity of the battery causes the large amounts of energy release (heat) and increases the fire risks for the electric car. Such problems with common batteries at electric vehicles are controllable to a certain degree but lithium-ion sources (more capacity, high discharge current, greater amounts of flammable substances) do not allow us to stop the chemical reaction and extinguish the fire swiftly or effectively. Further, due to its heavy mass, the battery is to be located on the electric car underside: this improves its balance (as the centre of gravity in cars is located there) but produces an adverse effect on its safety. Uneven roads and rocks on them are able to cause penetration in the battery body and its firing. Furthermore, the increase in the amount of the flammable substances in electric car batteries, inherent to the increase of their mass, leads to the further worsening in the ecological situation at battery recycling or disposal. Currently, the world is experiencing great amounts of the battery wastes, that demands building special facilities for their recycling. By Greenpeace report, 13 million tons of nickel-ion batteries are estimated to require recycling due to the end of their service life by 2030. Nissan Motor is planning that their new plants for recycling car batteries will have been built in USA and Europe by 2025 . Hydro Volt is commissioning the largest recycling plant with the facilities able to recycle all conventional electric car batteries which are out of service in Norway. At VW in Salzgitter, the pilot project has started in 2020 for recycling 3 000 batteries per year with the intention for the further increase in the capacity.

By connecting together several supercapacitors, one can assemble the unit equal to the capacity of the electric car battery. The weight of such a unit is 3-4 times heavier than that of the electric car battery, which is intolerable for the contemporary transportation means.

One of the latest concepts in the sphere of the electric transport is incorporating two different types of energy accumulation: graphene supercapacitor (or supercapacitor of other type) plus battery. The former possesses the specific capacity of as much as 1/4 – 1/5 from the lithium-ion battery storage and it is charged up to 3-7 kWh for 30 seconds. The battery is capable of having from 30 kWh up to 70-100 kWh but its charging, even a fast one, requires more than 5-6 hours. Eventually, supercapacitor charging can be carried out while electric car moving on the road equipped with wireless charging stations within it, or at its short stops the fast charging can be performed with high current [1 – 3].

The studies for the present publication analysed the global experience of the present day in the spheres of electric cars and supercapacitor production. Utilising this experience, the complex research has been carried out in the laboratories of Dnipro University of Technology. The research has revealed that the principal drawback of the batteries operated in electric cars is the issue of how fast they charge.

For the purpose of fast accumulation, the different approaches and devices are required, for instance, such as supercapacitors [4 – 5].

The research results allow the solution as described below. For the fast charging, the supercapacitors can be applied and the electric car battery obtains charging via charge-discharge system incorporated in the converter while the car is moving. The additional charge in this case is performed under the conditions suitable for the electric car battery: the rated currents of the charge, the losses through wire and equipment heating from high currents are minor; there are also opportunities to reduce the wire cross-sections and masses (the wires leading from the connectors arranged on the body to the electric car battery and placed under the electric car underside).

If required, the energy accumulated within the supercapacitor can assist the battery in overcoming the increased load and consumption peaks by decreasing the discharge currents. After the discharge, the supercapacitor is ready to accept the new portion of energy. Conducting the study how the supercapacitor can operate together with the electric car battery, the checking was carried out on the performance of charge-discharge system of supercapacitor and electric car battery. Within this system, there is a supercapacitor and a converter with the control unit for a battery. The converter control unit is designed with a purpose to provide the uniformity fast charging of the supercapacitor with high currents and its slow discharging into the battery (currents are not to be harmful for the battery) plus the opportunity to regulate the rate of these processes.

Further, in this case, the electric car battery works in harmony with the control unit (saving mode). This mode is required for increasing the travel distance covered without any additional charge.

The performance checking has been conducted at various modes and various operation conditions. The proposed system is being patented now.

Below we summarise the main advantages of supercapacitor application:

– fast charge (1000 times faster than that of the battery);

– relatively low expenses (from 2 to 4 times lower than at 1 kWh of the accumulated energy);

– electric energy density (especially that of graphene supercapacitor);

– ecological friendliness (wastes decomposition under the action of sun rays);

– fire safety (concerning electric car batteries).

Conclusions:

The proposed system equipped with a supercapacitor allows the opportunities of fast charging within the range of 0.5 – 4 minutes for the supercapacitor (with considerable amounts of energy up to the level of the battery installed) during the short-time stops and then transferring the accumulated energy (at small currents during tens of minutes) while electric car is moving.

References

1. V. Shurygina. Supercapacitors. Assistants or possible competitors to battery power supplies. «Electronics: Science, Technology, Business», Issue №3/2003.
2. Graphen-based supercapacitors increase the range of an electricvehicle. [electronic  resource]. – access mode : https://www.imena.ua/blog/electric-cars_supercapacitors/ date of access 17.10.22
3. S.R.C.Vivekchand, Chandra Sekhar Rout, K. S. Subrahmanyam, A. Govindaraj and C. N. R. Rao. Graphene-Based Electrochemical Supercapacitors // J. Chem. Set. Indian Academy of Sciences. – 2008. – C.9-13.
4. Graphene-Based Supercapacitor with an Ultrahigh Energy Density Chenguang Liu, Zhenning Yu, David Neff, Aruna Zhamu and Bor Z. Jang [electronic resource]. – access mode: https://pubs.acs.org/doi/10.1021/nl102661q date of access 17.10.22.
5. Ukrainian patent № 146811 U, 18.03.2021. Electric car. Ukrainian patent №146811. published 17.03.2021, bulletin № 11/2021./ Fedorets S.G., Bozhok І. M., Mazan N. М.

       Author:

Fedorets S. G., chief designer, Ukrainian Research and Scientific Institute of Machine-Building Technologies, Dniper, Ukraine

Area of ​​specialization: production and disposal of batteries for electric vehicles, innovative batteries (creation of new generation batteries), development of advanced power sources for electric vehicles.

Fedorov S. I., senior lecturer, Department of Electrical Engineering, Dnipro University of Technology, Dniper, Ukraine

Area of specialization: electricity, electrical engineering, classical and renewable energy sources, electric vehicles, mineral processing.

Bozhok I. M., chief engineer, Ukrainian Research and Scientific Institute of Machine-Building Technologies, Dniper, Ukraine

Area of specialization: Innovative technologies for the production and disposal of batteries for electric vehicles. Management of battery charging processes.

Mazan N. M., engineer, Ukrainian Research and Scientific Institute of Machine-Building Technologies, Dniper, Ukraine

Area of specialization: environmental and legal aspects of using batteries for electric vehicles, product certification, testing for compliance with technical regulations.