Charging technology

A vehicle can be charged in a number of ways; from above, the side or from below. To charge from the side would mean that an arm is pointing out to the side of the vehicle and that would be unacceptably dangerous for pedestrians and bicyclists. This alternative will not be considered here further.

To feed from above is a very well-known method. It has been used in rail traffic as well as trolley buses for more than one hundred years.

In order to use this method on trucks it  would not need too much development. To feed cars would, however, be more difficult. Elways conducted some initial tests, which are illustrated below.

Car with pantograph.

From security reasons the overhead line will have to be located around six meters above the road and it will be very difficult to have a pantograph that in a safe way can connect to the overhead line. It has to be much thicker than the one shown on the picture. Elways considered it possible but probably very expensive and a difficult concept to sell to the customers on the car market. As Elways is looking for a solution to suit all vehicles, this was not selected as an alternative to be developed.

Feeding from below

The option remaining is to feed the vehicles from below. The advantage with this alternative is that the visual impact is minimized and the distance between the car and the feeder is much shorter than in the overhead case.
Feeding from the road can, in principle, be made in two ways, by magnetic transmission of the energy, so called inductive transmission, or with transmission via sliding contacts so called conductive transmission.

Inductive feeding

Elways investigated a system of inductive feeding of vehicles. The picture below shows this principle.

Inductive feeding of a vehicle

For this concept, the road contains one or two conductors located together with magnetic material. Under the car there is a kind of open transformer with magnetic material and a coil. This appears to be a very attractive way to transmit power from the road to the vehicle. Unfortunately, the transformer is very inefficient as its lower part in the road is open and the part in the car cannot operate too close to the part in the road. In order to compensate for this, very high currents, high voltages and very high frequencies, have to be used in order to get useful power to the vehicle. The high voltage drop has to be compensated by big capacitors.

All this is technically possible, which has been demonstrated, for instance in Korea, where they have built a demonstration track.

Elways calculations showed that the cost would be very high if inductive feeding from the road should be used. Therefore, our investigations have concentrated on conductive feeding from the road, in order to achieve the greatest cost effectiveness.

Conductive feeding

The conductive feeding is done as shown in the figure below.

The vehicle is fed via a moveable arm. As long as the vehicle is situated above the conductor in the road the contact is in contact with the conductor. When the vehicle is moving too far away from the track the contact is lifted. This is for instance the case at overtaking. Then the car is operated on battery until it is back again in the vicinity of the track.

Evaluation

In the figure below the three different solutions are compared for their CO2 savings. The case is based on costs in Sweden. As the solutions have different costs per kilometer and overhead feeding does not handle cars, the CO2 saving will be different in the different cases. As shown above, the total for all solutions costs 120 GSEK each when optimized.

Length of electrification
in thousand km
CO2 saved (kton/year)
OH-line Inductive Conductive
Investment 10 Investment 15 Investment 4
Cars Trucks Cars Trucks Cars Trucks
< 8 1301 4550 1301 4550 1301
8 < 12 276 964 276
12 > 30 2179 623
CO2 saved in kton per year 1500 5800 9800
Road investment [GSEK] 120 120 120

The conclusion of the figure above is that conductive feeding has the biggest potential CO2 savings and hence also to save most cost as the least fuel is used at a national level.

Elways has since these investigations put all efforts into developing conductive feeding.

 

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