Case study:

Wireless Opportunity Charging with a fleet of 23 city buses in Turin (Italy)

To improve air quality in the historical city centre, Torino decided to convert it into a Limited Traffic Zone (LTZ), allowing access to a limited number of authorised vehicles. Torino launched in 2003 the STAR 1 line. A few months later, on citizens’ request, the service was expanded. The line serves essential points in the city centre. Its success led Torino’s public transport operator, GTT, to launch STAR 2 in September 2007 to cover crucial areas of the historical city centre, the Porta Susa railway station and to connect with other public transport lines and the metro. Both tracks – each around 13km long – use the inductive charging system.

The challenge
Electric buses are regarded as more comfortable than their traditional counterpart and produce no local emissions. However, the limited battery and the lack of a network of battery charging facilities have limited their expansion. Inductive charging systems tackle these problems by providing wireless charging points along bus routes. Turin has been using this technology on two of its bus lines for over 16 years.

The solutions
In the centre of Turin, two bus lines operated in 2003 on an IPT Charge Bus solution. On the two lines, there were 23 buses in use. Each track has a length of approximately 7 km, and the buses are recharged at the terminal stops with an inductive fast charging process. It takes only 7 minutes to recharge to a capacity of 80% (at the depot at the end of the day charging adds the remaining 20%, achieving 200V battery voltage).
The system works with magnetic resonance couplings. It consists of two main components: a primary coil that is connected via Track Supplies with the power grid, and a pickup coil, which is integrated into the underbody of the vehicle. The technology provides a non-contact and automated transfer. Wireless opportunity charging helped to significantly reduce the battery capacity required. Instead of driving around tons of batteries, the buses focus on transporting people.

Results
The system is user-friendly and safe: it uses available electrical infrastructure, charging is automated and possible under all weather conditions.

The inductive en-route charging technology increases the profitability of an electric bus fleet because the more frequent, but shorter, charging cycles reduce the required battery capacity and improves its service life. As a result, electric-bus-fleet operators can buy cheaper buses with smaller batteries. The bus routes with the IPT wireless charging systems haven’t only proven themselves from the economic point of view, but also because they are reticent and produce zero emissions.

As the chargers can be integrated almost invisibly, they neither compromise the cityscape nor detract from the tourist attractions. There’s nothing for people to get hurt by tripping over, and there are no secondary costs due to vandalism or rodent damage.

The technology and wireless opportunity charging
The wireless charging system is based on the IPT® Charge bus magnetic resonance coupling technology, which provides an efficient, automatic and contactless energy transfer.
The system consists of primary coils connected to the electrical grid, and a secondary coil integrated into the floor of each of the electric buses. The battery is fully charged overnight and topped up during the day (by about 10-15 per cent) along the bus route – for example, at terminals and railway stations – with short and relatively frequent charging sessions.

In normal operating conditions, 95% of the energy taken from the electricity grid is stored in the bus battery. The frequent top-ups mean that the capacity of the buses’ batteries can be kept at a minimum (reduced by as much as 75%) potentially saving money through the purchase of smaller batteries and making the vehicle lighter.

Two charging points were installed at the end of Turin’s STAR 1 line; 10-12 minutes of recharging are enough to keep buses in operation from 07:00 to 20:00. The buses are 7.5 metres long, and their maximum weight is 11,500 kg. They travel about 130 km a day, accommodate 40 passengers, and their maximum speed is 70 km/h. The 180Ah battery installed on the buses is fed at 336V and produces a power of 65kW. Operating time is 13 hours per day.

Author: Marco Valerio Salucci
Source: Eltis

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