The energy sector makes up nearly three-quarters of global emissions, followed by agriculture. Within the energy sector, the largest emitting sector is electricity and heat generation, followed by transportation and manufacturing as summarized in Fig.1. Excessive CO2 emissions cause climate change . Indeed, nowadays the number of air pollution-related deaths are increasing. It has been a while since the world is paying a great attention in reducing the CO2 emission and to use green energy (renewable energy) source.
Figure 1. CO2 emissions of different sectors in the world .
Nowadays, Electric Vehicles (EVs) are becoming more common specially in big cities like Milan. Electric cars improve air quality by reducing the CO2 emissions. Moreover, EV are less noisy compared petrol cars and are suitable in cities where speeds are generally low. However, there are several challenges related to EV, i.e., access to charging infrastructure, charging time, cost, weight, and future grid (two-way power flow).
As an electrical engineer it is always my interest to see the latest advancement in technologies specially in the field of EV. Therefore, I found an opportunity to enroll the ELECTRIC MOBILITY: TECHNOLOGIES, EXPERIENCES AND FUTURE TRENDS course organized by Politecnico di Milano. I didn’t even think two times to apply this course. The course started from details about fundamentals of electric mobility such as main mechanical laws, traction diagrams, energy consumption and storage systems for vehicle applications. Then it is followed by the details of the types of electric motor drives together with classification of Plug-in and Hybrid EV. The course also covered charging infrastructure in detail including the types of charging stations, and the communication protocols between EV and charging stations. Moreover, future perspectives in electric mobility considering the advancement of power electronics technology such as SiC Mosfets and GaN devices, and Ultra-fast charging systems and Inductive charging systems are covered.
As a part of this course, there was an opportunity to visit one of Milan’s electric bus charging stations where it has 5.5 MW total capacity. Two types of chargers are available in this station. One is DC fast charger (off-board) with maximum power of 100 kW. There are a total of 75 chargers of this kind. The 2nd type of charger is Pantograph in which only two is available with maximum power of 200 kW. In this case the buses are equipped with camera so that the bus driver can control the Pantograph and antenna position.
Figure 2. Picture captured while visiting one of the off-board chargers.
Figure 3. Picture captured while an Electric bus is charging with Pantograph.
There is an underground substation composed of three shelters, each contains transformer, rectifier circuits, circuit breakers and controllers. The transformer converts the 23 kV voltage from the main grid to 590 V for rectifier circuits (one rectifier supply 25 chargers) and to 400 V (for auxiliary loads and controllers).
There are a total of 5 transformers in this station. Three transformers are for the 75 chargers (each transformer supply 1 rectifier and each rectifier supply 25 chargers). One transformer is for Pantographs (two pantographs are available in the station) and another transformer is for other auxiliary loads. The Pantograph is supplied from the 800 kW rectifier and two DC-DC converters each 400 kW.
There is SCADA system is in the shelter to communicate between the charging outlet and the rectifier. The operator can see the state of charge of the batteries of each bus, how much power they consume for charging and in which charger the buses are connected. It is also possible to exchange data about power flows with the external grid. The buses recharge after their state of charge reaches to 60% (to have enough reserve for going and returning to the parking station).
Figure 4. Picture captured while visiting the control room of the Pantograph charger.
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