The batteries charging systems can be of two types: public chargers and residential chargers. Public chargers are an optimal solution to charge the batteries of the vehicles using energy from several sources of energy (as wind or sun) and can be deployed at strategic places around a town or city, like for example, at companies, public buildings and shopping centers parking lots. On the other hand, residential chargers are designed to deliver low power, in an efficient way, since in general they are used to make a complete charge of the batteries during long periods of time (slow charging). The main benefits of these two types of chargers are the comfort for the user, and the freedom of the user to charge the batteries when he wants, according with the best prices of energy. The main disadvantage is that, since each charging process is independent, the limit of overload of the electrical power grid can be easily reached.
Currently, the majority of EVs are designed with on-board unidirectional batteries charging systems. Besides the on-board batteries charging systems, some vehicles allow the charge of their batteries with off-board chargers. An on-board batteries charging system refers to a charger implemented inside the vehicle. The user only has access to the input of the charging system. This type of charger is connected to the AC electrical grid voltage and is used to slowly charge the batteries – it is denominated as “slow charging”. On the other hand, an off-board batteries charging system is implemented outside the vehicle. It is given access to the DC voltage of the batteries and is used to charge the batteries as fast as possible – it is denominated as “fast charging”.
US EPA Memo: Battery Charger Systems specification update
Regarding the way that the charger can be connected to the vehicle, there are two different approaches: conductive or inductive. The conductive batteries charging system is made through a physical contact between the vehicle and the power grid. In counterpart, with the inductive batteries charging system there is no physical contact between the vehicle and the power grid. Independently of the charger type, the interaction between the EVs and the power grid should comply with regulatory standards, as the International Electrotechnical Commission (IEC) norms (IEC 62196 and IEC 61851).
As previously commented, and as demonstrated in , the load profile of the EVs batteries charging systems has high importance to the power grid management. Depending on the design of the electrical grid and the type of charging and discharging processes, EVs can be a problem or a benefit to the power grid. The batteries charging and discharging processes can be realized in two different ways: controlled and uncontrolled.