Smart charging

The fast rising number of EVs require wider, reliable and more comprehensive charging infrastructure. As the number of EVs increases, their potenBal impacts on power grids ascends as well. Hence, efficient smart charging schemes and management become essenBal. In smart charging, an EV and a charging device are in data connecBon. This connecBon is further connected with a charging operator via the charging device. The charging operator/the owner of the charging device is able to monitor, control and re-strict the charging remotely, thus opBmizing the energy consumpBon effect to the grid.

If charging is not managed controllably, a large number of EVs can cause severe peak loads to the power grid by increased power and energy demand, hence having signifi-cant impact on the power quality. Other potenBal effects to the power grid are possible negaBve impacts on the various system components, e.g. transformers. Without regu-laBon and control, charging simultaneously a large number of EVs, i.e. fleets, can cause disrupBon to the stability of the whole power system. The rising demand of electricity requires enhanced control of DMS, having the capability and tools to uBlize the capaci-ty harnessed from EVs, their abilicapaci-ty of acBng as distributed energy storages and power generaBon units for the grid (BaronB et al., 2016; Mullan et al., 2012; Habib et al., 2015; Sharma et al., 2020).

Different EV charging technologies are:

• UnidirecBonal vs. bidirecBonal:

The charging of EVs can either be unidirecBonal or bidirecBonal. In the first model, aka grid-to-vehicle (G2V) soluBon, an EV uses the power grid to charge its baRery. In the later model, the EV baRery can also be used to supply power to the grid, i.e. V2G solu-Bon.

• On-board vs. off-board chargers:

When an EV is equipped with an on-board charger, it can be charged anywhere, where a power outlet (plug-in) exists. On-board charger adds more weight to an EV. Whereas, an off-board charger requires a charging point or a staBon with power raBng of approx-imately 50kW to charge the baRery of an EV.

• Integrated chargers:

An EV’s electric drive system components take part in charging, which reduces the size of an on-board charger, or it is not required at all. Thus, reducBons in cost, weight and space usage can be achieved.

• Wireless aka dynamic charging:

Electric power is transferred wirelessly to an EV through a power field. The system re-quires a large size antenna array, which can be supported by inducBve or magneBc res-onance coupling, microwaves, or laser radiaBon. However, wireless charging is sBll in the research stage, and its expenditures are high. Yet, once operaBonal and widely available, it has the potenBal to revoluBonize the whole transportaBon system (BaronB et al., 2016; Sharma et al., 2020).

In charging, the current and voltage needs to be constantly controlled. This can be best achieved by either keeping the current or voltage constant. AddiBonally, different lev-els of charging exist. Level 1 charging or slow charging is designed for residenBal out-lets, for on-board charger models with 120V AC ouRake. Level 2 aka semi-fast charging is suitable for charging staBons, and are capable for five Bmes faster charging than the level 1, thus being able to fully charge an EV in 5-7 hours. Level 3 aka fast charging uses DC power with constant current and voltage. Its charging power exceeds 100kW, re-quiring charging technology of considerable size, thus being suitable only for off-board charging. Fast charging is opBmal, e.g. in public transport and commercial logisBcs us-age, where baRery charging should not last more than 30-60 minutes (Sharma et al., 2020).

However, smart charging soluBons require new kind of charging schemes:

• Uncontrolled, Bme-of-use smart charging:

Smart charging based on opBmizaBon of Bme-of-use is the simplest form of smart charging. It incites the end-users to uBlize off-peak periods for charging from peak Bmes. AddiBonally, it is relaBvely straighgorward to implement Bme-of-use charging, since its external stakeholder control does not exist. Time-of-use charging has proven its effecBveness in delaying EV charging unBl off-peak periods at low EV penetraBon levels (Paulraj, 2019; Virta, 2021).

• UnidirecBonal controlled charging (V1G):

Either EVs or the charging infrastructure can adjust their charging rate in unidirecBonal controlled charging. The grid operator oversees the charging process via controlling signals. Daily esBmaBon of the local available charging capacity is provided by Open Smart Charging Protocol (OSCP), and Open Charging Point Protocol (OCPP) to the Charge Point/Spot Operator (CPO), which adjusts EVs’ charging profiles to the available charging capacity.

• BidirecBonal V2H / V2B / V2X smart charging:

Smart charging scheme, which provides an EV baRery’s power supply to be connected to its close surroundings, performing as a back-up power source increasing self-con-sumpBon. Hence, it does not stress the actual power grid but funcBons as an alternat-ive power source. This scheme can add flexibility and reliability to, e.g. homes (V2H), buildings (V2B) or some other objects’, e.g. facility, appliances, lighBng etc., electricity consumpBon (Paulraj, 2019; Virta, 2021).

•

With V2G soluBon, an EVs can be uBlized as a distributed power source and storage for the grid. Thus, it is more evolved smart charging method than controlled V1G or bidi-recBonal charging for self-consumpBon. Furthermore, in V2G smart charging/discharg-ing, EVs’ baReries can be uBlized in ancillary services, including voltage support and

frequency control, load following and funcBoning as secondary reserve for grid flexibili-ty and reliabiliflexibili-ty. In V2G smart charging, the TSO is capable of purchasing energy from EV owners if the peak demand requires it. Hence, V2G has higher commercial value, which can encourage consumers to acquire an EV (Paulraj, 2019; Virta, 2021; Habib et al., 2015).