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There are various EV technologies available in the market. Some of the manufacturers use HEVs to increase the efficiency of the car while others take another step towards all-electric mode with PHEVs. Some other manufacturers, such as Tesla Motors, dedicate their efforts on pure EVs which do not even have a tail pipe [200]. HEVs are classified as series, parallel and series parallel [206]. Figure 6.5 shows the typical diagram of a series hybrid power train. Fed

by fuel tank, the internal combustion engine (ICS) charges the batteries through the generator. The traction is provided to the wheels through battery-propulsion motor couple. In a series power train, the ICS engine is mechanically decoupled from the wheels. This gives the freedom to relocate ICS engine as desired. Despite expensive manufacturing costs, series power trains are easy to design, control and implement[206]. They are also popular for larger vehicles [134].

Figure 6.5. A HEV with a series hybrid power train

Figure 6.6 shows the topology of a parallel hybrid power train where both ICS engine and the electric motor are mechanically coupled to the wheels. The electric motor helps increase the efficiency of ICS engine and decrease its carbon emissions. One drawback of parallel power trains is the inability to operate in all-electric mode at high speeds [134].

Figure 6.7 shows a PHEV with series-parallel hybrid power train. It possesses the advantages of both the series and parallel hybrid trains. Since it has more components, an additional generator compared with parallel power train and an additional mechanical link compared with series power train. Hence, it is more expensive. Thanks to advancements in control and manufacturing technologies, these costs are reduced and series-parallel power trains are adopted more frequently [206]. Figure 6.7 also depicts the fundamental difference between HEVs and PHEVs. The battery system in PHEVs has an external connection and can be recharged independently from the operation of the ICS engine.

Figure 6.7. A PHEV with a series-parallel hybrid power train

The motivation behind hybridization is to increase the overall efficiency of the engines and decrease emissions per unit distance. The benefits of hybridization can be summarized as follows [134]:

Higher efficiency is obtained since electric propulsion machines are more efficient and faster than other systems

The flexibility provided by the electric propulsion systems makes it possible to operate heat engine at higher-efficiency region

Regenerative braking can be utilized to charge the batteries during braking

The hybridization factor of the vehicles may vary depending on the classification of HEVs. Micro hybrids have a hybridization factor of 5-10 % while mild hybrids have 10-25 %

hybridization factor. Higher values are found in energy hybrids [134]. Needless to say, when the need for ICS engine and the liquid fuel is completely eliminated, a pure EV is obtained. Furthermore, due to their external electrical connection, PHEVs as well as pure EVs allow for V2G operating modes. The standard modeling presented in this chapter provides a generic model for the smartgrids. The manufacturer, model or the type of PHEV or EV is not required for proper operation. This is a massive advantage for microgrids, especially when diversity of car manufacturers and their technologies are considered.

Battery charging seems to be a challenge for manufacturers, customers and other parties. EV charging may require special charging stations, supply devices and connectors. In addition to several issues such as charging through third parties, the most important concern is the time required to charge the batteries. Depending on the network parameters and availability of the special charging equipment, charging time varies between 18 hours and 20-50 minutes. Table 6.3 shows different set of charging options developed for an EV [134].

TABLE 6.3.TYPICAL SET OF EVCHARGING OPTIONS

Charging Set Utility Service Usage Charge Power (kW) Level 1 110 V, 15 A Opportunity 1.4

Level 2a 220 V, 15 A Home 3.3

Level 2b 220 V, 30 A Home/Public 6.6

Level 3 480 V, 167 A Public/Private 50-70

Only Level 1 may not require an upgrade of the existing electrical networks while the remaining three charging sets definitely would require a through electrical network improvement. Level 1 is called the `Opportunity` charging since it uses low-peak periods, costs less but takes very long. Level 2 can be used for home use. Public usage means charging EVs when parked in a public place such as railway stations or public car parks. Level 3, which is also called fast charging, can be used by private charging stations. EV owners can use these stations for charging in a similar fashion to petrol stations. Yet, in

addition to electric network upgrades, Level 3 charging may require special charging equipment [139].

TABLE 6.4.BATTERY CHARACTERISTICS OF DIFFERENT EVS

Manufacturer Model EV Type Electric Range (km) Battery Size (kWh)

Toyota Prius PHEV 8 4

Buick PHEV 16 8

Chevrolet Volt EREV 64 16 Fisker Karma PHEV 80 22

Nissan LEAF EV 160 24

Toyota RAV4 EV EV 190 27 Cooper (BMW) Mini E EV 251 28 Tesla Roadster EV 354 53

The battery characteristics of different EVs are given in Table 6.4 [200-203]. The corresponding charging curves for different EVs using different charging options are plotted in Figure 6.8. As shown, Level 1 is not feasible for some pure EVs with large battery sizes. Level 3 seems to be practical for all types, although it is expected to be the most expensive option of all. It is shown that Level 2a and 2b are quite sufficient for almost all EVs and can be implemented parking places for short to medium parking times (such as parks near schools, universities etc.)