Hybrid Electric Vehicle: Plug-In Hybrids H Mettlach, Adam Open GmbH, Ru ¨ esselsheim, Germany & 2009 Elsevier B.V. All rights reserved. Degrees of Hybridization There are different degrees of hybridization from micro- hybrids to extended-range electric vehicles (E-REVs). The complete range between nonhybridized vehicles and pure battery electric vehicles (EVs) is covered. Depending on the degree of hybridization, there are different functionalities available. Table 1 shows the functionality for full hybrid electric vehicles (full HEVs), plug-in hybrid electric-vehicles (PHEV Full HEV, full heavy electric vehicles; PHEVs) with 10 or 40 miles electric-only range, and E-REVs. Motivation for Plug-In Hybrid Electric Vehicles and Extended-Range Electric Vehicles Already today, there exists a large variety of HEVs from micro and mild hybrids to full hybrids. However, all these vehicles do have an internal combustion engine (ICE) as main propulsion source and fossil fuel (e.g., gasoline, diesel, CNG) remains the principal source of energy. Recently, interest increased in vehicles that can even further reduce the consumption of fossil fuels. Therefore, PHEVs and E-REVs have come into focus. PHEVs and E-REVs differ from the hybrid vehicles discussed before, since a portion of the fossil fuel will be replaced by electricity. Thus, it is possible to become more independent from fossil fuels, especially if the electricity is produced from renewables like wind or solar energy. In addition to the charge-sustaining mode – which is similar to the operation mode of full HEVs – there is a second mode which is called charge depletion mode. In the charge-sustaining mode, the batteries of both PHEVs and E-REVs will be discharged by the electric motor during start and boost operation. During regenerative braking and also when charging from the generator, the battery will be charged. By these means, the battery is kept around a certain state-of-charge (SoC). The SoC swing can vary between 75% and 715% depending on the type of vehicle and operating strategy. In the charge depletion mode, the battery will be discharged more than it is recharged during regenerative braking and charging from the generator. Therefore, the SoC of the battery at the end of the drive cycle will be lower as at the beginning. Afterward, the battery will be charged through a battery charger from the grid. Com- pared to a full HEVs, PHEVs or E-REVs comprise a larger battery, typically operated over a much higher SoC range. The electrical energy provided by the char- ger through the grid does not need to come from the generator and ICE anymore and, therefore, replaces (fossil) fuel by electricity that may originate from renewables. Figure 1 shows an example for battery power and SoC during the operation in the charge depletion mode. In this example, the battery is at a high SoC at the be- ginning of the drive cycle and is discharged to a low SoC at the end of the drive cycle. As a result, in this example around 50% of the totally stored energy of the battery is discharged and can be recharged through the grid. Since an electric motor has much a higher efficiency than an ICE (around 3–4 times better in typical drive cycles), the reduction of (fossil) fuel use is even higher than one would expect from the amount of energy recharged through the grid. Table 1 Functionality of different hybrid vehicles Function Full HEV PHEV (10 miles) PHEV (40 miles) E-REV Cold cranking üüüü Start–stop üüüü b Boosting üüüü Regenerative braking üüüü Electric driving (reduced power) (ü) a üüü Electric driving (full power) — — — ü Charging from generator üüüü Charging from grid — üüü a May not be selectable by the driver but chosen by the vehicle controller. b Technology that supports the internal combustion engine with additional torque and improving the acceleration performence of a vehicle. Full HEV, full heavy electric vehicle; PHEV, plug-in hybrid electric vehicle; E-REV, extended-range electric vehicle. 286 . Hybrid Electric Vehicle: Plug-In Hybrids H Mettlach, Adam Open GmbH, Ru ¨ esselsheim, Germany & 2009 Elsevier B.V. All rights reserved. Degrees of Hybridization There. are different degrees of hybridization from micro- hybrids to extended-range electric vehicles (E-REVs). The complete range between nonhybridized vehicles and pure battery electric vehicles (EVs). on the degree of hybridization, there are different functionalities available. Table 1 shows the functionality for full hybrid electric vehicles (full HEVs), plug-in hybrid electric- vehicles