*5.4. Size Optimization*

It is essential to optimize the sizing of propulsion system components without reducing performance to reduce the manufacturing costs and emissions associated with transport platforms. In a conventional vehicle, the size of the ICE is directly associated with the maximum power required for the vehicle. Similarly, in the case of pure electric vehicles, the range depends on the size of the battery. In general, it is the energy rather than the power that conditions the sizing of the batteries. There is not total freedom of design in either platform, because a single energy source powers the vehicle in both cases.

Extended-range electric vehicles have at least one degree of design freedom, that is, the sizes of their energy sources, because more than one energy source is integrated. The sizing of an EREV platform consists specifically of defining the size requirements in terms of power and/or energy. Then, the sizes of the energy sources and the vehicle's power requirements implicitly define the sizes of the power converters that make up the propulsion system. The choice of component size significantly affects vehicle's performance in terms of power availability, energy efficiency, manufacturing costs, and component life. Figure 15 shows the strategies for plant/controller optimization.

**Figure 15.** Optimization levels of an EREV.

#### **6. The Process of Designing an EREV**

Here we present a guide for designing an extended-range electric vehicle in general terms.

Once the kinds of technology have been analyzed and compared, after knowing the possible configurations and the interactions of the components, a conceptual design of an extended range electric vehicle can be generated. However, first, we must define the type of vehicle we are going to design. There are three types that cover the vast majority of vehicles, and they are compacts, pick ups, and trucks.

As a second step, depending on the type of vehicle we want to design, we select the type of traction that this may have, which varies depending on the type of vehicle; the three main types are FWD, RWD, and AWD.

As a third step, we define the technology of the electric motor that the EV will have and its position for its configuration. In-wheel motors are commonly used in compact vehicles.

As a fourth step, we have the selection of the range extender system. We can make our selection under certain criteria, and we are helped by Figure 16, where we compare these technologies. For practice, we define two selection criteria: the amount of power and the emissions. Large vehicles need high levels of autonomy; small vehicles can have medium or low levels of autonomy. Our selection criteria are the extra range needed, a high, medium, or low amount; and the space and weight that can be sacrificed.

As a fifth step, the controller selection (independent or general controllers) will depend on the control strategy to use; we can consult Table 1.

We can also optimize the controller selection (see Section 5) using the strategies shown, and our components' sizes.

Then, we will finally have our extended range electric vehicle, which should have ideal performance, optimal control, and optimized components. All steps are shown in Figure 16.

**Figure 16.** The process of designing an EREV.
