**2.2. HEV configurations**

Coming next, we briefly present the characteristics of some typical HEV configurations. After that, one typical HEV configuration will be selected for developing its dynamic equations. Then, several MPC scheme are built to control the speeds of the ICEs and the EMs for each part of this HEV. Simulation and calculated examples are also provided after each section to illustrate our main ideas for each section. Finally, some conclusions are drawn and some

The first concept of HEVs was initiated by Ferdinand Porsche at Lohner Coach Factory when he designed the "Mixte", a series hybrid vehicle based on his earlier electrical vehicle. This hybrid vehicle was installed with a gasoline ICE connected to an electrical generator and an EM propels the vehicle with a small battery for more reliability. This serial HEV concept grew until the late of 1960s. In 1972, Viktor Wouk developed his first prototype for parallel hybrid powertrain in General Motors namely "Godfather of the Hybrid". This turning point ignited the very fast growing progress in HEVs as we can see nowadays and branched in many different aspects such as regenerative braking issues, fuel consumption, emission, battery problems and so on. Worldwide sales of hybrid vehicles reached more than four (4) million units by December 2010 and sold over 80 countries and regions, led by the United States with more 2.5 million units. Regenerative braking, shutting down the engine at idle have reduced the fuel consumption and emissions. The main problem for HEVs now is relying on the cost

The recent technology of HEVs is the development of the diesel HEVs since diesel prices are cheaper than gasoline while diesels produce more energy, suffer less wear while operating at higher efficiency. Diesel ICE produces higher torque and offer longer mileage. Most diesel ICE can use 100% pure biodiesel and they don't need petroleum. Diesel ICEs are 20% to 40% more efficient and produce less carbon-dioxide emissions than gasoline ICEs. Diesels are widely popular in Europe, accounting for more than 50% of the car market there. If the diesel HEVs

Conventional vehicles are propelled by only igniting fossil fuel in an ICE and converting the ignition energy into mechanical rotation and translation. In contrast, HEVs are characterized by using some combination of a primary propulsion unit (PPU) that can be fuel cell (FC) of an ICE or EM that can be either an electrochemical storage system such as a battery or an electrostatic super capacitor [22]. In addition to the above mentioned components, at least one electric motor is necessary in any HEV to help propel the vehicle either fully or partially. This combination of electric and fossil fuel energy, supervised with a high level controller called energy management strategy (EMS), can improve the performance of the vehicle from a fuel consumption and emission point of view. Comparing HEVs with conventional vehicles shows

and the weight of the large batteries and the starter/generator motors.

were in use, higher benefits from this system can be achieved.

**2.1. Definitions**

suggestions for the future research are discussed.

30 New Applications of Electric Drives

**2. HEVs configurations and reviews**

As mentioned above, any HEV contains at least two sources of energy. These two sources can be coupled together in several different combinations according to the application. The most famous configurations are called series, parallel, series-parallel and heavy HEV [23]. The latter is though not a separate category but either a series or a parallel hybrid that is used in heavy delivery vehicles can run on gasoline or diesel. The following is a brief description of each configuration.

## **Series HEVs:**

Series powertrain architecture is used in large vehicles such as locomotives and heavy duty trucks and not in passenger vehicles according to efficiency problems due to their component inefficiencies [24]. In this configuration, the ICE is not directly connected to the final trans‐ mission but via two electric machines. In such architecture, the engine mechanical output is first converted into electric energy using an electric generator and then this electric energy can either charge the battery when needed or bypass the buffer and propel the vehicle via a separate electric motor or a combination of these as is shown in Figure 1. Regenerative braking is also possible using the traction motor in generator mode and storing the electric energy into the buffer. So a series HEV needs three machines: one engine, one electric generator, and one electric traction motor.

**B**: Battery; **E**: ICE; **F**: Fuel tank; **G**: Generator; **M**: Motor; **P**: Power converter; **T**: Transmission (including brakes, clutch‐ es and gears)

**Figure 1.** Series HEV Configuration.

### **Parallel HEVs:**

Since the model that is used in this study is a parallel hybrid, it is described here in more details. In parallel hybrid electric vehicles the propulsion energy is delivered to the final drive by the EM and the ICE in two separate parallel paths. Though the ICE is the primary propulsion unit, the EM will be considered as an assistant to the PPU. As shown in Figure 2, both the ICE and the EM are coupled to the final transmission via mechanical links in parallel HEVs. Also, it is worth mentioning that each energy flow path can have a separate clutch to engage/disengage the final transmission from either the ICE and/or the EM. Hence, six (6) different operating modes are possible for a parallel HEV as follows:


**Figure 2.** Parallel HEV configuration.

**Series HEVs:**

32 New Applications of Electric Drives

electric traction motor.

es and gears)

**Parallel HEVs:**

**Figure 1.** Series HEV Configuration.

modes are possible for a parallel HEV as follows:

the electric buffer via the lower path. See Figure 3**B**.

Series powertrain architecture is used in large vehicles such as locomotives and heavy duty trucks and not in passenger vehicles according to efficiency problems due to their component inefficiencies [24]. In this configuration, the ICE is not directly connected to the final trans‐ mission but via two electric machines. In such architecture, the engine mechanical output is first converted into electric energy using an electric generator and then this electric energy can either charge the battery when needed or bypass the buffer and propel the vehicle via a separate electric motor or a combination of these as is shown in Figure 1. Regenerative braking is also possible using the traction motor in generator mode and storing the electric energy into the buffer. So a series HEV needs three machines: one engine, one electric generator, and one

**B**: Battery; **E**: ICE; **F**: Fuel tank; **G**: Generator; **M**: Motor; **P**: Power converter; **T**: Transmission (including brakes, clutch‐

Since the model that is used in this study is a parallel hybrid, it is described here in more details. In parallel hybrid electric vehicles the propulsion energy is delivered to the final drive by the EM and the ICE in two separate parallel paths. Though the ICE is the primary propulsion unit, the EM will be considered as an assistant to the PPU. As shown in Figure 2, both the ICE and the EM are coupled to the final transmission via mechanical links in parallel HEVs. Also, it is worth mentioning that each energy flow path can have a separate clutch to engage/disengage the final transmission from either the ICE and/or the EM. Hence, six (6) different operating

**1.** Motor assist mode: Power from both the ICE and the EM are mixed together to provide the final drive power request. This can be the case in peak power demands. See Figure 3**A**.

**2.** Regenerative breaking mode: In this mode, the braking energy can be converted into electric energy, using the traction motor working in generator mode, and be stored into

As can be seen in Figure 2, one single electric machine can be used in parallel HEVs, working either as a motor or as an electric generator. This results in a decrease in expenses as well as in total vehicle mass that can prevent an excess in fuel consumption due to the vehicle weight. Different operating modes of a parallel HEV are shown in Figure 3. Note that the arrowheads show the direction of power flow in each operating mode of the vehicle powertrains.
