**Series-parallel HEVs:**

As shown in Figure 4, a third configuration of HEVs can be realized by just adding another power flow path to the parallel architecture having the features of both series and parallel HEV. In this configuration, an extra electric machine is added to the system via a mechanical and an electrical link so that all advantages of series and parallel hybrids can be kept together in one single vehicle. The disadvantage of series-parallel HEVs is though they have complex and costly structure, they are still preferred to be employed in some special cases.

**Figure 3.** Power flow in a parallel HEV.

**Figure 4.** Series-parallel HEV.

### **2.3. Parallel HEVs reviews**

There are four (4) different types of parallel hybrid vehicles: micro-hybrid, mild-hybrid, medium-hybrid, and full-hybrids. The differences are from their functionality relating to the electrical power and the input voltage level (Figure 5). Our research focuses only on the hybrid vehicle with light electrical power supplier up to approximately 10 kW. With these light electric power, some relatively high benefits can be obtained.

The input voltage for a mild-hybrid is usually applied at 36 V, but for this lightest electrical power, such a higher voltage level will not be needed and the 12 V will be a better solution. Due to the ability of some power assist for the regenerative braking, this configuration is categorized as mild-hybrid. The voltage level of medium-hybrid is 144 V while the voltage level for full-hybrid is 300 V. In this research, a full-hybrid vehicle is developed with two EMs. One main EM uses the synchronous DC 300 V and the other is a synchronous starter/generator DC 48 V.

A conventional vehicle powertrain consists of one electrical starter connecting to one electrical generator. The electrical starter can convert the electrical energy into mechanical torque and is used to rotate the engine. The electrical generator is basically differing, it connects to the crankshaft and runs as an electrical supplier, transforming the ICE's mechanical torque into the electrical energy and stores this power into the vehicle batteries. The integrated starter generator (ISG) is a new development and becomes the only one device that will combine both above functions. For generating mode, it will charge the vehicle batteries and for starting mode, it will discharge the vehicle batteries in order to start or assist the ICE.

There are several possible positions for the ISG to be assembled. Three (3) main typically configurations are, the crankshaft-mounted ISG (C-ISG), the belt driven ISG (B-ISG), and the drivetrain mounted ISG (D-ISG) as shown from Figure 6 to Figure 8. The C- and D-ISG are usually used for the larger electrical power levels than the B-ISG configuration. Reasons for these differences are the limited power suppliers that can be transferred without slip through the belt of the B-ISG configuration. In the case of D-ISG configuration, the clutch is installed between the ICE and the ISG, so that, the hybrid vehicle can operate from either the ISG or on the combination of both power supplier sources. Rationally, if the vehicle can be able to operate completely on the ISG, the electrical power supplier must be large adequate.

**Figure 5.** Different classes of hybridization [18].

**Figure 4.** Series-parallel HEV.

**2.3. Parallel HEVs reviews**

**Figure 3.** Power flow in a parallel HEV.

34 New Applications of Electric Drives

power, some relatively high benefits can be obtained.

There are four (4) different types of parallel hybrid vehicles: micro-hybrid, mild-hybrid, medium-hybrid, and full-hybrids. The differences are from their functionality relating to the electrical power and the input voltage level (Figure 5). Our research focuses only on the hybrid vehicle with light electrical power supplier up to approximately 10 kW. With these light electric

The input voltage for a mild-hybrid is usually applied at 36 V, but for this lightest electrical power, such a higher voltage level will not be needed and the 12 V will be a better solution. Due to the ability of some power assist for the regenerative braking, this configuration is categorized as mild-hybrid. The voltage level of medium-hybrid is 144 V while the voltage level for full-hybrid is 300 V. In this research, a full-hybrid vehicle is developed with two EMs.

One clear advantage of the D-ISG configuration regarding to other variants is that during deceleration the drag torque of the ICE can be removed by opening the clutch, letting more

**Figure 6.** Schematic representation of a B-ISG.

**Figure 7.** Schematic representation of a C-ISG.

**Figure 8.** Schematic representation of a D-ISG.

energy available for regenerative braking processes. However, because of the limited charging acceptance of the vehicle batteries, the full ability of regenerative braking process will be never employed unless the deceleration is very slow. Additionally, purchasing a B-ISG system is less cost, which will provide some important advantages over the use of the C-ISG and the D-ISG.

From the above overview of HEV configurations, we will select a typical parallel HEV configuration and start the full investigation with this new HEV model in the next section.
