Hybrid Electric Vehicle System Structure, Characteristics And Working Mode(Part 2)

Plug-in hybrid electric vehicle

1. Structure

Plug-in hybrid electric vehicles are hybrid electric vehicles that can use the power grid (including household power sockets) to charge the power battery. They are developed on the basis of oil-electric hybrid electric vehicles. It can travel long distances in pure electric mode or in full hybrid mode. Plug-in hybrid electric vehicles are divided into two structures: parallel and series. Plug-in hybrid electric vehicles are equipped with an on-board charger and can be directly charged from the power grid. Compared with pure electric vehicles, plug-in hybrid electric vehicles have an internal combustion engine; compared with oil-electric hybrid electric vehicles, plug-in hybrid electric vehicles can be charged from the external power grid; under the same vehicle model conditions, the battery power of plug-in hybrid electric vehicles is greater than that of oil-electric hybrid electric vehicles, and the power of internal combustion engines must be smaller than that of electric hybrid electric vehicles. In short, the design goal of plug-in hybrid electric vehicles is to combine the advantages of pure electric and oil-electric hybrid electric vehicles. For example, the plug-in model of Toyota Prius is a modified design based on the original hybrid model with an internal combustion engine added. The original positioning of Volt was to design and manufacture an extended-range hybrid electric vehicle, using a small electric motor and a large-capacity battery to achieve pure electric driving. However, since the power performance cannot meet the requirements, a clutch is added between the engine and the generator to enable the engine to participate in the drive when the power demand is large. The structure adopts a hybrid structure with a planetary gear coupling mechanism, but the working mode is not exactly the same as the Toyota Prius plug-in hybrid, which also adopts a planetary gear structure.

1. Features

1. Advantages

The characteristic of plug-in hybrid vehicles is that the power comes mainly from the battery, and the engine is only used as a backup power source and is activated when the battery is exhausted. That is to say, plug-in hybrid vehicles are mainly suitable for urban roads. In daily use, it can be used as a pure electric vehicle. As long as the single use does not exceed the driving range provided by the battery (such as HEV30, PHEV40, PHEV50, which can generally meet more than 50km), it can achieve zero emissions and zero fuel consumption. 

Therefore, plug-in hybrid vehicles have the following advantages:

1) Plug-in hybrid vehicles have all the advantages of pure electric vehicles, and can use the low-peak electricity at night to charge the battery, improve the unit efficiency of the power plant, and save energy.

2) Reduce the emission of greenhouse gases and various harmful substances; reduce dependence on petroleum fuels, reduce oil imports, and increase national energy security.

3) If driving in the city, the distance is short, use pure electric mode and do not consume fuel; if traveling long distances, use hybrid drive mode to increase the driving range.

4) The on-board battery pack can be charged using an external power grid.

2. Disadvantages

1) Determine the pure electric mileage according to specific needs, and affect the choice of battery size.

2) Pure electric driving places high demands on batteries, such as sufficient energy density and power density, long cycle life, and high discharge and charging performance requirements.

3) Requirements for charging facilities, including the construction of charging stations.

III. Working mode

According to the changing characteristics of the battery charge state on the vehicle, the working mode of PHEV can be divided into power consumption (CD), power retention (CS) and conventional charging (BC) modes, among which power consumption is divided into pure electric (HV) and hybrid power (HEV) two sub-modes.

PHEV gives priority to power consumption mode. In power consumption mode, PHEV specifically selects pure electric and hybrid power sub-modes according to the power demand of the whole vehicle.

In the power consumption-pure electric mode, the engine is turned off, the battery is the only energy source, the battery's state of charge is reduced, and the vehicle generally only reaches part of the power performance indicators. This mode is suitable for starting, low speed and low load.

In the power consumption-hybrid mode, the engine and the electric motor work at the same time, the battery provides the main part of the vehicle's power demand, the battery's state of charge is also reduced, and the engine is used to supplement the insufficient battery output power until the battery's state of charge reaches the minimum allowable value. This mode is suitable for high speed, especially when the power performance indicators are fully achieved.

In the power retention mode, the working method of PHEV is similar to the traditional HEV working mode, and the battery's state of charge remains basically unchanged.

The power consumption-pure electric, power consumption-hybrid and power retention modes can be seamlessly switched according to the vehicle management strategy. The main basis for switching is the vehicle power demand and the battery's state of charge.

Edited by Asiautos Auto Part