Plug-in hybrid electric vehicle (PHEV) is a new type of hybrid electric vehicle, which is between pure electric vehicle (BEV) and ordinary hybrid electric vehicle (HEV). Plug-in hybrid electric vehicles have become one of the mainstream development directions of new energy vehicles due to their advantages such as long driving range of pure electric vehicles, improved fuel economy, reduced emissions, and use of low power consumption at night to charge power batteries. According to the different structure of plug-in hybrid power system, it can be divided into four types: series hybrid power, parallel hybrid power, hybrid hybrid power and dual-mode hybrid power. This article introduces the first two, and the remaining two types will be introduced in the next article.
1) Series hybrid power system
Plug-in series hybrid electric vehicles, also known as extended-range electric vehicles, are equivalent to adding a range-extending device to pure electric vehicles. The structure of the series hybrid power system is shown in Figure 1, which is mainly composed of a drive motor , a set of range extension device composed of internal combustion engine and generator, transmission device, motor controller, power battery pack and external charging interface. The main feature of the hybrid power system structure is: the drive motor is the only power source for driving the vehicle. The electric motor controller combines the electric energy stored in the power battery pack and the electric energy generated by the generator driven by the internal combustion engine to realize power coupling in an electrical coupling manner, and finally drives the vehicle to travel by driving the electric motor.
The series hybrid power system, because there is no mechanical connection between the internal combustion engine and the wheels, it can control and adjust the operation mode of the internal combustion engine independently of the driving state of the car, so that the internal combustion engine can always run in an efficient working area with low fuel consumption, and reduce emissions at the same time; Because the electric motor has the characteristics of large torque at low speed and constant power at high speed, it is very suitable for the needs of automobile traction. Therefore, the transmission gear can be greatly reduced, so that the transmission system structure can be simplified; due to the simple mechanical structure of the series hybrid power system, the control strategy is relatively simple. However, since the power output by the internal combustion engine needs to be converted to the drive wheels through multiple energy conversions of the generator and the power battery, the fuel consumption of the car during high-speed cruising is rather high, which reduces the overall fuel economy. And because the drive motor is the only power source, it is necessary to use a drive motor, generator and power battery with larger power and size, thereby increasing the cost and quality of the car.
2) Parallel hybrid power system
The plug-in parallel hybrid power system is combined by two or more independent drive systems, and each drive system is connected to at least one on-board energy source. According to the different combination modes of the drive system, the parallel hybrid power system can be divided into three types: single-shaft parallel, double-shaft parallel and single drive system combined.
The structure of a typical dual-shaft parallel hybrid power system is shown in Figure 2. It is mainly composed of a drive motor, an internal combustion engine, a power coupling mechanism, a transmission device, a motor controller, a power battery pack, and an external charging interface. The main feature of the hybrid power system structure is that it has two relatively independent drive systems, namely the internal combustion engine drive system and the electric motor drive system. The two driving systems can work independently to drive the wheels, or they can be combined to drive mechanically to achieve dynamic coupling.
The plug-in parallel hybrid power system, because the pure electric single drive mode can be used when the vehicle speed is low, and the internal combustion engine can be used as the independent drive mode when the vehicle speed is high, and the power output by the internal combustion engine can be directly used to drive the vehicle, with less energy conversion times, the overall fuel efficiency is higher; Compared with the series structure, the parallel structure can use relatively small power drive motors and power battery packs, and eliminates the need for special generators, thereby reducing the cost and weight of the car. However, there is a mechanical connection between the internal combustion engine and the drive wheels of the parallel hybrid power system. when the vehicle is driven in conjunction with the drive motor, due to the lack of generator adjustment, the internal combustion engine cannot always run in a high-efficiency working area, which makes the efficiency of the internal combustion engine cannot be fully utilized.