Analysis of Electric Vehicle Classification
and Technical Characteristics
Electric vehicles are vehicles powered by batteries or other renewable energy sources, unlike traditional internal combustion engine vehicles, which rely on fuel cells or electric motors to provide power. According to the current technical status and vehicle driving principles, electric vehicles can be divided into three types: pure electric vehicles (BEV), fuel cell electric vehicles and hybrid electric vehicles (HEV).
1. Battery Electric Vehicle (BEV)
Pure electric vehicles have the advantages of zero emissions, low noise, simple structure, and mature technology. They are vehicles that are completely powered by batteries and driven by motors. The driving energy of the vehicle motors comes from on-board rechargeable batteries or other energy storage devices (including power batteries). , supercapacitor, flywheel battery, etc.).
Vehicle energy currently mainly uses power batteries, including lead-acid batteries, nickel-hydrogen batteries, nickel-copper batteries, sodium-sulfur batteries, carp-ion batteries, zinc-air batteries, etc.
(1) Principle and composition of pure electric vehicle system
Pure electric vehicles are generally driven by motors. The driving electric energy of the electric motors comes from on-board rechargeable batteries or other energy storage devices. The on-board energy supplies electric energy to the driving motor through the power conversion device (motor controller) and drives it to operate. The driving motor is driven by the transmission device. The wheels rotate to move the car.
Pure electric vehicles are mainly composed of power supply system, electric drive system, auxiliary system, body and chassis.
(2) Types of pure electric vehicles
A single battery is used as the power source of the vehicle: the specific energy and specific power of the battery are low, and the weight and volume of the battery pack are large.
Installing an auxiliary power source: Installing an auxiliary power source (supercapacitor, generator set, solar energy, etc.) on a pure electric vehicle can improve the starting performance of the pure electric vehicle and increase the driving range.
(3) Working principle of pure electric vehicles
Pure electric vehicles use the energy of the battery to drive the electric motor to move the wheels forward. The energy flow route is: battery → power regulator → electric motor → power transmission system → driving wheel. Among them, the battery provides current, which is output to the electric motor after passing through the power regulator. The electric motor provides torque, which drives the wheels through the transmission device to realize the driving of the vehicle.
2. Fuel Cell Electric Vehicle (FCEV)
Compared with traditional electric vehicles, the chemical reaction process of fuel cells does not produce harmful products, and has the advantages of high efficiency, no pollution, zero emissions, and no noise. Fuel cell vehicles usually use hydrogen, methanol, etc. as fuel, and generate electrical energy through chemical reactions to drive the motor. The mechanical energy generated by the motor is transmitted to the driving wheels through a variable speed transmission device, thereby driving the vehicle.
(1) Basic structure of fuel cell vehicles
A fuel cell vehicle (hydrogen-electric hybrid) consists of a Fuel Cell Stack, an Electric Traction Motor, a DCDC, a Thermal System (cooling), a Battery Pack, and a hydrogenation port. It is composed of subsystems such as Fuel Filler, FuelTank (hydrogen), Transmission, Power Electronic Controller, and Auxiliary Battery.
Fuel cell electric vehicles and ordinary electric vehicles have basically the same electric drive structure. Fuel cell vehicles are composed of four basic modules: power system, chassis, automotive electronic system and body. The power system provides power to the vehicle through the fuel cell system and electric motor.
According to different drive forms, it can be divided into pure fuel cell drive and hybrid drive;
According to different energy sources, it can be divided into two types: vehicle-mounted pure hydrogen and fuel reforming;
According to the proportion of the power provided by the fuel cell to the total power demand of the vehicle, it can be divided into two types: energy hybrid type and power hybrid type.
(2) Working principle of fuel cell vehicles
The heart of a fuel cell vehicle, the fuel cell stack, provides a container that accelerates the electrochemical reaction of hydrogen and oxygen, converting the energy released in the chemical reaction of hydrogen and oxygen into electrical energy. In a fuel cell vehicle, the fuel cell stack and the battery work together to provide energy to the motor, which in turn provides power to the vehicle and drives the vehicle. For the battery, it is the energy source itself. For the fuel cell stack, its energy source is hydrogen, and its current common storage method is to use high-pressure hydrogen storage tanks.
(3) Fuel cell vehicles overcome difficulties
Catalyst: Fuel cells must use reaction catalysts to generate electricity, and the rare metal platinum that makes up the catalyst is expensive and has scarce reserves. Therefore, the development of new catalysts is the key to directly affecting the development of fuel cell electric vehicles.
Source and storage of fuel: Hydrogen fuel cells require hydrogen. Hydrogen itself has no industrial chain support. Manufacturing, transportation, storage, and refueling are extremely inconvenient, costly, and dangerous. Compared with fuel vehicles and electric vehicles, Automobiles, hydrogen fuel cell vehicles are less mature.
3. Hybrid Electric Vehicle (HEV)
According to the recommendations of the Technical Committee on Electric Vehicles under the International Commission on Electromechanical Systems, hybrid electric vehicles refer to vehicles that use two or more accumulator energy sources or converters as driving energy, at least two of which can provide electric energy. Called a hybrid electric vehicle. Usually, models that mix internal combustion engine and battery power are called hybrid electric vehicles, that is, models that use traditional fuel with an electric motor and a generator, and the electric motor serves as the auxiliary power of the engine to improve low-speed power output and fuel consumption.
Depending on whether the vehicle requires an external charging plug for charging, hybrid electric vehicles can be divided into plug-in hybrid vehicles and non-plug-in hybrid vehicles. Hybrid electric vehicles can be divided into series, parallel, hybrid and compound hybrid vehicles according to the structural characteristics of the power system.
(1) Series Hybrid Electric Vehicle (SHEV)
The mechanical energy output by the series hybrid electric vehicle (SHEV) engine is first converted into electrical energy through the generator. Part of the converted electrical energy is used to charge the battery, and the other part is used to drive the wheels through the drive motor and transmission device.
The structure of a series hybrid vehicle is simple, and its power system consists of three power subunits: engine, generator and electric motor.
The working principle of a series hybrid vehicle: the engine drives the generator to generate electricity, and the electric energy is transmitted to the battery or electric motor through the controller, and the electric motor drives the vehicle through the transmission mechanism. When the load is small, the electric motor drives the wheels; when the load is large, the engine drives the generator to generate electricity and drive the motor.
(2) Parallel Hybrid Electric Vehicle (PHEV)
Both the parallel hybrid electric vehicle (PHEV) engine and electric motor are used to drive the wheels, and their power is delivered to the wheels in parallel. The vehicle selects these two power outputs according to the current working conditions.
The engine and electric motor usually drive the wheels through different clutches, and there are three operating modes: engine alone, electric drive system alone, and engine + electric drive system hybrid drive. When the power provided by the engine is greater than the driving power required by the vehicle, or when the vehicle is braking, the electric drive system works in the generator state to charge the battery.
The engine of a parallel hybrid vehicle can directly drive the wheels through the transmission mechanism, which is closer to the traditional vehicle drive system. The mechanical efficiency loss is similar to that of ordinary vehicles, and it is widely used.
(3) Series-parallel Hybrid Electric Vehicle (SPHEV)
A hybrid (series-parallel) hybrid electric vehicle (SPHEV) combines a series hybrid system and a parallel hybrid system, with the aim of maximizing the advantages of both systems and adding mechanical power compared to the series transmission route; compared with the parallel type, the transmission route of electric energy is increased.
The hybrid system has two electric motors. Depending on the driving conditions, the electric motor can be driven alone or the electric motor + engine can be jointly driven. Moreover, when needed, the system can also generate electricity through a generator while driving the wheels.
