Core technology of pure electric car

The development of electric vehicles must solve four key technologies: battery technology, motor drive and control technology, electric vehicle technology and energy management technology.
Battery technology Battery is the power source of electric vehicles, but also has been a key factor restricting the development of electric vehicles. The main performance indicators of electric vehicle batteries are specific energy (E), energy density (Ed), specific power (P), cycle life (L) and cost (C). In order for electric vehicles to compete with fuel vehicles, the key is to develop high-efficiency batteries with high specific energy, high specific power and long service life.
So far, electric vehicle batteries have been developed for 3 generations and have made breakthrough progress. The first generation is lead-acid batteries, currently mainly valve-controlled lead-acid batteries (VRLA), due to its higher specific energy, low price and high rate discharge, so it is the only mass-produced battery for electric vehicles. The second generation is alkaline batteries, mainly nickel cadmium (NJ-Cd), nickel metal hydride (Ni-MH), sodium sulfur (Na/S), lithium ion (Li-ion) and zinc Air (Zn/Air) and other batteries, its specific energy and specific power are higher than lead-acid batteries, so it greatly improves the power performance and driving range of electric vehicles, but its price is higher than lead-acid batteries. The third generation is a fuel cell based battery. Fuel cells directly convert the chemical energy of the fuel into electrical energy, high energy conversion efficiency, higher than energy and power, and can control the reaction process, the energy conversion process can be continuous, so it is an ideal automotive battery, but it is still in the development stage, and some key technologies need to be broken through.
Electric drive and its control technology Electric motor and drive system are the key components of electric vehicles, in order to make electric vehicles have good performance, the drive motor should have a wide speed range, high speed, large starting torque, small size, small mass, high efficiency and dynamic braking and energy feedback characteristics. At present, electric vehicle motors mainly include direct current motor (DCM), induction motor (IM), permanent magnet brushless motor (PMBLM) and switched reluctance motor (SRM).
In recent years, almost all electric vehicles driven by induction motors have adopted vector control and direct torque control. Because of the direct torque control means, simple structure, excellent control performance and rapid dynamic response, it is very suitable for the control of electric vehicles. Electric vehicles developed in the United States and Europe mostly use this electric motor. Permanent magnet brushless motor can be divided into brushless DC motor system driven by square wave (BLDCM) and brushless DC motor system driven by sine wave (PMSM), they have a high power density, and their control mode is basically the same as induction motor, so it has been widely used in electric vehicles. PMSM motor has high energy density and efficiency, small size, low inertia and fast response, which is very suitable for the drive system of electric vehicles and has application prospects. At present, electric vehicles developed by Japan mainly use this electric motor.
Switched reluctance motor (SRM) has the advantages of simple and reliable, efficient operation in a wide speed and torque range, flexible control, four-quadrant operation, fast response speed and low cost. In practical application, it is found that SRM has some disadvantages such as large torque fluctuation, large noise, and the need for position detector.
With the development of motor and drive system, the control system tends to be intelligent and digital. Variable structure control, fuzzy control, neural network, adaptive control, expert control, genetic algorithm and other nonlinear intelligent control technologies will be individually or combined in the electric vehicle motor control system.
Electric vehicle technology Electric vehicle is a high-tech comprehensive product, in addition to batteries, motors, the body itself also contains a lot of technology, some energy-saving measures than improve battery energy storage capacity is also easy to achieve. The use of light materials such as magnesium, aluminum, high-quality steel and composite materials, optimize the structure, can reduce the mass of the car itself by 30%-50%; Energy recovery during braking, downhill and idle; The high pressure radial tire made of high elastic retarding material can reduce the rolling resistance of the vehicle by 50%. The car body, especially the bottom of the car, is more streamlined, which can reduce the air resistance of the car by 50%.
Energy Management technology Battery is the energy storage power source of electric vehicle. In order to obtain very good power characteristics, electric vehicles must have high energy, long service life and high power battery as a power source. In order to make electric vehicles have good working performance, it is necessary to systematically manage the battery.
Energy management system is the intelligent core of electric vehicle. A well-designed electric vehicle, in addition to good mechanical properties, electric drive performance, the selection of the appropriate energy source (that is, battery), should also have a set of coordination of the various functional parts of the work of the energy management system, its role is to detect the state of charge of a single battery or battery pack, and according to a variety of sensing information, Including force, acceleration and deceleration commands, driving road conditions, battery conditions, environmental temperature, etc., reasonable allocation and use of limited vehicle energy; It is also able to select the best charging method based on the battery pack usage and charge and discharge history to extend the battery life as much as possible.
The research institutes of major automobile manufacturers in the world are conducting research and development of on-board battery energy management systems for electric vehicles. How much electric energy is currently stored in the electric vehicle battery and how many kilometers can be driven is an important parameter that must be known in the running of electric vehicles, and it is also an important function that the energy management system of electric vehicles should complete. The application of on-board energy management system of electric vehicle can more accurately design the electric energy storage system of electric vehicle, determine an optimal energy storage and management structure, and improve the performance of electric vehicle itself.
The difficulty in achieving energy management in electric vehicles is how to build a more accurate mathematical model to determine how much energy is left in each battery based on the historical data collected from each battery's voltage, temperature, and charge and discharge current.