In order to promote the development of new energy vehicle industry technology and meet increasingly stringent test standards and energy-saving emission limits, China has formulated the “technology roadmap for energy saving and new energy vehicle industry”, and proposed to develop pure electric vehicles, plug-in hybrid vehicles, fuel cell vehicles and other models; Promote small, efficient and clean special engines and electric motors and their efficient coupling technologies; promote lightweight technologies; develop intelligent networked vehicle technologies to realize intelligent transportation. At the same time, the various indicators of key technologies for new energy vehicles must continue to improve, the energy density of batteries will double within five years, and the cost will be reduced by half.
1. New energy vehicle power battery technology development trend
Pure electric vehicles rely on power batteries for energy storage, hybrid vehicles mainly rely on engine-generators for energy supply, and fuel cell vehicles mainly rely on fuel cells for energy supply. In addition to other power supply methods, power battery technology is gradually evolving into power source technology. The power source is mainly composed of electric energy storage unit, energy conversion and power generation unit (fuel cell, engine-generator), power management system, thermal management system, safety management system, internal and external packaging system, connection device, etc.
High performance energy storage materials with good market prospects include cathode materials (lithium iron phosphate, nickel cobalt manganese, high voltage lithium nickel manganate, lithium rich layered lithium manganate, etc.), anode materials (graphite, lithium titanate, graphite mixed soft carbon, silicon carbon, etc.), diaphragm materials (PP, coating PP, thin modified coating PP, etc.), electrolyte materials (lithium hexafluorophosphate containing functional additives). The above materials can theoretically support a single energy density of up to 400W·h/kg. By 2030, according to the development plans of various countries, the energy density of power batteries should be increased to 500~800W·h/kg. In the future, new technologies such as lithium sulfur, lithium air, magnesium ion and zinc air batteries will enter mainstream research projects.
2. Development trend of new energy vehicle drive technology
New energy vehicle drive technology includes three modules: pure electric drive device, power coupling device, and hybrid powertrain. With the development of control technology, the main functions of new energy vehicle engines will gradually shift to the two functions of power generation and range extension. After adopting the Atkinson cycle technology with extended work stroke and turbocharged low-idle start technology, the engine power per liter is increased, the displacement is reduced, and the engine will be miniaturized and specialized.
Drive motors are developing in the direction of permanent magnet synchronization, AC induction and switched reluctance. Permanent magnet synchronous motors can reach a high power density, but have poor heat resistance and consume rare earth resources. The AC induction motor has high speed, small torque, and large volume, but it does not use permanent magnet components and is low in cost. The switched reluctance motor has a high speed, a relatively large torque, does not use permanent magnet materials, and is low in cost, but there are torque fluctuations, and it is necessary to study the smoothness of the control. The effective coupling technology of multiple low-power motors is also one of the directions of motor development.
The development of motor control technology in the direction of high precision and high power density mainly relies on the technological advancement of high-temperature, low-loss, high-frequency power electronic devices (such as IGBT and MOSFET based on silicon carbide materials), and at the same time relies on high-efficiency liquid cooling technology. The vector control algorithm with high robustness has been applied, and the subsystem optimization control problem of braking energy recovery is improving.