Electric motor and control system
Pure electric vehicles use electric motors instead of fuel engines. Electric motors drive them without the need for an automatic transmission. Compared with automatic transmission, the electric motor is simple in structure, mature in technology, and reliable.
The traditional internal combustion engine can limit the speed when generating torque efficiently to a narrow range, which is why the conventional interior combustion engine car needs a large and complicated shifting mechanism. In contrast, the electric motor can generate torque efficiently at a reasonably wide speed range. Therefore, there is no need to shift the gear shifting device during the driving of the pure electric car, which is convenient and easy to operate with low noise.
Compared with hybrid cars, pure electric vehicles use a single electric energy source, the electric control system greatly reduces the internal mechanical transmission system of the car, the structure is more simplified, but also reduces the energy loss and noise caused by the friction of mechanical parts, saving the internal space and weight of the car.
The motor drive control system is the primary execution structure of the new energy vehicle driving, the drive motor and its control system is one of the core components (battery, motor, electric control) of the new energy vehicle, and its driving characteristics determine the main performance index of the vehicle driving, it is an important part of the electric vehicle. The three major types of electric vehicles, namely, FCV, HEV and EV, all use electric motors to drive their wheels. Therefore, it is extremely important to develop or improve the electric motor drive method that can meet all the performance requirements of the vehicle and has the characteristics of robustness, durability, low cost and high efficiency.
Power cells for pure electric vehicles
The power battery is the key technology of electric vehicles, which determines its range and cost.
1) Power battery required for pure electric vehicles
The functional and economic indicators of the power battery used for electric vehicles should include (1) safety; (2) specific energy; (3) specific power; (4) life; (5) cycle price; and (6) energy conversion efficiency. These factors directly determine the suitability and economy of electric vehicles.
2) Supercapacitor
The advantage of the supercapacitor is high mass to power and long cycle life, the weakness is low mass to energy and expensive purchase price, but the cycle life is up to 500,000 to 1 million times, so the single-cycle price is not high, and it can form a power supply system with excellent performance in parallel with lead-acid battery and energy type lithium-ion battery.
3) Lead-acid battery
Lead-acid battery production technology is mature, has good safety, low price, easy to recycle waste batteries. In recent years, through new technology, its low specific energy, short cycle life, acid mist occurs when charging, production may have lead pollution of the environment and other shortcomings in the continuous to overcome, the indicators have been greatly improved, not only can be better used as a power source for electric bicycles and electric motorcycles, and in electric vehicles can also play a good role.
4) Lithium-ion battery with lithium iron phosphate as the positive electrode
The negative electrode is carbon, positive electrode lithium iron phosphate lithium battery all-around performance: higher safety, without expensive raw materials, does not contain harmful elements, cycle life up to 2000 times, and has overcome the shortcomings of low electrical conductivity. Energy type battery mass-specific energy up to 120Wh/kg, used in parallel with supercapacitors, can form a comprehensive power supply performance. The power type also has a mass-to-energy ratio of 70-80 Wh/kg and can be used alone without parallel supercapacitors.
5) Lithium-ion battery with lithium titanate as the negative electrode
The volume change of lithium titanate in charge-discharge is very small, which ensures the stability of the motor mechanism and the long life of the battery; the higher electrode potential of lithium titanate (1.5V compared to Li+/Li electrode) can ensure the high safety of the battery by not generating lithium crystal branches when the battery is charged. However, because of the high electrode potential of lithium titanate, even when paired with lithium manganate electrode, the voltage of the battery is only about 2.2V, so the specific energy of the battery is only about 50-60Wh/kg. Even so, the outstanding advantages of the high safety and long life of this battery are incomparable to other batteries.