I. Overview
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The electric vehicle described in this section refers to an electric motor-driven vehicle that is powered by a battery or a fuel cell and travels on urban streets or inter-city roads. It does not include trolley buses and electric forklifts used at stations, terminals or factories. And ordinary battery car.
The world's first electric car was handcrafted by Britishman R. Peterson in 1873. Since then, electric vehicles have developed rapidly, and from the late 19th century to the beginning of the 20th century, electric vehicles have almost become the mainstream of automobiles. In the United States, for example, among the car ownership during this period, steam engine vehicles accounted for 40%, electric vehicles accounted for 38%, and internal combustion engines accounted for only 22%. In 1915, the annual output of electric vehicles in the United States reached 5,000. However, with the development and popularity of gasoline engine vehicles, electric vehicles have gradually declined. The reason is that the electric car has a long charging time and a short driving range, which limits its application. However, at the end of the 20th century, when environmental pollution became increasingly serious and oil resources were in crisis, countries around the world had a boom in research, development and use of electric vehicles. In order to encourage the production and use of electric vehicles, many countries implement a number of preferential policies: or allocate large sums of money to subsidize or subsidize manufacturers of electric vehicles and customers who purchase electric vehicles; or exempt license fees and road maintenance fees for electric vehicle users. And charging at night only charges half of the electricity bill. In 1990, the California State Assembly passed a regulation to force the promotion of electric vehicles. This regulation requires that in the total sales of automobiles in 1998, there must be 2% of zero-emission vehicles; by 2000, zero-emission vehicles accounted for 3% of total vehicle sales; in 2001, 5%; In 2003, it increased to 10%. At present, only electric vehicles can achieve zero emission pollution.
In recent years, electric vehicles have developed considerably. With the development of science and technology, especially high-tech, electric vehicle technology has also made great progress.
Car name car company name battery type Drive motor type Power
(kW)
Maximum speed
(km/h) driving range
(km) Year of production
EVI car universal lead-acid three-phase induction motor 102 128 1997
ALTRA EV sedan Nissan (North America) Cobalt-based lithium ion permanent magnet synchronous motor 64 120 1997
P2000 car Ford proton exchange membrane three-phase induction motor 67 128 160 2000
The fuel cell
NECAR5 sedan DaimlerChrysler methanol fuel 75 150 2000
battery
BMW EI sedan BMW Sodium Sulfur Permanent Magnet Brushless 32 120 160-230
DC motor
Insight
Hybrid sedan Honda Ni-MH permanent magnet synchronous motor 10
Three-cylinder engine 50kW
(5700r/min)
Prius
Hybrid car Toyota NiMH permanent magnet synchronous motor 33 160 2000
Four-cylinder engine 52kW (4500r/min)
Reva EV sedan Indian lead-acid-excited DC motor 13 65 80 2001
YW6-120DD Bus China Yuanwang Three-phase asynchronous motor 90 150 1996
The advantages of electric vehicles are:
1) No exhaust gas is emitted during driving, and it does not pollute the environment, so electric vehicles can be called "zero-emission pollution cars".
2) High energy efficiency. The total efficiency of energy utilization of electric vehicles and gasoline engines is compared by 10 driving modes.
3) The vibration and noise are small, and the inside and outside of the car are very quiet.
4) Simple structure and convenient maintenance.
Electric vehicles currently have the following shortcomings:
1) The mileage that can be traveled on a single charge is short. An electric vehicle loaded with a lead-acid battery of the same quality as gasoline has a driving range of only 1/70 of that of a gasoline engine.
2) High cost. The high cost of batteries and motor controllers is the main reason for the high cost of electric vehicles. In addition, the battery has a short life and high depreciation.
3) The charging time is long, generally takes 6 to 10 hours.
Second, the composition of electric vehicles
The electric vehicle consists of three parts: an electric drive system, a power supply system, and an auxiliary system.
The electric drive system includes an electronic controller, a power converter, an electric motor, a mechanical transmission and a wheel, and its function is to efficiently convert the electric energy stored in the battery into the kinetic energy of the wheel, and can drive the wheel when the vehicle is decelerating and braking. Kinetic energy is converted into electrical energy and charged into the battery. The latter function is called regenerative braking.
The power system includes a power source, an energy management system, and a charger, and its function is mainly to provide driving power to the motor, monitor power usage, and control the charger to charge the battery.
The auxiliary system includes an auxiliary power source, a power steering system, a navigation system, an air conditioner, a lighting and defrost device, a wiper, a radio, and the like, and the auxiliary device is used to improve the maneuverability of the car and the comfort of the occupant.
A typical electric car consisting of. In the figure, the double line indicates the mechanical connection, the thick line indicates the electrical connection, the thin line indicates the control signal connection, and the arrow on the line indicates the direction of transmission of the electric power or control signal.
The various systems are arranged on electric vehicles in a variety of ways, because the energy is transmitted through the flexible wires rather than through rigid couplings and shafts. Therefore, the various systems or components of the electric vehicles are arranged. Great flexibility. For example, an electric motor front-mounted, front-wheel-drive electric car. The charger charges the battery placed at the rear of the car via the charging interface at the front end of the car. When the car is running, the battery supplies power to the motor via the controller. The signal from the accelerator pedal is input to the controller and the torque or speed of the motor output is adjusted by the controller. The torque output by the motor drives the wheels through the automotive transmission system.
Third, electric drive system
The electric drive mode of electric vehicles can be basically divided into two types: motor central drive and electric drive. A motor central drive system composed of an electric motor, a fixed speed ratio reducer, and a differential. In such a drive system, the volume and quality of the mechanical transmission can be reduced because there is no clutch and transmission.
Another arrangement of the motor central drive system is similar to the arrangement of the front wheel drive and the lateral front engine fuel car. The motor, the fixed speed ratio reducer and the differential are integrated, and the two half shafts are connected to each other. Drive wheels, this type of arrangement is most commonly used on small electric vehicles.
The motor and fixed ratio planetary gear reducer are mounted inside the wheel without the drive shaft and differential, simplifying the drive train. However, the electric wheel drive method requires two or four motors, and its control circuit is also complicated. This type of drive has a wide range of applications in heavy-duty electric vehicles. 
The drive motor of electric vehicles mainly used DC motors before the 1990s. It has the advantages of large driving force when starting acceleration, simple speed control, and mature technology. However, the armature current of the DC motor is introduced by the brush and the commutator, and the electric spark is generated during the commutation. The commutator is easy to ablate, the brush is easy to wear, needs to be replaced frequently, and the maintenance workload is large. There is friction loss in the contact portion, which not only reduces the efficiency of the motor, but also limits the operating speed of the motor.
At present, a commutatorless brushless motor has been introduced, which consists of a motor body, a rotor angle sensor and an electronic switch control circuit. The electronic switch control circuit functions as a commutator in an ordinary DC motor. The DC brushless motor has many advantages such as simple structure, reliable operation, convenient maintenance, etc., and has the characteristics of high operating efficiency, no excitation loss, low operating cost and good speed regulation performance. Therefore, its application in electric vehicles is increasing day by day. For example, BMW EI electric vehicles produced by BMW and IZA electric vehicles developed by Tokyo Electric Power Co., Ltd. all use permanent magnet DC brushless motors as electric wheels.
AC induction motors are widely used in electric vehicles. This is because when the induction motor adopts variable frequency speed regulation, the mechanical transmission can be eliminated, and the stepless speed change can be realized, so that the transmission efficiency is greatly improved. In addition, the induction motor can easily achieve positive and negative reversal, and the recovery of regenerative braking energy is also simpler. When a squirrel-cage rotor is used, the induction motor also has the advantages of simple structure, sturdiness, low cost, reliable operation, high efficiency, and maintenance-free.
Another type of AC motor used in electric vehicles is an AC synchronous motor. When the field winding of the synchronous motor is replaced by a permanent magnet material, the permanent magnet synchronous motor can eliminate the brush and the slip ring, and there is no copper loss of the field winding, which is more efficient and smaller than the induction motor. . 
Switched reluctance motors are recognized as a promising electric vehicle drive motor. Its stator and rotor are laminated by ordinary silicon steel sheets. There are no windings or permanent magnets on the rotor, and only concentrated windings are wound around the stator. Switched reluctance motor has the advantages that ordinary DC motor and AC motor can't match: 1Simple structure, sturdy and durable, low cost, can work at very high speed, can adapt to high temperature and strong vibration working environment; 2Starting torque Large, low speed performance; 3 wide speed range, flexible control, easy to achieve a variety of special requirements of torque-speed characteristics; 4 high efficiency in a wide range of speed and power.
Power converters for electric vehicles are used for DC-DC conversion and DC-AC conversion at different frequencies. DC-DC converters, also known as DC choppers, are used in DC motor drive systems. The two-quadrant DC chopper converts the DC voltage of the battery into a variable DC voltage and reverse-converts the regenerative braking energy. A DC-AC converter, commonly referred to as an inverter, is used in an AC motor drive system that converts the battery's DC power into AC power that is adjustable in both frequency and voltage. Electric vehicles generally use only voltage input inverters, and because of their simple structure, they can perform two-way energy conversion.
Fourth, the power system
Power is a factor that restricts the development of electric vehicles. As the power source of electric vehicles, it should have high specific energy and high specific power to meet the requirements of the car's power and driving range. In addition, it should have the same cycle life, high efficiency, low cost and maintenance-free as the service life of the car.
The power sources currently used in electric vehicles are mainly batteries, followed by fuel cells. The battery is an energy storage device that realizes energy storage by external charging; the fuel cell is an energy generating device that generates electrical energy through a chemical reaction. The battery technology is mature and the price is reasonable, and the fuel cell is considered to be the most promising electric vehicle power source.
The main performance indicators of the battery are: 1 specific energy - the amount of energy that can be stored per unit battery quality (W·h/kg), which is an indicator for evaluating the overall vehicle quality and driving range of the electric vehicle; 2 energy density - unit battery volume The stored power (W·h/L), which affects the size of the battery; 3 specific power - the power output per unit of battery mass (W / kg), is to evaluate the acceleration of electric vehicles, climbing ability and maximum speed Indicators; 4 power density - the power output per unit of battery volume (W / L); 5 cycle life - battery charge, discharge once called a cycle, cycle life means the number of cycles can be completed before replacing the battery. Short cycle life will increase the maintenance cost of electric vehicles. 
Battery
Lead-acid batteries are widely used in electric vehicles. The main reasons are mature technology, low price, good reliability, and high rated voltage (2.0V). In addition, the output current is large and good high and low temperature performance are suitable for electric vehicles. However, lead-acid batteries have the disadvantages of lower specific energy, longer charging time and shorter service life.
Ni-Cb battery has high specific power, high specific energy, fast charging, long service life, strong resistance to current surge, wide operating temperature range (-40°C～85°C), and large discharge current range. The internal voltage changes are small, etc., and become an attractive power source for electric vehicles. However, the production cost is high (about 2 to 4 times that of lead-acid batteries), the rated voltage of the monomer is only 1.2V, and the heavy metal cadmium is carcinogenic, which limits its wide application in electric vehicles.
Nickel-metal hydride (Ni-MH) batteries have many of the same characteristics as Ni-Cd batteries, but because they are free of cadmium, there is no heavy metal contamination problem, which is called "green battery." The cost of mass production is about four times that of lead-acid batteries. The Ni-MH battery cell has a rated voltage of 1.2V, the negative electrode is a hydrogen storage alloy after hydrogen absorption treatment, the positive electrode is nickel hydroxide, and the electrolyte is KOH solution.
Sodium-sulfur (Na-S) batteries have high specific power and specific energy, but their high operating temperature, coupled with the activation and corrosivity of sodium, must be structurally robust and safe. The Na-S battery uses molten sodium as the negative electrode, molten sulfur as the positive electrode, and ceramic β-Al2O3 as the electrolyte, and acts as a separator for the ion conductive medium and the molten electrode to avoid self-discharge of the battery.
Lithium-ion (Li-Ion) batteries have developed rapidly since their introduction in the early 1990s. Although lithium-ion batteries are still in the development stage, lithium-ion batteries are used in electric vehicles such as Nissan FEV, Nissan Prairic Joy and Altra. It has the advantages of high single-rated voltage, high specific energy and energy density and long service life. The disadvantage is high self-discharge rate.
2. Fuel cell
A fuel cell is a device in which a fuel and an oxidant react directly through their electrodes to convert their chemical energy into electrical energy. The fuel cell does not need to be charged, and as long as the external fuel and the oxidant are continuously supplied, the power can be continuously and stably generated. The fuel for fuel cells for electric vehicles is hydrogen and methanol, and the oxidant is air. The fuel cell has the advantages of higher specific energy, long service life, less maintenance work, and continuous high-power supply. In addition, fuel cell electric vehicles can achieve the same driving range as fuel vehicles. (pictured below)
According to different electrolytes, fuel cells can be classified into alkaline fuel cells, phosphoric acid fuel cells, proton exchange membrane fuel cells, molten carbonate fuel cells, and solid oxide fuel cells. Suitable for electric vehicles are alkaline fuel cells and proton exchange membrane fuel cells. In the fuel cell, the working substance of the fuel as the negative electrode undergoes an oxidation reaction at the negative electrode; the working substance of oxygen (air) as a positive electrode undergoes a reduction reaction at the positive electrode. In an alkaline fuel cell, hydrogen and oxygen (air) are respectively adsorbed on an electrode made of activated carbon, and two electrodes are placed in a KOH electrolyte, and if an external circuit is turned on, a current flows through the load.
A catalyst using nickel as a positive electrode and a lithium nickel oxide as a catalyst for a negative electrode can accelerate the reaction process of the battery. A proton exchange membrane fuel cell uses a solid membrane as an electrolyte, a separator sandwiched between positive and negative electrodes, and platinum as a catalyst for electrode reaction.
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