Use different types of energy storage devices. For example, different batteries, fuel cells, super capacitors, and flywheel batteries can form five typical electric vehicle energy storage system structures, namely, battery structure, high energy battery + high power battery (dual battery composite) structure, hydrogen fuel Battery + storage battery structure, storage battery and super capacitor composite structure, storage battery and flywheel battery composite structure.
①Single cell structure
Figure 1 shows a structure unique to pure electric vehicles that only uses batteries as a power source. The storage battery can be arranged around the vehicle, or centrally arranged at the rear of the vehicle or under the chassis. The selected energy-saving battery should be able to provide sufficiently high specific energy and specific power (such as nickel-metal hydride batteries, lithium batteries), and can recover regenerative braking energy when the vehicle is braking. At the same time, a battery with high specific energy and high specific power is the most ideal power source for electric vehicles. The specific energy affects the mileage of the car, and the specific power affects the acceleration and climbing ability of the car.
②Double battery composite structure
(1) High-energy storage battery + high-power storage battery structure
In order to solve the problem that a battery cannot meet the requirements of contrast energy and specific power at the same time, two different batteries can be used in electric vehicles at the same time, one of which can provide high specific energy, and the other provides high specific power. Figure 2 shows the basic structure of this dual-battery hybrid energy source. This structure not only separates the requirements for contrast energy and specific power, but also uses the battery to recover energy when the car is going downhill or braking. However, batteries with good performance often have both high specific energy and high specific power at the same time, so this form of composite structure is basically not used.
(2) Hydrogen fuel cell + battery structure
In addition to batteries, fuel cells can also be used as energy storage devices. Fuel cells can provide high specific energy, but cannot recover regenerative braking energy. Therefore, it is best to be used in combination with a battery that can provide high specific power and can efficiently recover braking energy. Figure 3 shows a hybrid structure using fuel cells and batteries.
The hydrogen required by the fuel cell can not only be stored in the form of compressed hydrogen, liquid hydrogen or metal hydride, but can also be produced on the vehicle from liquid fuels (such as methanol or gasoline) at room temperature. Figure 4 is a simplified structural diagram of an electric vehicle with a small reformer. The hydrogen required by the fuel cell is produced by the reformer.
③Compound structure of battery and other energy devices
(1) Composite structure of battery and super capacitor
When using a battery and a super capacitor to mix, the selected battery must be able to provide high specific energy, because the super capacitor itself has a higher specific power and a more efficient ability to recover braking energy than the battery. Since the super capacitor used in electric vehicles has a relatively low voltage, a DC/DC power converter needs to be added between the battery and the super capacitor. Figure 5 shows the composite structure of the battery and the super capacitor.
(2) Composite structure of battery and flywheel battery
Similar to supercapacitors, flywheel batteries are another emerging energy storage device with high specific power and efficient braking energy recovery capabilities. The combination of a high-speed flywheel and a motor rotor with two working modes (motor and generator) can convert electrical and mechanical energy in both directions. Figure 6 shows the battery and flywheel battery composite structure, the selected battery should be able to provide high specific energy. The flywheel is best used in combination with a brushless AC motor, because the efficiency of this motor is higher than that of a DC motor, so an AC/DC converter should be added between the battery and the flywheel.