What is the high-voltage electrical system of a pure electric vehicle composed of?
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People are used to calling the 12V battery voltage of a car low voltage, and the power battery voltage is high voltage compared to conventional batteries. When repairing electric vehicles, you must first know the types and characteristics of high voltage electricity in the car in order to do a good job of high voltage safety protection.
1) The wiring harness between the AC charging pile and the vehicle slow charging port, and between the slow charging port and the charger is 220V AC, and the charger inputs 220V AC. The slow charging port, slow charging wiring harness, charger housing, and vehicle body are all equipped with protective ground wires.
2) The wiring harness between the DC charging pile and the fast charging port, the fast charging port and the high-voltage box (or PEU), the high-voltage box and other high-voltage components, as well as the power battery, PEU, and PTC are all 200~800V DC, and the specific voltage depends on the vehicle model.
3) The drive motor and air conditioning compressor use variable frequency three-phase AC power of several hundred volts.
High voltage electrical system of pure electric vehicles (picture from the Internet)
The main components of the high voltage electrical system
The motor controller, high-voltage box, charger, and DC/DC can be separated, as shown in Figure 1; the latter three are integrated and called a power distribution unit (PDU), as shown in Figure 2; the four are integrated and called a PEU, as shown in Figure 3. Due to different design ideas of each manufacturer, the integration method is different. For example, some models integrate the high-voltage box with the charger, and integrate the DC/DC with the electric compressor controller.
Figure 1 Split high-voltage system
Figure 2 Integrated high-voltage system PDU (three-in-one)
Figure 3 Integrated high-voltage system PEU (four-in-one)
The advantage of the split high-voltage system is low replacement cost, and the disadvantage is that there are many components and many connecting wires between components. The advantage of the integrated type is small size and light weight, and the disadvantage is high replacement cost. To facilitate learning for beginners, this book takes the split high-voltage system of BAIC New Energy EV150 as an example to introduce it. EV150 is the earliest model produced by BAIC New Energy. Although the technology has been updated long ago, it can lay a good foundation for the next step of learning. For easy memorization, this book calls it "big three electrics" and "small five electrics", as shown in Figure 4, the red words are "big three electrics", the blue words are "small five electrics", the red arrows are power battery discharge, and the yellow arrows are power battery charging.
Figure 4 Big Three Electrics and Small Five Electrics
1. Power battery
As shown in Figure 5, the power battery box functions like the fuel tank of a fuel vehicle, and mainly uses ternary lithium batteries or lithium iron phosphate batteries. The voltage of different models is 200-800V, and the energy is 15-120kW·h; the power battery's power source includes slow charging, fast charging, and kinetic energy recovery. It is mainly composed of a battery pack, a battery management system (BMS), auxiliary components, and a shell.
Figure 5 Power battery box
1—Low voltage socket 2—High voltage + 3—High voltage -
4—Maintenance of switch socket 5—Maintenance of switch
2. Drive motor
As shown in Figure 6, the drive motor acts like the engine of a fuel vehicle, but has a kinetic energy recovery function. Most of them use a three-phase AC synchronous motor equipped with a resolver sensor, and some use a three-phase AC asynchronous motor.
Figure 6 Three-phase AC synchronous motor
3. Motor controller
As shown in FIG7 , the function of the motor controller is to invert high-voltage direct current into three-phase alternating current high voltage and adjust the frequency. It is mainly composed of an insulated gate bipolar transistor (IGBT) and a controller mainboard.
Figure 7 Motor controller
1. High voltage box
As shown in Figure 8, the high-voltage box is also called a high-voltage distribution box or a high-voltage control box. It is used to distribute high-voltage electricity, just like the relay box of a 12V system. It has fast-charging high-voltage positive and high-voltage negative relays inside. Some cars have a PTC controller inside the high-voltage box.
Figure 8 High voltage box
2. On-board charger (OBC)
As shown in Figure 9, the function of the on-board charger is to charge the power battery. There is a rectifier inside. The input is 220V AC and the output is high-voltage DC.
Figure 9 On-board charger
3. DC voltage converter (DC/DC)
As shown in Figure 10, the DC/DC functions like a generator in a fuel vehicle, supplying power to the vehicle's low-voltage electrical equipment and charging the 12V battery.
4. Electric compressor
As shown in FIG11 , the refrigeration compressor of a fuel-powered vehicle is driven by the engine belt, while the compressor of an electric vehicle is driven by a high-voltage DC motor or a three-phase AC motor integrated with the compressor.
Figure 11 Electric compressor and controller
5. PTC
As shown in FIG12 , PTC is a positive temperature coefficient thermistor, also known as a heater, and its function is to heat the cab. FIG12 shows an air heater, and another type is a water heater.
High-voltage cables are divided into single-wire and double-wire systems. The former is used for high-power high-voltage equipment, and the latter is used for low-power and auxiliary high-voltage equipment, such as electric compressors and PTCs. The structure of a single-wire high-voltage cable is shown in Figure 13. The copper conductor is wrapped with an insulating layer and a shielding layer. The copper wire braided shielding layer is connected to the ground. Its function is to induce the electromagnetic waves generated by the conductor current to generate voltage and short-circuit it to the ground, so as not to interfere with other radio equipment and control units. The structure of a double-wire high-voltage cable is shown in Figure 14.
Figure 13 Single-wire high-voltage cable
1—Copper conductor (e.g. cross-sectional area 25 mm) 2—Shielding layer 3—Locking mechanism
Figure 14 Two-wire high-voltage cable
1—Two copper conductors (e.g. cross-sectional area 2×4mm) 2—Shield 3—Interlock wire 4—Interlock pin
The applications of high voltage cables in pure electric vehicles include:
(1) Slow charging cable: As shown in Figure a, it transmits 220V AC power from the slow charging port to the charger.
(2) Fast charging cable: As shown in Figure b, it transmits high-voltage direct current from the fast charging port to the high-voltage box.
(3) High-voltage box → motor controller cable: As shown in Figure c, it transmits high-voltage direct current.
(4) Motor controller → motor cable: As shown in Figure d, it transmits three-phase AC variable frequency high voltage electricity.
Figure 15 High voltage cable
5) High-voltage accessory harness: As shown in Figure 16, the high-voltage box is connected to the charger, DC/DC, electric compressor, and PTC through the high-voltage accessory harness.
Figure 16 High voltage accessory wiring harness
Fast charging port, slow charging port
The slow charging port and fast charging port that meet the national standards are shown in Figure 17. The installation positions of different models are not uniform. The slow charging port has 7 sockets, as shown in Figure 18a. The three middle sockets are connected to the neutral line (N), the protective ground line (PE) and the phase line (L) respectively; the fast charging port has 9 sockets, as shown in Figure 18b. The two middle sockets are the left high-voltage negative pole and the right high-voltage positive pole. The lower middle socket is connected to the protective ground line (PE).
Figure 17 Slow charging port and fast charging port
Figure 18 Slow charging port and fast charging port jack
The maintenance switch is also called the maintenance plug, as shown in Figure 19. The upper part is the maintenance switch, and the lower part is the base of the switch. The maintenance switch is a switch with a fast fuse. Some models install the fast fuse separately. The function of the fuse is to prevent discharge overcurrent and energy recovery overcurrent, generally 250A 500V. The maintenance switch is installed in the middle of the power battery series module, as shown in Figure 20. It can manually cut off or connect the high-voltage circuit. Its function is to ensure power-off operation when repairing the high-voltage system.
Figure 19 Maintenance switch
Figure 20 Maintenance switch installation location
The above pictures and texts are excerpted from "Structure and Principle of Pure Electric Vehicles (Color Illustrations)" published by Machinery Industry Press
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