electric vehicle definition
A pure electric vehicle is a car powered entirely by rechargeable batteries (such as lead-acid batteries, nickel-cadmium batteries, nickel-metal hydride batteries, or lithium-ion batteries) and driven by an electric motor. Its main power system consists of a power battery and a drive motor, drawing power from the grid or by replacing the batteries.
electric vehicle structure
Traditional internal combustion locomotives mainly consist of four parts: engine, body, chassis, and electrical equipment.
Pure electric vehicles mainly consist of four parts: electric drive control system , chassis, body, and auxiliary systems.
Figure 1. Schematic diagram of the overall control principle of a pure electric vehicle
A typical pure electric vehicle consists of the following components, as shown in the diagram above: a power system, an electric drive system, a vehicle controller , and auxiliary systems. The power battery outputs electrical energy, which drives the motor through the motor controller to generate power. This power is then transmitted to the drive wheels through a reduction gear, enabling the electric vehicle to move.
Power System
The power system mainly includes the power battery, power management system, on-board charger, and auxiliary power source.
**Power Battery:**
**The power source and energy storage device of electric vehicles are mainly lithium-ion batteries;
**Power Management System:**
**Real-time monitoring of the power battery's usage status, detecting power battery status parameters such as terminal voltage, internal resistance, temperature, electrolyte concentration, remaining battery capacity, discharge time, discharge current, or depth of discharge, and adjusting the temperature according to the power battery's requirements for ambient temperature. Current limiting control is used to prevent overcharging and over-discharging of the power battery. Relevant parameters are displayed and alarms are triggered, and the signals flow to the auxiliary system, combined with the instrument display to provide relevant information so that the driver can keep abreast of vehicle information.
**On-board charger:**
**Convert the grid power supply system to the system required for charging the power battery, that is, convert the AC power (220V or 380V) to the corresponding DC power (240~410V), and control its charging current as required (household charging is generally 10 or 16A).
Auxiliary power source:
It is generally a 12V~24V DC low-voltage power supply, mainly used to power various auxiliary electrical devices such as power steering, braking force adjustment and control, lighting, air conditioning, and power windows.
Figure 2 Power System
Electric drive system
The electric drive subsystem is the core of an electric vehicle and the biggest difference between it and an internal combustion engine vehicle. The drive system generally consists of an electronic controller, power converter, drive motor, mechanical transmission, and wheels. The function of the drive system is to efficiently convert the electrical energy stored in the battery into the kinetic energy of the wheels to propel the vehicle, and it can also perform regenerative braking when the vehicle decelerates, brakes, or goes downhill.
Figure 3 Electric drive system
The function of a drive motor is to convert electrical energy into mechanical energy, which is then used to drive the wheels via a transmission device or directly. Early electric vehicles widely used DC series motors, which have "soft" mechanical characteristics that are well-suited to the driving characteristics of automobiles. However, due to drawbacks such as commutation sparks, low power density, low efficiency, and high maintenance requirements, DC motors are gradually being replaced by brushless DC motors (BCDM), switched reluctance motors (SRM), and AC asynchronous motors as motor and motor control technologies have developed.
Vehicle controller
The vehicle controller (VCU) is the control center of the motor system, also known as the central control unit (CCU) in Figure 1. It processes all input signals and sends information about the motor control system's operating status to the VCU. Based on the driver's input signals from the accelerator and brake pedals, it issues corresponding control commands to the motor controller to control the motor's start, acceleration, deceleration, and braking. During deceleration and downhill coasting in a pure electric vehicle, the VCU works with the battery management system of the power system to generate electricity, causing the power battery to charge in reverse. The VCU also controls the charging and discharging process of the power battery. Information related to the vehicle's driving conditions, such as speed, power, voltage, and current, is transmitted to the onboard information display system for corresponding digital or analog display.
The motor controller contains a functional diagnostic circuit. When an abnormality is detected, it will activate an error code and send it to the vehicle controller. The motor control system uses the following sensors to provide information about the motor's operation.
**Current sensor:**
**Used to detect the actual current (including bus current and three-phase AC current) of the motor.
**Voltage sensor:**
**Used to detect the actual voltage supplied to the motor controller (including high-voltage battery voltage and storage battery voltage).
Temperature sensor :
Used to detect the operating temperature of the motor control system (including module temperature and motor controller temperature).
auxiliary systems
Assistance systems include in-vehicle information display systems, power steering systems, navigation systems, air conditioning, lighting and defrosting devices, windshield wipers, and radios, which enhance vehicle handling and passenger comfort.
Figure 4 Auxiliary System
Possible structural forms of electric vehicles
Due to the diversity in electric drive characteristics and energy sources, there may be various EV (Electric Vehicle) structural forms, as shown in the figure below.
Figure 5. Possible structural forms of electric vehicles
Figure 5a shows a centrally driven electric motor configuration, borrowing the drive system from internal combustion engine vehicles. The electric drive unit replaces the traditional internal combustion engine in the vehicle's drive system. It consists of an electric motor, clutch, transmission, and differential. The clutch and transmission can be replaced by an automatic transmission. The clutch connects or disengages the electric motor's power to the drive wheels. The transmission provides a set of gear ratios to meet different speed requirements. The differential is a mechanical device (usually a set of planetary gears) that causes the wheels on either side to rotate at different speeds when the vehicle travels along a curved path.
Figure 5b shows a centrally driven configuration using an electric motor. Utilizing the constant power characteristic of the electric motor across a wide range of speeds, a fixed-gear transmission can replace a multi-speed gearbox, reducing the need for a clutch. This structure not only reduces the size and weight of the mechanical transmission but also simplifies drive system control because gear shifting is unnecessary.
Figure 5c is similar to the drive system in Figure 4b, representing another form of centrally driven motor. The fixed-gear transmission and differential can be further integrated into a single assembly, with shafts on both sides connecting the drive wheels. This allows for further simplification and miniaturization of the entire drive system.
Figure 5d shows a dual-motor electric wheel drive system, where the mechanical differential is replaced by two traction motors. These two motors drive the wheels on their respective sides, operating at different speeds when the vehicle travels along a curved path.
Figure 5e shows a hub motor drive system. To further simplify the drive system, the traction motor can be housed inside the wheel. This configuration is commonly referred to as wheel drive. A thin planetary gear set can be used to reduce the motor speed and increase the motor torque. This thin planetary gear set has the advantages of a high reduction ratio and longitudinal arrangement of the input and output shafts.
Figure 5f illustrates another hub motor drive method. By completely eliminating any mechanical transmission between the motor and the drive wheels, a low-speed external rotor motor used in wheel drives can be directly connected to the drive wheels. In this case, motor speed control is equivalent to wheel speed control, i.e., vehicle speed control. However, this configuration requires the motor to have high torque performance during vehicle start-up and acceleration.
