Electric Vehicle System Structure

Electric drive
Electric vehicle refers to the vehicle that is powered by the on-board power supply and drives the wheel with the motor, and meets the requirements of road traffic and safety regulations. It uses electricity stored in a battery to start it. Sometimes 12 or 24 batteries are used to power the car, sometimes more.
The components of electric vehicles include: electric drive and control system, driving force transmission and other mechanical systems, and work devices to complete established tasks. The electric drive and control system is the core of electric vehicles and the biggest difference from internal combustion engine vehicles. The electric drive and control system consists of a drive motor, a power supply and a speed control device of the motor. Other components of an electric car are basically the same as those of an internal combustion engine car.
Power source
It provides electrical energy for the drive motor of the electric vehicle, which converts electrical energy from the power supply into mechanical energy. The most widely used power supply is lead-acid batteries, but with the development of electric vehicle technology, lead-acid batteries are gradually replaced by other batteries due to low energy, slow charging speed and short life. The power supplies under development are mainly sodium-sulfur batteries, nickel-cadmium batteries, lithium batteries, fuel cells, etc. The application of these new power supplies has opened up broad prospects for the development of electric vehicles.
Drive motor
The role of the drive motor is to convert the electrical energy of the power supply into mechanical energy, through the transmission device or directly drive the wheels and working devices. But DC motor because of the commutation spark, the power is small, the efficiency is low, the maintenance workload is large; With the development of motor control technology, it is bound to be gradually replaced by brushless DC motor (BLDCM), switched reluctance motor (SRM) and AC asynchronous motor, such as the DC series motor with axial magnetic field without shell.
Speed control
The motor speed control device is set for the speed change and direction change of electric vehicles, its role is to control the voltage or current of the motor, and complete the control of the motor's driving torque and rotation direction.
On early electric vehicles, the speed regulation of DC motors is realized by connecting series resistors or changing the number of turns of the motor's magnetic field coil. Because its speed regulation is graded, and will produce additional energy consumption or use the structure of the motor is complex, it is now rarely used. The thyristor chopper speed regulation is widely used to realize the stepless speed regulation by uniformly changing the end voltage of the motor and controlling the current of the motor. In the continuous development of electronic power technology, it has gradually been replaced by other power transistors (such as GTO, MOSFET, BTR and IGBT, etc.) chopper speed regulation devices. From the perspective of technological development, with the application of new drive motors, the speed control of electric vehicles will be transformed into the application of DC inverter technology, which will become an inevitable trend.
In the rotation change control of drive motor, DC motor relies on contactor to change the current direction of armature or magnetic field to realize the rotation change of motor, which makes the circuit complicated and reduces the reliability. When the AC asynchronous motor is used, the change of the motor steering only needs to change the phase sequence of the three-phase current of the magnetic field, which can simplify the control circuit. In addition, the AC motor and its frequency conversion speed control technology make the braking energy recovery control of electric vehicles more convenient and the control circuit more simple.
Driving gear
The role of the electric vehicle transmission device is to pass the motor's drive torque to the car's drive shaft, and most parts of the transmission device can often be ignored when electric wheel drive is used. Because the motor can be started with a load, the clutch of a traditional internal combustion engine car is not needed on an electric vehicle. Because the rotation of the drive motor can be changed by circuit control, electric vehicles do not need to reverse the transmission of internal combustion engine vehicles. When the motor is stepless speed control, the electric vehicle can ignore the transmission of the traditional car. When using electric wheel drive, electric vehicles can also omit the differential of the transmission system of traditional internal combustion engine vehicles.