Electric Vehicle Electric Drive

Electric vehicle refers to a vehicle that is powered by an on-board power source and uses an electric motor to drive its wheels, meeting various requirements of road traffic and safety regulations. It uses electricity stored in the battery to start. Sometimes 12 or 24 batteries are used to drive the car, and sometimes more are needed.
The composition of electric vehicles [4] includes: electric drive and control systems, mechanical systems such as driving force transmission, and working devices to complete predetermined 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 driving motor, a power supply, and a speed control device for the motor. The other devices of electric vehicles are basically the same as those of internal combustion engines.
Power Supply
Provide electrical energy for the driving motor of electric vehicles, which converts the electrical energy from the power source into mechanical energy. The most widely used power source is lead-acid batteries, but with the development of electric vehicle technology, lead-acid batteries are gradually replaced by other batteries due to their low energy, slow charging speed, and short lifespan. The main developing power sources include sodium sulfur batteries, nickel cadmium batteries, lithium batteries, fuel cells, etc. The application of these new power sources has opened up broad prospects for the development of electric vehicles.
Drive motor
The function of the driving motor is to convert the electrical energy of the power supply into mechanical energy, and drive the wheels and working devices through the transmission device or directly. However, due to the presence of commutation sparks, the DC motor has low power, low efficiency, and a large maintenance workload; 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 caseless disc axial field DC universal motor.
Speed control
The electric motor speed control device is set for the speed change and direction change of electric vehicles, and its function is to control the voltage or current of the electric motor, completing the control of the driving torque and rotation direction of the electric motor.
In early electric vehicles, the speed control of DC motors was achieved by connecting series resistors or changing the number of turns of the motor's magnetic field coil. Due to its stepwise speed regulation and additional energy consumption or the complex structure of using an electric motor, it is now rarely used. The widely used method is thyristor chopper speed regulation, which achieves stepless speed regulation of the motor by uniformly changing the terminal 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) chopper speed control devices. From the perspective of technological development, with the application of new drive motors, the transformation of speed control in electric vehicles into the application of DC inverter technology will become an inevitable trend.
In the direction change control of the driving motor, the DC motor relies on the contactor to change the current direction of the armature or magnetic field, achieving the direction change of the motor's rotation, which makes the circuit complex and reduces reliability. When using AC asynchronous motor drive, the change in motor direction only requires changing the phase sequence of the three-phase current in the magnetic field, which can simplify the control circuit. In addition, the use of AC motors and their variable frequency speed control technology makes the braking energy recovery control of electric vehicles more convenient and the control circuit simpler.