Components

The components of an electric vehicle include: the electric drive and control system, the mechanical system such as the drive power transmission, and the working device to accomplish the given task. The electric drive and control system is the core of an electric vehicle and is what distinguishes it from an internal combustion engine vehicle. The electric drive and control system consists of the drive motor, the power supply and the speed control device for the motor. The other devices of an electric vehicle are basically the same as those of an internal combustion engine vehicle.

The power supply provides the electrical energy for the drive motor of an electric vehicle, and the motor converts the electrical energy from the power supply into mechanical energy. The most widely used power source is the lead-acid battery, but with the development of electric vehicle technology, the lead-acid battery is gradually being replaced by other batteries due to its low energy, slow charging speed and short life. The main power sources under development are sodium-sulphur batteries, nickel-cadmium batteries, lithium batteries and fuel cells, etc. The application of these new power sources opens up broad prospects for the development of electric vehicles.

The role of the drive motor is to convert the electrical energy from the power supply into mechanical energy, through the transmission device or directly drive the working device of the wheel. However, due to the presence of commutation sparks, DC motors have low power, low efficiency and high maintenance workload; with the development of motor control technology, they are bound to be gradually replaced by brushless DC motors (BLDCM), switched reluctance motors (SRM) and AC asynchronous motors, such as casingless disc axial field DC series excitation motors.

Speed control devices

Pure electric vehicles

The motor speed control device is set up for the speed change and direction change of electric vehicles. Its function is to control the voltage or current of the motor and to complete the control of the driving torque and direction of rotation of the motor.

In the early days of electric vehicles, the speed control of DC motors was achieved by connecting a resistor in series or by changing the number of turns of the motor's magnetic field coil. Because the speed regulation is graded, and will produce additional energy consumption or use the motor structure is complex, now rarely used. The more widely used is the thyristor chopper speed control, which controls the motor current by uniformly changing the terminal voltage of the motor to achieve stepless speed control of the motor. In the continuous development of electronic power technology, it is also gradually replaced by other power transistor (into GTO, MOSFET, BTR and IGBT, etc.) chopper speed control device. From the development of technology, along with the application of new drive motors, it will become inevitable that the speed control of electric vehicles will be transformed into the application of DC inverter technology.

In the spin-change control of drive motors, DC motors rely on contactors to change the direction of the current in the armature or magnetic field to achieve the spin-change of the motor, which makes the circuit complex and less reliable. When an AC asynchronous motor is used, the change of motor direction is simply a matter of changing the phase sequence of the three phases of the magnetic field current, which simplifies the control circuit. In addition, the use of AC motors and their variable frequency speed control technology makes it easier to control the braking energy recovery of electric vehicles and makes the control circuit simpler.