The function of driving an electric motor is to convert the electrical energy of the power source into mechanical energy, which can be transmitted through a transmission device or directly drive the wheels and working devices. DC series excited motors are widely used in electric vehicles, which have “soft” mechanical characteristics and are very consistent with the driving characteristics of cars., Low power, low efficiency, and heavy maintenance workload; With the development of motor control technology, it is bound to be gradually replaced by brushless DC motors (BLDCM), switched reluctance motors (SRM), and AC asynchronous motors, such as shell less axial magnetic field DC series excited motors.

Speed control device

The motor speed control device is set up for the speed change and direction change of electric vehicles, and its function is to control the voltage or current of the motor, complete the control of the driving torque and rotation direction of the 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 coils. Due to its stepwise speed regulation and the additional energy consumption or 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 In the continuous development of electronic power technology, it has gradually been replaced by other power transistors (such as GTO, MOSFET, BTR, and IGBT) for chopper speed regulation. From the perspective of technological development, with the application of new drive motors, the transformation of speed control in electric vehicles to the application of DC inverter technology will become an inevitable trend.

In the control of the rotation direction change of the driving motor, the DC motor relies on the contactor to change the direction of the armature or magnetic field current, achieving the rotation direction change of the motor, 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. Inoltre, 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.