Motor speed control devices are designed for speed changes and direction switching in electric vehicles. Their function is to control the motor's voltage or current to control the driving torque and rotation direction.
Early electric vehicles used series resistors or changing the number of turns in the motor's field coil to control the speed of the DC motor. Because this speed control was stepped and resulted in additional energy consumption or complex motor structure, it is rarely used now. Thyristor chopper speed control is more widely used, which controls the motor current by uniformly changing the motor's terminal voltage to achieve stepless speed regulation. With the continuous development of electronic power technology, it has gradually been replaced by chopper speed control devices using other power transistors (such as GTOs, MOSFETs, BTRs, and IGBTs). From a technological development perspective, with the application of new drive motors, the transformation of electric vehicle speed control to the application of DC inverter technology will inevitably become a trend.
In the rotation direction control of the drive motor, the DC motor relies on contactors to change the direction of the armature or field current to achieve rotation direction switching. This makes the circuit complex and reduces reliability. When an AC asynchronous motor is used for driving, changing the motor's direction of rotation only requires changing the phase sequence of the three-phase current in the magnetic field, which simplifies the control circuit. Furthermore, using an AC motor and its variable frequency speed control technology makes regenerative braking control of electric vehicles more convenient and the control circuit simpler.
