DC motors have fast response, large starting torque, and can provide rated torque performance from zero speed to rated speed, but the advantages of DC motors are also its shortcomings, because DC motors have to produce constant rotation under rated load. For torque performance, the armature magnetic field and the rotor magnetic field must be maintained at 90° constantly, which requires the use of carbon brushes and commutators. Carbon brushes and commutators will generate sparks and carbon powder when the motor rotates. Therefore, in addition to damage to the components, the use occasions are also restricted. AC motors do not have carbon brushes and commutators, are maintenance-free, sturdy, and have a wide range of applications. However, in order to achieve the performance equivalent to DC motors, complex control technology can be used to achieve them. Nowadays, the rapid development of semiconductors has accelerated the switching frequency of power components to improve the performance of the drive motor. The speed of the microprocessor is also getting faster and faster, which can realize the control of the AC motor in a rotating two-axis rectangular coordinate system, and appropriately control the current components of the AC motor in the two axes, achieving similar control of the DC motor and equivalent to the DC motor performance.
In addition, many microprocessors have built the necessary functions for controlling the motor in the chip, and the size is getting smaller and smaller; such as analog-to-digital converter (adc), pulse width modulation (pulse wide modulator, pwm)...etc. The brushless DC motor is to electronically control the commutation of the AC motor, and obtain an application similar to the characteristics of the DC motor without the lack of the DC motor mechanism.