Understand brushless DC motor system

    The brush motor is also called DC motor or carbon brush motor. The DC motor often referred to is the brush DC motor. It adopts mechanical commutation, the external magnetic pole does not move, the internal coil (armature) moves, the commutator and rotor coil rotate together, and the brush and magnet do not move. Therefore, the commutator and brush rub against each other to complete the switching of current direction.

    Stepper motor is also called pulse motor. Based on the most basic electromagnet principle, it is a kind of electromagnet that can rotate freely. Its action principle is to generate electromagnetic torque by the change of air gap magnetic conductivity.

    Brushless motor is also called DC variable frequency motor (BLDC) in some fields. It uses electronic commutation (Hall sensor), and the coil (armature) does not move. At this time, the permanent magnet can be outside the coil or inside the coil. Therefore, there are external rotor brushless motor and internal rotor brushless motor.

    Some of the braver motor drive experts I know may say "single phase AC input, polyphase AC input or DC input", classifying each motor according to its input mechanism rather than specific motor type. I admit, this is a very clever answer. There must be different possible groups in the motor classification, from the use of position sensors to the supply voltage to the realization of drivers; Some engineers may be tempted to try to answer in these ways, even if the response does not always fit into three different categories. In this technical article, I will introduce a new way to look at the classification of motors.

    Recently, I have been fascinated by the idea that we should classify motors by function. Many applications use different types of motors, depending on the whim of the designer, but the same motor solution may not even be applicable to different applications using the same type of motor. If this sentence gives you a headache (my communication colleague assured me that it has this effect on her), let me give you a better example: you can use a stepping motor to realize a translation tilt zoom (PTZ) camera axis, a brushless DC motor or even a brush DC motor. Brushless DC motor is also the most common type of motor in ceiling fan. However, you cannot use the same brushless DC motor solution for both terminal device types. The ceiling fan drive circuit, no matter how excellent its performance, is a bad choice for PTZ camera, and the product cannot work normally. Why do I know this? Intuitively, I realized (as you probably know) that the "function" of the ceiling fan motor is very different from that of the PTZ camera motor, although both use brushless DC motors. From the application point of view, the motor function must have an attribute that can help establish different motor type classifications.

    So what are these motors actually doing? The function of the ceiling fan is to rotate at a uniform speed to circulate the air in the room. The function of PTZ camera is to move the camera to a certain position and keep it there. I can add a third example - cordless electric drill. The user controls the torque of the drill bit by pressing the trigger, perhaps by drilling a bit through the wall nail. These motors have very different implementations; Therefore, I have a question about "what are the three motor types?" The answer is an emphasis on "speed, torque and position". See Table 1 below.

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