The brushless DC motor uses semiconductor switching devices to achieve electronic commutation, that is, electronic switching devices are used to replace traditional contact commutators and brushes. It has the advantages of high reliability, no commutation sparks, and low mechanical noise, and is widely used in high-end audio recorders, video recorders, electronic instruments and automated office equipment.

      The brushless DC motor consists of a permanent magnet rotor, a multi-pole winding stator, and a position sensor. According to the change of the rotor position, the position sensor commutates the current of the stator winding along a certain order (that is, detects the position of the rotor magnetic pole relative to the stator winding, and generates a position sensing signal at the determined position, which is processed by the signal conversion circuit. To control the power switch circuit, and switch the winding current according to a certain logical relationship). The operating voltage of the stator winding is provided by an electronic switching circuit controlled by the output of the position sensor.

      There are three types of position sensors: magnetic, photoelectric and electromagnetic. A brushless DC motor using a magneto-sensitive position sensor, its magneto-sensitive sensor devices (such as Hall elements, magneto-sensitive diodes, magneto-sensitive pole tubes, magneto-sensitive resistors or special integrated circuits, etc.) To detect changes in the magnetic field generated by the rotation of permanent magnets and rotors.

      The brushless DC motor using the photoelectric position sensor is equipped with a photoelectric sensor device at a certain position on the stator assembly, a shading plate is installed on the rotor, and the light source is a light-emitting diode or a small light bulb. When the rotor rotates, due to the action of the shading plate, the photosensitive components on the stator will intermittently generate pulse signals at a certain frequency.

      The brushless DC motor with electromagnetic position sensor is equipped with electromagnetic sensor components (such as coupling transformer, proximity switch, LC resonance circuit, etc.) on the stator assembly. When the position of the permanent magnet rotor changes, the electromagnetic effect will make the electromagnetic sensor A high-frequency modulated signal is generated (the amplitude of which varies with rotor position).

      The DC motor has fast response, large starting torque, and can provide rated torque from zero speed to rated speed. The performance of the torque, the armature magnetic field and the rotor magnetic field must be maintained at 90°, which requires carbon brushes and commutators. Carbon brushes and commutators will generate sparks and carbon powder when the motor rotates, so in addition to causing damage to the components, the application is also limited. The AC motor has no carbon brushes and commutators, and is maintenance-free, sturdy, and widely used. However, in order to achieve the performance equivalent to the DC motor, complex control technology can be used to achieve it. With the rapid development of semiconductors today, the switching frequency of power components is much faster, which improves the performance of the drive motor. The speed of the microprocessor is also getting faster and faster, and the control of the AC motor can be placed in a rotating two-axis orthogonal coordinate system, and the current components of the AC motor in the two axes can be properly controlled to achieve similar control of the DC motor and equivalent to the DC motor. performance.

      In addition, many microprocessors have implemented the functions necessary to control the motor in the chip, and the volume 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 an application that electronically controls the commutation of the AC motor to obtain similar characteristics of the DC motor without the lack of the DC motor mechanism.

      The brushless DC motor is a type of synchronous motor, that is to say, the speed of the motor rotor is affected by the speed of the rotating magnetic field of the motor stator and the number of rotor poles (p):

      n=120. f/p. When the number of rotor poles is fixed, changing the frequency of the stator rotating magnetic field can change the rotor speed. The brushless DC motor is a method of adding a synchronous motor to an electronic control (driver) to control the frequency of the rotating magnetic field of the stator and feedback the rotational speed of the motor rotor to the control center for repeated correction, in order to achieve close to the characteristics of the DC motor. That is to say, the DC brushless motor can still control the motor rotor to maintain a certain speed when the load changes within the rated load range.

      The brushless DC driver includes a power supply part and a control part. The power supply part provides three-phase power to the motor, and the control part converts the input power frequency according to the requirements.

      The power supply can be directly input with DC power (usually 24v) or input with AC power (110v/220v). If the input is AC power, it must first be converted to DC through a converter. Whether it is DC input or AC input, the DC voltage must be converted from an inverter (Inverter) to a 3-phase voltage to drive the motor before it is transferred to the motor coil. Inverter is generally divided into upper arm (q1, q3, q5)/lower arm (q2, q4, q6) by 6 power transistors (q1 ~ q6) connected to the motor as a switch that controls the flow through the motor coil. The control unit provides pwm (pulse width modulation) to determine the switching frequency of the power transistor and the timing of the inverter (Inverter) commutation. The brushless DC motor generally hopes to use the speed control in which the speed can be stabilized at the set value without changing too much when the load changes, so the motor is equipped with a Hall sensor (Hall-sensor) that can sense the magnetic field, as a function of the speed. Closed-loop control is also used as the basis for phase sequence control. But this is only used for speed control and not for positioning control.

      To make the motor turn, the control part must determine the order of turning on (or turning off) the power transistors in the inverter according to the position of the motor rotor sensed by the Hall-sensor, and then according to the stator winding, so that the current flows in sequence A forward (or reverse) rotating magnetic field is generated by the motor coil and interacts with the magnets of the rotor, so that the motor can be rotated clockwise/counterclockwise. When the motor rotor rotates to the position where the Hall-sensor senses another set of signals, the control unit turns on the next group of power transistors, so that the circulating motor can continue to rotate in the same direction until the control unit decides to turn off the power if the motor rotor stops. transistor (or only turn on the lower arm power transistor); if the motor rotor is to be reversed, the power transistor turn-on sequence is reversed.

      The general brushless DC motor is essentially a servo motor, which is composed of a synchronous motor and a driver, and is a variable frequency speed motor. The brushless DC motor with variable voltage speed regulation is a real brushless DC motor. It consists of a stator and a rotor. The stator consists of an iron core. The fixed magnetic field of the group, the rotor is composed of a cylindrical magnet (with a shaft in the middle), or composed of an electromagnet and a collector ring, this brushless DC motor can generate torque, but cannot control the direction. It is a very meaningful invention. When used as a DC generator, the present invention can generate continuous amplitude DC current, thus avoiding the use of filter capacitors, and the rotor can be permanent magnet, brush-excited or brushless-excited. When used as a large motor, the motor will generate self-inductance, and a protection device is required.