First, the working principle of brushless DC motor
Brushless DC motor by the brushless DC motor body and drive components, brushless DC motor is a typical mechanical and electrical integration products. DC brushless motor stator windings made of three symmetrical star connection, with three-phase asynchronous brushless DC motor is very similar. DC brushless motor on the rotor sticky magnetized permanent magnet, in order to detect the polarity of the brushless DC motor, DC brushless motor with a position sensor. The driver is composed of power electronic devices and integrated circuits. Its function is to accept the start, stop and brake signals of the brushless DC motor to control the start, stop and braking of the DC brushless motor. Accept the position sensor signal and forward and reverse Signal, used to control the inverter bridge power tube on and off, resulting in continuous torque; accept speed command and speed feedback signal, used to control and adjust the speed; provide protection and display, and so on.
DC motor with fast response, large starting torque, from zero speed to rated speed with rated torque can provide the performance, but the advantages of DC motor is also its shortcomings, because the DC motor to produce a constant load under constant load Moment performance, then the armature magnetic field and rotor magnetic field to be constant to maintain 90 °, which will rely on carbon brush and commutator. Carbon brush and commutator in the motor rotation will produce sparks, toner in addition to the components will cause damage, the use of occasions are also limited. AC motor without carbon brush and commutator, maintenance-free, strong, wide application, but the characteristics of the DC motor to achieve the equivalent of the performance of complex control technology to be used to achieve. Now the rapid development of semiconductor power components to switch the frequency of many, to enhance the performance of the drive motor. Microprocessor speed is faster and faster, can be achieved AC motor control placed in a rotating two-axis rectangular coordinate system, the appropriate control AC motor in the two-axis current component, to achieve similar DC motor control and DC motor with the equivalent performance.
Second, the brushless DC motor structure
DC brushless motor is a synchronous motor, which means that the motor rotor speed by the stator stator rotation magnetic field speed and the number of rotor (p): n = 60. F / p. DC brushless motor in the rotor number of fixed cases, change the frequency of the stator rotating magnetic field can change the rotor speed. DC brushless motor is the synchronous motor with electronic control (drive), control the frequency of the stator rotating magnetic field and the motor rotor speed back to the control center repeated correction, in order to achieve close to the DC motor characteristics of the way. That is, DC brushless motor can be in the rated load range when the load changes can still control the motor rotor to maintain a certain speed.
DC brushless drive, including the power supply and control: the Ministry of power to provide three-phase power to the motor, the control unit will be converted according to the needs of input power frequency. The power supply unit can be directly DC input (usually 24v) or AC input (110v / 220v), if the input is AC must first converter (converter) into DC. Either DC input or AC input to be transferred to the motor coil before the DC voltage from the inverter (inverter) into three-phase voltage to drive the motor. Inverter (inverter) is usually divided into upper arm (q1, q3, q5) / lower arm (q2, q4, q6) by 6 power transistors (q1 ~ q6) to connect the motor as a switch to control the flow through the motor coil. The control section provides pwm (pulse width modulation) to determine the frequency of the switching frequency of the power transistor and the commutation of the inverter. DC brushless motors generally want to use when the load changes in the speed can be stable at the set value without changing the speed of control, so the brushless DC motor equipped with a magnetic field can be sensitive hall (sensor) As the speed of the closed loop control, but also as the basis for phase control control. But this is only used as a speed control and can not be used as a positioning control.