brushless dc motor is a kind of synchronous motor, that is to say, the motor rotor speed of the motor speed rotating magnetic field of the stator and rotor pole (P)Effect: N = 120. f / P。 In case the number of rotor fixed, change the frequency of the stator rotating magnetic field can change the speed of the rotor. Brushless dc motor is a synchronous motor with electronic control (Drive), control the frequency of the stator rotating magnetic field and the motor rotor speed feedback to the control center of repeated correction, in order to achieve close to the way the characteristics of dc motor. That is to say, brushless dc motor can be within the rated load when the load changes can still maintain control motor rotor speed. brushless dc drives including power department and control department as shown in figure (1): power supply provides the three-phase power supply to the motor, control of the transformation input power frequency in accordance with the requirements. power supply can be directly to dc input (Generally for 24 v)Or in an alternating current input (110V/220 V)Will have to the first, if the input is an alternating current converter (converter)Converted to dc. Both input dc or ac input to turn to motor coil must be before the dc voltage by the inverter (inverter)Into three phase voltage to drive motor. Inverter (inverter)By six power transistor (commonlyQ1～Q6)Divided into the upper arm (Q1和Q3, Q5)/ lower arm,Q2、Q4、Q6)Connected to the motor as control flows through the motor coil switch. Control department provides PWM (Pulse width modulation)Decision power transistor switching frequency and the inverter (inverter)The timing of the commutation. Brushless dc motor is generally want to use in the speed can be stable in value when the load changes will not change speed control, so the motor can be induced magnetic field of hall sensor mounted inside (大厅-传感器)As the speed closed loop control, and at the same time as the basis of phase sequence control. But that is only used as a speed control and is not to be used as a positioning control.
