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Brushless DC Motor Drive Circuit
The basic model of BLDC motor drive circuit is shown in figure below. The energizing state of motor three-phase winding can be controlled by switching tube Q0~Q5. The switching tube can be IGBT or power MOS tube. Among them, the switch tube located at the top that is connected to the positive end of the power supply is called "upper bridge", and the switch tube located at the bottom that is connected to the negative end of the power supply is called "lower bridge".
For example, if Q1 and Q4 are turned on and all other switches are turned off, the current flows from the positive end of the power supply to the negative end of the power supply through Q1, A phase winding, C phase winding and Q4 phase winding. The current flowing through the stator windings of phase A and C produces a magnetic field. The direction of the current flowing through the stator windings of phase A and C is parallel to that of phase B according to the right hand. Because the rotor is a permanent magnet, it will rotate in the direction parallel to the stator magnetic field under the action of magnetic force, that is, to the position parallel to the B phase winding, so that the north magnetic pole of the rotor is aligned with the south magnetic pole of the stator magnetic field.
Similarly, by opening different combinations of upper and lower bridge arm MOS transistors, the flow direction of current can be controlled, magnetic fields in different directions can be generated, and the permanent magnet rotor can be transferred to the designated position. In order to make the BLDC motor rotate continuously in the specified direction, it is necessary to electrify the sub-windings in a certain order. The switchover from one power-on state to another is called "commutation", for example, from AB to AC. The commutation rotates the rotor to the next position. There are six combinations of three switching tubes in each upper and lower bridge arm, so the motor can rotate for an electrical cycle after six-step commutation if it changes every 60 degrees. This is the so-called "six-step commutation method".
To maximize the rotor torque, the ideal situation is to make the stator magnetic field perpendicular to the rotor magnetic field direction. But in fact, because the direction of the stator magnetic field changes every 60 degrees, and the rotor rotates continuously, it is impossible to keep the phase difference of 90 degrees at all times. The optimum method is to make the stator magnetic field 120 degrees ahead of the rotor magnetic field direction at each commutation. During the next 60 degrees rotation, the angle between the stator magnetic field and the rotor magnetic field direction changes from 120 degrees to 60 degrees, and the utilization of the torque is the highest. In order to determine which winding will be electrified in the order of electrification, it is necessary to know the current position of the rotor. In BLDC motor with Hall, the rotor position is detected by the Hall effect sensor embedded in the stator. Hall sensorless BLDC motors do not use position sensors, but use the characteristic signals of the motor itself to achieve similar results with position sensors. Among them, the most widely used method is back electromotive force method.
For example, if Q1 and Q4 are turned on and all other switches are turned off, the current flows from the positive end of the power supply to the negative end of the power supply through Q1, A phase winding, C phase winding and Q4 phase winding. The current flowing through the stator windings of phase A and C produces a magnetic field. The direction of the current flowing through the stator windings of phase A and C is parallel to that of phase B according to the right hand. Because the rotor is a permanent magnet, it will rotate in the direction parallel to the stator magnetic field under the action of magnetic force, that is, to the position parallel to the B phase winding, so that the north magnetic pole of the rotor is aligned with the south magnetic pole of the stator magnetic field.
Similarly, by opening different combinations of upper and lower bridge arm MOS transistors, the flow direction of current can be controlled, magnetic fields in different directions can be generated, and the permanent magnet rotor can be transferred to the designated position. In order to make the BLDC motor rotate continuously in the specified direction, it is necessary to electrify the sub-windings in a certain order. The switchover from one power-on state to another is called "commutation", for example, from AB to AC. The commutation rotates the rotor to the next position. There are six combinations of three switching tubes in each upper and lower bridge arm, so the motor can rotate for an electrical cycle after six-step commutation if it changes every 60 degrees. This is the so-called "six-step commutation method".
To maximize the rotor torque, the ideal situation is to make the stator magnetic field perpendicular to the rotor magnetic field direction. But in fact, because the direction of the stator magnetic field changes every 60 degrees, and the rotor rotates continuously, it is impossible to keep the phase difference of 90 degrees at all times. The optimum method is to make the stator magnetic field 120 degrees ahead of the rotor magnetic field direction at each commutation. During the next 60 degrees rotation, the angle between the stator magnetic field and the rotor magnetic field direction changes from 120 degrees to 60 degrees, and the utilization of the torque is the highest. In order to determine which winding will be electrified in the order of electrification, it is necessary to know the current position of the rotor. In BLDC motor with Hall, the rotor position is detected by the Hall effect sensor embedded in the stator. Hall sensorless BLDC motors do not use position sensors, but use the characteristic signals of the motor itself to achieve similar results with position sensors. Among them, the most widely used method is back electromotive force method.
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