How to control 48v brushless dc motor?
As mentioned above, the key to control the rotation of the rotor is to reverse the current passing through the coil when the rotor turns to the appropriate angle, so as to change the magnetic pole at the end of the coil, and generate repulsion force or attraction on the rotor, so as to make the rotor rotate the angle of the next stage.
How to grasp the timing of current commutation? In other words, how do I know where the rotor is now?
This requires the use of Hall sensors. In the interior of BLDCM, Hall sensors are installed, the number is generally 3.
1. Hall sensor
Hall sensor can detect the change of magnetic field intensity through Hall effect. According to the left-handed rule learned in high school physics, in the circuit where the hall sensor is located, the magnetic field deflects the motion of charged particles, and the charged particles "collide" with the two sides of the hall sensor, resulting in potential difference. At this time, a voltmeter can be connected to the two sides of the hall sensor to detect the voltage change, so as to detect the change of magnetic field strength. The principle is shown in the figure below.
2. How does Hall sensor get rotor position?
With the hall sensor, we can know the position of the rotor.
According to ha, Hb, HC are the rising edge and the falling edge, we can know the angle of the rotor position. For example, if HA is the falling edge, we can know that the rotor is between 180 degrees and 240 degrees (electrical angle). When three Hall sensors are used, the resolution is an electrical angle of 60 degrees.
In this answer, the electrical angle is equal to the mechanical angle. According to the number of poles of permanent magnet rotor, the proportion of electrical angle and mechanical angle will be different.
3. How to control the rotation direction of BLDCM?
Change the order of current commutation. For example, from u → V to V → U.
4. How to control the speed of 48v brushless dc motor?
We know that the permanent magnet rotor of 48v brushless dc motor is driven by the repulsive force and attraction of electromagnet (coil). Therefore, the greater the current through the coil, the stronger the magnetic force, the faster the rotor will rotate.
Because the power supply is DC, we usually use PWM (pulse width modulation) to control the current through the coil. The simple principle of PWM is as follows.
Therefore, when the 48v brushless dc motor is powered on, the opening and closing of FET can be controlled continuously by single chip microcomputer, which can make the coil in the state of power on and power off repeatedly. If the power on time is long, the electromagnetic force generated by the coil will be strong, and the rotor will rotate quickly.
Remember the six step communication current commutation sequence table above? According to the current commutation sequence table and PWM control of motor speed, the state of u, V and W can be obtained.