How to control the rotor of the brushless motor?

The term "commutation", which describes the process of switching the current (in some fashion) in order to move the actual shaft, is used to describe all motors. The shaft rotates as a result of the current flowing through the coil, creating a magnetic field (often produced by a permanent magnet), which may either attract or repel the original magnetic field. The rotor, the motor's moving component, moves in relation to the stator, its stationary component, as a result of this force. A excellent comparison for commutation is with magnets. On a table, two magnets with opposing poles repel one another. The two homopoles will come to a stop when they are sufficiently apart. Due to same-sex repulsion, if one magnet is placed close to a second magnet, the second magnet will also be pushed away. The magnet will keep moving if this keeps happening, which is a linear case of commutation.

The history of the mini motor brushless is initially rather straightforward: the majority of issues with the brushed DC motor are caused by the brush. Brushes Due to friction and wear, brushes will generate high temperatures and sparks, which may lead to a motor failure as well as lower motor efficiency. Second, the brush has some influence on the motor's charged noise, which can impair the motor's electromagnetic compatibility and cause electrical interference and other issues. Third, the friction noise produced by the brush itself will also have an impact on how the motor operates and the user experience. Finally, brushes need to be replaced frequently because they only last a limited time. This means that you cannot use brushed motors in high-speed or high-power systems, around anything combustible, or in applications that call for long service life, silence, or high efficiency. These are the brush's main weaknesses. Cancelling the brush can address these issues, but the drawback is that doing so also ends mechanical commutation. Lack of mechanical commutation can cause other problems, so brushless motors use electrical commutation. Do you think that is amazing? You must make sure that during this commutation, the motor's current always generates a magnetic field capable of moving the rotor.

But before you can consider applying an electric current to move the rotor, you first need to know where it is. There are two ways to tell where the rotor is if you need assistance:

1. There is a sensor method, the sensor method refers to the use of the motor built-in magnetic sensor or Hall sensor, by reading the feedback signal of these sensors to determine the position of the motor rotor. This method is not affected by the external magnetic field, so it is more accurate.

  a.Set the initial position. Before starting the motor, it is necessary to set the motor to a known initial position. This can be achieved by certain means, such as turning the motor to the mechanical limit and then reversing to the initial position.

  b. Read the sensor signal. After starting the motor, it is necessary to read the signals fed back by the built-in sensors of the motor in real time, which can be magnetic sensors or Hall sensors.

  c. Calculate the rotor position. According to the feedback signal of the sensor, the current position can be known. Then, through a complex calculation formula, the difference between the position and the initial position can be judged, so as to know the current rotor Angle and speed.

  d. Adjust the control signal. After the position and speed are obtained, the control signal needs to be adjusted. Advanced control algorithms are usually used to optimize the working state of it according to the position and speed to achieve more accurate and stable motion.

2. Sensorless method is generally divided into two kinds, one is to measure the rotor position by the motor itself, and the other is to judge the relationship between the current waveform of the motor and the position. The principle of measuring the position by the back electromotive force is that when the motor rotor rotates, the back electromotive force will be generated, and its size is related to the position. By measuring the size and direction of the back electromotive force, the position of the rotor can be known. This method has high accuracy, but it needs to add more complex algorithms in the control circuit, and there is also a locking problem, that is, when the motor starts, it needs to find a starting point to run normally. Another method is to observe the relationship between the current waveform of the motor and the position of the rotor. When the motor rotor rotates, because the three-phase winding of the motor only two phase current changes, so the current waveform will change according to a certain law. By observing the changing law of the current waveform, the position of the rotor can be known. The implementation of this method is simple, but the accuracy is low, especially at low speed rotation is easy to be affected by noise.

The second major structural decision for a permanent magnet brushless motor system is the control method. There are three main ways to control the rotor of brushless DC motor: induction control, Hall control and encoder control.
1. Induction control is to use the motor's own back electromotive force to sense the position and speed of the motor, and then control the position and speed of the motor rotor. This method is simple, low cost, but has limited accuracy.
2. Hall control is to sense the position and speed of the motor through the Hall sensor inside the motor, and then control the position and speed of the motor rotor. The accuracy of this method is relatively high, but for complex applications, multiple sensors are needed for collaborative control.
3. Encoder control is to sense the position and speed of the motor through an externally mounted encoder, and then control the position and speed of the motor rotor. This method is the most accurate, but also relatively expensive.

The above are some professional knowledges on dc brushless motor by VSD Motors. For more relevant information, please contact us.