3-phase BLDC Motor Control with Hall Sensor

The DC electric motor has appeared for a long time. The electric coil rotates due to the magnetic field generated by the permanent magnet or excitation coil within the electric motor. To electric motors with only one pair of magnetic poles, the space between the electrodes is 180°. The DC electric motor's rotor in the early period was an electric coil, and the direction was changed by every half circle of current. Under the condition, the commutator and electric brush were invented. Since the electric brush and the commutator contact with each other every half a circle, electric sparks generate. Though adoption of graphite materials by the electric brush has cut the abrasion costs, the electric brush should be changed once for a period of time. Therefore, the DC electric motor has limited application scenarios and cannot be applied to inflammable and explosive scenarios. Meanwhile, its maintenance is troublesome and costly.
Therefore, is it possible to adopt the permanent magnet as the rotor and the electric coil as the stator? If yes, the puzzlement facing exchange of the electric brush can be addressed and the generation of electric sparks can be avoided. In fact, the new-type specialized electric motor, high torque BLDC motor, adopts this structure. The electrification sequence of the coil is controlled, and the coils at the opposite direction are put in the same group. Meanwhile, through galvanization, the magnetic field at the same direction is generated. Take the three-phase BLDC motor for example. The number of the electric motor's pole pairs is three. Every pair of magnetic poles is connected with power according to certain sequence to achieve the effect of rotating the magnetic field. Under the effect of the magnetic field, the permanent magnet's rotor moves in the direction the same to the magnetic field, and will move together with the rotating magnetic field. This means that constant changes of the electrification sequence can ensure the stator to rotate.
To ensure the three coils to turn on and off according to certain sequence requires adoption of certain control strategies. H1/H2/H3 denotes the Hall sensor installed at the excitation coil's air gap. As the electric components to detect the magnetic field, they can switch the voltage according to the direction of the magnetic field, and the output is the digital signal. For example, if the sensor has N magnetic poles, it will output a high electric level, namely the logic signal "1" and output "0" In this way, the output signals of three Hall sensors should be ranked in certain sequence. Among them, there must be two "1" and one "0" Then, we can judge the rotating state of the rotor according to the returned triad numbers.
Though it is more difficult to adopt three phases than to adopt two phases, it is necessary to judge the dead zone. As long as it is powered on, the Hall sensor will return the state of the current rotor. According to the state, the stator coil can be connected with power in certain sequence. There should be certain included angle between the rotor magnetic field and stator magnetic field. Therefore, the stator coil will undoubtedly rotate. In this way, there is no need to judge whether the electric motor has been started or not. One just needs to implement the order of the next step according to the working status sent back by the Hall sensor. The order sent out is on and off status of three pairs of coils, which can be theoretically controlled by three switches. In fact, these switches are realized via the triode. Therefore, one just needs to switch on or off three pairs of triodes according to certain sequence to realize rotation of the three-phase BLDC motor.