Learn the basic principles of BLDC in Simulink during a meal

Catalog

One 、 Basic knowledge of

Two 、 Back EMF Test

3、 ... and 、 Principle of rotation

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One 、 Basic knowledge of

Rotational motion is generated by the attraction and repulsion of permanent magnet and electromagnet poles

BLDC Adopted Electronic commuting The way , The utility model overcomes the defect that the brush of a brush DC motor is worn, thereby affecting the performance of the motor

BLDC It can be regarded as the reverse installation of brush DC motor , That is, the rotor becomes a permanent magnet , The stator is composed of coil winding

Its magnetic poles are arranged in many ways , The stator has a different number of coil windings , The rotor has a different number of pole pairs

It is associated with PMSM Has a similar structure , They are all called Synchronous motor

BLDC And PMSM The back EMF is different , The corresponding control strategies are also different ,BLDC The back EMF is trapezoidal , It is generally used Trapezoidal control ; and PMSM The back EMF is sinusoidal , It is generally used Field oriented control

 

Two 、 Back EMF Test

Here's the picture simulink Model

By running the model , You can see BLDC The back EMF of is trapezoid

 

3、 ... and 、 Principle of rotation

to A/B/C Three phases, two of which apply voltage , Form a combined magnetic field （ As shown in the figure, the dotted line ）, rotor （ Red is the North Pole , Blue is the South Pole ） Start rotating to align with the stator magnetic field

Six power on combinations , They represent different angles , The difference between the angles 60°, The angle measurement is based on the horizontal axis

In practice, the mode of commutation occurs ： The rotor is never aligned with the stator magnetic field , Instead, let the rotor chase the stator magnetic field , This is because when the rotor is aligned with the stator magnetic field , The torque produced by the motor is 0; And when it is different from the stator magnetic field 90° The maximum torque is produced at , So the goal should be to keep the magnetic field as far away from the rotor as possible 90°, But in fact, it can not reach 90°, This is due to the characteristics of the ladder control itself , And the angle between the rotor and the magnetic field will fluctuate within a certain range , stay 60°~120° Between , See the Yellow range in the figure below

Therefore, three-phase current control is adopted for DC control , utilize Three phase inverter Complete the conversion , It controls the positive voltage （ The red part ）, The following controls the negative voltage （ The blue part ）, And the three-phase inverter will convert the voltage into a constant point voltage , To make the motor rotate at a constant speed , To rotate at different speeds , The corresponding control voltage shall be applied , One way is to PWM