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Speed regulation method of BLDCM

2020-03-19 14:57:15

The speed regulation method of BLDCM, blue nine small make-up to give you a brief introduction:

According to the speed formula of DC servo motor, there are three basic speed regulation modes of DC motor, i.e. regulation of resistance R, regulation of armature voltage U and regulation of flux Ф. But armature resistance speed regulation is not economical, and the range of speed regulation is limited, so it is rarely used.

(1) When adjusting the armature voltage, if the armature current I is kept constant, the magnetic flux Ф remains unchanged. It can be seen that the electromagnetic torque T of the motor remains unchanged, which is a constant value. Therefore, the voltage regulation is also called constant torque regulation.

(2) During the speed regulation of magnetic field, the armature voltage U is usually kept as the rated voltage. Since the current of the excitation circuit cannot exceed the rated value, the excitation current is always adjusted to the decreasing trend, so that the magnetic flux drops, which is called the speed regulation of weak magnetic field. At this time, the torque T also drops, and the speed rises. In the process of speed regulation, the armature voltage U remains unchanged, and if the armature current I remains unchanged, the output power remains unchanged, so the magnetic speed regulation is also called constant power speed regulation.


Figure is the mechanical characteristic curve of DC motor in regulating armature voltage and flux speed regulation. In the figure, NN is rated speed at rated torque TN, and Δ NN is rated speed difference. It can be seen from the figure that when adjusting the armature voltage, the mechanical characteristics of the DC motor are a group of parallel lines, that is, the slope of the mechanical characteristics curve is unchanged, but only the ideal speed of the motor is changed, and the original mechanical characteristics are maintained, so the speed regulation of the servo feed system of the CNC machine tool adopts the method of adjusting the armature voltage. The mechanical characteristics of permanent magnet DC servo motor just meet the speed regulation requirements. Therefore, permanent magnet DC motor is often used in the feed system of CNC machine tools.

It can be seen from the figure that the magnetic speed regulation not only changes the ideal speed of the motor, but also softens the mechanical characteristics of the DC motor, so the magnetic speed regulation is mainly used for the speed regulation of the spindle motor of the machine tool.


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