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Bldc Motor Working Principle

By May | Published on Sep 17,2015
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Bldc motor, a typical mechatronic product is composed of synchronous motor and driver. The stator windings of synchronous motor is shaped into three-phase symmetrical star connection which is very similar to three-phase asynchronous motor while the rotor have the magnetized permanent magnet struck to itself and the position sensor is fixed to detect polarity of the rotor. The driver is complicated with power electronic devices and integrated circuits and have the function to receive the signal of the motor to start, stop, brake to control the motor starting, stopping and braking and to receiving the signal from position sensor and reversing signal to control the switch of the inverse variable bridge, produce a continuous torque, receive speed command and signal of speed feedback to control and adjust the speed and provide protection and display.

The coding of the position sensor of bldc motor coding enables the position where two-phase winding forms axial of magnetic field exceeds the position of the rotor’ magnetic field axis position so no matter where starting position of the rotor is, the motor will start instantly to generate a sufficiently large starting torque, so there is no need setting separate start winding on the rotor. Since the magnetic field of stator is perpendicular to the axis, the winding current is proportional to the average electromagnetic torque in if the core is not saturated, which is characteristics of excitation current DC motor.

The bldc motor does not have to get excitation current from the grid as the asynchronous machine does since the excitation is from permanent magnets; the efficiency is about 10% higher than that of asynchronous motor with the same high capacity since there is no alternating magnetic flux on the rotor and neither copper losses nor iron loss and the power pointer (ηcosθ) of bldc motor is 12% to 20% higher than the asynchronous motor with the same capacity.


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