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A Lag Angle Compensation Strategy of Phase Current for High-Speed BLDC Motors

For brushless dc motor operating at ideal commutation point, the angle of the phase current vector will lag behind that of the back electromotive force (EMF) vector due to the motor phase inductance. The lag angle increases the root-mean-square (rms) value of phase current under a certain average torque output, which results in more heat and less efficiency, especially at high rotational velocity. The principle that the angle of ideal current vector is equal to that of the back EMF vector at the center of a conduction sector is analyzed. A novel advance compensation method for commutation point is proposed based on the principle. The advance angle is calculated in real time according to the phase current, the inductance, and the flux linkage established by the magnet of the motor. By conducting the voltage vector of voltage source inverter before the ideal commutation point in advance, the lag of the phase current would be eliminated. Thereby, the rms value of the phase current is reduced. Finally, both simulation and experiments verify the effectiveness of the proposed method.