What are the benefits of lead angle control in brushless motors?

The motor achieves maximum torque when the magnetic field of the magnet is behind the magnetic field of the coil by 90 degrees in phase. Since the induced voltage leads the magnetic field of the magnet by 90 degrees in phase, and the motor current is in phase with the magnetic field of the coil, maximum torque can be obtained when the phases of the induced voltage and the motor current are the same. Under this condition, the motor can be driven most efficiently.
However, as the figure below shows, when the drive voltage is applied in phase with the induced voltage, the phase of the motor current is delayed due to the coil’s inductive reactance. This results in a braking torque, consequently leading to lower efficiency.
To improve this, a correction method is employed that involves advancing the phase of the drive voltage, which in turn advances the phase of the motor current, aligning it with the induced voltage and thereby eliminating braking torque. This is known as the lead angle control, which can improve the efficiency of brushless DC motors.