An analytical determination of the torque-speed and efficiency-speed characteristics of a BLDC motor

The paper presents a complete mathematical analysis of a BLDC motor commutation which results in the motor static characteristics torque-speed and efficiency-speed. The motor, having a sinusoidal back emf, is supplied from a DC source via a 6-leg inverter using the 120degON operation. The formulas for the phase currents and voltages are derived. The first harmonic of the phase voltage is determined, which is used in combination with the classical BLDC motor theory to obtain simple formulas for the motor torque and efficiency. The model is verified using a measurement on a small industrial BLDC motor.