Commutation effects on motor current and torque in five-phase PM BLDC drives

Five-phase PM BLDC drives are a viable solution for safety-critical applications in road traction and aeronautics sectors. A common supply technique for these drives consists in the injection of square-wave currents into the motor phases, synchronized with the flat-top portion of the back-emf to produce both constant torque and maximum torque per ampere. In practice, the currents deviate from the ideal shape during the phase commutations, which further affects the torque characteristics of the drives. This paper analyzes the current behavior during the phase commutations for the five-phase PM BLDC drives as they exhibit some differences with respect to the three-phase counterpart. Then it uses the outcomes of the current analysis to derive the effective torque developed and the torque ripple exhibited by the drive as a function of the motor speed. The base speed of the drive is also determined. Throughout the paper, the differences from the well-known operation of the three-phase PM BLDC drives are pointed out.