Establishing electromagnetic torque in brushless direct current motors by numerical methods

Abstract

Progresses obtained in command and power electronics have increased the technical and economic performances of brushless direct current motors. Consequently, the problem of optimum design and operation of these motors, frequently used for driving small vehicles, is a very present one. Studies presented in literature show that high oscillations of torque occur in these motors in a complete rotation. That is why, the research carried out and the simulations presented aim at identifying the slots producing high torques, respectively low torques, in a complete rotation, thus justifying the oscillations. The conclusion emerged has been that the optimum variant of maximum torque implies supplying the brushless direct current motor with six pulses per period in direct direction, also indicating the value of the command angle. The most unfavourable situation, of low torque and high oscillations, occurs in case of supply with three pulses per period and reverse sequence of phases. In this case, the average value of the torque decreases by 56.7% as against the optimum machine. Eliminating oscillations in this type of motor in not possible, but an optimal design can reduce them much.