A new ripple-free torque brushless DC motor without requirement for square-shape magnet flux distribution

A new structure of the brushless DC motor with ripple-free torque performance is first proposed. The steady torque of the motor is guaranteed even if the shape of rotor magnet flux distribution is arbitrary. It adopts 180° square-wave current and 120° or less flux distribution. The reason of torque ripple in conventional square-shape brushless DC motor is presented. The theoretic proof of ripple-free performance of torque in novel brushless DC motor is given under commutating and noncommutating stage. The principle of novel motor design including one tooth pitch skewed slot in stator and method for decrease the 60° residual magnet flux is given, the influence to effective width of uniform current density by skewed slot is analyzed. Serial connected and parallel connected power circuit topology is discussed. The experiment comparison between novel and conventional brushless DC motor is investigated. Experimental results verify that the output torque is constant in noncommutating stage. The method to decrease current fluctuating caused by commutation is given.