Method for measuring rotation speed of brushless direct-current motor

The invention relates to a method for measuring the rotation speed of a brushless direct-current motor. The method is applicable to an outer-rotor brushless direct-current motor, an inner-rotor brushless direct-current motor or a permanent-magnet synchronous motor. The method is characterized in that when the pole pair number of the motor is assumed as p, magnetic steel number is 2*p, the polarity arrangement of magnetic steel in the motor is in NS alternating arrangement, and three 120-degree switch type Hall sensors are used to detect the change of motor rotor poles; when the total electric cycle is assumed as T and the mechanical cycle is assumed as omega, the relation between the electric angle cycle and the mechanical cycle is T=p*omega, that is to say, p Hall signal cycles, namely 6*p states are generated when a motor rotor rotates one cycle, the rotation speed of the to-be-measured motor is n r/minute, and n=M*60/6*p*t. 种无刷直流电机转速测量方法，用于外转子无刷直流电机、内转子无刷直流电机或者永磁同步电机，假设电机的极对数为p，则磁钢数为2*p，磁钢在电机内部的极性排列为NS交替排列