The invention relates to a method for regulating a speed of a brushless
direct current motor supplied with power by a four-switch three-phase
inverter, and belongs to the field of speed regulation of a
direct current motor. The method solves the problem that unfixed switch frequency of
hysteresis loop modulation in the control of the conventional brushless
direct current motor. The method is realized based on a
speed loop PI regulator, a speed calculation unit, a current
shape function unit, a given current coordinate conversion unit, an alpha-axis current
PI regulator, a beta-axis current
PI regulator, a
flux linkage tracing PWM unit, a feedback current coordinate conversion unit, a four-switch three-phase
inverter, a
current sensor and a Hall pole sensor, and adopts rotational speed and current double closed-
loop control; an outer loop is a rotational speed ring; the outputs of the rotational speed ring are given as current values; the method multiples the current values by the current
shape function unit respectively to realize the preset of three-phase 120-degree symmetrical square-wave current, establishes a current
closed loop in a two-phase stationary coordinate
system by coordinate conversion, and realizes the control of the four-switch three-phase
inverter through the
flux linkage tracing PWM unit. The method is used for controlling the speed regulation of the brushless direct current motor.