MAGNETIC POLE POSITION DETECTING DEVICE OF ROTOR

PROBLEM TO BE SOLVED: To surely avoid the influence of vibrating waveform appearing in an induced voltage with a simple configuration by detecting whether the induced voltage of stator coil winding crosses zero, at rising or falling of a clock for generating triangular waves. SOLUTION: In a terminal voltage waveform 33, a transitional vibration phenomenon 35 is generated immediately after the rising of a back electromotive voltage, and an induced voltage is formed after the transitional response. Therefore, for stably and reliably extracting a zero-cross point, the time when the induced voltage is formed after the vibration phenomenon 35 must be set to a zero-cross point extraction timing. Although the vibration phenomenon 35 of a transitional response is basically determined by the time constant of a drive circuit, even when the frequency of a speed signal becomes larger than that of a speed command signal and a duty ratio becomes considerably smaller, the vibration phenomenon 35 normally stabilizes with one cycle, and no large vibration continues to the extent of exceeding the center position of the rectangular pulse of a PWM control signal.