| 摘要 |
PURPOSE:To attain a multiplex structure of a detection system with high reliability by using the count value of another counter or using the majority logic to detect a phase angle in case the count value of a prescribed counter has a fault. CONSTITUTION:A comparator 4 uses three different phases of voltage Vu, Vv and Vw as inputs and detects a zero-cross point. Then the comparator 3 deliveres reset pulses S1, S2 and S3 to counters 1, 2 and 3 respectively. The approximate of the phase angle of this time is equal to the value obtained by adding the change amount of a phase control angle to the preceding phase angle as long as this angle is known when the count value is abnormal. Thus the phase angle of this time is used as the estimated value of a phase detecting angle. Otherwise >=2 detection arithmetic values are used as the detection value based on the majority logic when these values are set within a prescribed range, or a digital processor is used for processing of said arithmetic values. This improves the reliability of a digital phase detecting system. |
