| 摘要 |
PURPOSE:To prevent commutation failure caused by variations in frequency by detecting the variation in the power source frequency and correcting the control phase angle. CONSTITUTION:A frequency detector 11 which inputs a reference pulse theta0 from a zero cross detector 10 and outputs a frequency detection signal (f) is provided, and a pulse generator 8A has an input terminal for reading out the signal (f) as a correction signal. The detector 11 has a clock pulse generator for generating a pulse at every prescribed period and a counter for counting the pulse during a period of the pulse theta0, and outputs the counted value of the counter as the signal (f). Accordingly, when the frequency of the power source is small, the counted value (f) of the counter is large, and when the frequency is high, the counted value (f) is, on the contrary, small, and the generator 8A performs the correcting operation so that the value (f) becomes zero correction in case of rated frequency f0. |
