| 摘要 |
PROBLEM TO BE SOLVED: To prevent mis-commutation and realize a stable operation, when the waveform of an AC power source is distorted by higher harmonics or the like, and exclude error of communication, when a DC component or even higher harmonic flows out by mis-communication. SOLUTION: A voltage waveform of only the AC component is detected from each 3-phase line voltage, by using insulating transformers 10-1 to 10-3. From the voltage waveform, the positive and negative peak values are detected by a peak detecting circuit 11. By an intermediate point detecting circuit 12, the middle point between the positive and the negative peaks is detected and made a zero-crossing point. This point is set as a reference, and an ignition circuit 13 forms each ignition signal to each of the thyristors 2-1 to 2-6. |
