| 摘要 |
PURPOSE:To prevent an inverter from damaging over the whole range of a speed control range by reducing a frequency/voltage reference signal in case of an overload and maintaining the output of a converter constant in a PWM control range. CONSTITUTION:An AND gate 25 outputs a current feedback signal SA in a PAM range, a zero signal in a PWM range and a gate OFF signal of a converter 3 at the time of the trouble of the converter 3. A voltage command SE abuts against the signal SA in the PAM range. An AND gate 25 blocks the application of the signal SA to a current controller 16 in the PWM range, while it applies the output of a voltage setter 26 to a voltage controller 15. Thus, the output voltage of the converter 3 is maintained constant. In case of an overload, the output of a pattern circuit 14 is reduced upon increase of the signal SA, thereby alleviating the load. |
