| 摘要 |
PURPOSE:To reduce the electromagnetic noise from a motor by holding down the maximum value of conduction current of an inverter section which drives the fan motor and reducing other frequency components than a specified one. CONSTITUTION:Comparing a current command value 6a corresponding to a difference between a rotating speed command 5 and an actual rotating speed of a motor 3 with a triangular signal 11a from an oscillation circuit 11, a PWM signal generating circuit 12 generates a PWM signal 12a which has a duty ratio corresponding to the current command value 6a. The current command value 6a is so set that the maximum duty ratio of the PWM signal 12a may be 100% or smaller. When the conduction current I of an inverter section 2 reaches the current limit value IL, a current limiting circuit 10 generates current limiting signals 10a, 10b. A cycle of the PWM signal 12a is held down by the current limiting signal 10a in a composite circuit 7 and the duty ratio of the PWM signal 12a is made smaller by making the duration of the current limiting signal 10a and the current command value 6a smaller in a calculating and controlling circuit 6. The thus generated signal 7a is a driving signal of the inverter section 2. |
