| 摘要 |
PROBLEM TO BE SOLVED: To reduce a common-mode current in an earthing conductor of a PWM-controlled motor-driving circuit. SOLUTION: There is used an active filter containing a buffer amplifier that branches the common-mode current from the earthing conductor by linear- driving two junction-type transistors or a MOSFET transistor through the transistor. The transistor is connected between a positive and negative DC bus that feeds a DC voltage to a PWM inverter to drive an AC motor, and the AC motor generates a common-mode earthing current in the earthed frame. A current transformer monitors the common-mode current of which the output is connected to an input of the buffer amplifier to control the transistor. An internal power source for the amplifier is formed at a node that is positioned between two current sources and two Zener diodes connected between the DC bus conductors. A headroom-voltage control circuit establishes a sufficient headroom voltage for each transistor under any condition of an AC voltage input. |
