Patent ID: 6636107
Filing Date: 2003-10-21
Classification: H02M,H02P

Abstract:
An active filter for reducing a common mode current in a pulse width modulated motor drive circuit; said motor drive circuit comprising an a-c source, a rectifier connected to said a-c source and producing a rectified output voltage connected to a positive d-c bus and a negative d-c bus, a PWM inverter having input terminals coupled to said positive d-c bus and negative d-c bus and having a controlled a-c output, a motor driven by said a-c output of said PWM inverter, a ground wire extending from said motor, and a current sensor for measuring the common mode current in said drive circuit in said ground wire, said current sensor producing an output current related to said common mode current;said active filter comprising a first and second transistor, each having first and second main electrodes and a control electrode, and at least one first buffer amplifier; said first electrode of said first and second transistor coupled to a common node, said second electrodes of said first and second transistors being coupled to said positive d-c bus and said negative d-c respectively; said at least one first buffer amplifier having an input coupled to said output of said current sensor and an output connected to at least one of said control electrodes; and a d-c isolating capacitor connecting said common node of said first electrode of said first and second transistors to said ground wire, said current sensor being coupled such that the current sensor is in a current loop comprising said active filter, said d-c bus, said PWM inverter, said motor, said ground wire and said capacitor.