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ACTIVE FILTER FOR REDUCTION OF COMMON MODE CURRENT

  • US 20080180164A1
  • Filed: 03/26/2008
  • Published: 07/31/2008
  • Est. Priority Date: 03/28/2000
  • Status: Active Grant
First Claim
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1. An active filter for reducing the common mode current in a pulse width modulated drive circuit driving a load;

  • said 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 load driven by said a-c output of said PWM inverter, a ground wire extending from said load, and a current sensor for measuring the common mode current in said drive circuit, 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 an amplifier circuit driving said transistors;

    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 amplifier circuit having an input coupled to said output of said current sensor and having an output connected to 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; and

    wherein said current sensor is a current transformer having a primary winding connected in series with said ground wire and a secondary winding connected as the signal input to the amplifier circuit.

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