Active filter for reduction of common mode current

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, 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, said first electrode of said first and second transistor coupled to a common node, said second electrodes of said first and second transistors being connected to said positive d-c bus and said negative d-c bus respectively;
• 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 comprising a differential current transformer having first and second windings connected in series with said positive and negative d-c busses respectively and an output winding for producing said output current related to said common mode current;
• said
• output winding being coupled to said control electrodes;
• said active filter comprising a circuit having an architecture comprising a feed forward system with unity amplification by said current transformer and said transistors, 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.

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, 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, said first electrode of said first and second transistor coupled to a common node, said second electrodes of said first and second transistors being connected to said positive d-c bus and said negative d-c respectively;
• said current sensor output coupled 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;
• and a headroom voltage control circuit coupled to said first and second transistors for maintaining sufficient voltage between the first and second electrodes of said transistors to permit linear amplification operation of said transistors over substantially the full rectified cycle of said a-c source, 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.

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, 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, 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 bus respectively;
• said current sensor output being coupled to at least one of said control electrodes;
• a d-c isolating capacitor connecting said common node of said first electrode of said first and second transistors to said ground wire;
• and a reduced voltage filter bus coupled to said d-c bus;
• said second electrode of said first transistor being connected to said reduced voltage filter bus, and wherein said reduced voltage filter bus has a reduced positive voltage bus and a reduced negative voltage bus, one of said reduced positive voltage bus and said reduced negative voltage bus being connected in common with a corresponding one of said positive d-c bus and negative d-c bus, 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.

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, 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, said first electrode of said first and second transistor coupled to a common node, said second electrodes of said first and second transistors being connected to said positive d-c bus and said negative d-c bus respectively;
• 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 comprising a differential current transformer sensing current in said ground wire and producing an output current related to said common mode current;
• said output current being supplied to said control electrodes;
• said active filter comprising a circuit having an architecture comprising a feed forward system with unity amplification by said current transformer and said transistors, 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.

An active filter for reducing a common mode current in a pulse width modulated drive circuit for 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 for driving the load, a ground wire extending from said load, 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 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 load, said ground wire and said capacitor.

An active filter for reducing a common mode current in a pulse width modulated drive circuit for 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 for driving the load, 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, said first electrode of said first and second transistor coupled to a common node, said second electrodes of said first and second transistors being connected to said positive d-c bus and said negative d-c bus respectively;
• 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 comprising a differential current transformer having first and second windings connected in series with said positive and negative d-c busses respectively and an output winding for producing said output current related to said common mode current;
• said output winding being coupled to said control electrodes;
• said active filter comprising a circuit having an architecture comprising a feed forward system with unity amplification by said current transformer and said transistors, 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 load, said ground wire and said capacitor.

An active filter for reducing a common mode current in a pulse width modulated drive circuit for 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 for driving the load, 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, 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 current sensor output coupled 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;
• and a headroom voltage control circuit coupled to said first and second transistors for maintaining sufficient voltage between the first and second electrodes of said transistors to permit linear amplification operation of said transistors over substantially the full rectified cycle of said a-c source, 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 load, said ground wire and said capacitor.

An active filter for reducing a common mode current in a pulse width modulated drive circuit for 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 for driving the load, 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, 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 bus respectively;
• said current sensor output being coupled to at least one of said control electrodes;
• a d-c isolating capacitor connecting said common node of said first electrode of said first and second transistors to said ground wire;
• and a reduced voltage filter bus coupled to said d-c bus;
• said second electrode of said first transistor being connected to said reduced voltage filter bus, and wherein said reduced voltage filter bus has a reduced positive voltage bus and a reduced negative voltage bus, one of said reduced positive voltage bus and reduced negative voltage bus being connected in common with a corresponding one of said positive d-c bus and negative d-c bus, 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 load, said ground wire and said capacitor.

An active filter for reducing a 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 for driving the load, 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, said first electrode of said first and second transistor coupled to a common node, said second electrodes of said first and second transistors being connected to said positive d-c bus and said negative d-c bus respectively;
• 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 comprising a current transformer sensing current in said ground wire and producing an output current related to said common mode current;
• said output current being supplied to said control electrodes;
• said active filter comprising a circuit having an architecture comprising a feed forward system with unity amplification by said current transformer and said transistors, 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 load, said ground wire and said capacitor.

An active filter for reducing a common mode current in a pulse width modulated drive circuit for 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 for driving the load, 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, said first electrode of said first and second transistor coupled to a common node, said second electrodes of said first and second transistors being connected to said positive d-c bus and said negative d-c bus respectively;
• 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 comprising a differential current transformer having first and second windings connected in series with said positive and negative d-c busses respectively and an output winding for producing said output current related to said common mode current;
• said output winding being coupled to said control electrodes;
• said active filter comprising a circuit having an architecture comprising a feed forward system;
• 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 load, said ground wire and said capacitor;
• said feed forward system comprising said current transformer having said first and second windings connected in series with said positive and negative d-c buses, respectively, whereby said first and second windings are disposed between said active filter and said PWM inverter.

An active filter for reducing a 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 for driving the load, 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, said first electrode of said first and second transistor coupled to a common node, said second electrodes of said first and second transistors being directly connected to said positive d-c bus and said negative d-c bus respectively;
• 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 comprising a current transformer sensing current in said ground wire and producing an output current related to said common mode current;
• said output current being supplied to said control electrodes;
• said active filter comprising a circuit having an architecture comprising a feed forward system;
• 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 load, said ground wire and said capacitor;
• said feed forward system comprising said current transformer having a primary disposed in said ground wire between said load and a connection of said isolating capacitor to said ground wire.