ACTIVE FILTER FOR REDUCTION OF COMMON MODE CURRENT
First Claim
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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Accused Products
Abstract
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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Citations
18 Claims
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1. An active filter for reducing the common mode current in a pulse width modulated drive circuit driving a load;
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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; andwherein 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. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. An active filter for reducing the common mode current in a pulse width modulated drive circuit driving a load;
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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;further including a reduced voltage positive filter bus coupled to said d-c bus;
said second electrodes of said first and second transistors being connected to said reduced voltage positive filter d-c bus and said negative d-c bus respectively.
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9. An active filter for reducing the common mode current in a pulse width modulated drive circuit driving a load;
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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; andwherein said amplifier circuit has at least first and second power supply inputs, and a power supply circuit for applying bias voltages to said amplifier circuit inputs;
said power supply circuit comprising first and second current sources and first and second zener diodes;
the anode of said first zener diode connected to the cathode of said second zener diode at a first node;
said cathode of said first zener diode connected to one terminal of said first current source;
said anode of said second zener diode connected to one terminal of said second current source;
the second terminal of said first and second current sources being coupled to said positive and negative d-c busses respectively;
the node between said first current source and said first zener diode connected to said first power supply input; and
the node between said second current source and said second zener diode connected to said second power supply input.
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10. An active filter for reducing a common mode current in a PWM switched power supply, said power supply comprising an AC source, a rectifier connected to said AC source which produces a rectified output voltage between a positive DC bus and a negative DC bus a PWM inverter having input terminals coupled to said positive DC bus and negative DC bus and having a controlled AC output adapted to be connected to a load device, a ground wire adapted for connection to the load device, and a current sensor which measures a common mode current, and produces an output current related to the common mode current;
said active filter comprising; first and second transistors, each having first and second electrodes providing a controlled current path and a control electrode, and a DC isolating capacitor, wherein; said first electrodes of said first and second transistors are connected to a common node; said second electrodes of said first and second transistors are connected to said positive DC bus and said negative DC respectively; said DC isolating capacitor is connected between said common node and said ground wire; and said current sensor output is coupled to at least one of said control electrodes; 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 AC source; further including a reduced voltage positive filter bus coupled to said DC bus;
said second electrodes of said first and second transistors being connected to said reduced voltage positive filter DC bus and said negative DC bus respectively.- View Dependent Claims (11, 12)
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13. An active filter for reducing a common mode current in a PWM switched power supply, said power supply comprising an AC source, a rectifier connected to said AC source which produces a rectified output voltage between a positive DC bus and a negative DC bus a PWM inverter having input terminals coupled to said positive DC bus and negative DC bus and having a controlled AC output adapted to be connected to a load device, a ground wire adapted for connection to the load device, and a current sensor which measures a common mode current, and produces an output current related to the common mode current;
said active filter comprising; first and second transistors, each having first and second electrodes providing a controlled current path and a control electrode, and a DC isolating capacitor, wherein; said first electrodes of said first and second transistors are connected to a common node; said second electrodes of said first and second transistors are connected to said positive DC bus and said negative DC respectively; and said DC isolating capacitor is connected between said common node and said ground wire; and said current sensor output is coupled to at least one of said control electrodes; and a reduced voltage filter bus coupled to said DC bus; and
further wherein;said second electrode of said first transistor is connected to said reduced voltage filter bus; said reduced voltage filter bus has a reduced positive voltage bus and a reduced negative voltage bus; and one of said reduced positive voltage bus and said reduced negative voltage bus is connected in common with a corresponding one of said positive DC bus and said negative DC bus. - View Dependent Claims (14, 15)
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16. An active filter for reducing a common mode current in a PWM switched power supply, said power supply comprising an AC source, a rectifier connected to said AC source which produces a rectified output voltage between a positive DC bus and a negative DC bus a PWM inverter having input terminals coupled to said positive DC bus and negative DC bus and having a controlled AC output adapted to be connected to a load device, a ground wire adapted for connection to the load device, and a current sensor which measures a common mode current, and produces an output current related to the common mode current;
said active filter comprising; first and second transistors, each having first and second electrodes providing a controlled current path and a control electrode, and a DC isolating capacitor, wherein; said first electrodes of said first and second transistors are connected to a common node; said second electrodes of said first and second transistors are connected to said positive DC bus and said negative DC respectively; said DC isolating capacitor is connected between said common node and said ground wire; and said current sensor output is coupled to at least one of said control electrodes; and further comprising; a reduced voltage filter bus coupled to said DC bus, wherein; said second electrode of said first transistor is connected to said reduced voltage filter bus; said reduced voltage filter bus has a reduced positive voltage bus and a reduced negative voltage bus; and one of said reduced positive voltage bus and reduced negative voltage bus is connected in common with a corresponding one of said positive DC bus and negative DC bus. - View Dependent Claims (17, 18)
Specification