Hybrid filter for reducing distortion in a power system
First Claim
1. An apparatus for reducing distortion currents present in an alternating current power system supplying power to a load, the apparatus comprising:
- a passive filter operably connected to the power system across the load;
an active filter; and
switching means for selectively connecting the passive filter to the active filter to form a series combination, the switching means further operably connecting the series combination to the power system across the load.
1 Assignment
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Accused Products
Abstract
An apparatus and method for reducing distortion currents present in an alternating current power system supplying power to a load which includes a passive filter and an active filter. In a first embodiment, the passive filter is operably connected to the power system across the load by a switching device. An active filter is then connected across the switching device and operated to draw a current equal to the current through the passive filter. The active filter and the passive filter are thereby connected in series across the load. The active filter is controlled to draw a fundamental frequency component and to provide distortion currents required by the load. In a second embodiment, the active filter is connected in parallel with a first circuit, the parallel combination of which is connected in series with a second circuit across the load. Besides providing distortion currents required by the load, the active filter is controlled to draw a current substantially in phase with the voltage across it in order to provide damping.
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Citations
22 Claims
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1. An apparatus for reducing distortion currents present in an alternating current power system supplying power to a load, the apparatus comprising:
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a passive filter operably connected to the power system across the load; an active filter; and switching means for selectively connecting the passive filter to the active filter to form a series combination, the switching means further operably connecting the series combination to the power system across the load. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. An apparatus for reducing distortion currents present in an alternating current power system supplying power to a load, the apparatus comprising:
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a passive filter; an active filter; first switching means for selectively connecting the passive filter to the power system across the load; second switching means for selectively connecting the passive filter to the active filter to form a series combination, the second switching means further operably connecting the series combination to the power system across the load; and a controller connected to the first switching means and the second switching means to control the first switching means and the second switching means. - View Dependent Claims (11)
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12. A method for connecting a passive filter and an active filter across a load on an alternating current power system, the method comprising:
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connecting a passive filter across the load with a switching device and an active filter in parallel with the switching device; and operating the active filter to draw a current substantially equal to a current through the passive filter. - View Dependent Claims (13, 14, 15, 16)
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17. An apparatus for reducing distortion currents present in an alternating current power system supplying power to a load, the alternating current power system having a fundamental frequency, the apparatus comprising:
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a first circuit having an impedance at the fundamental frequency that is greater than an impedance at any harmonic of the fundamental frequency; a second circuit having an impedance at the fundamental frequency that is less than an impedance at any harmonic of the fundamental frequency; and an active filter connected in parallel with the second circuit, the active filter drawing a current substantially in phase with a voltage at a selected frequency and providing a distortion current to the load. - View Dependent Claims (19, 20)
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18. A method for reducing distortion currents in an alternating current power system supplying power to a load, the alternating current power system having a fundamental frequency, the method comprising:
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connecting a circuit to the power system, the circuit comprising a first circuit component having an impedance at the fundamental frequency that is greater than an impedance at any harmonic of the fundamental frequency connected to a second circuit component having an impedance at the fundamental frequency that is less than an impedance at any harmonic of the fundamental frequency, and an active filter connected in parallel with the second circuit component; and operating the active filter to draw a current substantially in phase with a voltage at a selected frequency. - View Dependent Claims (21, 22)
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Specification