EMI reduction circuit
AssigneeSundstrand Corporation
InventorTimothy F. Glennon
Life of this patent
Estimating the term…
Abstract
Prior types of power conversion circuits for converting AC power into DC power have generated large amounts of undesirable electromagnetic interference (EMI) due to the rectification of the AC power. Such EMI has been reduced in the past by large and heavy filters which have undesirably increased the size and weight of such conversion circuits. In order to overcome this problem, a harmonic reduction circuit according to the present invention includes a current sensor for sensing the current in the AC lines, circuitry for developing a pulse width modulated (PWM) waveform having a duty cycle dependent upon the sensed AC line current and a switching circuit coupled to the AC power line and controlled by the PWM waveform developing circuitry for compensating the AC line current whereby undesired harmonics therein are reduced.
Claims25
In an AC/DC converter having a rectifier circuit for rectifying AC power from a power source carried by an AC power line to produce DC power, a harmonic reduction circuit for reducing harmonics in the AC power caused by operation of the rectifier circuit, comprising:
- means for sensing the current in the AC power line;
- means for developing a pulse width modulated (PWM) waveform having a duty cycle dependent upon the sensed AC line current;
- and
- a switching circuit including a transformer having a secondary winding coupled to the AC power line between the power source and the rectifier and a primary winding coupled to at least one switch, the switch being controlled by the PWM waveform developing means for compensating the AC line current whereby undesired harmonics therein are reduced.
An electromagnetic interference (EMI) reduction circuit for reducing harmonics in AC power carried on a power line caused by rectification of the AC power by a rectifier circuit, comprising:
- first means for developing a current signal representing the current carried by the AC power line;
- second means coupled to the first developing means for developing an error signal from the current signal;
- means coupled to the second developing means for deriving compensating current from the error signal;
- and
- means coupled to the deriving means and to the power line for combining the compensating current with the AC current to reduce the harmonics therein.
An electromagnetic interference (EMI) reduction circuit for reducing harmonics in N-phase AC power carried on a set of power lines caused by rectification of the N-phase AC power by a rectifier circuit, comprising:
- first means for developing a set of N current signals representing the current in each of the power lines;
- second means coupled to the first developing means for developing a set of N pulse width modulated (PWM) waveforms from the set of current signals, each waveform having a duty cycle dependent upon the current in an associated one of the power lines, the second developing means including N reference sine wave generating means, N summing junctions each having an input coupled to the output of a reference sine wave generator, a further input which receives one of the current signals and an output which develops an error signal, the PWM waveforms being derived from the error signals;
- and
- a plurality of switching circuits, each of which is coupled to an AC power line and controlled by the PWM waveform associated with such power line for compensating the AC line current whereby undesired harmonics therein are reduced.
An electromagnetic interference (EMI) reduction circuit for reducing harmonics in N-phase AC power carried on a set of power lines caused by rectification of the N-phase AC power by a rectifier circuit, comprising:
- first means for developing a set of N current signals representing the current in each of the power lines;
- second means coupled to the first developing means for developing a set of N pulse width modulated (PWM) waveforms from the set of current signals, each waveform having a duty cycle dependent upon the current in an associated one of the power lines, the second developing means including means for generating a reference sine wave, N-1 phase shifters coupled to the reference sine wave generating means for developing N-1 phase-shifted versions of the reference generator output, wherein the reference sine wave generating means and the phase shifters together generate a succession of N reference sine waves each displaced 2.pi./N electrical degrees with respect to successive reference sine waves and N summing junctions each receiving one of the succession of N reference sine waves and a current signal so that the summing junctions develop N error signals which are used to derive the N PWM waveforms;
- and
- a plurality of switching circuits, each of which is coupled to an AC power line and controlled by the PWM waveform associated with such power line for compensating the AC line current whereby undesired harmonics therein are reduced.
An electromagnetic interference (EMI) reduction circuit for reducing harmonics in N-phase AC power carried on a set of power lines caused by rectification of the N-phase AC power by a rectifier circuit, comprising:
- first means for developing a set of N current signals representing the current in each of the power lines;
- second means coupled to the first developing means for developing a set of N pulse width modulated (PWM) waveforms from the set of current signals, each having a duty cycle dependent upon the current in an associated one of the power lines;
- and
- a plurality of switching circuits, each of which is coupled to an AC power line and controlled by the PWM waveform associated with such power line for compensating the AC line current whereby undesired harmonics therein are reduced, each switching circuit including a transformer and a pair of switches, the transformer having a primary winding including two ends each coupled to the output of the rectifier circuit and a secondary winding coupled to one of the AC power lines.
Dependencies are inferred from the claim text.