Ripple rejection filter
First Claim
Patent Images
1. A ripple rejection filter for filtering ripple from a signal in a phase-control system having an adjustable firing point, the filter comprising:
- (a) first filter means shaving an input for receiving a signal to be filtered and having an output for providing a filtered signal according to a low pass characteristic and a first filter means time constant;
(b) firing point synchronized sampling means having an input connected to the signal to be filtered and having an output for providing a sampled signal sampled in synchronism with a firing point of a phase control system in which the ripple rejection filter is operating;
(c) second filter means for receiving the sampled signal and for providing a filtered representation of the sampled signal according to a high pass characteristic with an effective time constant substantially equal to the first filter means time constant; and
(d) combining means for combining the signals provided by the first and second filter means such that the resulting signal is representative of the signal to be filtered with the ripple substantially rejected.
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Abstract
A ripple rejection filter for removing the fundamental frequency of load voltage from control signals in closed-loop phase controlled systems operating from an AC power source. A low-pass filter is connected in parallel with a firing point synchronized sample and hold and high-pass filter series combination. The output of the low-pass and high-pass filters are combined to produce a resulting signal representative of an input signal but with ripple rejected.
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Citations
39 Claims
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1. A ripple rejection filter for filtering ripple from a signal in a phase-control system having an adjustable firing point, the filter comprising:
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(a) first filter means shaving an input for receiving a signal to be filtered and having an output for providing a filtered signal according to a low pass characteristic and a first filter means time constant; (b) firing point synchronized sampling means having an input connected to the signal to be filtered and having an output for providing a sampled signal sampled in synchronism with a firing point of a phase control system in which the ripple rejection filter is operating; (c) second filter means for receiving the sampled signal and for providing a filtered representation of the sampled signal according to a high pass characteristic with an effective time constant substantially equal to the first filter means time constant; and (d) combining means for combining the signals provided by the first and second filter means such that the resulting signal is representative of the signal to be filtered with the ripple substantially rejected. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17)
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18. A method of filtering a signal in a system having a firing point for phase control of power from an alternating current source, the method comprising:
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(a) passing the signal to be filtered through an analog low pass filter having a long time constant to provide an analog filtered signal; (b) simultaneously passing the signal to be filtered through a sampling switch synchronized to the phase control firing point to provide a sampled signal; (c) passing the sampled signal through a digital high pass filter having an effective time constant equal to the time constant of the analog low pass filter to provide a digital filtered signal; and (d) adding the analog filtered signal and digital filtered signal together to provide an output signal representative of the signal to be filtered with ripple attributable to the alternating current source substantially attenuated. - View Dependent Claims (19, 20, 21)
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22. A combined analog and digital filter for filtering a predetermined ripple frequency from a signal, the filter comprising:
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(a) an analog filter having an input, an output and a low pass characteristic time constant; (b) a sampler synchronized in frequency to a predetermined ripple frequency and having an input connected in parallel with the analog filter input and having an output for providing a sampled signal; (c) a digital filter having an input connected in series with the sampler output, an output, and a high pass characteristic time constant equal to the low pass characteristic time constant of the analog filter; (c) means for combining the outputs of the analog and digital filters into a resulting output representative of an input signal but with the predetermined ripple frequency component substantially reduced. - View Dependent Claims (23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34)
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35. A ripple rejection filter comprising:
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(a) an input port for receiving an input signal with a fixed frequency ripple; (b) analog filter means connected to input port and having a series resistance and a shunt capacitance for providing a filtered signal corresponding to the low frequency components of the input signal; (c) sampler means connected to the input port and sampling at a frequency having an average value equal to the fixed frequency of the ripple for providing a sampled signal; (d) digital filter means connected to the sampler means for providing a filtered representation for the sampled signal corresponding to the high frequency components of the input signal; (e) combining means for combining the filtered signal from the analog filter means and the filtered representation of the sampled signal from the digital filter means and for providing an output signal representative of the input signal with the ripple attentuated. - View Dependent Claims (36, 37, 38)
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39. A ripple rejection filter in combination with a phase control system comprising:
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(a) a phase control system having an adjustable firing point in each phase; (b) first filter means having an input for receiving signal to be filtered and having an output for providing a filtered signal according to a low pass characteristic and a first filter means time constant; (c) firing point synchronized sampling means having an input connected to the signal to be filtered and having an output for providing a sampled signal sampled in synchronism with the firing point in each phase of the phase control system; (d) second filter means for receiving the sampled signal and for providing a filtered representation of the sampled signal according to a high pass characteristic with an effective time constant substantially equal to the first filter means time constant; and (e) combining means for combining the signals provided by the first and second filter means such that the resulting signal is representative of the signal to be filtered with the ripple substantially rejected.
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Specification