Method and apparatus for compensating phase distortion caused by a high impedance voltage source
First Claim
1. A method for generating an internal timebase phase reference for providing a sequence of phase angle firing signals to couple an AC line voltage source to a load, the method comprising:
- A. generating the internal timebase phase reference;
B. measuring the AC line voltage to determine its phase error relative to the internal timebase phase reference;
C. estimating phase distortion generated by the coupling of the AC line voltage source to the load as a result of the load being energized from the phase angle firing control in the presence of line impedance;
D. adjusting the internal timebase phase reference in response to the estimated phase distortion.
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Abstract
A phase control system has a stable timebase phase reference generated by an internal phase reference generator. The control includes a method for estimating and compensating phase distortion when an inductive load is driven by an AC voltage source having significant line impedance. A digital phase comparator estimates a phase error between the timebase phase reference and the voltage source. At the initialization of the phase control system, the phase reference clock period is frozen for a fixed number of cycles to determine an average phase error due to the phase distortion caused by the line impedance. The estimated phase error is then corrected to account for the average phase distortion error.
58 Citations
19 Claims
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1. A method for generating an internal timebase phase reference for providing a sequence of phase angle firing signals to couple an AC line voltage source to a load, the method comprising:
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A. generating the internal timebase phase reference; B. measuring the AC line voltage to determine its phase error relative to the internal timebase phase reference; C. estimating phase distortion generated by the coupling of the AC line voltage source to the load as a result of the load being energized from the phase angle firing control in the presence of line impedance; D. adjusting the internal timebase phase reference in response to the estimated phase distortion. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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11. The method of claim 10 wherein the phase error is estimated on a present cycle and the internal timebase phase reference is compensated on the next cycle of the AC line voltage.
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12. A closed loop control for reducing a phase error between an AC line voltage source and an internal timebase phase reference which is used to generate a sequence of firing commands for a controller to switch the AC line voltage at predetermined phase angles to provide a phase angle controlled output, the closed loop control comprising:
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A. a phase reference clock for generating the internal timebase phase reference at a nominal frequency of twice the AC line frequency; B. an error estimator for generating an estimated phase error between the AC line voltage and the internal timebase phase reference; C. a phase distortion compensator utilizing the estimated phase error for estimating phase distortion generated by switching the AC line voltage into an inductive load in the presence of line impedance; and D. a phase reference compensator for reducing the phase distortion compensated phase error between the internal timebase phase reference and the AC line voltage to synchronize the phase reference clock with the AC line frequency. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19)
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Specification