Method and apparatus for estimating a phase error between two independent timebases
AssigneeSquare D Company
InventorsPaul R. Buda, Jonathan H. Bailey
Life of this patent
Estimating the term…
Abstract
A phase control system has a stable timebase phase reference generated by an internal phase reference generator which has improved transient response in the presence of spurious noise generated by other external equipment coupled to the same voltage source. A digital phase comparator estimates a phase error between the timebase phase reference and the voltage source. The internal phase reference generator constructs the timebase using a normalized difference between the volt-time-areas between two adjacent quadrants of the internal timebase phase reference. This allows corrections to the phase reference generator to be made on the next cycle of the phase reference generator based on the error estimate of the present cycle.
Claims20
A method for generating a closed loop feedback phase error signal between an AC line voltage source and an internal timebase phase reference which is used to provide phase angle firing control, the internal timebase phase reference having a nominal frequency that is twice the AC line frequency, the method comprising:
- A. measuring a volt-time-area of the AC line voltage source between two adjacent half cycles of the timebase phase reference;
- B. subtracting the two adjacent half-cycle volt-time-areas measurements from each other to provide a difference;
- C. normalizing the difference by dividing the difference by the sum of the two adjacent half cycles volt-time-areas measurements;
- and
- D. multiplying the normalized difference by a scaling factor to create the estimate of the phase error.
A method for generating a closed loop feedback phase error signal between an AC line voltage source and an internal timebase phase reference, the method comprising:
- A. generating the internal timebase phase reference at a nominal frequency that is twice the AC line frequency;
- B. measuring the volt-time-area of the AC line voltage source between two adjacent half cycles of the timebase phase reference;
- C. subtracting the two half-cycle volt-time-areas measurements from each other to provide a difference;
- D. normalizing the difference by dividing the difference by the sum of the two adjacent half cycles volt-time-areas measurements;
- E. multiplying the normalized difference by a scaling factor to create the estimate of the phase error;
- and
- F. compensating the internal timebase phase reference for reducing the phase error to synchronize the timebase phase reference with the AC line voltage.
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 firing commands for switching the AC line voltage at predetermined phase angles to provide a phase angle controlled output, the closed loop control comprising:
- A. a phase reference generator for generating the timebase phase reference at a nominal frequency of twice the AC line frequency;
- B. an integrator for determining the volt-time-area of the AC line voltage source between two adjacent half cycles of the timebase phase reference;
- C. a subtractor for subtracting the two half-cycle volt-time-areas measurements from each other to provide a difference signal;
- D. an adder for adding the two half-cycle volt-time-areas measurements to provide a summation signal;
- E. an error generator for generating and normalizing an estimated phase error by multiplying the difference signal by a scaling factor and dividing by the summation signal to create the phase error between the measured AC line voltage relative phase angle and the timebase phase reference;
- and
- F. a compensator for reducing the phase error in the internal timebase phase reference to synchronize the timebase phase reference with the AC line voltage.
Dependencies are inferred from the claim text.