THAT WHICH IS CLAIMED:

1. A method comprising:

recursively computing respective phasor values from respective ones of a series of signal samples for a node of a power system such that each phasor value is computed from a previously computed phasor value; and

recursively computing frequency values from the phasor values for respective ones of the signal samples.

2. The method of claim 1, wherein recursively computing frequency values comprises:

computing respective phase angle values from respective ones of the phasor values; recursively computing coefficient values for a polynomial that fits the phase angle values; and

recursively computing the frequency values from the coefficient values.

3. The method of claim 1, wherein recursively computing frequency values comprises:

computing a first phase angle value from a first phasor value for a first sample; computing a first value for a coefficient of a polynomial that fits the phase angle value from the first phase angle value;

computing a first frequency value for the first sample from the first value for the coefficient;

computing a second phase angle value for a second phasor value for a second sample; computing a second value for the coefficient from the second phase angle value; and computing a second frequency value for the second sample from the second value for the coefficient and the first frequency value.

4. The method of claim 1, wherein recursively computing frequency values is preceded by:

computing a plurality of phasor values from a set of signal samples;

computing a plurality of phase angle values from the plurality of phasor values; and computing a frequency value from the plurality of phase angle values.

5. The method of claim 1, further comprising filtering the frequency values to generate a filtered frequency value.

6. The method of claim 1, wherein the samples are generated at a sampling rate and wherein the phasor values and the frequency values are produced at a rate that is the same as the sampling rate.

7. An apparatus configured to perform the method of claim 1.

8. A computer readable medium having computer instructions embodied therein that, when executed on a data processing device, perform the method of claim 1.

9. A method comprising:

computing a plurality of first phase angle values from a plurality of first signal samples; computing a first value for a coefficient of a polynomial that fits the first phase angle values;

computing a first frequency value from the first value for the coefficient; computing a second phase angle value from a second signal sample;

computing a second value for the coefficient from the first value for the coefficient and the second phase angle value; and

computing a second frequency value from the second value for the coefficient.

10. The method of claim 9, wherein computing the plurality of first phase angle values comprises:

recursively computing a plurality of first phasor values for respective ones of the first signal samples such that each of the first phasor values is computed from a previously computed one of the first phasor values; and

computing the plurality of first phase angle values from the first phasor values.

11. The method of claim 10, wherein computing the second phase angle value from the second signal sample comprises:

computing a second phasor value from one of the first phasor values and the second sample; and

computing the second phase angle value from the second phasor value.

12. The method of claim 10, wherein recursively computing the plurality of first phasor values for respective ones of the first signal samples is preceded by computing an initial phasor value from an initial plurality of signal samples using a discrete Fourier transform (DFT) and wherein recursively computing the plurality of first phasor values for respective ones of the first signal samples comprises computing a first one of the first phasor values from the initial phasor value.

13. The method of claim 9, further comprising:

computing a third phase angle value from a plurality of third signal samples; computing a third value for the coefficient from the second value for the coefficient and the third phase angle value; and

computing a third frequency value from the third value for the coefficient.

14. The method of claim 9, wherein the phase angle values and the frequency values are produced at a rate at which the samples are generated.

15. An apparatus configured to perform the method of claim 9.

16. A computer readable medium having computer instructions embodied therein that, when executed on a data processing device, perform the method of claim 9.

17. An apparatus comprising:

a sensor circuit coupled to a node of an electrical power system and configured to generate a series of samples of a signal at the node; and

a data processor configured to recursively compute respective phasor values from respective ones of a series of signal samples for the node such that each phasor value is computed from a previously computed phasor value and to recursively compute frequency values from the phasor values for respective ones of the signal samples.

18. The apparatus of claim 17, wherein the data processor is configured to recursively compute the frequency values by:

computing respective phase angle values from respective ones of the phasor values; recursively computing coefficient values for a polynomial that fits the phase angle values; and

computing the frequency values from the coefficient values.

19. The apparatus of claim 17, wherein the data processor recursively computes frequency values by:

computing a first phase angle value from a first phasor value for a first sample; computing a first value for a coefficient of a polynomial that fits the phase angle value; computing a first frequency value for the first sample from the first value for the coefficient;

computing a second phase angle value for a second phasor value for a second sample; computing a second value for the coefficient from the second phase angle value; and computing a second frequency value for the second sample from the second value for the coefficient.

20. The apparatus of claim 17, wherein the sensor generates the samples at a sampling rate and wherein the data processor produces the phasor values and the frequency values at a rate that is the same as the sampling rate.