A frequency measurement device includes a sampling unit that outputs a voltage sampling value in accordance with a voltage to be sampled and a sampling frequency; an single-cycle DFT angle shift computation unit that computes and outputs a first angle shift in accordance with the voltage sampling value; an multi-cycle DFT angle shift computation unit that computes and outputs a second angle shift in accordance with the voltage sampling value; a selection unit that selects and outputs one of the first and second angle shifts as a selected angle offset; a sampling frequency computation and outputting unit that computes a sampling frequency in accordance with the selected angle offset and outputs the same to the sampling module unit as a new sampling frequency; and a frequency measurement value computation and outputting unit that computes and outputs a frequency measurement value in accordance with the selected angle offset.

A frequency measurement device includes a sampling unit that outputs a voltage sampling value in accordance with a voltage to be sampled and a sampling frequency; an single-cycle DFT angle shift computation unit that computes and outputs a first angle shift in accordance with the voltage sampling value; an multi-cycle DFT angle shift computation unit that computes and outputs a second angle shift in accordance with the voltage sampling value; a selection unit that selects and outputs one of the first and second angle shifts as a selected angle offset; a sampling frequency computation and outputting unit that computes a sampling frequency in accordance with the selected angle offset and outputs the same to the sampling module unit as a new sampling frequency; and a frequency measurement value computation and outputting unit that computes and outputs a frequency measurement value in accordance with the selected angle offset.

A system frequency detector includes an orthogonal coordinate signal generator generating an orthogonal two-phase voltage signal from a three-phase voltage signal of three-phase alternating current power by converting the three-phase voltage signal into a two-phase voltage signal orthogonal to the three-phase voltage signal, converting the two-phase voltage signal into a voltage signal of a rotating coordinate system, calculating a moving average of the voltage signal of the rotating coordinate system, and performing an inverse transformation of the voltage signal of the rotating coordinate system after calculating the moving average. A frequency calculator calculates an angular frequency based on the two-phase voltage signal, and an arithmetic unit calculates a system frequency of the power system from the angular frequency. The frequency calculator includes a rate limiter in series with the arithmetic unit, the rate limiter limiting a change of the system frequency equal to or greater than a prescribed change rate.

Apparatus and methods for phase tracking an oscillatory signal are provided. In one arrangement, an input signal is received. First and second reference oscillatory signals are received at the frequency of a target frequency component of the input signal. The first and second reference oscillatory signals are phase shifted relative to each other. Weights of a weighted sum of the first and second reference oscillatory signals are iteratively varied to match the weighted sum to the input signal. The weights of the matched weighted sum are used to provide real time estimates of the phase of the target frequency component of the input signal.

A system frequency detector includes an orthogonal coordinate signal generator generating an orthogonal two-phase voltage signal from a three-phase voltage signal of three-phase alternating current power of a power system by converting the three-phase voltage signal into a two-phase voltage signal orthogonal to the three-phase voltage signal, converting the two-phase voltage signal into a voltage signal of a rotating coordinate system, calculating a moving average of the voltage signal of the rotating coordinate system, and performing an inverse transformation of the voltage signal of the rotating coordinate system after calculating the moving average; and a frequency calculator including an angular frequency calculator calculating an angular frequency of the power system based on the two-phase voltage signal, and an arithmetic unit calculating a system frequency of the power system from the angular frequency, the frequency calculator further including a low-pass filter provided in series with the arithmetic unit.

A frequency detection circuit includes: a first signal source for outputting a first clock signal; a second signal source for outputting a second clock signal having the same frequency as but a different phase from those of the first clock signal; a first sample hold circuit for undersampling a reception signal using the first clock signal; a second sample hold circuit for undersampling the reception signal using the second clock signal; and a frequency calculating circuit for calculating the frequency of the reception signal using a phase difference between output signals of the first sample hold circuit and the second sample hold circuit.

An apparatus may include one or more measurement sensors, which may measure power coupled to one or more process stations of the apparatus. The apparatus may additionally include one or more analog-to-digital converters coupled to an output port of a corresponding one of the one or more measurement sensors, which may provide a digital representation of a RF signal measured by the one or more measurement sensors. A processor, coupled to a memory, may determine a crossing of the digital representation of the signal with a reference signal level and may thus determine a frequency content of the RF signal and the characteristic, which may permit the nulling out of phase lag of the one or more measurement sensors.

An apparatus may include one or more measurement sensors, which may measure power coupled to one or more process stations of the apparatus. The apparatus may additionally include one or more analog-to-digital converters coupled to an output port of a corresponding one of the one or more measurement sensors, which may provide a digital representation of a RF signal measured by the one or more measurement sensors. A processor, coupled to a memory, may determine a crossing of the digital representation of the signal with a reference signal level and may thus determine a frequency content of the RF signal and the characteristic, which may permit the nulling out of phase lag of the one or more measurement sensors.

A frequency detection circuit includes a signal source that outputs a first clock signal and a second clock signal that has the same frequency as the first clock signal and a different phase from the first clock signal, a S/H circuit that undersamples a frequency-detection target signal using the first clock signal output from the signal source and outputs a first sampling signal indicating a result of undersampling, and undersamples the frequency-detection target signal using the second clock signal output from the signal source and outputs a second sampling signal indicating a result of undersampling, and a frequency calculation circuit that calculates a phase difference between the first sampling signal output from the S/H circuit and the second sampling signal output from the S/H circuit and calculates the frequency of the frequency-detection target signal on the basis of the phase difference.

A frequency detection circuit includes a signal source that outputs a first clock signal and a second clock signal that has the same frequency as the first clock signal and a different phase from the first clock signal, a S/H circuit that undersamples a frequency-detection target signal using the first clock signal output from the signal source and outputs a first sampling signal indicating a result of undersampling, and undersamples the frequency-detection target signal using the second clock signal output from the signal source and outputs a second sampling signal indicating a result of undersampling, and a frequency calculation circuit that calculates a phase difference between the first sampling signal output from the S/H circuit and the second sampling signal output from the S/H circuit and calculates the frequency of the frequency-detection target signal on the basis of the phase difference.