CN114167135A - Voltage and current phase angle discrimination method for power meter - Google Patents
Voltage and current phase angle discrimination method for power meter Download PDFInfo
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- CN114167135A CN114167135A CN202111399033.4A CN202111399033A CN114167135A CN 114167135 A CN114167135 A CN 114167135A CN 202111399033 A CN202111399033 A CN 202111399033A CN 114167135 A CN114167135 A CN 114167135A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R25/00—Arrangements for measuring phase angle between a voltage and a current or between voltages or currents
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R21/00—Arrangements for measuring electric power or power factor
- G01R21/006—Measuring power factor
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R21/00—Arrangements for measuring electric power or power factor
- G01R21/133—Arrangements for measuring electric power or power factor by using digital technique
Abstract
The invention provides a voltage and current phase angle discrimination method for a power meter, and relates to the technical field of electrical parameter measurement. The voltage and current signals are calculated by software to obtain active power P, effective voltage value U and effective current value I, the power factor cos alpha is calculated according to cos alpha (P/(U I)), the current signals are phase-shifted for a sampling period, and a new power factor lambda is calculatedNewCalculating an angular difference beta obtained by folding a sampling period relative to the frequency of the current sine wave signal to be measured, further calculating sin beta and cos beta, calculating sin alpha by utilizing a trigonometric function and a difference angle formula, confirming a specific quadrant where alpha is positioned, and confirming only alpha. Compared with the prior art, the method carries out the phase angle judgment of the voltage and the current by shifting the phase for one sampling period and combining the trigonometric function and the difference angle formula, and abandons the way of identifying the phase by using a sine wave to square wave circuitAnd unnecessary circuits are saved, the material cost is reduced, and the identification precision is improved.
Description
Technical Field
The invention relates to the technical field of electrical parameter measurement, in particular to a voltage and current phase angle judgment method for a power meter.
Background
The power meter is used as a basic instrument for measuring electrical parameters, is widely applied, can simultaneously measure a plurality of electrical parameters, such as voltage effective values, current effective values, power factors and the like, and has an electrical parameter measuring function, namely a middle-high-end power meter can be standardized, namely a phase angle of voltage and current, which is called a voltage current phase angle for short.
The phase angle of the voltage and the current is directly related to the power factor, the power factor is obtained by performing cosine operation on the parameter, but the phase angle cannot be directly obtained by performing inverse cosine operation on the power factor, because the inverse cosine operation can obtain more than one angle, for example, the phase angle of the voltage and the current is 60 degrees, the power factor is 0.5, but the phase angle of the voltage and the current is-60 degrees, and the power factor is also 0.5. That is, the power factor obtained in the case that the voltage leads or lags the current by 60 degrees is 0.5, so that only the absolute value of the phase angle of the voltage and the current can be obtained by only depending on the parameter of the power factor, and the specific leading or lagging cannot be determined. The common method is to amplify the waveforms of the voltage and the current and then convert the amplified waveforms into square waves, and detect the leading or lagging of the square waves in a digital mode as the basis for judging the phases of the voltage and the current. However, this method needs to add extra circuits on one hand, and on the other hand, it is not satisfactory when the frequency of the sine wave is relatively high, because the sine wave introduces new phase errors during the process of converting into square wave due to the frequency response property of the device such as operational amplifier.
Disclosure of Invention
The invention aims to provide a voltage and current phase angle judging method for a power meter, which reduces the design of hardware circuits and improves the phase identification precision.
The specific technical scheme is a voltage and current phase angle discrimination method for a power meter, wherein the voltage and current phase angle is alpha, and a power factor lambda is cos alpha and P/(U I), and the method comprises the following steps:
s100, under the detection condition, the voltage and current signals are calculated by software to obtain active power P, a voltage effective value U and a current effective value I, a power factor cos alpha is calculated according to cos alpha which is P/(U I),
s200, shifting the phase of the current signal by software for a sampling period, obtaining active power P' through software operation of voltage and current after phase shifting, enabling the effective value of the voltage to be still U and the effective value of the current after phase shifting to be still I, and calculating a new power factor lambdaNew，
S300, calculating an angular difference beta obtained by folding a sampling period relative to the frequency of the current sine wave signal to be measured, further calculating sin beta and cos beta,
s400, calculating sin alpha by utilizing a trigonometric function and a difference angle formula, confirming a specific quadrant where alpha is located according to sin alpha and cos alpha signs, and confirming only alpha.
Preferably, in steps S100 and S200, the ADC collects the voltage and current signals and performs software operation.
Preferably, in step S200, one sampling period is 10 microseconds.
Preferably, in S300, the angular difference β is 360 × T/T, T representing the sampling period, and T representing the sine wave period.
Preferably, in step S200, the current signal is phase-shifted backward by one sampling period by software, and the new power factor λ is obtainedNewP'/(U × I), i.e. cos (α + β); in step S400, sin α is calculated using a trigonometric function and an angle formula cos (α + β) ═ cos α cos β -sin α sin β.
Compared with the prior art, the method and the device perform voltage and current phase angle judgment by shifting a phase for a sampling period and combining a trigonometric function and a difference angle formula, abandon the way of identifying the phase by a sine wave-to-square wave circuit, save unnecessary circuits, reduce material cost and improve identification precision.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the invention and, together with the description, serve to explain the invention and not to limit the invention. In the drawings:
FIG. 1 is a schematic diagram of the phase angle of voltage and current in step S100 in example 1;
fig. 2 is a schematic diagram of the voltage and current phase angles after shifting the phase backward by one sampling period in step S200 in embodiment 1.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail with reference to the following embodiments and accompanying drawings. The exemplary embodiments and descriptions of the present invention are provided to explain the present invention, but not to limit the present invention.
The voltage and current phase angle α and the power factor λ are directly related, and the power factor λ is obtained by performing cosine operation on the parameter, and the formula is λ ═ cos α, where λ ═ P/(U × I). In power meter design, the phase difference of voltage and current is calculated according to λ ═ cos α, and α ═ arccos λ can be used for calculation. But since the inverse cosine operation can result in more than one angle, e.g. the phase angle of the voltage and current is 60 degrees and the power factor is 0.5, but the phase angle of the voltage and current is-60 degrees and the power factor is also 0.5. That is, the power factor obtained in the case that the voltage leads or lags the current by 60 degrees is 0.5, so that only the absolute value of the phase angle of the voltage and the current can be obtained by only depending on the parameter of the power factor, and the specific leading or lagging cannot be determined.
A voltage and current phase angle discrimination method for a power meter is disclosed, wherein the voltage and current phase angle is alpha, and a power factor lambda is cos alpha and P/(U I), and the method comprises the following steps:
s100, under the detection condition, the voltage and current signals are calculated by software to obtain active power P, a voltage effective value U and a current effective value I, a power factor cos alpha is calculated according to cos alpha which is P/(U I), a phase difference is calculated by alpha which is arccos lambda, and the voltage lead or lag current cannot be determined at the moment,
s200, shifting the phase of the current signal by software for a sampling period, wherein in one embodiment, the sampling speed is 100ksps, then the sampling period is 10 microseconds, the active power P' is obtained by the software operation of the voltage and the current after the phase shifting, the effective value of the voltage is still U, the effective value of the current after the phase shifting is still I, and then a new power factor lambda is calculatedNew，
S300, calculating an angular difference beta obtained by folding a sampling period relative to the frequency of the current sine wave signal to be measured, further calculating sin beta and cos beta,
s400, calculating sin alpha by utilizing a trigonometric function and a difference angle formula, confirming a specific quadrant where alpha is located according to signs of sin alpha and cos alpha, confirming only alpha, and determining voltage lead or lag current.
In one embodiment, the voltage and current signals are collected by the ADC and then processed by software in steps S100 and S200. The method always uses the signal sampled by the ADC to carry out operation, signal delay of a sine wave-to-square wave circuit does not exist in the operation process, and a new phase error is not generated in the whole process, so that the accuracy of phase identification is ensured.
In one embodiment, in S300, the angular difference β is 360 × T/T, T representing the sampling period, and T representing the sine wave period. When the frequency is 50Hz, the sine wave period T is 20 milliseconds, and when the sampling period T is 10 microseconds, the angular difference beta is calculated by substitution and is 0.18 degrees.
Example 1: a voltage and current phase angle discrimination method for a power meter is disclosed, wherein the voltage and current phase angle is alpha, and cos alpha is P/(U I), and the method comprises the following steps:
s100, under the detection condition, the voltage and current signals are calculated by software to obtain active power P, a voltage effective value U and a current effective value I, cos alpha is calculated according to cos alpha as P/(U I), as shown in figure 1, the phase difference between the voltage effective value U and the current effective value I is alpha,
s200, shifting a phase of a current signal backwards for a sampling period through software, obtaining active power P 'through software operation of voltage and current after phase shifting, enabling a voltage effective value to be still U and enabling a current effective value after phase shifting to be still I, calculating cos (alpha + beta) according to a formula cos (alpha + beta) ═ P'/(U x I), as shown in figure 2, shifting the phase of the current signal backwards for a sampling period on the basis of S100, enabling a phase difference between the voltage effective value U and the current effective value I to be changed into (alpha + beta),
s300, calculating an angular difference beta obtained by folding a sampling period relative to the frequency of the current sine wave signal to be measured, further calculating sin beta and cos beta,
s400, calculating sin alpha by using a trigonometric function and an angular formula cos (alpha + beta) ═ cos alpha × cos beta-sin alpha × sin beta, confirming the specific quadrant where alpha is located according to sin alpha and the signs of cos alpha, confirming only alpha, and determining voltage lead or lag current.
Example 2: unlike embodiment 1, in step S200, the current signal is shifted forward by one sampling period by software, and the new power factor λ is obtainedNewP'/(U × I), i.e. cos (α - β); in step S400, sin α is calculated using a trigonometric function difference angle formula cos (α - β) ═ cos α × cos β + sin α × sin β.
Wherein, for the formula cos α ═ P/(U ═ I) the following is stated:
the voltage and current phase angle α and the power factor λ are directly related, and the power factor λ is obtained by performing cosine operation on the parameter, and the formula is λ ═ cos α, and λ ═ P/(U × I).
And (4) prompting:
(1) u (n) represents a voltage instantaneous value;
(2) i (n) represents a current transient;
(3) n represents the nth measurement interval;
(4) AVG [ ] denotes a simple average of the sampled data in [ ] over the data measurement period.
The sampling and operation process is roughly as follows:
s1, using FPGA as interface unit of CPU and ADC (analog-digital converter), reading ADC sampling digital quantity of voltage signal and current signal respectively and synchronously at 100ksps speed, then generating external interrupt to inform CPU to read;
s2, the CPU obtains the digital quantity and then carries on the corresponding operation, if the voltage signal carries on the root mean square operation to get the voltage effective value U, the current signal carries on the root mean square operation to get the current effective value I, the voltage and the current signal synchronously sample the instantaneous value to multiply and accumulate one by one to get the active power P, the active power P divides the product of the voltage effective value U and the current effective value I to get the power factor Lambda;
s3, multiplying each sampled current instantaneous value with the last sampled voltage instantaneous value and accumulating to obtain new active power, and dividing the new active power by the product of the voltage effective value and the current effective value to obtain a new power factor;
s4, the cosine value of the phase angle can be calculated by using the formula introduced in the above section, and whether the voltage is a leading current or a lagging current is further judged according to the judging method in the application.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention in any way, and any person skilled in the art may modify or modify the technical details disclosed above into equivalent embodiments with equivalent variations. However, any simple modification, equivalent change and modification of the above embodiments according to the technical essence of the present invention are within the protection scope of the technical solution of the present invention.
Claims (5)
1. A voltage and current phase angle discrimination method for a power meter is disclosed, wherein the voltage and current phase angle is alpha, and a power factor lambda is cos alpha and P/(U I), and the method is characterized by comprising the following steps:
s100, under the detection condition, the voltage and current signals are calculated by software to obtain active power P, a voltage effective value U and a current effective value I, a power factor cos alpha is calculated according to cos alpha which is P/(U I),
s200, shifting the phase of the current signal by software for a sampling period, obtaining active power P' through software operation of voltage and current after phase shifting, enabling the effective value of the voltage to be still U and the effective value of the current after phase shifting to be still I, and calculating a new power factor lambdaNew，
S300, calculating an angular difference beta obtained by folding a sampling period relative to the frequency of the current sine wave signal to be measured, further calculating sin beta and cos beta,
s400, calculating sin alpha by utilizing a trigonometric function and a difference angle formula, confirming a specific quadrant where alpha is located according to sin alpha and cos alpha signs, and confirming only alpha.
2. The method of claim 1, wherein the ADC collects voltage and current signals and performs software operation in steps S100 and S200.
3. The method of claim 1, wherein in step S200, a sampling period is 10 μ S.
4. The method of claim 1, wherein in step S300, the angular difference β is 360 × T/T, T represents a sampling period, and T represents a sine wave period.
5. The method of claim 1, wherein in step S200, the current signal is phase-shifted backward by one sampling period by software, and the new power factor λ is determinedNewP'/(U × I), i.e. cos (α + β); in step S400, sin α is calculated using a trigonometric function and an angle formula cos (α + β) ═ cos α cos β -sin α sin β.
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