Single-phase electric reactive power symbol judgment method and system

Abstract

The invention discloses a single-phase electric reactive power symbol judgment method and system, and the method comprises the steps: calculating a current average value Iavg of a current in a corresponding half period when a voltage phase angle cosine value is smaller than 0, if Iavgt; if Iavglt is greater than 0, the reactive power is greater than 0; if not, the reactive power is less than 0. The method has the advantages of small calculation amount and high accuracy and reliability of reactive power measurement.

Description

Technical Field

[0001] The invention relates to the field of signal processing, and in particular to a method and system for judging the sign of single-phase reactive power. Background Art

[0002] At present, the judgment of positive and negative single-phase reactive power is realized in the digital signal processor, mainly through the following steps:

[0003] 1. Sampling and preprocessing

[0004] First, the DSP's A / D converter is used to synchronously sample the voltage and current of the single-phase power to ensure the accuracy and synchronization of the sampling points. The sampled data needs to be preprocessed, such as filtering and denoising, to improve the accuracy of subsequent calculations.

[0005] 2. Calculate the fundamental components of voltage and current

[0006] Next, the preprocessed voltage and current signals are processed using algorithms such as fast Fourier transform (FFT) to extract their fundamental components. The fundamental component extraction method is, for example, a real-time measurement method for time-varying power of a power system disclosed in Chinese Patent Publication No. CN102445595A. The fundamental component is the component with the lowest frequency in the signal and is also the main component we need to calculate reactive power.

[0007] 3. Calculate the phase difference

[0008] With the fundamental components of voltage and current, the phase difference between them can be calculated. The phase difference can be obtained by calculating the cross-correlation function of the two signals or using the inverse tangent function. The phase difference reflects the degree of lag or lead of the current relative to the voltage and is the key to reactive power judgment.

[0009] 4. Determine the positive and negative of reactive power

[0010] According to the value of the phase difference, the positive or negative of the reactive power can be determined. Specifically:

[0011] When the current lags behind the voltage (the phase difference is positive), it means that the circuit absorbs reactive power from the external system, and the reactive power is positive at this time.

[0012] When the current leads the voltage (the phase difference is negative), it means that the circuit outputs reactive power to the external system, and the reactive power is negative at this time.

[0013] The above method has the following defects:

[0014] Large amount of calculation: Although algorithms such as Fast Fourier Transform (FFT) are accurate, the amount of calculation is relatively large and has certain requirements on the computing power of DSP.

[0015] High requirements for synchronous sampling: Algorithms such as FFT are based on synchronous sampling, which requires that the signal be intercepted in the entire cycle and sampled at strictly equal intervals, otherwise spectrum leakage will occur, affecting the measurement accuracy.

[0016] Affected by harmonics: Harmonics and non-integer harmonics (interharmonics) in the power grid may interfere with the measurement of reactive power and affect the accuracy of the algorithm.

[0017] Strong hardware dependence: The implementation of the algorithm depends on the performance of hardware platforms such as DSP. Different hardware platforms may have differences, which affects the versatility and stability of the algorithm.

[0018] Based on the above defects, the existing methods and systems for determining the sign of single-phase reactive power generally have the problems of large amount of calculation and low accuracy and reliability of reactive power measurement. Summary of the invention

[0019] The technical problem to be solved by the present invention is that the existing methods and systems for judging the sign of single-phase reactive power generally have the problems of large amount of calculation and low accuracy and reliability of reactive power measurement.

[0020] The present invention solves the above technical problems through the following technical means: a method for determining the sign of single-phase reactive power, the method comprising:

[0021] Calculate the current average value Iavg in the half cycle corresponding to the cosine value of the voltage phase angle being less than 0. If Iavg>0, the reactive power is greater than 0; if Iavg<0, the reactive power is less than 0.

[0022] The present invention only needs to calculate the positive or negative current average value in the half cycle corresponding to the cosine value of the voltage phase angle within one cycle being less than 0, that is, the positive or negative current integral (average value), to determine the positive or negative reactive power. The amount of calculation is small, and no algorithm such as FFT is required to process the signal, so that spectrum leakage will not occur and the measurement accuracy will not be affected. The calculation process does not involve harmonic components and is not affected by harmonics. The accuracy is high, the performance of hardware platforms such as DSP is not dependent on it, and the stability and reliability are strong.

[0023] Furthermore, the current average value Iavg of the current in the half cycle corresponding to the cosine value of the voltage phase angle being less than 0 is calculated by calculating the integral result of the current in the half cycle corresponding to the cosine value of the voltage phase angle being less than 0.

[0024] Furthermore, the method further comprises:

[0025] Assume that the voltage phase is θ, then the cosine value of the voltage phase angle is cosθ. If the integral of the current in the half cycle corresponding to cosθ<0 is greater than 0, the reactive power is greater than 0; if the integral of the current in the half cycle corresponding to cosθ<0 is less than 0, the reactive power is less than 0.

[0026] Furthermore, the phase difference between the current and the voltage is The sine value of the phase difference is The integral result of the current in the half cycle corresponding to cosθ<0 is the sine value of the phase difference The product of the current amplitude and a coefficient term, wherein the coefficient term is a negative number.

[0027] Furthermore, when the integral result is greater than 0, that is, the sine value of the phase difference If the product of the current amplitude and the coefficient term is greater than 0, the sine value of the phase difference is less than 0, and the phase difference between current and voltage is The voltage leads the current, and the reactive power is positive; when the integral result is less than 0, the phase difference is the sine value. If the product of the current amplitude and the coefficient term is less than 0, the sine value of the phase difference is greater than 0, and the phase difference between current and voltage is The voltage lags the current and the reactive power is negative.

[0028] The present invention also provides a single-phase electric reactive power sign judgment system, the system is used for:

[0029] Calculate the current average value Iavg in the half cycle corresponding to the cosine value of the voltage phase angle being less than 0. If Iavg>0, the reactive power is greater than 0; if Iavg<0, the reactive power is less than 0.

[0030] The current average value Iavg in the half cycle corresponding to when the cosine value of the voltage phase angle is less than 0 is calculated by calculating the integral result of the current in the half cycle corresponding to when the cosine value of the voltage phase angle is less than 0.

[0031] Furthermore, the system is also used for:

[0032] Assume that the voltage phase is θ, then the cosine value of the voltage phase angle is cosθ. If the integral of the current in the half cycle corresponding to cosθ<0 is greater than 0, the reactive power is greater than 0; if the integral of the current in the half cycle corresponding to cosθ<0 is less than 0, the reactive power is less than 0.

[0033] Furthermore, the phase difference between the current and the voltage is The sine value of the phase difference is The integral result of the current in the half cycle corresponding to cosθ<0 is the sine value of the phase difference The product of the current amplitude and a coefficient term, wherein the coefficient term is a negative number.

[0034] Furthermore, when the integral result is greater than 0, that is, the sine value of the phase difference If the product of the current amplitude and the coefficient term is greater than 0, the sine value of the phase difference is less than 0, and the phase difference between current and voltage is The voltage leads the current, and the reactive power is positive; when the integral result is less than 0, the phase difference is the sine value. If the product of the current amplitude and the coefficient term is less than 0, the sine value of the phase difference is greater than 0, and the phase difference between current and voltage is The voltage lags the current and the reactive power is negative.

[0035] The advantages of the present invention are:

[0036] The present invention only needs to calculate the positive or negative current average value in the half cycle corresponding to the cosine value of the voltage phase angle within one cycle being less than 0, that is, the positive or negative current integral (average value), to determine the positive or negative reactive power. The amount of calculation is small, and no algorithm such as FFT is required to process the signal, so that spectrum leakage will not occur and the measurement accuracy will not be affected. The calculation process does not involve harmonic components and is not affected by harmonics. The accuracy is high, the performance of hardware platforms such as DSP is not dependent on it, and the stability and reliability are strong. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 A schematic diagram of a situation where voltage lags current by 90° in a method for determining a sign of single-phase reactive power disclosed in an embodiment of the present invention;

[0038] Figure 2 A schematic diagram of a method for determining a sign of single-phase reactive power disclosed in an embodiment of the present invention, in which the voltage leads the current by 90°;

[0039] Figure 3 It is a schematic diagram of a case where reactive power is positive in a method for determining a sign of single-phase reactive power disclosed in an embodiment of the present invention, wherein: Figure 3 (a) means Voltage and current waveforms in the case of Figure 3 (b) means Voltage and current waveforms under the condition of .

[0040] Figure 4 It is a schematic diagram of a case where reactive power is negative in a method for determining a sign of single-phase reactive power disclosed in an embodiment of the present invention, wherein: Figure 4 (a) means Voltage and current waveforms in the case of Figure 4 (b) means Voltage and current waveforms under the condition of . DETAILED DESCRIPTION

[0041] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] Example 1

[0043] The power calculation formula for single-phase TV is S=V rms I rms , where V rms Indicates the effective value of voltage, I rms represents the effective value of current; assuming the voltage phase is θ, the difference between the current phase and the voltage phase is The calculation formula for single-phase active power is: The absolute value calculation formula of single-phase reactive power is: Due to the existence of inductance / capacitance, the voltage may lead / lag the current, so Q may be greater than 0 or less than 0, such as Figure 1 2 is a schematic diagram showing a situation where the voltage lags behind the current by 90°, and 3 is a schematic diagram showing a situation where the voltage leads the current by 90°. Based on the above reasons, it is necessary to determine the sign of the reactive power of single-phase electricity, that is, the positive or negative sign. Therefore, the present invention provides a method for determining the sign of reactive power of single-phase electricity, the method comprising:

[0044] Assume the voltage phase is θ, the difference between the current phase and the voltage phase is If the integral (average value) of the current in the half cycle corresponding to cosθ<0 is greater than 0, the reactive power is greater than 0; if the integral (average value) of the current in the half cycle corresponding to cosθ<0 is less than 0, the reactive power is less than 0.

[0045] The following is a proof of the conclusions of the above method:

[0046] Let voltage v = V m sinθ, current From the properties of trigonometric functions, we know that when cosθ<0, The integral (average value) of the current in the corresponding range is

[0047]

[0048] Among them, V m Indicates the voltage amplitude, I m Indicates the current amplitude.

[0049] because is the phase difference, so

[0050] when Right now Right now The voltage leads the current, and the reactive power is positive; Figure 3 A schematic diagram is given for the case where the reactive power is positive. Figure 3 The two lines perpendicular to the horizontal axis represent the range of cosθ<0, and the shaded area filled with oblique lines represents the area enclosed by the current and the coordinate axis, that is, the integral result of the current in the half cycle corresponding to cosθ<0. This integral result is the average value of the current in the half cycle corresponding to cosθ<0, where Figure 3 (a) means Voltage and current waveforms in the case of Figure 3 (b) means Voltage and current waveforms under the condition of .

[0051] when Right now Right now The voltage lags behind the current, and the reactive power is negative. Figure 4 A schematic diagram is given for the case where the reactive power is negative. Figure 4 (a) means Voltage and current waveforms in the case of Figure 4 (b) means Voltage and current waveforms under the condition of .

[0052] Through the above technical scheme, the present invention only needs to calculate the positive and negative current average value in the half cycle corresponding to the cosine value of the voltage phase angle less than 0 in one cycle, that is, the positive and negative current integral (average value) value, to determine the positive and negative reactive power. The amount of calculation is small, and no algorithm such as FFT is required to process the signal, so that spectrum leakage will not occur, and the measurement accuracy will not be affected. The calculation process does not involve harmonic components and is not affected by harmonics. It has high accuracy, does not rely on the performance of hardware platforms such as DSP, has high stability, and strong reliability.

[0053] Example 2

[0054] Based on Embodiment 1, Embodiment 2 of the present invention further provides a single-phase reactive power sign determination system, the system being used for:

[0055] Calculate the current average value Iavg in the half cycle corresponding to the cosine value of the voltage phase angle being less than 0. If Iavg>0, the reactive power is greater than 0; if Iavg<0, the reactive power is less than 0.

[0056] The current average value Iavg in the half cycle corresponding to when the cosine value of the voltage phase angle is less than 0 is calculated by calculating the integral result of the current in the half cycle corresponding to when the cosine value of the voltage phase angle is less than 0.

[0057] Specifically, the system is also used for:

[0058] Assume that the voltage phase is θ, then the cosine value of the voltage phase angle is cosθ. If the integral of the current in the half cycle corresponding to cosθ<0 is greater than 0, the reactive power is greater than 0; if the integral of the current in the half cycle corresponding to cosθ<0 is less than 0, the reactive power is less than 0.

[0059] More specifically, the phase difference between the current and the voltage is The sine value of the phase difference is The integral result of the current in the half cycle corresponding to cosθ<0 is the sine value of the phase difference The product of the current amplitude and a coefficient term, wherein the coefficient term is a negative number.

[0060] More specifically, when the integral result is greater than 0, the sine value of the phase difference If the product of the current amplitude and the coefficient term is greater than 0, the sine value of the phase difference is less than 0, and the phase difference between current and voltage is The voltage leads the current, and the reactive power is positive; when the integral result is less than 0, the phase difference is the sine value. If the product of the current amplitude and the coefficient term is less than 0, the sine value of the phase difference is greater than 0, and the phase difference between current and voltage is The voltage lags the current and the reactive power is negative.

[0061] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for determining the sign of single-phase reactive power, characterized in that: The method comprises: Calculate the current average value Iavg in the half cycle corresponding to the cosine value of the voltage phase angle being less than 0. If Iavg>0, the reactive power is greater than 0; if Iavg<0, the reactive power is less than 0.

2. A method for determining the sign of single-phase reactive power according to claim 1, characterized in that: The current average value Iavg in the half cycle corresponding to when the cosine value of the voltage phase angle is less than 0 is calculated by calculating the integral result of the current in the half cycle corresponding to when the cosine value of the voltage phase angle is less than 0.

3. A method for determining the sign of single-phase reactive power according to claim 2, characterized in that: The method further comprises: Assume that the voltage phase is θ, then the cosine value of the voltage phase angle is cosθ. If the integral of the current in the half cycle corresponding to cosθ<0 is greater than 0, the reactive power is greater than 0; if the integral of the current in the half cycle corresponding to cosθ<0 is less than 0, the reactive power is less than 0.

4. A method for determining the sign of single-phase reactive power according to claim 3, characterized in that: The phase difference between the current and voltage is The sine value of the phase difference is The integral result of the current in the half cycle corresponding to cosθ<0 is the sine value of the phase difference The product of the current amplitude and a coefficient term, wherein the coefficient term is a negative number.

5. A method for determining the sign of single-phase reactive power according to claim 4, characterized in that: When the integral result is greater than 0, the sine value of the phase difference If the product of the current amplitude and the coefficient term is greater than 0, the sine value of the phase difference is less than 0, and the phase difference between current and voltage is The voltage leads the current, and the reactive power is positive; when the integral result is less than 0, the phase difference is the sine value. If the product of the current amplitude and the coefficient term is less than 0, the sine value of the phase difference is greater than 0, and the phase difference between current and voltage is The voltage lags the current and the reactive power is negative.

6. A single-phase reactive power sign judgment system, characterized in that: The system is used to: Calculate the current average value Iavg in the half cycle corresponding to the cosine value of the voltage phase angle being less than 0. If Iavg>0, the reactive power is greater than 0; if Iavg<0, the reactive power is less than 0.

7. A single-phase reactive power sign determination system according to claim 6, characterized in that: The current average value Iavg in the half cycle corresponding to when the cosine value of the voltage phase angle is less than 0 is calculated by calculating the integral result of the current in the half cycle corresponding to when the cosine value of the voltage phase angle is less than 0.

8. A single-phase reactive power sign determination system according to claim 7, characterized in that: The system is also used to: Assume that the voltage phase is θ, then the cosine value of the voltage phase angle is cosθ. If the integral of the current in the half cycle corresponding to cosθ<0 is greater than 0, the reactive power is greater than 0; if the integral of the current in the half cycle corresponding to cosθ<0 is less than 0, the reactive power is less than 0.

9. A single-phase reactive power sign determination system according to claim 8, characterized in that: The phase difference between the current and voltage is The sine value of the phase difference is The integral result of the current in the half cycle corresponding to cosθ<0 is the sine value of the phase difference The product of the current amplitude and a coefficient term, wherein the coefficient term is a negative number.

10. A single-phase reactive power sign judgment system according to claim 9, characterized in that: When the integral result is greater than 0, the sine value of the phase difference If the product of the current amplitude and the coefficient term is greater than 0, the sine value of the phase difference is less than 0, and the phase difference between current and voltage is The voltage leads the current, and the reactive power is positive; when the integral result is less than 0, the phase difference is the sine value. If the product of the current amplitude and the coefficient term is less than 0, the sine value of the phase difference is greater than 0, and the phase difference between current and voltage is The voltage lags the current and the reactive power is negative.

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