A Distributed Photovoltaic and Wind Power Grid-Connected Harmonic Measurement System and Method

Abstract

The present invention relates to a harmonic measurement system for distributed photovoltaic and wind power grid connection, which includes a harmonic measurement device, a wind power grid connection power generation line and a system side line that are connected to each other. The system side line is connected to a photovoltaic and user side line, and the user side line is connected to a plurality of electrical devices. The harmonic measurement device includes a voltage transformer, a current transformer, a band-pass filter circuit, a single-chip microcomputer and a display screen. The voltage transformer and the current transformer are respectively connected to a test point PCC. The band-pass filter circuit is respectively connected to the voltage transformer and the current transformer, and is sequentially connected to the single-chip microcomputer and the display screen. Compared with the prior art, the present invention has the advantages of simple measurement and high accuracy, etc.

Description

Technical Field

[0001] The present invention relates to harmonic power metering technology, and in particular to a distributed photovoltaic and wind power grid-connected harmonic measurement system and method. Background Technique

[0002] Internationally, a large number of articles on harmonics have been published since the early 20th century. Since the 1990s, issues such as power quality phenomena, power quality measurement, and power quality improvement have received increasing attention. In China, although the fundamental wave power metering technology has developed rapidly, the research on harmonic power metering started late and has developed relatively slowly. At present, regarding the influence of harmonics on power metering, scientific research reports basically still rely on experimental evidence. How to find a reasonable and feasible metering method and how to properly handle the dynamic error situation of metering have not been effectively and accurately explained within the power grid at present.

[0003] According to the superposition theorem, the generation of harmonics at the grid-connected point of distributed photovoltaic power generation and wind power can be regarded as the result of the combined contribution of user-side harmonics and background harmonic sources. How to calculate and analyze the background harmonics at the grid-connected point to obtain the true injected harmonics of distributed photovoltaic power generation and wind power is crucial for the analysis of power quality and power metering. In the measurement of distributed photovoltaic and wind power grid-connected harmonics, the existing system impedance estimation method will reduce the power quality injected into the power grid because it needs to inject a disturbance signal into the power grid. Therefore, it is particularly important to find a suitable method to quantitatively measure the distributed photovoltaic and wind power grid-connected harmonics. Summary of the Invention

[0004] The purpose of the present invention is to overcome the above-mentioned defects existing in the prior art and provide a distributed photovoltaic and wind power grid-connected harmonic measurement system and method.

[0005] The purpose of the present invention can be achieved through the following technical solutions:

[0006] A distributed photovoltaic and wind power grid-connected harmonic measurement system includes a harmonic measurement device, a wind power grid-connected power generation line and a system-side line connected to each other. The system-side line is connected to the photovoltaic and user-side line, and the user-side line is connected to a plurality of electrical devices. The harmonic measurement device includes a voltage transformer, a current transformer, a band-pass filter circuit, a single-chip microcomputer and a display screen. The voltage transformer and the current transformer are respectively connected to the test point PCC. The band-pass filter circuit is respectively connected to the voltage transformer and the current transformer, and is sequentially connected to the single-chip microcomputer and the display screen;

[0007] The voltage transformer and the current transformer respectively acquire the current signal and voltage signal of the test point PCC, and detect the harmonic voltage and harmonic current The single-chip microcomputer, based on the harmonic voltage and harmonic current obtains the harmonic power factor angle, and calculates the true harmonic current injection at the grid connection point according to the harmonic voltage, harmonic current and harmonic power factor angle.

[0008] The test point PCC is the access point of the grid connection dedicated line, which is set between the system-side line and the wind power grid connection power generation line. A plurality of band-pass filter circuits are provided, and the center frequencies of the plurality of band-pass filter circuits are not equal;

[0009] The voltage transformer and the current transformer are respectively used to obtain the voltage signal and current signal at the system-side line port. The plurality of band-pass filter circuits are used to detect the harmonic components in the current signal and voltage signal to obtain harmonic voltage and harmonic current

[0010] The harmonic measurement device further includes an input amplifier and an A / D converter. One end of the input amplifier is respectively connected to the voltage transformer and the current transformer, and the other end is connected to the band-pass filter circuit, and is used to amplify the harmonic voltage and harmonic current signal amplitude. One end of the A / D converter is connected to the band-pass filter circuit, and the other end is connected to the single-chip microcomputer, and is used to complete the analog-to-digital conversion of the signal.

[0011] In the present invention, the model of the voltage transformer can be selected as JDZF7-10GUW1, the model of the current transformer can be selected as LZZBJ9-100A3G, the model of the input amplifier can be selected as TSM103A, the model of the A / D converter can be selected as AD7671, the single-chip microcomputer can be selected as the OTP type MDT20 series single-chip microcomputer, and the display screen can be selected as the LCD display screen.

[0012] A harmonic measurement method for a distributed photovoltaic and wind power grid-connected harmonic measurement system as described above includes the following steps:

[0013] S1: Establish an equivalent harmonic model at the system-side line port and calculate the system-side equivalent impedance;

[0014] S2: Obtain the background harmonic voltage by using the system-side equivalent impedance and the equivalent harmonic model;

[0015] S3: Calculate the true harmonic current injection at the grid connection point.

[0016] The formula of the equivalent harmonic model is:

[0017]

[0018] Among them, is the harmonic voltage, is the harmonic current, and Z h is the equivalent impedance on the system side, is the background harmonic voltage.

[0019] The equivalent impedance on the system side is solved by the double-dominant fluctuation difference quotient impedance method based on the relative phase angle, specifically including:

[0020] S11: Select the harmonic voltage and harmonic current that meet the double-dominant fluctuation screening rule;

[0021] The expression of the double-dominant fluctuation screening rule is:

[0022]

[0023] Among them, ΔU is the difference in equivalent harmonic voltages of two adjacent internal power sources, and μ ΔU is the mean value of the harmonic voltage difference ΔU, σ ΔU is the standard deviation of the harmonic voltage difference ΔU, ΔI is the difference in equivalent harmonic currents of two adjacent internal power sources, and μ ΔI is the mean value of the harmonic current difference ΔI, σΔI is the standard deviation of the harmonic current difference ΔIΔU, α1 is the Neel coefficient of the harmonic voltage difference ΔU, and α2 is the Neel coefficient of the harmonic current difference ΔI; the value range of the Neel coefficient α1 of the harmonic voltage difference ΔU is 1 - 1.5, and the value range of the Neel coefficient α2 of the harmonic current difference ΔI is 1 - 1.5.

[0024] S12: Calculate the equivalent impedance on the system side according to the difference quotient impedance method.

[0025] The calculation formula of the equivalent impedance on the system side is:

[0026]

[0027] Among them, U h (i), I h (i) and are respectively the hth harmonic voltage, harmonic current, and harmonic power factor angle of the i-th group of measurement data at the test point PCC;

[0028] U h (i + 1), I h (i + 1) and are respectively the hth harmonic voltage, harmonic current, and harmonic power factor angle of the (i + 1)-th group of monitoring data at the test point PCC.

[0029] The calculation formula of the true harmonic current injection at the grid connection point is:

[0030]

[0031]

[0032] Among them, is the true harmonic current injection at the point of common coupling (PCC), is the equivalent harmonic current injection from the background harmonic source at the test point PCC to the user side, is the measured harmonic current at the test point PCC, and Z Ah is the equivalent harmonic impedance on the user side.

[0033] Compared with the prior art, the present invention has the following advantages:

[0034] 1) By setting the test point PCC at the access point of the grid-connected dedicated line (i.e., between the system-side line and the wind power grid-connected power generation line) and connecting it to the harmonic measurement device, the harmonic voltage and harmonic current at the system-side line port are obtained, and finally the true harmonic current injection at the point of common coupling is calculated by establishing an equivalent harmonic model, realizing the measurement of harmonics in distributed photovoltaic and wind power grid connection;

[0035] 2) The harmonic measurement device in the present invention has a simple structure, does not require a module for injecting disturbance signals into the power grid, reduces costs, and does not reduce the power quality injected into the power grid;

[0036] 3) In the method of the present invention, the harmonic voltage, harmonic current and harmonic power factor angle are used to solve the equivalent impedance on the system side by the double dominant wave differential quotient impedance method based on the relative phase angle. There is no need to inject disturbance signals into the power grid. The measurement of these three parameters is convenient, and the accurate equivalent impedance on the system side can be obtained, improving the calculation efficiency and accuracy of the equivalent impedance on the system side; BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 is a schematic structural diagram of the system of the present invention;

[0038] Figure 2 is a schematic structural diagram of the harmonic detection device;

[0039] Figure 3 is a schematic flow diagram of the method of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0040] The present invention will be described in detail below with reference to the drawings and specific embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0041] Embodiment

[0042] As Figure 1 shown, the present invention provides a distributed photovoltaic and wind power grid-connected harmonic measurement system, including a harmonic measurement device, a wind power grid-connected power generation line and a system-side line connected to each other, the system-side line is connected to a photovoltaic and user-side line, and the user-side line is connected to a plurality of electrical devices. Among them, a test point PCC is set between the system-side line and the wind power grid-connected power generation line, and this point is the access point of the grid-connected dedicated line.

[0043] As Figure 2 shown, the harmonic measurement device includes a voltage transformer, a current transformer, a band-pass filter circuit, a single-chip microcomputer and a display screen. The voltage transformer and the current transformer are respectively connected to the test point PCC, and the input amplifier is respectively connected to the voltage transformer and the current transformer, and is sequentially connected to the band-pass filter circuit, the single-chip microcomputer, the A / D converter and the display screen. Among them, a plurality of band-pass filter circuits are provided, and the center frequencies are f1, f2... f N , and each center frequency is fixed as an integer multiple of the power frequency, and f1 < f2... < f N , so that the harmonic components in the current signal and the voltage signal can be detected from high to low.

[0044] The working process of this system is as follows:

[0045] The harmonics of the user-side line and the background harmonic source jointly superimpose and contribute to the generation of harmonics at the distributed photovoltaic and wind power grid-connected point. The voltage transformer and the current transformer respectively obtain the current signal and the voltage signal of the test point PCC, and after amplifying the signal amplitude by the input amplifier, pass through a plurality of band-pass filter circuits to detect the harmonic voltage and harmonic current The harmonic voltage and harmonic current are converted into digital signals through the A / D converter. Finally, the single-chip microcomputer obtains the harmonic power factor angle according to the harmonic voltage and harmonic current , and calculates the true harmonic current injection at the grid-connected point according to the harmonic voltage, harmonic current and harmonic power factor angle.

[0046] In addition, in this embodiment, the model of the voltage transformer is selected as JDZF7-10GUW1, the model of the current transformer is selected as LZZBJ9-100A3G, the model of the input amplifier is selected as TSM103A, the model of the A / D converter is selected as AD7671, the single-chip microcomputer selects the OTP type MDT20 series single-chip microcomputer, and the display screen selects the LCD display screen.

[0047] As Figure 3 shown, the present invention also provides a distributed photovoltaic and wind power grid-connected harmonic measurement method, including the following steps:

[0048] S1: Establish an equivalent harmonic model at the line port on the system side and calculate the equivalent impedance on the system side;

[0049] S2: Obtain the background harmonic voltage using the equivalent impedance and equivalent harmonic model on the system side;

[0050] S3: Calculate the true harmonic current injection at the grid connection point.

[0051] The formula for the equivalent harmonic model is:

[0052]

[0053] Among them, is the harmonic voltage, is the harmonic current, Z h is the equivalent impedance on the system side, is the background harmonic voltage.

[0054] In this equivalent harmonic model, the solution of the equivalent impedance Z h (i.e., the system harmonic impedance) on the system side is crucial. However, the estimation of the equivalent impedance on the system side is a very complex problem. The system harmonic impedance may change significantly over time, so there is a severe lack of reliable data. Even advanced computer programs and network analyzers are difficult to compensate for this problem.

[0055] To obtain the accurate equivalent harmonic impedance on the system side, the present invention uses the double-dominant fluctuation difference quotient impedance method based on the relative phase angle to solve the system impedance. This impedance method is an improvement of the difference quotient impedance method. First, two adjacent data with negligible equivalent voltage difference of the internal power sources are selected through the double-dominant fluctuation screening rule, and then according to the idea of the difference quotient impedance method, the selected data is used to calculate the approximate equivalent harmonic impedance, specifically including:

[0056] S11: Select harmonic voltages and harmonic currents that conform to the double-dominant fluctuation screening rule;

[0057] The expression of the double-dominant fluctuation screening rule is:

[0058]

[0059] Among them, ΔU is the equivalent harmonic voltage difference between two adjacent internal power sources, μ ΔU is the mean value of the harmonic voltage difference ΔU, σ ΔU is the standard deviation of the harmonic voltage difference ΔU, ΔI is the equivalent harmonic current difference between two adjacent internal power sources, μ ΔIis the mean value of the harmonic current difference ΔI, σΔI is the standard deviation of the harmonic current difference ΔIΔU, α1 is the Neel coefficient of the harmonic voltage difference ΔU, and α2 is the Neel coefficient of the harmonic current difference ΔI; the value range of the Neel coefficient α1 of the harmonic voltage difference ΔU is 1 - 1.5, and the value range of the Neel coefficient α2 of the harmonic current difference ΔI is 1 - 1.5.

[0060] S12: Calculate the equivalent impedance on the system side according to the difference quotient impedance method.

[0061] The calculation formula for the equivalent impedance on the system side is:

[0062]

[0063] Among them, U h (i), I h (i) and are respectively the h - th harmonic voltage, harmonic current and harmonic power factor angle of the i - th group of measurement data at the test point PCC;

[0064] U h (i + 1), I h (i + 1) and are respectively the h - th harmonic voltage, harmonic current and harmonic power factor angle of the (i + 1) - th group of monitoring data at the test point PCC.

[0065] After obtaining the accurate equivalent impedance on the system side, the background harmonic voltage can be obtained through the equivalent harmonic model:

[0066] U oh = U ph - Z h I ph

[0067] The equivalent harmonic current injection of the background harmonic source into the user can be solved by the background harmonic voltage and the equivalent impedance of each part, and then superimposed with the measured harmonic current at the point of common coupling to obtain the true harmonic current injection from the distributed photovoltaic and wind power generation sides to the system side. Its calculation formula is:

[0068]

[0069]

[0070] Among them, is the true harmonic current injection at the point of common coupling, is the equivalent harmonic current injection of the background harmonic source on the user side at the test point PCC, is the measured harmonic current at the test point PCC, Z Ah is the equivalent harmonic impedance on the user side.

[0071] As described above, it is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of various equivalent modifications or substitutions within the technical scope disclosed by the present invention, and these modifications or substitutions should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. A distributed photovoltaic and wind power grid-connected harmonic measurement system, characterized in that, It includes a harmonic measurement device, a wind power grid-connected power generation line and a system-side line that are interconnected. The system-side line is connected to a photovoltaic and user-side line, and the user-side line is connected to multiple electrical devices. The harmonic measurement device includes a voltage transformer, a current transformer, a band-pass filter circuit, a single-chip microcomputer and a display screen. The voltage transformer and the current transformer are respectively connected to the test point PCC. The band-pass filter circuit is respectively connected to the voltage transformer and the current transformer, and is sequentially connected to the single-chip microcomputer and the display screen. A plurality of band-pass filter circuits are provided, and the center frequencies of the plurality of band-pass filter circuits are not equal to each other. The harmonic measurement device further includes an input amplifier and an A / D converter. One end of the input amplifier is respectively connected to the voltage transformer and the current transformer, and the other end is connected to the band-pass filter circuit for amplifying the harmonic voltage and harmonic current signal amplitude. One end of the A / D converter is connected to the band-pass filter circuit, and the other end is connected to the single-chip microcomputer for completing the analog-to-digital conversion of the signal; The voltage transformer and current transformer respectively obtain the current signal and voltage signal of the test point PCC, and detect the harmonic voltage through a band-pass filter circuit and harmonic current The single-chip microcomputer obtains the harmonic power factor angle according to the harmonic voltage and harmonic current and calculates the true harmonic current injection at the grid connection point according to the harmonic voltage, harmonic current and harmonic power factor angle.

2. The harmonic measurement system for distributed photovoltaic and wind power grid connection according to claim 1, characterized in that The test point PCC is the access point of the grid-connection dedicated line, which is set between the system-side line and the wind power grid-connection power generation line; The voltage transformer and the current transformer are respectively used to obtain a voltage signal and a current signal at the line port on the system side, and the multiple band-pass filter circuits are used to detect harmonic components in the current signal and the voltage signal to obtain harmonic voltage and harmonic current 3. A distributed photovoltaic and wind power grid-connected harmonic measurement system according to claim 2, characterized in that The model of the voltage transformer is JDZF7-10GUW1, and the model of the current transformer is LZZBJ9-100A3G.

4. A distributed photovoltaic and wind power grid-connected harmonic measurement system according to claim 2, characterized in that The model of the input amplifier is TSM103A, the model of the A / D converter is AD7671, the single-chip microcomputer is the OTP-type MDT20 series single-chip microcomputer, and the display screen is an LCD display screen.

5. A harmonic measurement method for a distributed photovoltaic and wind power grid-connected harmonic measurement system according to any one of claims 1-4, characterized in that, It includes the following steps: S1: Establish an equivalent harmonic model at the system-side line port and calculate the system-side equivalent impedance; S2: Obtain the background harmonic voltage using the system-side equivalent impedance and the equivalent harmonic model; S3: Calculate the true harmonic current injection at the grid connection point; The formula of the equivalent harmonic model is: Among them, is the harmonic voltage, is the harmonic current, Z h is the equivalent impedance on the system side, is the background harmonic voltage; The system-side equivalent impedance is solved by the double-dominant fluctuation difference quotient impedance method based on the relative phase angle, specifically including: S11: Select harmonic voltage and harmonic current that conform to the double-dominant fluctuation screening rule; S12: Calculate the system-side equivalent impedance according to the difference quotient impedance method; The expression of the double-dominant fluctuation screening rule is: Among them, ΔU is the difference in equivalent harmonic voltages of two adjacent internal power sources, μΔU is the mean value of the harmonic voltage difference ΔU, σΔU is the standard deviation of the harmonic voltage difference ΔU, ΔI is the difference in equivalent harmonic currents of two adjacent internal power sources, μΔI is the mean value of the harmonic current difference ΔI, σΔI is the standard deviation of the harmonic current difference ΔIΔU, α1 is the Neyman coefficient of the harmonic voltage difference ΔU, and α2 is the Neyman coefficient of the harmonic current difference ΔI; The calculation formula of the equivalent harmonic impedance is: Among them, U h (i), I h (i) and are respectively the h - th harmonic voltage, harmonic current and harmonic power factor angle of the i - th group of metering data at the test point PCC; U h (i + 1), I h (i + 1) and are respectively the h - th harmonic voltage, harmonic current and harmonic power factor angle of the (i + 1)-th group of monitoring data at the test point PCC; The calculation formula of the true harmonic current injection at the grid connection point is: Among them, is the true harmonic current injection at the point of common coupling, is the equivalent harmonic current injection from the background harmonic source at the PCC of the test point to the user side, is the measured harmonic current at the PCC of the test point, Z Ah is the equivalent harmonic impedance on the user side; The value range of the Neyman coefficient α1 of the harmonic voltage difference ΔU is 1 - 1.5, and the value range of the Neyman coefficient α2 of the harmonic current difference ΔI is 1 - 1.5.

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