Power quality detection method and device for distributed photovoltaic grid-connected equipment, and terminal

Abstract

The invention provides an electric energy quality detection method and device for distributed photovoltaic grid-connected equipment, and a terminal, and belongs to the field of electric energy quality detection. The method comprises the following steps: acquiring a first sampling signal from a first sampling chip and a second sampling signal from a second sampling chip, and carrying out signal superposition and fusion on the first sampling signal and the second sampling signal to obtain a third sampling signal; the harmonic distortion rate of the distributed photovoltaic grid-connected equipment is calculated based on the third sampling signal, and if the harmonic distortion rate is larger than a preset threshold value, it is considered that the electric energy quality of the distributed photovoltaic grid-connected equipment is unqualified; wherein the sampling frequencies of the first sampling signal and the second sampling signal are the same, and the difference between the sampling starting time and the sampling starting time is half a sampling period. According to the invention, high-precision sampling under the condition of low cost is realized, so that the accuracy of electric energy quality detection of the distributed photovoltaic grid-connected equipment is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of power quality detection, and particularly to a method and device for detecting the power quality of distributed photovoltaic grid-connected equipment. Background Art

[0002] At present, distributed photovoltaics are increasingly widely used. It mainly configures a small photovoltaic power generation and supply system at the user site or near the power consumption site. Such systems are generally built on the roofs of households and other places. Distributed photovoltaics have the characteristics of generating electricity, grid-connecting, converting, and using nearby. They usually grid-connect at 380V voltage and also have the characteristics of small floor area, short transmission distance, small investment, and short construction period.

[0003] With the substantial increase in the total proportion of the installed capacity of distributed photovoltaics, nowadays, through the construction of a distributed photovoltaic centralized control mechanism and the use of intelligent devices such as photovoltaic access units, rigid and flexible regulation of distributed photovoltaics has been realized, enabling them to participate in power grid peak shaving and local treatment of problems such as grid-connected overvoltage and power quality. However, to achieve the above functions, the user's grid-connected photovoltaic equipment must meet the technical requirements of the distributed photovoltaic grid-connection technical specifications.

[0004] Currently, the grid-connection acceptance work of distributed photovoltaics mostly relies on checking the factory certificates and function specifications of photovoltaic equipment, lacking acceptance detection means and detection technical capabilities, which cannot effectively ensure the functions and technical indicators of distributed photovoltaic grid-connected equipment after installation. Therefore, there is an urgent need for special distributed photovoltaic grid-connection quality analysis equipment to actually detect the power quality of distributed photovoltaic grid-connected equipment.

[0005] In distributed photovoltaic grid-connected equipment, the harmonic proportion is an important factor affecting power quality. The accuracy of harmonic detection is affected by the signal sampling frequency. The higher the sampling frequency, the more accurate the harmonic detection. However, the higher the sampling frequency, the higher the hardware requirements for the sampling chip, which will lead to an increase in cost and is not conducive to the popularization of distributed photovoltaic grid-connection quality analysis equipment. Summary of the Invention

[0006] The present invention provides a method and device for detecting the power quality of distributed photovoltaic grid-connected equipment to achieve high-precision sampling under low-cost conditions, thereby improving the accuracy of detecting the power quality of distributed photovoltaic grid-connected equipment.

[0007] In a first aspect, an embodiment of the present invention provides a method for detecting the power quality of a distributed photovoltaic grid-connected device, including: obtaining a first sampling signal from a first sampling chip and a second sampling signal from a second sampling chip; performing signal superposition and fusion on the first sampling signal and the second sampling signal to obtain a third sampling signal; calculating the harmonic distortion rate of the distributed photovoltaic grid-connected device based on the third sampling signal, and if the harmonic distortion rate is greater than a preset threshold, it is considered that the power quality of the distributed photovoltaic grid-connected device is unqualified; wherein, the sampling frequencies of the first sampling signal and the second sampling signal are the same, and the sampling start times differ by half a sampling period.

[0008] In a possible implementation manner, the performing signal fusion on the first sampling signal and the second sampling signal to obtain a third sampling signal includes: superimposing the first sampling signal and the second sampling signal based on the sampling time to obtain a third sampling signal.

[0009] In a possible implementation manner, the third sampling signal includes: a third sampling signal in a light illumination scenario and a third sampling signal in a light occlusion scenario; the calculating the harmonic distortion rate of the distributed photovoltaic grid-connected device based on the third sampling signal, and if the harmonic distortion rate is greater than a preset threshold, it is considered that the power quality of the distributed photovoltaic grid-connected device is unqualified includes: calculating a first harmonic distortion rate of the distributed photovoltaic grid-connected device based on the third sampling signal in the light illumination scenario; calculating a second harmonic distortion rate of the distributed photovoltaic grid-connected device based on the third sampling signal in the light occlusion scenario; if the first harmonic distortion rate is greater than a first preset threshold, or the second harmonic distortion rate is greater than a second preset threshold, or the change rate of the second harmonic distortion rate relative to the first harmonic distortion rate is greater than a third preset threshold, it is considered that the power quality of the distributed photovoltaic grid-connected device is unqualified.

[0010] In a possible implementation manner, the method further includes: obtaining a first actual output power corresponding to the third sampling signal in the light illumination scenario, and determining the first preset threshold based on the first actual output power; obtaining a second actual output power corresponding to the third sampling signal in the light occlusion scenario, and determining the second preset threshold based on the second actual output power.

[0011] In a possible implementation, the method further includes: adjusting the actual output power of the distributed photovoltaic grid-connected device through flexible control to determine the actual output power corresponding to the minimum harmonic distortion rate; obtaining a power offset coefficient based on the deviation rate of the actual output power corresponding to the minimum harmonic distortion rate relative to the rated output power; correcting the first actual output power and the second actual output power based on the power offset coefficient; correspondingly, the determining the first preset threshold based on the first actual output power includes: determining the first preset threshold based on the corrected first actual output power; and the determining the second preset threshold based on the second actual output power includes: determining the second preset threshold based on the corrected second actual output power.

[0012] In a possible implementation, before performing signal superposition and fusion on the first sampling signal and the second sampling signal to obtain a third sampling signal, it further includes: correcting the second sampling signal using a preset period correction curve.

[0013] The performing signal superposition and fusion on the first sampling signal and the second sampling signal to obtain a third sampling signal includes: performing signal superposition and fusion on the first sampling signal and the corrected second sampling signal to obtain a third sampling signal.

[0014] In a possible implementation, the method further includes: obtaining a fourth sampling signal and a fifth sampling signal, where the fourth sampling signal is homologous to the first sampling signal, the fifth sampling signal is homologous to the second sampling signal, the sampling frequencies of the fourth sampling signal and the fifth sampling signal are the same, and the sampling start times are also the same; using the fourth sampling signal as a standard signal to compare the fifth sampling signal with the standard signal to obtain a period correction curve.

[0015] In a possible implementation, the calculating the harmonic distortion rate of the distributed photovoltaic grid-connected device based on the third sampling signal includes: performing frequency-domain analysis on the third sampling signal using fast Fourier transform to obtain a signal spectrum; identifying fundamental wave and harmonic components through the signal spectrum; and calculating the harmonic distortion rate based on the fundamental wave and harmonic components.

[0016] In a second aspect, an embodiment of the present invention provides a power quality detection device for a distributed photovoltaic grid-connected device, including:

[0017] A signal acquisition unit, configured to acquire a first sampling signal from a first sampling chip and a second sampling signal from a second sampling chip, where the sampling frequencies of the first sampling signal and the second sampling signal are the same, and the sampling start times differ by half a sampling period;

[0018] A signal fusion unit, configured to perform signal superposition and fusion on the first sampling signal and the second sampling signal to obtain a third sampling signal;

[0019] A harmonic calculation unit is used to calculate the harmonic distortion rate of the distributed photovoltaic grid-connected device based on the third sampling signal. If the harmonic distortion rate is greater than a preset threshold, it is considered that the power quality of the distributed photovoltaic grid-connected device is unqualified.

[0020] In a possible implementation manner, the signal fusion unit is specifically configured to superimpose the first sampling signal and the second sampling signal based on the sampling time to obtain a third sampling signal.

[0021] In a possible implementation manner, the third sampling signal includes: a third sampling signal under a light illumination scenario and a third sampling signal under a light occlusion scenario;

[0022] Correspondingly, the harmonic calculation unit is specifically configured to: calculate the first harmonic distortion rate of the distributed photovoltaic grid-connected device based on the third sampling signal under the light illumination scenario; calculate the second harmonic distortion rate of the distributed photovoltaic grid-connected device based on the third sampling signal under the light occlusion scenario; if the first harmonic distortion rate is greater than a first preset threshold, or the second harmonic distortion rate is greater than a second preset threshold, or the change rate of the second harmonic distortion rate relative to the first harmonic distortion rate is greater than a third preset threshold, it is considered that the power quality of the distributed photovoltaic grid-connected device is unqualified.

[0023] In a possible implementation manner, the signal acquisition unit is further configured to acquire a first actual output power corresponding to the third sampling signal under the light illumination scenario, and determine the first preset threshold based on the first actual output power; acquire a second actual output power corresponding to the third sampling signal under the light occlusion scenario, and determine the second preset threshold based on the second actual output power.

[0024] In a possible implementation manner, the device further includes a threshold determination unit, which is configured to adjust the actual output power of the distributed photovoltaic grid-connected device through flexible control to determine the actual output power corresponding to the minimum harmonic distortion rate; obtain a power offset coefficient based on the deviation rate of the actual output power corresponding to the minimum harmonic distortion rate relative to the rated output power; correct the first actual output power and the second actual output power based on the power offset coefficient; correspondingly, the determining the first preset threshold based on the first actual output power includes: determining the first preset threshold based on the corrected first actual output power; the determining the second preset threshold based on the second actual output power includes: determining the second preset threshold based on the corrected second actual output power.

[0025] In a possible implementation manner, the device further includes a signal correction unit, which is configured to correct the second sampling signal using a preset periodic correction curve before superimposing and fusing the first sampling signal and the second sampling signal to obtain a third sampling signal; correspondingly, the signal fusion unit is specifically configured to perform signal superimposing and fusion on the first sampling signal and the corrected second sampling signal to obtain a third sampling signal.

[0026] In a possible implementation, the device further includes a correction curve acquisition unit configured to acquire a fourth sampling signal and a fifth sampling signal, where the fourth sampling signal is homologous to the first sampling signal, the fifth sampling signal is homologous to the second sampling signal, the fourth sampling signal and the fifth sampling signal have the same sampling frequency and the same sampling start time; using the fourth sampling signal as a reference signal, comparing the fifth sampling signal with the reference signal to obtain a period correction curve.

[0027] In a possible implementation, the harmonic calculation unit is specifically configured to perform frequency-domain analysis on the third sampling signal by using fast Fourier transform to obtain a signal spectrum; identify fundamental wave and harmonic components through the signal spectrum; calculate the harmonic distortion rate based on the fundamental wave and harmonic components.

[0028] In a third aspect, an embodiment of the present invention provides a power quality detection terminal for a distributed photovoltaic grid-connected device, including a memory, a processor, a first sampling chip, and a second sampling chip; the first sampling chip is configured to collect signals from the grid-connected node of the distributed photovoltaic grid-connected device to obtain a first sampling signal; the second sampling chip is configured to collect signals from the grid-connected node of the distributed photovoltaic grid-connected device to obtain a second sampling signal; the memory is configured to store a computer program, and the processor is configured to call and run the computer program stored in the memory to execute the power quality detection method for the distributed photovoltaic grid-connected device according to any one of the above first aspects.

[0029] The present invention provides a power quality detection method, device, and terminal for a distributed photovoltaic grid-connected device. By setting two chips to perform sampling respectively, a first sampling signal and a second sampling signal are obtained respectively, and the first sampling signal and the second sampling signal are subjected to signal fusion to obtain a third sampling signal; since the two signals have the same sampling frequency and the sampling start time difference is half a sampling period, a third sampling signal with a sampling accuracy equivalent to twice the accuracy of the original sampling signal can be generated after fusion; then, based on the third sampling signal, the harmonic distortion rate of the distributed photovoltaic grid-connected device is calculated, and when the harmonic distortion rate is greater than a preset threshold, it is determined that the power quality of the distributed photovoltaic grid-connected device is unqualified. It can be seen that the present invention uses two low-precision sampling chips for sampling, and obtains a high-precision sampling signal through signal processing, without purchasing high-cost high-precision chips, realizing high-precision sampling under low-cost conditions and improving the accuracy of power quality detection of distributed photovoltaic grid-connected devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0031] Figure 1 is an application scenario diagram of the distributed photovoltaic grid-connected device provided by the embodiment of the present invention;

[0032] Figure 2 is an implementation flowchart of the power quality detection method for the distributed photovoltaic grid-connected device provided by the embodiment of the present invention;

[0033] Figure 3 is a structural schematic diagram of the power quality detection device for the distributed photovoltaic grid-connected device provided by the embodiment of the present invention;

[0034] Figure 4 is a structural schematic diagram of the power quality detection terminal for the distributed photovoltaic grid-connected device provided by the embodiment of the present invention. Detailed implementation manners

[0035] In the following description, for the purpose of illustration rather than limitation, specific details such as specific system structures and technologies are presented to thoroughly understand the embodiments of the present invention. However, those skilled in the art should clearly understand that the present invention can also be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to avoid unnecessary details from interfering with the description of the present invention.

[0036] To make the purpose, technical solutions, and advantages of the present invention clearer, the following will be described through specific embodiments in conjunction with the drawings.

[0037] Figure 1 is an application scenario diagram of the distributed photovoltaic grid-connected device provided by the embodiment of the present invention. As Figure 1 shown, a distributed photovoltaic grid-connected device includes a solar cell array, a voltage and charge-discharge controller, a storage battery, and a grid-connected inverter. The grid-connected inverter is connected to the 220V power grid through a metering and switching controller, and electrical loads in some areas, such as air conditioners, televisions, and lighting, can be powered through the metering and switching controller.

[0038] A solar cell array (also known as a photovoltaic array) is an area composed of multiple solar panels arranged in an array. The solar panels are connected by cables and junction boxes to form a whole, which can achieve the purpose of converting solar energy into electrical energy; the voltage and charge-discharge controller has the function of controlling the charge-discharge state of the battery and protecting the battery from being damaged in overcharge and over-discharge states, which can ensure the application performance of the battery; grid-connected inverters can be divided into two types: passive inverters and active inverters. Passive inverters have the function of connecting alternating current to the grid, and active inverters have the function of transmitting power resources to the loads on the power user side. Distributed photovoltaic grid-connected equipment can use grid power when the photovoltaic power generation and energy storage are insufficient, and can supply power to the grid when there is a surplus of electrical energy in photovoltaic power generation.

[0039] When the distributed photovoltaic grid-connected equipment supplies power to the grid, it will cause harmonic pollution problems. Specifically, when the harmonic ratio (harmonic distortion rate) of the distributed photovoltaic power generation grid-connected equipment exceeds a certain range, it will affect the power quality. The main reasons for such problems are as follows:

[0040] First, the non-linear characteristics of the grid-connected inverter. The grid-connected inverter included in the distributed photovoltaic grid-connected equipment has the function of converting direct current into alternating current. However, due to the limitation of the non-linear characteristics of the grid-connected inverter, it is difficult for the output current and voltage of the grid-connected inverter to present a sinusoidal waveform state, and there are harmonic elements in it, resulting in a decline in power quality.

[0041] Second, the control method of the grid-connected inverter. Improper control of the grid-connected inverter will also cause harmonic pollution problems. For example, the application of the pulse width modulation inverter control method can optimize the operation efficiency of the grid-connected inverter, but it will increase the harmonic ratio in the output current and voltage of the grid-connected inverter.

[0042] Third, the characteristics of solar panels. Due to the limitation of the characteristics of solar panels, harmonic pollution problems will occur. The reason is that the magnitude of solar radiation is proportional to the current and voltage values output by the solar panels. Therefore, the power of the photovoltaic power generation equipment is in an unstable state, and the power harmonics gradually increase under the condition of large power changes.

[0043] In view of the above factors, before the distributed photovoltaic grid-connected equipment is put into operation, it is necessary to conduct power quality detection to ensure that the grid-connected operation of the distributed photovoltaic grid-connected equipment will not affect the normal operation of the grid and will not introduce a large number of harmonics into the grid.

[0044] Most of the current acceptance work relies on checking the factory certificates and function manuals of distributed photovoltaic grid-connected equipment, lacking acceptance testing means and testing technical capabilities. There is an urgent need for special distributed photovoltaic grid-connected quality analysis equipment, such as power quality detection terminals, to actually detect the power quality of distributed photovoltaic grid-connected equipment. The accuracy of harmonic detection depends on the sampling accuracy of the signal, that is, the sampling frequency.

[0045] The Nyquist theorem (also known as the sampling theorem) states that in order to reconstruct a continuous analog signal without distortion, the sampling frequency must be at least twice the highest frequency component in the signal. This lowest sampling frequency is called the Nyquist frequency. If the sampling frequency is lower than twice the highest frequency of the signal, aliasing will occur, resulting in signal distortion and affecting the accuracy of harmonic detection. Exemplarily, for alternating current with a power frequency of 50Hz, the 11th harmonic frequency that the distributed photovoltaic grid-connected equipment may introduce is about 550Hz. Then, the required sampling frequency should be at least above 1100Hz to avoid signal distortion, which requires a high-precision sampling chip, that is, a high-precision analog-to-digital converter ADC. Generally, high-precision sampling chips have a high cost. The present invention provides a method, device, and terminal for achieving high-precision sampling through signal processing under the condition of low hardware cost (using low-precision sampling chips) to accurately detect the harmonics of distributed photovoltaic grid-connected equipment.

[0046] Figure 2 FIG. 7 is a flowchart of an implementation of the power quality detection method for a distributed photovoltaic grid-connected equipment provided by an embodiment of the present invention, which is described in detail as follows:

[0047] Step 201, obtain a first sampling signal from a first sampling chip and a second sampling signal from a second sampling chip;

[0048] The power quality detection method for the distributed photovoltaic grid-connected equipment in the embodiment of the present invention is applied to a power quality detection terminal, which is provided with dual sampling chips, such as a first sampling chip and a second sampling chip. Both sampling chips can be low-precision sampling chips. For example, in an application scenario, the required sampling frequency is 1600Hz. Below this sampling frequency, aliasing will occur, resulting in signal distortion and affecting the detection accuracy.

[0049] Currently, the sampling chips with lower cost and applicability are low-precision chips with a sampling frequency of 800Hz. Then, in this embodiment, two low-precision sampling chips with a sampling frequency of 800Hz can be used to achieve high-precision sampling through signal processing.

[0050] In an embodiment of the present invention, signal sampling is performed on the grid - connection nodes of distributed photovoltaic grid - connection equipment. A first sampling signal is obtained by using a first sampling chip with a sampling frequency of 800 Hz; a second sampling signal is obtained by using a second sampling chip with a sampling frequency of 800 Hz. Among them, the sampling frequencies of the first sampling signal and the second sampling signal are the same, both being 800 Hz, and the sampling start times differ by half a sampling period. Exemplarily, the sampling period corresponding to a sampling frequency of 800 Hz is 1.25 milliseconds, and the difference in sampling start times by half a sampling period is 0.625 milliseconds. That is to say, the second sampling chip starts sampling 0.625 milliseconds after the first sampling chip starts sampling.

[0051] It should be noted that in this embodiment, if the difference in sampling start times is 1.5 sampling periods, or 2.5 periods, etc., it is equivalent to the difference in sampling start times being half a sampling period.

[0052] Step 202: Perform signal superposition and fusion on the first sampling signal and the second sampling signal to obtain a third sampling signal.

[0053] In an embodiment of the present invention, the first sampling signal and the second sampling signal obtained by two sampling chips can be subjected to signal superposition and fusion to obtain a third sampling signal.

[0054] Specifically, in one implementation, the first sampling signal and the second sampling signal can be superimposed based on the sampling time to obtain a third sampling signal.

[0055] Exemplarily, assuming the sampling frequency is 800 Hz and a sampling period calculated according to the power frequency is 20 milliseconds, then the sampling time sequence of the first sampling signal is {0, 1.25, 2.5, 3.75, 5, 6.25, 7.5, 8.75, 10, 11.25, 12.5, 13.75, 15, 16.25, 17.5, 18.75, 20} (the time unit is milliseconds); since the difference in sampling start times by half a sampling period is 0.625 milliseconds, then the sampling time sequence of the second sampling signal is {0.625, 1.875, 3.125, 4.375, 5.625, 6.875, 8.125, 9.375, 10.625, 11.875, 13.125, 14.375, 15.625, 16.875, 18.125, 19.375, 20.625} (the time unit is milliseconds). After the two signals are superimposed, a third sampling signal is obtained, and the sampling time sequence corresponding to a sampling period of 20 milliseconds of the third sampling signal is {0, 0.625, 1.25, 1.875, 2.5, 3.125, 3.75, 4.375, 5, 5.625, 6.25, 6.875, 7.5, 8.125, 8.75,

[0056] 9.375, 10, 10.625, 11.25, 11.875, 12.5, 13.125, 13.75, 14.375, 15, 15.625, 16.25, 16.875, 17.5, 18.125, 18.75, 19.375, 20}. It can be seen that the number of sampling points of the third sampling signal is approximately twice that of the first sampling signal or the second sampling signal, that is, the sampling accuracy is improved by about 2 times.

[0057] It should be noted that when performing signal superposition, the signal part before the first half cycle of the superposition part can be deleted, and the signal part after the second half cycle of the superposition part can be deleted, and the signal of the remaining part is greater than one cycle.

[0058] Step 203, calculate the harmonic distortion rate of the distributed photovoltaic grid-connected device based on the third sampling signal. If the harmonic distortion rate is greater than the preset threshold, it is considered that the power quality of the distributed photovoltaic grid-connected device is unqualified.

[0059] In the embodiment of the present invention, the harmonic distortion rate of the distributed photovoltaic grid-connected device can be calculated based on the third sampling signal. Specifically, the third sampling signal can be a current signal, so the harmonic current distortion rate can be calculated. The third sampling signal can also be a voltage signal, so the harmonic voltage distortion rate can be calculated; the third sampling signal can also include both a current signal and a voltage signal, so the total harmonic distortion rate can be calculated.

[0060] The preset threshold can be determined according to the regulations of relevant standard documents such as the harmonics of the public power grid for power quality. When the harmonic distortion rate is greater than the preset threshold, it is considered that the power quality of the distributed photovoltaic grid-connected device is unqualified.

[0061] Exemplarily, some standards stipulate that the harmonic voltage distortion rate should not exceed 5%, so the threshold can be preset to 5%.

[0062] Another example is that some standards also stipulate that for the 3rd to 7th harmonics, the harmonic current of each phase should not be greater than 5% of its fundamental current; for the 9th harmonic, the harmonic current of each phase should not be greater than 1% of its fundamental current; for the 11th and higher harmonics, the harmonic current of each phase should not be greater than 0.5% of its fundamental current. In practical applications, multiple thresholds can be set according to the standards, and the harmonic currents of each phase are compared separately. If any one is greater than the threshold, it is considered that the power quality of the distributed photovoltaic grid-connected device is unqualified.

[0063] In an embodiment of the present invention, a harmonic detection method based on Fourier transform can be used to calculate the harmonic distortion rate of a distributed photovoltaic grid-connected device. Specifically, it includes: performing frequency-domain analysis on the third sampling signal using the fast Fourier transform to obtain the signal spectrum; identifying the fundamental wave and harmonic components through the signal spectrum; and calculating the harmonic distortion rate based on the fundamental wave and harmonic components. In this embodiment, by performing fast Fourier transform (FFT) analysis on the sampled voltage or current signal, the harmonic components of each order in the current can be obtained. An improved harmonic detection method, such as a sliding window iterative DFT harmonic detection, can also be used.

[0064] In another embodiment, a harmonic detection method based on instantaneous reactive power theory can also be used to calculate the harmonic distortion rate of a distributed photovoltaic grid-connected device. For example, the pq method, the ip-iq method, and the dq method can be used. These methods can all measure the total harmonic value of a symmetric three-phase three-wire circuit in real time and accurately. Among them, the ip-iq method has a relatively wide range of applications and can be used in both cases of grid voltage distortion and grid voltage asymmetry.

[0065] In an embodiment of the present invention, the third sampling signal can also include two types: the third sampling signal in the light illumination scenario and the third sampling signal in the light occlusion scenario. That is, the first sampling signal and the second sampling signal are collected in the light illumination scenario and fused to obtain the third sampling signal in the light illumination scenario; the first sampling signal and the second sampling signal are collected again in the light occlusion scenario and fused to obtain the third sampling signal in the light occlusion scenario.

[0066] The above step 203 may include: calculating the first harmonic distortion rate of the distributed photovoltaic grid-connected device based on the third sampling signal in the light illumination scenario; calculating the second harmonic distortion rate of the distributed photovoltaic grid-connected device based on the third sampling signal in the light occlusion scenario; if the first harmonic distortion rate is greater than the first preset threshold, or the second harmonic distortion rate is greater than the second preset threshold, or the change rate of the second harmonic distortion rate relative to the first harmonic distortion rate is greater than the third preset threshold, it is considered that the power quality of the distributed photovoltaic grid-connected device is unqualified.

[0067] This embodiment takes into account that there are many scenario changes during the actual operation of the distributed photovoltaic grid-connected device, such as the light illumination scenario and the light occlusion scenario. Since the maximum power point (MPP) changes with the light intensity and environmental temperature, the output power of the distributed photovoltaic grid-connected device will change in different scenarios, and the change in output power will cause the harmonics to change. Therefore, detecting the harmonics in only one scenario cannot ensure the qualified power quality of the distributed photovoltaic grid-connected device. In this embodiment, sampling is performed in two scenarios respectively, the harmonic distortion rates are calculated respectively, and threshold comparisons are made respectively, so as to more accurately detect and evaluate the power quality of the distributed photovoltaic grid-connected device.

[0068] In one embodiment of the present invention, the power quality detection method for a distributed photovoltaic grid-connected device may further include: obtaining a first actual output power corresponding to a third sampling signal in a light illumination scenario, and determining a first preset threshold based on the first actual output power; obtaining a second actual output power corresponding to the third sampling signal in a light occlusion scenario, and determining a second preset threshold based on the second actual output power.

[0069] In the embodiments of the present invention, the harmonic thresholds in the two scenarios of light illumination and light occlusion are different. For example, if the first actual output power corresponding to the third sampling signal in the light illumination scenario is greater than the second actual output power corresponding to the third sampling signal in the light occlusion scenario, the corresponding thresholds can be determined based on the actual output powers in different scenarios. The correspondence between the actual output power and the threshold can be obtained based on the factory test report of the distributed photovoltaic grid-connected device. For example, when the actual output power is 80% of the rated power, the harmonic threshold can be 4.8%; when the actual output power is 100% of the rated power, the harmonic threshold can be 2.8%. By determining different thresholds according to different actual output powers and then comparing the harmonic distortion rates with their respective thresholds, a more accurate detection and evaluation result of the power quality of the distributed photovoltaic grid-connected device can be obtained.

[0070] As can be seen from the above, the present invention provides a power quality detection method for a distributed photovoltaic grid-connected device. By setting two chips to perform sampling respectively, a first sampling signal and a second sampling signal are obtained respectively, and the first sampling signal and the second sampling signal are subjected to signal fusion to obtain a third sampling signal; since the sampling frequencies of the two signals are the same and the sampling start times differ by half a sampling period, a third sampling signal with a sampling accuracy equivalent to twice the accuracy of the original sampling signal can be generated after fusion; then, based on the third sampling signal, the harmonic distortion rate of the distributed photovoltaic grid-connected device is calculated. When the harmonic distortion rate is greater than the preset threshold, it is determined that the power quality of the distributed photovoltaic grid-connected device is unqualified. It can be seen that the present invention uses two low-precision sampling chips for sampling, and obtains a high-precision sampling signal through signal processing, without purchasing high-cost high-precision chips, realizing high-precision sampling under low-cost conditions and improving the accuracy of the power quality detection of the distributed photovoltaic grid-connected device.

[0071] In addition, in one embodiment of the present invention, the power quality detection method for a distributed photovoltaic grid-connected device may further include:

[0072] Adjust the actual output power of the distributed photovoltaic grid-connected device through flexible control to determine the actual output power corresponding to the minimum harmonic distortion rate; obtain a power offset coefficient based on the deviation rate of the actual output power corresponding to the minimum harmonic distortion rate relative to the rated output power; and correct the first actual output power and the second actual output power based on the power offset coefficient.

[0073] In this embodiment, the power quality detection terminal may further include a flexible control module, which adjusts the output power of the distributed photovoltaic grid-connected device through flexible control. When signal sampling is performed, the harmonic distortion rate is displayed in real time on the display screen of the power quality detection terminal. The harmonic distortion rate changes with the adjustment of the output power. Record the actual output power corresponding to the minimum harmonic distortion rate. Theoretically, this actual output power should be the rated output power, which is recognized as the actual rated output power. However, due to the influence of the application scenario and the hardware factors of the distributed photovoltaic grid-connected device itself, the actual rated output power may deviate from the theoretical value of the rated output power at the time of factory. In this embodiment, the theoretical value of the rated output power is corrected through actual detection to obtain the actual rated output power, and the power offset coefficient is obtained based on the offset rate between the actual rated output power and the theoretical value of the rated output power. This power offset coefficient represents the degree of deviation of the actual application scenario from the theoretical value due to the influence on the output power. Since the above first preset threshold and second preset threshold are both obtained based on the factory theoretical value, there are biases in the first preset threshold and second preset threshold obtained by looking up the factory report based on the actual output power. It is necessary to first correct the actual output power using the power offset coefficient to ensure the detection accuracy.

[0074] Correspondingly, in the above embodiment, determining the first preset threshold based on the first actual output power may include: determining the first preset threshold based on the corrected first actual output power;

[0075] Correspondingly, in the above embodiment, determining the second preset threshold based on the second actual output power may include: determining the second preset threshold based on the corrected second actual output power.

[0076] In one embodiment, before the above signal fusion of the first sampling signal and the second sampling signal to obtain the third sampling signal, it may further include:

[0077] Correct the second sampling signal using a preset period correction curve;

[0078] Correspondingly, the above signal fusion of the first sampling signal and the second sampling signal to obtain the third sampling signal may include: performing signal fusion on the first sampling signal and the corrected second sampling signal to obtain the third sampling signal.

[0079] In this embodiment, since the first sampling signal and the second sampling signal are obtained based on different hardware chips, there may be certain hardware deviations in the sampling of different hardware chips. That is, even if two chips sample the same signal synchronously, there may still be some differences in the sampled results, which are determined by the differences in the hardware itself and are difficult to avoid. In this embodiment, the differences between the two chips are preset as a periodic correction curve. This periodic correction curve represents the curve differences within one period when the two sampling chips perform signal sampling. By using the periodic correction curve to correct one of the sampling signals, the differences caused by hardware factors in the two sampling signals are reduced, and the detection accuracy is improved.

[0080] In an embodiment of the present invention, the power quality detection method for distributed photovoltaic grid-connected equipment may further include: obtaining a fourth sampling signal and a fifth sampling signal, where the fourth sampling signal is homologous to the first sampling signal, the fifth sampling signal is homologous to the second sampling signal, the sampling frequencies of the fourth sampling signal and the fifth sampling signal are the same, and the sampling start times are also the same; using the fourth sampling signal as the standard signal, comparing the fifth sampling signal with the standard signal to obtain a periodic correction curve.

[0081] In this embodiment, the above periodic correction curve can be obtained by comparing the synchronous sampling of the same signal.

[0082] It should be understood that the magnitudes of the sequence numbers of the steps in the above embodiments do not imply the order of execution. The execution order of each process should be determined according to its function and internal logic, and should not constitute any limitation to the implementation process of the embodiments of the present invention.

[0083] The following is an apparatus embodiment of the present invention. For the details not described in detail herein, reference can be made to the corresponding method embodiments above.

[0084] Figure 3 FIG. shows a schematic structural diagram of a power quality detection apparatus for distributed photovoltaic grid-connected equipment provided by an embodiment of the present invention. For the sake of convenience of description, only the parts related to the embodiment of the present invention are shown and are described in detail as follows. As Figure 3 shown, the power quality detection apparatus 3 for distributed photovoltaic grid-connected equipment includes: a signal acquisition unit 31, a signal fusion unit 32, and a harmonic calculation unit 33.

[0085] The signal acquisition unit 31 is configured to obtain a first sampling signal from a first sampling chip and a second sampling signal from a second sampling chip, where the first sampling signal and the second sampling signal have the same sampling frequency and the sampling start times differ by half a sampling period.

[0086] The signal fusion unit 32 is configured to perform signal superposition and fusion on the first sampling signal and the second sampling signal to obtain a third sampling signal;

[0087] A harmonic calculation unit 33 is configured to calculate the harmonic distortion rate of the distributed photovoltaic grid-connected device based on the third sampling signal. If the harmonic distortion rate is greater than a preset threshold, it is considered that the power quality of the distributed photovoltaic grid-connected device is unqualified.

[0088] Wherein, the sampling frequencies of the first sampling signal and the second sampling signal are the same, and the sampling start times differ by half a sampling period.

[0089] In a possible implementation manner, the signal fusion unit 32 is specifically configured to superimpose the first sampling signal and the second sampling signal based on the sampling time to obtain a third sampling signal.

[0090] In a possible implementation manner, the third sampling signal includes: a third sampling signal in a light illumination scenario and a third sampling signal in a light occlusion scenario.

[0091] Correspondingly, the harmonic calculation unit 33 is specifically configured to: calculate the first harmonic distortion rate of the distributed photovoltaic grid-connected device based on the third sampling signal in the light illumination scenario; calculate the second harmonic distortion rate of the distributed photovoltaic grid-connected device based on the third sampling signal in the light occlusion scenario; if the first harmonic distortion rate is greater than a first preset threshold, or the second harmonic distortion rate is greater than a second preset threshold, or the change rate of the second harmonic distortion rate relative to the first harmonic distortion rate is greater than a third preset threshold, it is considered that the power quality of the distributed photovoltaic grid-connected device is unqualified.

[0092] In a possible implementation manner, the signal acquisition unit 31 is further configured to acquire a first actual output power corresponding to the third sampling signal in the light illumination scenario, and determine the first preset threshold based on the first actual output power; and acquire a second actual output power corresponding to the third sampling signal in the light occlusion scenario, and determine the second preset threshold based on the second actual output power.

[0093] In a possible implementation manner, the power quality detection device 3 further includes a threshold determination unit, configured to adjust the actual output power of the distributed photovoltaic grid-connected device through flexible control, and determine the actual output power corresponding to the minimum harmonic distortion rate; obtain a power offset coefficient based on the deviation rate of the actual output power corresponding to the minimum harmonic distortion rate relative to the rated output power; and correct the first actual output power and the second actual output power based on the power offset coefficient.

[0094] Correspondingly, the determining the first preset threshold based on the first actual output power includes: determining the first preset threshold based on the corrected first actual output power; and the determining the second preset threshold based on the second actual output power includes: determining the second preset threshold based on the corrected second actual output power.

[0095] In a possible implementation, the power quality detection device 3 further includes a signal correction unit, configured to correct the second sampling signal by using a preset periodic correction curve before performing signal superposition and fusion on the first sampling signal and the second sampling signal to obtain a third sampling signal; correspondingly, the signal fusion unit is specifically configured to perform signal superposition and fusion on the first sampling signal and the corrected second sampling signal to obtain a third sampling signal.

[0096] In a possible implementation, the power quality detection device 3 further includes a correction curve acquisition unit, configured to acquire a fourth sampling signal and a fifth sampling signal, where the fourth sampling signal is homologous to the first sampling signal, the fifth sampling signal is homologous to the second sampling signal, the sampling frequencies of the fourth sampling signal and the fifth sampling signal are the same, and the sampling start times are also the same; using the fourth sampling signal as a reference signal, comparing the fifth sampling signal with the reference signal to obtain a periodic correction curve.

[0097] In a possible implementation, the harmonic calculation unit 33 is specifically configured to perform frequency-domain analysis on the third sampling signal by using fast Fourier transform to obtain a signal spectrum; identify fundamental wave and harmonic components through the signal spectrum; calculate the harmonic distortion rate based on the fundamental wave and harmonic components.

[0098] As can be seen from the above, the present invention provides a power quality detection device for a distributed photovoltaic grid-connected device. By setting two chips to perform sampling respectively, a first sampling signal and a second sampling signal are obtained respectively, and the first sampling signal and the second sampling signal are subjected to signal fusion to obtain a third sampling signal; since the sampling frequencies of the two signals are the same and the sampling start times differ by half a sampling period, a third sampling signal with a sampling accuracy equivalent to twice the accuracy of the original sampling signal can be generated after fusion; then, based on the third sampling signal, the harmonic distortion rate of the distributed photovoltaic grid-connected device is calculated. When the harmonic distortion rate is greater than a preset threshold, it is determined that the power quality of the distributed photovoltaic grid-connected device is unqualified. It can be seen that the present invention uses two low-precision sampling chips for sampling, and obtains a high-precision sampling signal through signal processing, without purchasing high-cost high-precision chips, realizing high-precision sampling under low-cost conditions and improving the accuracy of power quality detection of distributed photovoltaic grid-connected devices.

[0099] Figure 4 FIG. shows a schematic structural diagram of a power quality detection terminal of a distributed photovoltaic grid-connected device provided by an embodiment of the present invention. For the sake of convenience of description, only parts related to the embodiment of the present invention are shown and are described in detail as follows. Figure 4As shown in the figure, the power quality detection terminal includes a memory, a processor, a first sampling chip, and a second sampling chip. The power quality detection terminal may further include a flexible control module and a display screen. The flexible control module is used to output a control signal to adjust the output power of the distributed photovoltaic grid-connected device. The display screen is used to display the harmonic distortion rate calculated by the processor. The first sampling chip is used to collect signals at the grid-connected node of the distributed photovoltaic grid-connected device to obtain a first sampling signal; the second sampling chip is used to collect signals at the grid-connected node of the distributed photovoltaic grid-connected device to obtain a second sampling signal. The memory is used to store a computer program, and its processor is used to call and run the computer program stored in the memory, and execute the steps of the power quality detection method of the distributed photovoltaic grid-connected device described in any of the above embodiments.

[0100] It can be seen that through the provided power quality detection terminal of the distributed photovoltaic grid-connected device, the present invention respectively obtains a first sampling signal and a second sampling signal by setting two chips for sampling, and performs signal fusion on the first sampling signal and the second sampling signal to obtain a third sampling signal; since the sampling frequencies of the two signals are the same and the sampling start times differ by half a sampling period, a third sampling signal with a sampling accuracy equivalent to twice the accuracy of the original sampling signal can be generated after fusion; then, based on the third sampling signal, the harmonic distortion rate of the distributed photovoltaic grid-connected device is calculated, and when the harmonic distortion rate is greater than a preset threshold, it is determined that the power quality of the distributed photovoltaic grid-connected device is unqualified. It can be seen that the present invention uses two low-precision sampling chips for sampling, and obtains a high-precision sampling signal through signal processing, without purchasing high-cost high-precision chips, realizing high-precision sampling under low-cost conditions, and improving the accuracy of power quality detection of distributed photovoltaic grid-connected devices.

[0101] In the above embodiments, the descriptions of the respective embodiments have their own emphases. For parts not detailed or recorded in a certain embodiment, reference may be made to the relevant descriptions of other embodiments.

[0102] Those of ordinary skill in the art can realize that the templates, units, and algorithm steps of the examples described in combination with the embodiments disclosed in this article can be implemented by electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are executed in a hardware or software manner depends on the specific application and design constraints of the technical solution. Professionals can adopt different methods to implement the described functions for each specific application, but such implementation should not be considered to exceed the scope of the present invention.

[0103] If the above-mentioned module / unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, to implement all or part of the processes in the above-mentioned embodiment methods of the present invention, it can also be completed by a computer program instructing relevant hardware. The computer program can be stored in a computer-readable storage medium. When the computer program is executed by a processor, the steps of the above-mentioned embodiments of the power quality detection method for each distributed photovoltaic grid-connected device can be implemented. Among them, the computer program includes computer program code, and the computer program code can be in the form of source code, object code, executable file, or some intermediate form, etc. The computer-readable medium can include: any entity or device capable of carrying the computer program code, recording medium, USB flash drive, mobile hard disk, magnetic disk, optical disk, computer memory, read-only memory, random access memory, electrical carrier signal, telecommunication signal, and software distribution medium, etc.

[0104] The above-mentioned embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included in the protection scope of the present invention.

Claims

1. A method for detecting power quality of distributed photovoltaic grid-connected equipment, characterized in that: include: Step 1: acquiring a first sampling signal from a first sampling chip and a second sampling signal from a second sampling chip, wherein the sampling frequencies of the first sampling signal and the second sampling signal are the same, and the sampling start times differ by half a sampling period; Step 2: performing signal superposition and fusion on the first sampling signal and the second sampling signal to obtain a third sampling signal; Step three, calculating the harmonic distortion rate of the distributed photovoltaic grid-connected equipment based on the third sampling signal. If the harmonic distortion rate is greater than a preset threshold, it is considered that the power quality of the distributed photovoltaic grid-connected equipment is unqualified.

2. The power quality detection method for distributed photovoltaic grid-connected equipment according to claim 1, characterized in that: The second step comprises: The first sampling signal and the second sampling signal are superimposed based on a sampling time to obtain a third sampling signal.

3. The power quality detection method for distributed photovoltaic grid-connected equipment according to claim 1, characterized in that: The third sampling signal includes: a third sampling signal in a light-illuminated scene and a third sampling signal in a light-blocked scene; The step three comprises: Calculating a first harmonic distortion rate of the distributed photovoltaic grid-connected device based on a third sampling signal under the illumination scene; Calculating the second harmonic distortion rate of the distributed photovoltaic grid-connected device based on the third sampling signal in the light-blocked scene; If the first harmonic distortion rate is greater than a first preset threshold, or the second harmonic distortion rate is greater than a second preset threshold, or the rate of change of the second harmonic distortion rate relative to the first harmonic distortion rate is greater than a third preset threshold, then the power quality of the distributed photovoltaic grid-connected equipment is considered to be unqualified.

4. The power quality detection method for distributed photovoltaic grid-connected equipment according to claim 3 is characterized in that: The method further comprises: Acquire a first actual output power corresponding to a third sampling signal under a lighting scene, and determine a first preset threshold based on the first actual output power; A second actual output power corresponding to the third sampling signal in a light-blocked scene is acquired, and a second preset threshold is determined based on the second actual output power.

5. The power quality detection method for distributed photovoltaic grid-connected equipment according to claim 4 is characterized in that: The method further comprises: By adjusting the actual output power of the distributed photovoltaic grid-connected equipment through flexible control, the actual output power corresponding to the minimum harmonic distortion rate is determined; The power deviation coefficient is obtained based on the deviation rate of the actual output power corresponding to the minimum harmonic distortion rate relative to the rated output power; Correcting the first actual output power and the second actual output power based on the power offset coefficient; Accordingly, determining the first preset threshold based on the first actual output power includes: determining the first preset threshold based on the corrected first actual output power; Determining the second preset threshold based on the second actual output power includes: determining the second preset threshold based on the corrected second actual output power.

6. The method for detecting power quality of distributed photovoltaic grid-connected equipment according to any one of claims 1 to 5, characterized in that: Before the step 2, the method further includes: Correcting the second sampling signal using a preset period correction curve; The step 2 further comprises: The first sampling signal and the corrected second sampling signal are superimposed and fused to obtain a third sampling signal.

7. The power quality detection method for distributed photovoltaic grid-connected equipment according to claim 6, characterized in that: The method further comprises: Acquire a fourth sampling signal and a fifth sampling signal, wherein the fourth sampling signal is homologous to the first sampling signal, the fifth sampling signal is homologous to the second sampling signal, the fourth sampling signal and the fifth sampling signal have the same sampling frequency and the same sampling start time; The fourth sampling signal is used as a standard signal, and the fifth sampling signal is compared with the standard signal to obtain a period correction curve.

8. The method for detecting power quality of distributed photovoltaic grid-connected equipment according to any one of claims 1 to 5, characterized in that: The step three comprises: Performing frequency domain analysis on the third sampling signal by using fast Fourier transform to obtain a signal spectrum; Identify fundamental and harmonic components through signal spectrum; Calculates the harmonic distortion based on the fundamental and harmonic components.

9. A power quality detection device for distributed photovoltaic grid-connected equipment, characterized in that: include: A signal acquisition unit, used to acquire a first sampling signal from a first sampling chip and a second sampling signal from a second sampling chip, wherein the sampling frequencies of the first sampling signal and the second sampling signal are the same, and the sampling start times differ by half a sampling period; a signal fusion unit, configured to perform signal superposition fusion on the first sampling signal and the second sampling signal to obtain a third sampling signal; The harmonic calculation unit is used to calculate the harmonic distortion rate of the distributed photovoltaic grid-connected equipment based on the third sampling signal. If the harmonic distortion rate is greater than a preset threshold, it is considered that the power quality of the distributed photovoltaic grid-connected equipment is unqualified.

10. A power quality detection terminal for distributed photovoltaic grid-connected equipment, characterized in that: include: A memory, a processor, a first sampling chip and a second sampling chip; The first sampling chip is used to collect signals from the grid-connected nodes of the distributed photovoltaic grid-connected equipment to obtain a first sampling signal; The second sampling chip is used to collect signals from the grid-connected nodes of the distributed photovoltaic grid-connected equipment to obtain a second sampling signal; The memory is used to store computer programs, and the processor is used to call and run the computer programs stored in the memory to execute the power quality detection method of the distributed photovoltaic grid-connected equipment according to any one of claims 1 to 8.

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