Three-phase grid-connected inverter direct-current side leakage detection method, electronic device and medium

Abstract

The application provides a three-phase grid-connected inverter DC side leakage detection method, electronic equipment and medium, the application extracts the amplitude, frequency, waveform and the like of the residual current signal generated on the AC side of the three-phase grid-connected inverter, analyzes the amplitude-frequency curve of the residual current signal, and obtains the cause of the leakage current generated on the DC side, the method is relatively simple, and no current or voltage sensor needs to be additionally added on the DC side, thereby reducing the equipment cost. The application adjusts the monitoring time by detecting the amplitude of the residual current signal, so as to reduce the workload and detection cost of real-time monitoring.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of leakage detection, and particularly relates to a three-phase grid-connected inverter DC side leakage detection method, electronic equipment and medium. BACKGROUND

[0002] The grid-connected inverter is a key device for converting the direct current generated by the power generation system into alternating current. In the power generation system, direct current side leakage is a common fault condition that may cause energy loss, equipment damage and even safety hazards. Therefore, direct current side leakage detection is crucial for ensuring the safe operation and performance optimization of the power generation system.

[0003] Traditional grid-connected inverter DC side leakage detection methods usually require the use of specialized detection equipment and sensors, which have high costs, thereby increasing the overall cost of the system. In addition, these detection devices need to be calibrated and maintained regularly, which further increases the maintenance cost and time investment of the system. At the same time, the detection equipment is sensitive to environmental conditions, such as temperature, humidity, etc., which may affect its detection results, resulting in inaccurate detection results.

[0004] Patent CN107179492B discloses a leakage detection method for a power distribution line, which needs to simultaneously obtain the residual current signal and voltage signal of the power distribution line, and according to the amplitude and phase relationship of the residual current and voltage at each frequency, the resistive component of the residual current is separated and calculated to obtain the resistive leakage current in the residual current. The resistive leakage current is compared with a predefined threshold to determine the leakage condition of the power distribution line. The method is relatively complex, and requires additional voltage sensors and current sensors, which increases the cost of equipment. SUMMARY

[0005] The purpose of the present application is to overcome the shortcomings of the prior art and provide a three-phase grid-connected inverter DC side leakage detection method that does not require additional current or voltage sensors on the DC side, thereby reducing equipment costs.

[0006] To achieve the above purpose, the technical solution adopted by the present application is:

[0007] A grid-connected inverter DC side leakage detection method, comprising the following steps:

[0008] S1: Collecting the grid-connected current signal of the grid-connected inverter AC side, and adding the three-phase grid-connected current signals to obtain a residual current signal;

[0009] S2: Performing fast Fourier transform on the residual current signal to obtain the frequency, amplitude and waveform characteristics of the residual current signal;

[0010] S3: If the amplitude of the residual current signal is lower than the high frequency threshold, it is determined that no leakage occurs, and if the amplitude of the residual current signal is higher than or equal to the high frequency threshold, it is determined that leakage occurs.

[0011] The application extracts the amplitude, frequency, waveform, etc. of the residual current signal generated by the three-phase grid-connected inverter AC side, analyzes the amplitude-frequency curve of the residual current signal, and obtains the DC side leakage condition; the application analyzes the leakage condition of the DC side through the residual current of the three-phase inverter AC measurement, which is a simple method. The inverter grid-connected system AC measurement has an AC sensor, and no additional current or voltage sensor is needed on the DC side, reducing the equipment cost.

[0012] Further, according to the frequency of the residual current signal, the type of leakage current is determined.

[0013] Further, the type of leakage current includes:

[0014] If the harmonic component frequency in the residual current signal is distributed at 3f and 9f, the leakage current is the zero sequence leakage current caused by the low frequency harmonic voltage generated by the dead zone effect, wherein f represents the fundamental frequency;

[0015] If the harmonic component frequency in the residual current signal is distributed at f s and 2f s , the leakage current is the zero sequence leakage current caused by the high frequency harmonic voltage component generated by the inverter modulation effect, wherein f s represents the switching frequency;

[0016] If the harmonic component frequency in the residual current signal is distributed at 3f, 9f, f s , 2f s , the leakage current includes the zero sequence leakage current caused by the high frequency harmonic voltage component generated by the inverter modulation effect and the zero sequence leakage current caused by the low frequency harmonic voltage generated by the dead zone effect.

[0017] Since the phase of the carrier integer multiple harmonic voltage component generated by the three phases of the three-phase inverter AC side is the same, the three-phase inverter will generate a certain amount of zero sequence voltage, and also generate a zero sequence current. The harmonic order of this current is an integer multiple of the carrier, that is, an integer multiple of the switching sub-harmonic; in order to prevent the upper and lower switch tubes of the inverter from being turned on at the same time, causing a short circuit fault of the main circuit, the trigger signal generally sets a dead time, due to the existence of the dead time, the inverter will generate low frequency harmonics, and the harmonic current generated by the dead zone effect is mainly low frequency odd harmonics. By judging whether the harmonic component of the residual current has a switching integer multiple frequency component and a low frequency odd order fundamental component, the cause of the leakage can be known, so that appropriate repair measures can be taken in time to avoid the further deterioration of the leakage problem and ensure the safe and stable operation of the three-phase grid-connected inverter system.

[0018] Further, according to a ratio range of the amplitude of the residual current signal and the high-frequency threshold value, the collection interval of the grid-connected current signal is set.

[0019] Further, the process of setting the collection interval of the grid-connected current signal comprises:

[0020] calculating a ratio k of the amplitude of the residual current signal and the high-frequency threshold value, k = amplitude of residual current signal / high-frequency threshold value;

[0021] when 0%≤k≤40%, the collection interval of the grid-connected current signal is 3 days;

[0022] when 40%<k≤80%, the collection interval of the grid-connected current signal is 1 day;

[0023] when 80%<k≤100%, the collection interval of the grid-connected current signal is 1h.

[0024] The present application adjusts the leakage monitoring frequency according to the size of the residual current, performs segmented monitoring, and can reduce the workload and detection cost of real-time monitoring. When the residual current value is very small and cannot cause leakage hazards, the monitoring frequency is reduced to save detection cost. When the residual current value approaches the high-frequency threshold value, the monitoring frequency is increased, and the monitoring interval is reduced to monitor the harmonic component of the residual current in time and determine whether there is a potential possibility of leakage.

[0025] Based on the same inventive concept, the present application also provides an electronic device comprising:

[0026] one or more processors;

[0027] a memory having one or more programs stored thereon, which, when executed by the one or more processors, cause the one or more processors to implement the steps of the three-phase grid-connected inverter DC side leakage detection method.

[0028] Based on the same inventive concept, the present application also provides a computer readable storage medium storing a computer program, which, when executed by a processor, implements the steps of the three-phase grid-connected inverter DC side leakage detection method.

[0029] Compared with the prior art, the present application has the following advantages:

[0030] The application analyzes the leakage of the DC side through the residual current of the three-phase inverter AC measurement, the method is relatively simple, the inverter grid-connected system AC measurement is provided with an AC sensor, and no current or voltage sensor needs to be additionally added to the DC side, thereby reducing the equipment cost; the application can know the cause of the leakage by judging whether the harmonic component of the residual current has a switch sub-integer frequency component and a low-frequency odd-order fundamental component, so that corresponding repair measures can be taken in time to avoid the further deterioration of the leakage problem and ensure the safe and stable operation of the three-phase grid-connected inverter system; the application adjusts the monitoring frequency by detecting the amplitude of the residual current to reduce the workload and detection cost of real-time monitoring. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 is a three-phase grid-connected inverter DC side leakage detection module of the application;

[0032] Figure 2 is a flowchart of the three-phase grid-connected inverter DC side leakage detection method of the application;

[0033] Figure 3 is a flowchart of leakage current judgment;

[0034] Figure 4 is a gradient diagram of segmented monitoring. DETAILED DESCRIPTION

[0035] The application will be described in detail below with reference to the embodiments. It should be noted that the embodiments in the application and the features in the embodiments can be combined with each other without conflict. For the convenience of description, if the words "up", "down", "left", "right" appear in the following text, they only mean the up, down, left and right directions of the drawings themselves, and do not limit the structure.

[0036] EMBODIMENT

[0037] The embodiment provides a three-phase grid-connected inverter DC side leakage detection method, one of the purposes of which is to reduce the equipment cost and analyze the frequency spectrum characteristics by measuring the residual current generated by the AC measurement, so as to understand the specific situation of the inverter DC side leakage. The second purpose is to adjust the detection time by detecting the amplitude of the residual current to reduce the workload of real-time monitoring.

[0038] Figure 1 is a three-phase grid-connected inverter DC side leakage detection module related to the embodiment, which comprises a data acquisition unit, a frequency spectrum analysis unit, a leakage identification unit and a segmented monitoring unit. As shown in Figure 2Since the leakage current is generated in the loop of the power grid and the parasitic impedance and the ground, the data acquisition unit first collects the amplitude, frequency and other information of the AC measured grid-connected current by using the AC measured current sensor. Since the residual current is the sum of the currents of the three phases A, B and C, the amplitude, frequency and other information of the residual current can be obtained by adding the grid-connected currents of the three phases. The residual current data is transmitted to the frequency spectrum analysis unit, and the frequency spectrum analysis unit uses the fast Fourier transform (FFT) technology to analyze the frequency, phase and waveform of the collected residual current signal, obtains the frequency, amplitude and waveform characteristics of the residual current signal, converts the residual current signal into an amplitude-frequency curve, and then sends it to the leakage identification unit to identify different characteristic harmonic frequencies of the residual current. Finally, the segmented monitoring unit collects data in different time periods according to the residual current amplitude and feeds back to the leakage detection module.

[0039] Figure 3 is a leakage current judgment flowchart of the leakage identification unit. The following is an explanation of the leakage identification mechanism:

[0040] Due to the modulation effect of the three-phase inverter, a voltage component of the switching sub-harmonic will be generated. The Fourier series expression of the A-phase voltage waveform of the three-phase inverter is as follows:

[0041]

[0042] In the formula, ω = 2πf, f is the fundamental frequency; E d is the DC power supply voltage; M is the modulation degree; N is the carrier ratio; m is the harmonic number relative to the carrier; n is the harmonic number relative to the modulation wave; is the initial phase of the modulation wave; J0, J n is the first Bessel function.

[0043] The phase voltage waveforms of the three-phase inverter are mutually different by 120° in phase. The Fourier series expression of the B-phase voltage waveform of the three-phase inverter is as follows:

[0044]

[0045] The Fourier series expression of the C-phase voltage waveform of the three-phase inverter is as follows:

[0046]

[0047] The first term in the above three expressions is the voltage fundamental wave, the second term is the mth harmonic of the carrier, and the third term is the upper and lower sideband harmonics of the mth harmonic of the carrier.

[0048] Wherein the attention of the second carrier m harmonic, since the A, B, C three-phase carrier integer harmonic voltage component of the same phase in the item, will produce a certain amount of zero sequence voltage, but also will produce zero sequence current, the harmonic frequency should be the integer multiple of the carrier, namely the integer multiple of the switching sub-harmonic. The switching frequency is generally high frequency of kilohertz, so the leakage current can be generated, the form is the integer multiple of the high frequency zero sequence leakage current.

[0049] In order to prevent the upper and lower switch tubes of the inverter from being turned on at the same time, causing the main circuit to be short-circuited, the trigger signal is generally provided with a dead time t d . Due to the existence of the dead time, the inverter will appear low frequency harmonics. The harmonic voltage expression is shown in the following formula:

[0050]

[0051] In the formula, ω represents the angular frequency, f is the fundamental frequency, U s is the DC side voltage, N1 is the number of switching within a cycle, t d is the dead time, is the power factor angle. The amplitude of each harmonic voltage is E mi , i represents the harmonic voltage frequency generated by the dead time effect.

[0052]

[0053] From the above formula, it is easy to know that the harmonic voltage generated by the dead time effect is mainly low frequency odd harmonic, and the harmonic frequency f h satisfies:

[0054] f h = (2i-1)*f i = 1, 2, 3…

[0055] Therefore, the low frequency harmonic voltage generated by the dead time effect can also cause the leakage, at this time the form of the leakage current is the low frequency odd harmonic zero sequence leakage current.

[0056] From the analysis of the above two cases, it can be seen that when the inverter generates leakage, it can generate high frequency zero sequence leakage current with integer multiple of the switching frequency or low frequency odd harmonic zero sequence leakage current. Therefore, based on the above analysis, a judgment mechanism as shown in Figure 3 is established: the residual current amplitude frequency curve generated by the frequency spectrum analysis unit is transmitted to the leakage identification unit, which first judges the amplitude of the residual current. Generally, the high frequency threshold is lower than the low frequency threshold. If the detected residual current amplitude is lower than the high frequency threshold, no leakage occurs. If it is higher than the high frequency threshold, the harmonic frequency corresponding to the leakage current is judged. If the residual current frequency is only the integer multiple of the high frequency switching (the harmonic component frequency in the residual current is distributed in f s and 2fs If the frequency of the residual current is only the low-frequency fundamental odd times (the harmonic component frequency distribution in the residual current is at 3f and 9f), the leakage current is the zero sequence leakage current caused by the low-frequency harmonic voltage generated by the dead-time effect, and if both are met, the leakage current is the zero sequence leakage current caused by the high-frequency harmonic voltage generated by the inverter modulation effect and the low-frequency harmonic voltage generated by the dead-time effect. The high-frequency threshold of the zero sequence leakage current caused by the high-frequency harmonic voltage generated by the inverter modulation effect and the low-frequency threshold of the zero sequence leakage current caused by the low-frequency harmonic voltage generated by the dead-time effect are found in the "People's Republic of China National Standard".

[0057] Figure 4 The segmented monitoring module gradient graph is shown in the figure, the vertical axis is the monitoring interval (the sampling interval of the grid-connected current signal), the horizontal axis is the ratio k of the amplitude of the residual current to the high-frequency threshold, k = amplitude of residual current / high-frequency threshold, 0%≤k≤40% is set as the first gradient, 40%<k≤80% is set as the second gradient, and 80%<k≤100% is set as the third gradient. Among them, when the residual current amplitude is between the first gradient, the monitoring interval of the leakage current is set to 3 days, when the residual current amplitude is between the second gradient, the monitoring interval of the leakage current is set to 1 day, and when the residual current amplitude is between the third gradient, the monitoring interval of the leakage current is set to 1h. The reason for setting the gradient monitoring is to reduce the monitoring frequency when the residual current value is small enough to cause leakage hazards, so as to save costs and be more in line with the actual situation; when the residual current value approaches the leakage current threshold, the monitoring frequency increases, achieving segmented monitoring and minimizing the harm caused by leakage current. When 40%<k≤80%, the monitoring intensity will increase, and the monitoring interval will decrease to monitor the characteristic harmonic components of the residual current in time and determine whether there is a potential possibility of leakage.

[0058] The three-phase grid-connected inverter DC side leakage detection method has always been one of the key factors for safe and reliable operation of the inverter system. The traditional detection method is often limited by high equipment cost, complex operation and online monitoring difficulties. However, by analyzing the frequency spectrum of the inverter AC side leakage current, the specific situation of the DC side leakage current can be clearly understood in a more economical and efficient way, without increasing additional equipment cost, and only with the existing system supporting equipment, the operation can be completed, greatly improving the feasibility and practicality of the method.

[0059] The embodiment effectively overcomes various limitations faced by the conventional technology in leakage current monitoring of the three-phase grid-connected inverter, such as complicated operation and high cost, and thus not only improves the detection efficiency of the leakage current measurement of the DC side of the inverter, but also enhances the reliability of the existing grid-connected system of the inverter in actual application, thereby providing more reliable technical support for the safe operation and stable access to the grid of the inverter system.

[0060] The method of the embodiment is simple in operation, can improve the detection accuracy, accurately judges the leakage condition of the DC side, and based on the existing AC sensor of the system, can reduce the number of current sensors and the detection cost, and through the frequency spectrum distribution characteristics of the AC output current of the inverter, the monitoring timing is formulated in a targeted manner, the online monitoring of the leakage of the DC side of the three-phase grid-connected inverter is realized on the premise of reducing the calculation amount, so that corresponding repair measures can be taken in time to avoid the further deterioration of the leakage problem and ensure the safe and stable operation of the three-phase grid-connected inverter system.

[0061] The embodiment provides an electronic device, comprising:

[0062] one or more processors;

[0063] a memory having one or more programs stored thereon, which when executed by the one or more processors, cause the one or more processors to implement the steps of the leakage detection method of the DC side of the three-phase grid-connected inverter.

[0064] In some implementations, the memory can be a high-speed random access memory (RAM: Random Access Memory), and can also include a non-volatile memory, such as at least one disk memory.

[0065] In other implementations, the processor can be a central processing unit (CPU), a digital signal processor (DSP), or various types of general-purpose processors, without limitation.

[0066] The embodiment provides a computer-readable storage medium having a computer program stored thereon, which when executed by the processor, implements the steps of the leakage detection method of the DC side of the three-phase grid-connected inverter.

[0067] The content illustrated in the above embodiments should be understood as that the embodiments are only used to more clearly illustrate the present application, and are not used to limit the scope of the present application, and after reading the present application, various equivalent modifications of the present application made by those skilled in the art all fall within the scope defined by the appended claims of the present application.

Claims

1. A method for detecting leakage current on the DC side of a three-phase grid-connected inverter, characterized in that, Includes the following steps: S1: Collect the grid-connected current signal on the AC side of the grid-connected inverter, and add the grid-connected current signals of the three phases to obtain the residual current signal; S2: Perform a fast Fourier transform on the residual current signal to obtain the frequency, amplitude, and waveform characteristics of the residual current signal; S3: If the amplitude of the residual current signal is lower than the high-frequency threshold, it is determined that no leakage has occurred; if the amplitude of the residual current signal is higher than or equal to the high-frequency threshold, it is determined that leakage has occurred. The type of leakage current is determined based on the frequency of the residual current signal. The types of leakage current generation include: If the frequency distribution of the harmonic components in the residual current signal is at 3f and 9f, the leakage current is the zero-sequence leakage current caused by the low-frequency harmonic voltage generated by the dead zone effect, where f represents the fundamental frequency. If the frequency distribution of the harmonic components in the residual current signal is within f s and 2f s At this point, the leakage current is the zero-sequence leakage current caused by the high-frequency harmonic voltage components generated by the inverter modulation effect, where f s Indicates the switching frequency; If the frequency distribution of harmonic components in the residual current signal is at 3f, 9f, f s and 2f s At this point, the leakage current includes the zero-sequence leakage current caused by the high-frequency harmonic voltage component generated by the inverter modulation effect and the zero-sequence leakage current caused by the low-frequency harmonic voltage generated by the dead-zone effect.

2. The method for detecting leakage current on the DC side of a three-phase grid-connected inverter according to claim 1, characterized in that, The sampling interval of the grid-connected current signal is set according to the ratio range of the residual current signal amplitude and the high-frequency threshold.

3. The method for detecting leakage current on the DC side of a three-phase grid-connected inverter according to claim 2, characterized in that, The process of setting the acquisition interval of the grid-connected current signal includes: Calculate the ratio k of the amplitude of the residual current signal to the high-frequency threshold, where k = amplitude of the residual current signal / high-frequency threshold; When 0%≤k≤40%, the sampling interval for the grid-connected current signal is 3 days; When 40% < k ≤ 80%, the sampling interval for the grid-connected current signal is 1 day; When 80% < k ≤ 100%, the sampling interval of the grid-connected current signal is 1 hour.

4. An electronic device, characterized in that, include: One or more processors; A memory having stored one or more programs that, when executed by one or more processors, cause the one or more processors to perform the steps of the method according to any one of claims 1-3.

5. A computer-readable storage medium, characterized in that, It stores a computer program that, when executed by a processor, implements the steps of the method according to any one of claims 1-3.

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