Method and device for monitoring reverse power and electric energy quality of transformer in low-voltage transformer area

Abstract

The invention relates to the technical field of power distribution network monitoring, and particularly provides a low-voltage transformer area transformer reverse power and electric energy quality monitoring method and device, and the method comprises the steps: carrying out the multi-channel synchronous collection of the electrical data of the low-voltage side of a low-voltage transformer area, enabling the low-voltage side to be connected with a distributed photovoltaic, and enabling the sampling frequency to be determined by the bandwidth of an electromagnetic voltage transformer; calculating an active power and a first power quality index based on the steady-state electrical data; determining a reverse power monitoring result based on the active power, a preset amplitude threshold and a duration threshold; calculating the maximum value of the dynamic electrical data of each channel in the updating period based on the dynamic electrical data, comparing the difference value between the maximum value and a reference value with a preset threshold value, and updating the reference value or latching an internal overvoltage waveform; and determining a power quality monitoring result according to the first power quality index and the internal overvoltage waveform. The problems that the reverse power working condition of the low-voltage side is difficult to identify timely and accurately and the electric energy quality is difficult to monitor online in real time in the prior art are solved.

Description

Technical Field

[0001] This invention relates to the field of power system distribution network operation monitoring technology, and in particular to a method and device for monitoring the reverse power and power quality of low-voltage transformer substations. Background Technology

[0002] With the continuous advancement of the national "dual carbon" strategic goals, the installed capacity of distributed photovoltaic power generation in urban and rural power distribution networks has grown rapidly. A large number of distributed photovoltaic systems are connected to low-voltage power distribution networks in the form of "self-generation and self-consumption, with surplus power fed into the grid", especially concentrated in residential areas, industrial and commercial user areas and the end of rural power distribution networks.

[0003] Without considering distributed photovoltaic (PV) integration, low-voltage transformers in distribution areas operate under forward power conditions, meaning electricity flows from the high-voltage side to the low-voltage side. However, with high penetration of distributed PV, especially during midday when sunlight is abundant and local load is low, PV power output may significantly exceed the load demand within the distribution area. Excess electricity is then fed back to the transformer via the low-voltage bus and further fed into the upstream distribution network. When this reverse power transmission persists or exceeds the transformer's rated capacity or permissible reverse operation capability, it can damage the transformer and affect power supply stability. Current technologies for monitoring transformer operation on the distribution network side primarily focus on high-voltage side current and power statistics, as well as low-voltage side meter reading data analysis. These technologies struggle to identify low-voltage side reverse power conditions promptly and accurately, and also make real-time online monitoring of power quality difficult.

[0004] There is currently no effective solution to the aforementioned problems in the relevant technologies. Summary of the Invention

[0005] The present invention provides a method and apparatus for monitoring reverse power and power quality of a low-voltage distribution transformer, which at least solves the problem in the related art that it is difficult to identify the reverse power condition on the low-voltage side of a distribution transformer connected to distributed photovoltaics in a timely and accurate manner, and that it is difficult to monitor the power quality online in real time.

[0006] This invention provides a method for monitoring reverse power and power quality of a low-voltage distribution transformer, comprising: acquiring steady-state electrical data and dynamic electrical data of the low-voltage side of the low-voltage distribution transformer using multi-channel synchronous sampling, wherein the low-voltage side of the low-voltage distribution transformer is connected to distributed photovoltaic power, and the sampling frequency of the multi-channel synchronous sampling is determined according to Shannon's sampling theorem and the bandwidth of an electromagnetic voltage transformer, wherein the electromagnetic voltage transformer is used at least to acquire dynamic electrical data; calculating active power and a first power quality index based on the steady-state electrical data; and determining the reverse power monitoring result based on the direction and amplitude of the active power, combined with preset amplitude thresholds and duration thresholds. The process involves: calculating the maximum dynamic electrical data value for each channel within the update cycle based on dynamic electrical data; updating the reference value based on the maximum dynamic electrical data value when the difference between the maximum dynamic electrical data value and the reference value for each channel does not exceed a preset threshold, wherein the update cycle is determined based on the power frequency cycle and a preset number of cycles; latching the internal overvoltage waveform collected within a first recording time when the difference between the maximum dynamic electrical data value and the reference value for any channel exceeds a preset threshold, wherein the first recording time is the sum of the update cycle and a preset second recording time; and determining the power quality monitoring result based on a first power quality indicator and the internal overvoltage waveform. The first power quality indicator includes at least three-phase voltage imbalance, voltage deviation, frequency deviation, harmonic content, flicker, voltage fluctuation, and intermittent waveform.

[0007] Preferably, the calculation of the maximum value of dynamic electrical data for each channel within the update cycle based on dynamic electrical data includes: performing absolute value processing on the dynamic electrical data collected from each channel to obtain first processed data; filtering the first processed data after each power frequency cycle to obtain second processed data, wherein the update cycle is equal to the product of the number of cycles n and the power frequency cycle; solving for the maximum value of each channel within each power frequency cycle based on the second processed data; collecting n maximum values ​​of each channel in each update cycle, removing the lowest and highest values ​​among the n maximum values ​​of each channel, and taking the largest of the remaining n-2 maximum values ​​as the maximum value of dynamic electrical data.

[0008] Preferably, the maximum value of dynamic electrical data for each channel in the earliest update cycle is used as the initial reference value; if the current update cycle is not the earliest update cycle, and the difference between the maximum value of dynamic electrical data for each channel in the current update cycle and the corresponding reference value does not exceed a preset threshold, the reference value corresponding to the current update cycle is updated based on the maximum value of dynamic electrical data for each channel in the current update cycle; if the current update cycle is not the earliest update cycle, and the difference between the maximum value of dynamic electrical data for any channel in the current update cycle and the corresponding reference value exceeds a preset threshold, the internal overvoltage waveform collected within the first recording time corresponding to the current update cycle is latched.

[0009] Preferably, before calculating the active power and the first power quality index based on steady-state electrical data, the above method further includes: determining a zero-point suppression threshold based on noise level and sampling frequency; judging the effectiveness of zero-point crossing on steady-state electrical data based on the zero-point suppression threshold and discrimination conditions; after passing the discrimination, determining the first zero-crossing time based on adjacent sampling points using linear difference calculation; averaging the first zero-crossing times corresponding to multiple power frequency cycles to obtain the second zero-crossing time, wherein the second zero-crossing time is used to determine the phase difference between voltage and current, and the phase difference is used to determine the active power.

[0010] Preferably, the zero-crossing validity determination of steady-state electrical data is based on a zero-point suppression threshold and a discrimination condition, including: if the discrimination condition is met, a valid zero-crossing event is considered to have occurred, and the zero-crossing validity determination is passed. The discrimination condition includes: the waveform sample value in the steady-state electrical data changes from a positive value to a negative value, or from a negative value to a positive value, in consecutive sampling points; the values ​​before and after the positive and negative changes of the waveform sample value are both outside the interval determined based on the zero-point suppression threshold; and the positive and negative directions of the waveform sample value change are consistent within the sampling window corresponding to the positive and negative changes of the waveform sample value.

[0011] Preferably, the reverse power monitoring result is determined based on the direction and amplitude of the active power, combined with preset amplitude thresholds and duration thresholds, including: when the direction of the active power is negative, the amplitude of the active power is greater than or equal to a first preset amplitude threshold, and the duration is greater than or equal to a first preset time threshold, the low-voltage transformer is determined to be in a reverse power operation state; when the low-voltage transformer is in a reverse power operation state, the amplitude of the active power is greater than or equal to a second preset amplitude threshold, and the duration is greater than or equal to a second preset time threshold, the low-voltage transformer is determined to be in a reverse power overload state; wherein, the preset amplitude thresholds include a first preset amplitude threshold and a second preset amplitude threshold, the preset duration thresholds include a first preset time threshold and a second preset time threshold, and the reverse power monitoring result includes the low-voltage transformer being in a reverse power operation state and being in a reverse power overload state.

[0012] Preferably, before acquiring steady-state electrical data and dynamic electrical data of the low-voltage side of the low-voltage transformer using multi-channel synchronous sampling, the method further includes: isolating the electrical signals transmitted by the voltage transformer and the current transformer to obtain isolated signals, wherein the voltage transformer and the current transformer are located on the low-voltage side of the low-voltage transformer; and acquiring data from the isolated signals using multi-channel synchronous sampling to obtain steady-state electrical data and dynamic electrical data.

[0013] This invention also provides a monitoring device for reverse power and power quality of a low-voltage distribution transformer, comprising: a data acquisition module, which acquires steady-state electrical data and dynamic electrical data of the low-voltage side of the low-voltage distribution transformer using a multi-channel synchronous sampling method, wherein the low-voltage side of the low-voltage distribution transformer is connected to distributed photovoltaics, and the sampling frequency of the multi-channel synchronous sampling is determined according to Shannon's sampling theorem and the bandwidth of an electromagnetic voltage transformer, wherein the electromagnetic voltage transformer is used at least to acquire dynamic electrical data; the data acquisition module includes an electromagnetic voltage transformer; a main control module, which calculates active power and a first power quality index based on the steady-state electrical data; determines the reverse power monitoring result based on the direction and amplitude of the active power, combined with a preset amplitude threshold and duration threshold; calculates the maximum value of dynamic electrical data of each channel within the update cycle based on the dynamic electrical data; and compares the maximum value of dynamic electrical data of each channel with a reference value. If the differences do not exceed a preset threshold, the reference value is updated based on the maximum value of the dynamic electrical data. The update cycle is determined based on the power frequency cycle and a preset number of cycles. If the difference between the maximum value of the dynamic electrical data of any channel and the reference value exceeds a preset threshold, the internal overvoltage waveform collected within a first recording time is latched. The first recording time is the sum of the update cycle and a preset second recording time. The power quality monitoring result is determined based on the first power quality index and the internal overvoltage waveform. The storage module stores the raw sampling data collected by the data acquisition module, as well as the active power data, power quality data, and event record information determined by the main control module. The communication module connects to the main control module and is used for periodic data reporting, event-triggered data active reporting, and remote command issuance and response. The power module connects to the main control module and has an internal battery and an external power interface for power supply.

[0014] Preferably, an isolation transformer with a turns ratio of 1:1 is connected in series on the power input side of the power module.

[0015] Preferably, the data acquisition module is equipped with 6+m synchronous sampling channels, each of which is connected to the low-voltage side of the low-voltage distribution transformer through an isolation transformer; among them, the 6 synchronous sampling channels are used to acquire three-phase voltage signals and three-phase current signals, which are used to determine steady-state electrical data and dynamic electrical data, and the m synchronous sampling channels are set as redundant channels and extended channels.

[0016] This invention provides a method for monitoring reverse power and power quality of a low-voltage transformer substation. It involves synchronously acquiring electrical data from the low-voltage side of the substation via multiple channels. The sampling frequency is determined by Shannon's sampling theorem and the bandwidth of an electromagnetic voltage transformer. Based on steady-state electrical data, active power and a first power quality index are calculated. Based on the direction and amplitude of the active power, combined with preset amplitude and duration thresholds, the reverse power monitoring result is determined. Based on dynamic electrical data, the maximum value of dynamic electrical data for each channel within the update cycle is calculated. The difference between the maximum value and a reference value is compared with a preset threshold to update the reference value or latch the internal overvoltage waveform. The power quality monitoring result is determined by the first power quality index and the internal overvoltage waveform. This method enables real-time quantification of the reverse power operating status of the substation substation from the low-voltage side. When monitoring power quality, it can measure both steady-state power quality and dynamic internal overvoltage in real time, thereby improving the accuracy of power quality monitoring. It can solve the problems in related technologies where it is difficult to identify the reverse power condition on the low-voltage side of the transformer connected to distributed photovoltaic power generation in a timely and accurate manner, and it is also difficult to monitor the power quality online in real time. Attached Figure Description

[0017] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention, and those skilled in the art can obtain other embodiments based on these drawings without creative effort.

[0018] Figure 1 This is a flowchart illustrating the steps of a method for monitoring the reverse power and power quality of a low-voltage transformer in an embodiment of the present invention.

[0019] Figure 2 This is a schematic diagram of the process for updating the baseline value and latched data in an embodiment of the present invention.

[0020] Figure 3 This is a schematic diagram of a module for monitoring the reverse power and power quality of a low-voltage transformer in an embodiment of the present invention.

[0021] Figure 4 This is a schematic diagram of the hardware architecture of a monitoring device for reverse power and power quality of a low-voltage transformer in an embodiment of the present invention.

[0022] The above figures include the following reference numerals: 31. Data acquisition module; 32. Main control module; 33. Storage module; 34. Communication module; 35. Power supply module. Detailed Implementation

[0023] Embodiments of the present invention will now be described in more detail with reference to the accompanying drawings. While some embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the present invention. It should be understood that the drawings and embodiments of the present invention are for illustrative purposes only and are not intended to limit the scope of protection of the present invention.

[0024] By the end of 2025, China's installed power generation capacity showed rapid growth, and significant progress was made in energy structure transformation. The total installed power generation capacity nationwide reached 3.99 billion kilowatts, a year-on-year increase of 19.2%; the installed capacity of new energy sources surpassed traditional thermal power for the first time, reaching 1.92 billion kilowatts, accounting for 48.2%; photovoltaic (PV) installed capacity reached 1.26 billion kilowatts, a year-on-year increase of 35.5%, accounting for 31.6% of the total installed capacity; and distributed PV installed capacity was approximately 570 million kilowatts, a year-on-year increase of 33.5%. Distributed PV installed capacity already accounted for 45.2% of the total PV installed capacity.

[0025] The installed capacity of distributed photovoltaic (PV) power generation in urban and rural power distribution networks is growing rapidly, now accounting for nearly 50% of the total PV installed capacity. A large number of distributed PV systems are connected to low-voltage distribution networks using a "self-consumption with surplus power fed into the grid" model, particularly concentrated in residential transformer substations, industrial and commercial transformer substations, and the ends of rural power distribution networks. Low-voltage transformer substations typically use 10kV / 0.4kV distribution transformers as the core for power conversion and supply, designed to step down medium-voltage power before supplying it to low-voltage users.

[0026] Before the integration of distributed photovoltaic (PV) systems, the transformer in the distribution area operates under forward power conditions, meaning that electrical energy flows from the high-voltage side to the low-voltage side. However, after the high penetration rate of distributed PV systems, especially when sunlight conditions are good at midday and local load levels are low, the PV power output may significantly exceed the load demand within the distribution area. The excess electrical energy will be fed back to the transformer in the distribution area via the low-voltage busbar and further fed into the upstream distribution network.

[0027] When reverse power transmission persists or even exceeds the rated capacity or permissible reverse operation capability of the transformer, the following problems will occur: the transformer changes from step-down operation to step-up operation, altering its original electromagnetic design conditions; the transformer core, windings, and auxiliary equipment may be subjected to electromagnetic and thermal stresses in directions other than the design direction for a long time, accelerating insulation aging; it may cause problems such as low-voltage side voltage exceeding limits, power quality deterioration, and protection configuration mismatch; in extreme cases, it may cause overload, tripping, or even damage to the transformer.

[0028] The main monitoring methods for the operating status of transformer substations on the distribution network side are concentrated on high-voltage side current and power statistics and low-voltage side meter reading data analysis. It is difficult to identify the reverse power condition on the low-voltage side in a timely and accurate manner, and it is also difficult to monitor power quality online in real time.

[0029] Therefore, please refer to Figure 1 As shown, the present invention provides a method for monitoring the reverse power and power quality of a low-voltage transformer, including steps S101 to S107.

[0030] Step S101: The steady-state electrical data and dynamic electrical data of the low-voltage side of the low-voltage transformer are collected using a multi-channel synchronous sampling method. The low-voltage side of the low-voltage transformer is connected to a distributed photovoltaic system. The sampling frequency of the multi-channel synchronous sampling is determined based on Shannon's sampling theorem and the bandwidth of the electromagnetic voltage transformer. The electromagnetic voltage transformer is used at least to collect dynamic electrical data.

[0031] Step S102: Calculate the active power and the first power quality index based on steady-state electrical data.

[0032] Step S103: Based on the direction and amplitude of active power, and combined with preset amplitude threshold and duration threshold, determine the reverse power monitoring result.

[0033] Step S104: Calculate the maximum value of dynamic electrical data for each channel within the update cycle based on the dynamic electrical data.

[0034] Step S105: If the difference between the maximum value of the dynamic electrical data of each channel and the reference value does not exceed the preset threshold, the reference value is updated based on the maximum value of the dynamic electrical data. The update cycle is determined based on the power frequency cycle and the preset number of cycles.

[0035] Step S106: If the difference between the maximum value of the dynamic electrical data of any channel and the reference value exceeds a preset threshold, latch the internal overvoltage waveform collected within the first recording time, wherein the first recording time is the sum of the update period and the preset second recording time.

[0036] Step S107: Determine the power quality monitoring results based on the first power quality index and the internal overvoltage waveform.

[0037] The low-voltage side of a low-voltage distribution transformer refers to the side of the transformer that outputs low-voltage electrical energy. It is the side that directly connects the transformer to the low-voltage distribution lines, user loads, and distributed photovoltaic grid-connected systems within the distribution area.

[0038] Steady-state electrical data refers to the long-term, stable, and periodically monitorable electrical quantities of low-voltage transformers during operation. These data are used to calculate active power, determine reverse power status, and analyze primary power quality indicators. Steady-state electrical data includes at least the steady-state RMS values ​​of the three-phase voltages, the steady-state RMS values ​​of the three-phase currents, and the power factor.

[0039] The primary power quality indicators should include at least three-phase voltage imbalance, voltage deviation, frequency deviation, harmonic content, flicker, voltage fluctuation, and intermittent waves.

[0040] Dynamic electrical data refers to the instantaneous and intermittent electrical quantities that occur during the operation of a low-voltage distribution area. These quantities need to be captured synchronously at a high frequency (e.g., 100Hz) to monitor dynamic events such as internal overvoltage. Dynamic electrical data includes at least instantaneous waveform data, such as internal overvoltage waveforms.

[0041] Based on synchronously acquired voltage, current and power factor, the three-phase active power of the low-voltage side of the low-voltage transformer is calculated in real time, and the three-phase power is summed to obtain the total active power on the low-voltage side.

[0042] Specifically, within any sampling period (the reciprocal of the sampling frequency), based on the synchronously acquired three-phase voltage and three-phase current data, the instantaneous active power of the three phases is calculated, and then averaged over the power frequency period to obtain the three-phase active power. , and Total active power on the low-voltage side of the transformer in the distribution area. .

[0043] Based on the direction and amplitude of active power, combined with preset amplitude and duration thresholds, the reverse power monitoring result is determined. Introducing both time and amplitude criteria avoids misjudgments caused by instantaneous fluctuations or measurement errors. The reverse power monitoring result includes whether the low-voltage transformer is operating in reverse power mode or in reverse power overload mode, which will be explained in detail later.

[0044] The difference between the maximum value of the dynamic electrical data and the reference value is compared with a preset threshold. This involves comparing whether the absolute value of the difference exceeds the absolute value of the preset threshold. The specific value of the preset threshold can be determined by those skilled in the art in conjunction with the monitoring environment and a limited number of experiments.

[0045] Compared to internal overvoltage, external overvoltage is lightning overvoltage. Due to the extremely high frequency (1MHz) of lightning waves, a sampling frequency of at least 60MHz is required to collect lightning overvoltage data, and it is also necessary to ensure that the high energy of the lightning waves does not cause breakdown. Therefore, there is currently a lack of instruments that can measure external overvoltage. Thus, the monitoring method provided in this embodiment only considers internal overvoltage when monitoring overvoltage, a power quality indicator.

[0046] Regarding the monitoring of internal overvoltage, the frequency of internal overvoltage is usually concentrated around 3kHz, while the voltage waveform of electromagnetic transformers has a frequency below 5kHz, which can be used to measure the overvoltage waveform of step-up transformers in low-voltage distribution areas.

[0047] Since the voltage waveform is sinusoidal, at least 10 sampling points per cycle are needed to record a complete sinusoidal wave. Furthermore, Shannon's sampling theorem requires that the actual sampling rate be twice the theoretical sampling rate, meaning a sinusoidal wave requires at least 20 sampling points. Taking an electromagnetic voltage transformer with a bandwidth of 5kHz as an example, the sampling frequency for multi-channel synchronous sampling needs to be set to 100kHz.

[0048] Specifically, relevant power quality measurement methods can measure the power quality of steady-state quantities without requiring strict phase angle measurement, but they cannot measure the waveform of internal overvoltages (dynamic events) and cannot record waveform data (dynamic electrical data) at fault and abnormal moments. Furthermore, considering steady-state measurement, the recording amplitude of internal overvoltages is limited to no more than twice the rated value; any excess is limited by hardware to protect the measurement circuit. In other words, even if internal overvoltage measurements are performed, the complete internal overvoltage waveform cannot be obtained.

[0049] The monitoring method provided in this embodiment, by employing multi-channel synchronous sampling, can obtain accurate phase differences. While ensuring the accuracy of the phase angle between voltage and current waveforms (which directly determines the direction and magnitude of active power), it also guarantees the strict synchronous measurement requirements for internal overvoltage measurement in power quality indicators. This avoids the phase difference caused by using a single A / D acquisition chip controlled by a shunt switch, which could affect the measured values ​​of the three-phase overvoltage waveform. The monitoring device subsequently provided in this embodiment will be specifically described using an 8-channel synchronous acquisition structure data acquisition module as an example.

[0050] In other words, the monitoring method provided in this embodiment can measure both steady-state power quality (the first power quality index) and dynamic internal overvoltage in real time when monitoring power quality, thereby improving the accuracy of power quality monitoring.

[0051] Furthermore, by using channel isolation (non-common ground) and passive transformer isolation of the power supply, internal overvoltages up to 5 times the rated voltage can be recorded for extended periods, while higher internal overvoltages can be tolerated for shorter periods, further ensuring accurate recording of the entire internal overvoltage waveform. Details regarding channel isolation (non-common ground) and passive transformer isolation of the power supply will be explained later.

[0052] The latching of the internal overvoltage waveform acquired during the first recording time means that all data acquired by each synchronous sampling channel during the first recording time is saved. In this embodiment, the following explanation will be based on an example with a power frequency of 50Hz, a cycle count of 10, a second recording time of 4.8s, a power frequency period of 20ms, an update period of 200ms, and a first recording time of 5s.

[0053] The initial reference value (the initial value of the reference value) can be predetermined by those skilled in the art through a limited number of experiments, or the maximum value of the dynamic electrical data of each channel in the earliest update cycle can be used as the initial reference value. In this embodiment, the preferred method is to use the maximum value of the dynamic electrical data of each channel in the earliest update cycle as the initial reference value.

[0054] By updating the reference value, it is possible to accurately determine whether an internal overvoltage event exists within one update cycle (200ms), regardless of whether the voltage rises or falls sharply.

[0055] In summary, the monitoring method provided in this embodiment can quantify the reverse power operating status of transformers in low-voltage areas in real time, monitoring both reverse power and power quality simultaneously, thus meeting the comprehensive monitoring needs of low-voltage distribution areas. By using multi-channel, high-sampling-rate synchronous acquisition and collecting the complete waveform of internal overvoltages, monitoring accuracy can be improved. This solves the problems in related technologies where it is difficult to identify the reverse power condition on the low-voltage side of transformers connected to distributed photovoltaic systems in a timely and accurate manner, and where it is difficult to monitor power quality online in real time.

[0056] During the grid-connected operation of distributed photovoltaic systems in low-voltage distribution areas, the voltage and current signals on the low-voltage side of the transformer typically contain superimposed harmonics, random disturbances, and switching noise. Especially near the zero-crossing points of the voltage and current waveforms, jitter, jumps, or multiple zero-crossings are prone to occur. Directly detecting zero-crossing points based on single sampling points or asynchronous sampling results will lead to errors in phase difference calculation, thus affecting the accuracy of power direction determination and reverse power overload criteria. Therefore, this embodiment introduces zero-crossing jitter suppression based on the aforementioned monitoring method, which helps improve monitoring accuracy.

[0057] Specifically, in multi-channel synchronous sampling, each analog-to-digital sampling channel starts synchronously under the control of the same sampling clock; each analog-to-digital sampling channel completes sampling and data latching within the same sampling period; and the voltage and current data corresponding to the same sampling moment in multi-channel synchronous sampling are consistent on the time axis. This helps to avoid phase offset errors introduced by multi-channel polling sampling or asynchronous sampling, and provides a unified time reference for subsequent phase difference calculation.

[0058] Specifically, in step S102, before calculating the active power and the first power quality index based on steady-state electrical data, the method further includes: determining a zero-point suppression threshold based on noise level and sampling frequency; determining the validity of zero-point crossings in the steady-state electrical data based on the zero-point suppression threshold and discrimination conditions; after passing the discrimination, determining the first zero-crossing time based on adjacent sampling points using linear difference calculation; averaging the first zero-crossing times corresponding to multiple power frequency cycles to obtain the second zero-crossing time, wherein the second zero-crossing time is used to determine the phase difference between voltage and current, and the phase difference is used to determine the active power.

[0059] Synchronous sampling acquires voltage sampling sequences within one or more power frequency cycles. and current sampling sequence Set the zero-point suppression threshold. and .exist In this case, it is determined to be the interval near the voltage zero point. In this case, it is determined to be the interval near the zero current point.

[0060] Specifically, the zero-crossing validity is determined based on the zero-point suppression threshold and discrimination conditions. This includes: if the discrimination conditions are met, a valid zero-crossing event is considered to have occurred, and the zero-crossing validity is determined. The discrimination conditions include: the waveform sample value in the steady-state electrical data changes from a positive value to a negative value, or from a negative value to a positive value, in consecutive sampling points; the values ​​before and after the positive and negative changes of the waveform sample value are both outside the interval determined based on the zero-point suppression threshold; and the positive and negative directions of the waveform sample value change are consistent within the sampling window corresponding to the positive and negative changes of the waveform sample value.

[0061] Specifically, taking the effective zero-point crossing between sampling point n1 and sampling point n1+1 as an example, the zero-point crossing time t0 is calculated as follows: take the voltage value U(n1) corresponding to sampling point n1 and the voltage value U(n1+1) corresponding to sampling point n1+1, or take the current value corresponding to sampling point n1 and sampling point n1+1; use the linear interpolation method to calculate the precise time position when the waveform is zero.

[0062] To further improve measurement stability, the zero-crossing calculation process described above can be repeated over multiple power frequency cycles, and the obtained zero-crossing times can be averaged to reduce the impact of occasional disturbances on single-cycle measurement results.

[0063] Specifically, the phase difference between voltage and current for: ; ; In the formula, Indicates the power frequency period, This indicates the time when the voltage of the same phase crosses zero. This indicates the moment when the corresponding phase current crosses zero.

[0064] By combining multi-channel synchronous sampling, zero-point jitter suppression, and accurate zero-crossing calculation, it is possible to ensure strict synchronization of voltage and current sampling in time, effectively suppress false zero-crossings caused by noise and harmonics near the zero point, improve the accuracy and stability of voltage and current phase difference calculation, and provide reliable basic data for the determination of reverse power and reverse power overload in low-voltage distribution areas.

[0065] Preferably, before step S101, which involves acquiring steady-state and dynamic electrical data from the low-voltage side of the low-voltage transformer using multi-channel synchronous sampling, the method further includes: isolating the electrical signals transmitted by the voltage transformer and current transformer to obtain isolated signals, wherein the voltage transformer and current transformer are located on the low-voltage side of the low-voltage transformer. The isolated signals are then acquired using multi-channel synchronous sampling to obtain steady-state and dynamic electrical data.

[0066] By employing a non-common-ground electrical isolation sampling method, sampling interference caused by ground potential difference, common-mode voltage, and ground loop current can be effectively suppressed. This improves the accuracy and stability of voltage and current zero-crossing detection and phase difference calculation under multi-channel synchronous sampling conditions, thereby providing a reliable guarantee for the identification of reverse power and reverse power overload in low-voltage distribution areas. The monitoring device provided later in this embodiment will further illustrate this.

[0067] Preferably, step S103, based on the direction and amplitude of active power, combined with preset amplitude threshold and duration threshold, determines the reverse power monitoring result, including: when the direction of active power is negative, the amplitude of active power is greater than or equal to the first preset amplitude threshold and the duration is greater than or equal to the first preset time threshold, it is determined that the low-voltage transformer is in reverse power operation state.

[0068] If a low-voltage transformer is in reverse power operation mode, and the amplitude of its active power is greater than or equal to the second preset amplitude threshold and the duration is greater than or equal to the second preset time threshold, the low-voltage transformer is determined to be in reverse power overload mode.

[0069] The preset amplitude thresholds include a first preset amplitude threshold and a second preset amplitude threshold; the preset duration thresholds include a first preset time threshold and a second preset time threshold; and the reverse power monitoring results include the low-voltage transformer being in reverse power operation state and in reverse power overload state.

[0070] Specifically, when the low-voltage transformer is in forward power operation (forward power supply), electrical energy flows from the high-voltage side to the low-voltage side through the transformer. When the low-voltage transformer is in reverse power operation, electrical energy is fed back from the low-voltage side to the high-voltage side.

[0071] The first preset amplitude threshold can be determined proportionally to the rated capacity of the low-voltage transformer, for example, 5% to 10% of the rated capacity. The second preset amplitude threshold can be the rated capacity of the low-voltage transformer or the upper limit of permissible reverse power confirmed by operation and maintenance. The first preset time threshold and the second preset time threshold can be determined by those skilled in the art based on a limited number of experiments, for example, several consecutive power frequency cycles or several seconds.

[0072] Preferably, step S104, calculating the maximum value of dynamic electrical data for each channel within the update cycle based on dynamic electrical data, includes: performing absolute value processing on the dynamic electrical data collected from each channel to obtain first processed data. After each power frequency cycle, the first processed data is filtered to obtain second processed data, where the update cycle is equal to the product of the number of cycles n and the power frequency cycle. Based on the second processed data, the maximum periodic value for each channel within each power frequency cycle is calculated. For each channel, n maximum periodic values ​​are collected in each update cycle. The lowest and highest values ​​among the n maximum periodic values ​​are removed, and the largest of the remaining n-2 maximum periodic values ​​is taken as the maximum value of the dynamic electrical data.

[0073] The filtering algorithms used for filtering can be, but are not limited to, amplitude limiting filtering and median filtering.

[0074] Preferably, the maximum value of the dynamic electrical data of each channel in the earliest update cycle is used as the initial reference value.

[0075] If the current update cycle is not the earliest update cycle, and the difference between the maximum value of the dynamic electrical data of each channel in the current update cycle and the corresponding reference value does not exceed the preset threshold, the reference value corresponding to the current update cycle is updated based on the maximum value of the dynamic electrical data of each channel in the current update cycle.

[0076] If the current update cycle is not the earliest update cycle, and the difference between the maximum value of the dynamic electrical data of any channel within the current update cycle and the corresponding reference value exceeds a preset threshold, the internal overvoltage waveform acquired within the first recording time corresponding to the current update cycle is latched. For example, with a power frequency of 50Hz, a cycle count of 10, and a second recording time of 4.8s, the power frequency cycle is 20ms, the update cycle is 200ms, and the first recording time is 5s. Please refer to... Figure 2As shown, the internal overvoltage waveform latched within the first recording time of 5 seconds includes the internal overvoltage waveform within the earliest update cycle, as well as the internal overvoltage waveform acquired within 4.8 seconds after the end of the current update cycle.

[0077] Please refer to Figure 3 As shown in the figure, the present invention also provides a monitoring device for the reverse power and power quality of a low-voltage transformer, including a data acquisition module 31, a main control module 32, a storage module 33, a communication module 34 and a power supply module 35.

[0078] The data acquisition module 31 uses a multi-channel synchronous sampling method to acquire steady-state electrical data and dynamic electrical data of the low-voltage side of the low-voltage transformer. The low-voltage side of the low-voltage transformer is connected to distributed photovoltaics. The sampling frequency of the multi-channel synchronous sampling is determined according to Shannon's sampling theorem and the bandwidth of the electromagnetic voltage transformer. The electromagnetic voltage transformer is used to acquire dynamic electrical data at least. The data acquisition module 31 includes an electromagnetic voltage transformer.

[0079] The main control module 32 calculates active power and a first power quality index based on steady-state electrical data; determines the reverse power monitoring result based on the direction and amplitude of active power, combined with preset amplitude and duration thresholds; calculates the maximum value of dynamic electrical data for each channel within the update cycle based on dynamic electrical data; updates the reference value based on the maximum value of dynamic electrical data for each channel if the difference between the maximum value of dynamic electrical data for each channel and the reference value does not exceed a preset threshold, wherein the update cycle is determined based on the power frequency cycle and a preset number of cycles; latches the internal overvoltage waveform collected within a first recording time if the difference between the maximum value of dynamic electrical data for any channel and the reference value exceeds a preset threshold, wherein the first recording time is the sum of the update cycle and a preset second recording time; and determines the power quality monitoring result based on the first power quality index and the internal overvoltage waveform.

[0080] The storage module 33 is used to store the raw sampling data collected by the data acquisition module 31, as well as the active power data, power quality data and event log information determined by the main control module 32.

[0081] The communication module 34 is connected to the main control module 32 and is used for periodic data reporting, event-triggered active data reporting, and remote command issuance and response.

[0082] The power module 35 is connected to the main control module 32 and is equipped with an internal battery and an external power interface for power supply.

[0083] The monitoring device provided in this embodiment may also be equipped with an auxiliary interface module.

[0084] The monitoring device provided in this embodiment is deployed near the low-voltage transformer and directly connected to the low-voltage side busbar or low-voltage outgoing line of the transformer.

[0085] The monitoring device provided in this embodiment actively triggers a data upload mechanism when a reverse power overload occurs, uploading the reverse power amplitude, voltage, current, and related power quality data to the remote centralized control station monitoring platform; under normal operating conditions, it continuously calculates power quality indicators and uploads power quality data on demand or at set times according to the instructions of the remote centralized control station monitoring platform.

[0086] Based on the monitoring device provided in this embodiment, high-precision synchronous acquisition and analysis of electrical quantities on the low-voltage side of the transformer in the distribution area allows for real-time determination of whether the transformer is operating under reverse power conditions. When the reverse power exceeds a set threshold, monitoring data is actively uploaded, making the reverse power in the low-voltage distribution area perceptible and quantifiable. This enables real-time quantification of the reverse power operating status of the transformer in the low-voltage side, monitoring power quality while simultaneously monitoring reverse power, thus meeting the comprehensive monitoring needs of low-voltage distribution areas. Multi-channel, high-sampling-rate synchronous acquisition, along with the acquisition of the complete waveform of internal overvoltages, improves monitoring accuracy.

[0087] Preferably, the data acquisition module 31 of the aforementioned monitoring device is configured to isolate the electrical signals transmitted from the voltage transformer and current transformer. All analog electrical quantities use dual-ended input, and all channels are isolated from each other, overcoming common ground interference between channels. Each signal is isolated from the others and simultaneously converted, proportionally reducing the voltage to isolate the primary and secondary voltages. This method is suitable for measuring voltage and current parameters from power frequency to intermediate frequency, and can avoid high-intensity interference signals from internal overvoltage.

[0088] Specifically, by setting up an electrical isolation structure between the signal acquisition channel and the main control system, the sampling channel has an independent reference ground: cutting off the ground potential conduction path between different devices or measuring points; preventing ground potential differences from being superimposed on the sampling signal; and ensuring the stability of the zero-point position of the sampling signal. This effectively suppresses the influence of ground potential differences and significantly improves AC zero-crossing detection and phase difference calculation.

[0089] Non-common-ground sampling blocks common-mode voltage through isolation structures, making it difficult for power frequency common-mode voltage to couple into the sampling system. This significantly attenuates harmonics and high-frequency interference, resulting in a marked reduction in waveform noise levels. Measurement results show a smoother waveform, reduced jitter amplitude near zero, and improved phase measurement stability. It also significantly reduces the introduction of common-mode interference.

[0090] By isolating and eliminating ground loop paths under multi-point grounding conditions, induced interference caused by ground loop currents, the impact of external large current changes on the sampling system, and the propagation of lightning strikes or surges to the measurement channel through the ground wire can be effectively avoided. This improves the operational stability of the entire monitoring device in complex power distribution sites.

[0091] In a non-common-ground structure, electrical isolation between synchronous sampling channels prevents interference from a single channel from spreading to other channels. This ensures consistent phase relationships during multi-channel synchronous sampling, significantly improving the consistency of three-phase voltage and current measurements. This advantage is particularly important for power direction determination and reverse power overload monitoring based on synchronous sampling.

[0092] Preferably, an isolation transformer with a 1:1 turns ratio is connected in series on the power input side of the power module 35. This enables electrical isolation between the power supply system of the monitoring device and the low-voltage distribution area power supply system, effectively suppressing ground potential coupling, common-mode interference, and transient impacts, improving the stability and reliability of the device's power supply, and ensuring the long-term stable operation of the monitoring device in complex low-voltage distribution area environments. It is particularly suitable for distribution areas with a high proportion of distributed photovoltaic access, rural or suburban distribution areas with frequent power fluctuations, and installation environments without dedicated voltage regulation power supply conditions.

[0093] Specifically, in low-voltage distribution areas, the power supply is typically drawn from the low-voltage side of the distribution transformer. Its power quality is susceptible to voltage fluctuations, surges, and transient interference due to factors such as load fluctuations, distributed photovoltaic grid connection, and the operation of power electronic equipment. If the monitoring device's power system is directly electrically connected to the low-voltage distribution area's power supply system, these unstable factors can easily be transmitted to the device, affecting its long-term stable operation and the reliability of measurement data. Therefore, a passive isolation transformer structure is introduced on the power input side as a pre-stage step for power connection.

[0094] By connecting an isolation transformer with a 1:1 ratio in series on the power input side, the internal power supply system of the monitoring device is electrically isolated from the power supply system of the low-voltage distribution area. This cuts off the direct connection between the external power ground and the internal reference ground of the device, avoids interference and drift caused by ground potential difference, and prevents the impact of external grounding system fluctuations on the stability of the internal power supply of the device.

[0095] Low-voltage distribution lines commonly experience power frequency and high-order harmonics, transient impacts caused by switching equipment operation, and high-frequency interference from distributed photovoltaic inverters. Isolation transformers have a natural ability to suppress these interferences, blocking and attenuating common-mode interference, and providing low-pass filtering characteristics for high-frequency noise, thus reducing the probability of interference energy entering the device.

[0096] In low-voltage distribution areas, voltage surges or transient overvoltages may occur on the power supply side under conditions such as lightning strikes, capacitor switching, and sudden load changes. By using an isolation transformer as a front-end buffer unit, energy transfer of transient overvoltages can be achieved through magnetic coupling, reducing the amplitude of the surge directly affecting the downstream power supply module and improving the overall impact resistance and safety margin of the device.

[0097] An isolation transformer with a 1:1 turns ratio is connected in series on the power input side of the power module 35. This structure is simple and highly reliable, and does not rely on control circuits or software logic. Its introduction helps to reduce the probability of device reset or crash due to power transient abnormalities, improves the long-term continuous operation capability of the monitoring device in complex transformer substation environments, and provides more stable input conditions for downstream voltage regulation, energy storage or backup power units.

[0098] Preferably, the data acquisition module 31 is equipped with 6+m synchronous sampling channels, each of which is connected to the low-voltage side of the low-voltage distribution transformer via an isolation transformer. The 6 synchronous sampling channels are used to acquire three-phase voltage and current signals, which are used to determine steady-state and dynamic electrical data. The m synchronous sampling channels are configured as redundant and extended channels.

[0099] Each synchronous sampling channel is connected to the low-voltage side of the low-voltage distribution transformer via an isolation transformer, which helps to ensure personal safety and improve system reliability.

[0100] For example, the data acquisition module 31 is provided with 8 synchronous sampling channels, each of which is equipped with an A / D acquisition chip, and 2 of the synchronous sampling channels serve as redundant channels and expansion channels. The sampling frequency of the 8 synchronous sampling channels is synchronized at 100kHz.

[0101] For example, the hardware architecture of the above monitoring device is described in reference to... Figure 4 As shown.

[0102] The data acquisition module 31, with a sampling frequency set to 100kHz, can acquire a sufficient number of discrete sampling points within one power frequency cycle, providing high-time-resolution raw data for power calculation and power quality analysis, ensuring accurate measurement of internal overvoltages. The eight sampling channels employ eight A / D converters, with synchronous sampling initiated by the same clock source, avoiding the impact of phase deviations between channels on power direction determination.

[0103] The main control module 32 adopts an embedded control platform based on the PC104 bus architecture, which has the advantages of small size, strong vibration resistance, and good adaptability to industrial environments. It has a built-in high-performance processor, enabling real-time processing and analysis of large-scale data at the target monitoring site. It runs an embedded operating system and includes built-in power calculation programs, reverse power overload detection algorithms, power quality analysis algorithms, and a communication protocol stack.

[0104] When a reverse power overload event is detected, the main control module 32 immediately triggers the event flag and performs the following operations: 1) latches the voltage, current and power data within a preset time window (update cycle) before and after the event; 2) calculates and organizes the key indicators during the event, including the peak reverse power, duration, voltage change amplitude, etc.; 3) actively uploads the event data and analysis results to the remote centralized control station monitoring platform through the communication module 34.

[0105] The main control module 32 calculates the power quality indicators according to the preset algorithm, and uploads a set of power quality data at a specified time when it receives the instruction from the remote control station; or uploads the power quality statistics results at preset intervals.

[0106] Storage module 33 uses high-capacity flash memory (e.g., 64MB-2GB) to store raw sampling data and calculation results within at least one preset time window (e.g., update cycle) before and after a reverse power event. When communication conditions are limited, data can be cached locally first and then uploaded uniformly after communication is restored.

[0107] The communication module 34 adopts a mobile GPRS communication unit to establish a data channel with the remote central control station monitoring platform through a public wireless network.

[0108] The power module 35 adopts a military-grade wide-temperature battery power supply design, with an operating temperature range covering -40℃ to 50℃. When the external AC power supply is normal, the external power supply powers the device and charges the battery; when the external power supply fails, it automatically switches to battery power supply mode, maintaining continuous and stable operation of the device for no less than 1 hour, ensuring no loss of power during critical events such as reverse power overload. After the external power supply is restored, it automatically switches back to external power supply and manages battery charging.

[0109] Preferably, the process of reverse power overload monitoring by the monitoring device provided in this embodiment includes system initialization, synchronous acquisition of low-voltage side electrical quantities, active power calculation, reverse power start-up discrimination, reverse power overload discrimination, event latching and data processing, event data uploading, state recovery and continuous monitoring.

[0110] After system initialization and power-on of the monitoring device, the main control module 32 completes self-test, reads the transformer capacity parameters of the distribution area, the reverse power start threshold (the first preset amplitude threshold and the first preset time threshold corresponding to the reverse power operation state), and the reverse power overload threshold (the second preset amplitude threshold and the second preset time threshold corresponding to the reverse power overload state), and enters the normal monitoring state.

[0111] The electrical quantities on the low-voltage side are synchronously acquired. The data acquisition module 31 performs 8-channel synchronous sampling of the three-phase voltage and three-phase current on the low-voltage side of the transformer at a sampling frequency of 100kHz, and sends the sampled data to the main control module 32 in real time.

[0112] Active power calculation: The main control module 32 processes the collected voltage and current data within the power frequency cycle to calculate the three-phase active power and sum them to obtain the total active power on the low-voltage side. .

[0113] Reverse power start-up detection, when active power is detected When the value is negative, its absolute value is greater than or equal to the first preset amplitude threshold, and the duration reaches the first preset time threshold, the transformer area is determined to have entered a stable reverse power operation state, and the system enters the reverse power key monitoring mode to improve the time resolution of power calculation and discrimination.

[0114] In reverse power overload detection, under the reverse power key monitoring mode, the main control module 32 continuously compares the absolute value of reverse power with the second preset amplitude threshold. When the absolute value of reverse power is greater than or equal to the second preset amplitude threshold and the duration reaches the second preset time threshold, a reverse power overload event is determined to have occurred.

[0115] Event latching and data processing: After the reverse power overload event is determined, the main control module 32 latches the voltage, current, power and power factor data within a preset time window (e.g., update cycle) before and after the event occurs, and calculates key indicators such as reverse power peak value, duration and voltage change.

[0116] Event data upload: The main control module 32 actively uploads reverse power overload event information and related monitoring data to the remote centralized control station monitoring platform through the communication module 34 using an event triggering method.

[0117] Status recovery and continuous monitoring: When the absolute value of the reverse power recovers to below the second preset amplitude threshold and remains below it for a certain period of time, the system automatically exits the reverse power key monitoring mode, returns to the normal monitoring state, and continues to execute the above process.

[0118] For example, the application scenario of the monitoring device provided in this embodiment includes a rural low-voltage distribution area.

[0119] In this rural low-voltage distribution area, the transformer capacity is 200kVA, and multiple rooftop distributed photovoltaic (PV) systems are connected to the low-voltage side, with a total installed capacity of approximately 260kW. During the midday hours in summer, the residential load in this rural low-voltage distribution area is low, and the PV output is concentrated, which can easily lead to a situation where the PV power generation exceeds the local load.

[0120] Before the deployment of the monitoring device provided in this embodiment, the transformer in this rural low-voltage distribution area was in a reverse power supply state for a long time. However, due to the lack of real-time monitoring means on the low-voltage side, it was difficult for maintenance personnel to grasp the frequency of reverse power occurrence and the degree of overload in a timely manner.

[0121] After installing the monitoring device provided in this embodiment on the low-voltage side of the transformer in the distribution area, the monitoring device collects the three-phase voltage, current, and power factor of the low-voltage side in real time and calculates the total active power on the low-voltage side. When the photovoltaic output reaches its peak at noon, the monitoring device detects that the total active power on the low-voltage side is negative, and its absolute value exceeds the first preset amplitude threshold and the duration exceeds the first preset time threshold, thus determining that the transformer in the rural low-voltage distribution area has entered the reverse power operation state.

[0122] When the absolute value of the reverse power exceeds the rated capacity of the transformer in the distribution area and the duration exceeds the second preset time threshold, the monitoring device determines that a reverse power overload event has occurred, immediately latches the data before and after the event, and actively uploads alarm information and related data to the remote centralized control station monitoring platform through the GPRS communication module.

[0123] Based on the uploaded data, the remote centralized control station monitoring platform analyzes the matching between the photovoltaic grid connection scale and transformer capacity in the rural area, providing a basis for decision-making in subsequent photovoltaic output regulation, grid capacity expansion, or operation mode adjustment.

[0124] The present invention also provides a non-transitory machine-readable medium storing a computer program, wherein the computer program, when executed by a computer's processor, is used to cause the computer to perform a method according to an embodiment of the present invention.

[0125] The present invention also provides a computer program product, including a computer program, wherein the computer program, when executed by a computer's processor, is used to cause the computer to perform the method of the embodiments of the present invention.

[0126] It should be noted that the term "comprising" and its variations used in the embodiments of this invention are open-ended, meaning "including but not limited to". The term "based on" means "at least partially based on". The term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one additional embodiment"; the term "some embodiments" means "at least some embodiments". The modifications of "one" and "a plurality" mentioned in the embodiments of this invention are illustrative and not restrictive, and those skilled in the art should understand that unless explicitly indicated otherwise in the context, they should be understood as "one or more". The descriptions of terms such as "first", "second", etc., are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of indicated technical features.

[0127] The user information (including but not limited to user device information, user personal information, etc.) and data (including but not limited to data used for analysis, stored data, displayed data, etc.) involved in the embodiments of this invention are all information and data authorized by the user or fully authorized by all parties.

[0128] The steps described in the method embodiments provided by the present invention can be performed in different orders and / or in parallel. Furthermore, the method embodiments may include additional steps and / or omit the steps shown. The scope of protection of the present invention is not limited in this respect.

[0129] The term "embodiment" in this specification refers to a specific feature, structure, or characteristic described in connection with an embodiment that may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily imply the same embodiment, nor does it imply independence or alternativeity from other embodiments. The various embodiments in this specification are described in a related manner, with reference to each other for similar or identical parts. In particular, for apparatus, device, and system embodiments, since they are substantially similar to method embodiments, the description is relatively simple, and relevant details are referred to in the description of the method embodiments.

[0130] The above-described embodiments are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of protection. It should be noted that those skilled in the art can make various modifications and improvements without departing from the inventive concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the appended claims.

Claims

1. A method for monitoring the reverse power and power quality of a low-voltage distribution transformer, characterized in that, include: Steady-state electrical data and dynamic electrical data of the low-voltage side of the low-voltage transformer are collected using a multi-channel synchronous sampling method. The low-voltage side of the low-voltage transformer is connected to a distributed photovoltaic system. The sampling frequency of the multi-channel synchronous sampling is determined based on Shannon's sampling theorem and the bandwidth of the electromagnetic voltage transformer. The electromagnetic voltage transformer is used at least to collect the dynamic electrical data. The active power and the first power quality index are calculated based on the steady-state electrical data. Based on the direction and amplitude of the active power, combined with the preset amplitude threshold and duration threshold, the reverse power monitoring result is determined; The maximum value of the dynamic electrical data for each channel within the update cycle is calculated based on the dynamic electrical data. If the difference between the maximum value of the dynamic electrical data of each channel and the reference value does not exceed a preset threshold, the reference value is updated based on the maximum value of the dynamic electrical data, wherein the update cycle is determined based on the power frequency cycle and a preset number of cycles; If the difference between the maximum value of the dynamic electrical data of any channel and the reference value exceeds the preset threshold, the internal overvoltage waveform collected within the first recording time is latched, wherein the first recording time is the sum of the update period and the preset second recording time; The power quality monitoring results are determined based on the first power quality index and the internal overvoltage waveform.

2. The method according to claim 1, characterized in that, Based on the dynamic electrical data, the maximum value of the dynamic electrical data for each channel within the update cycle is calculated, including: The dynamic electrical data collected from each channel is processed by absolute value to obtain the first processed data; The first processed data is filtered after each power frequency cycle to obtain the second processed data, wherein the update cycle is equal to the product of the number of cycles n and the power frequency cycle. Based on the second processed data, the maximum period value of each channel in each power frequency cycle is calculated; For each channel, n maximum values ​​are collected in each update cycle. The lowest and highest values ​​among the n maximum values ​​are removed, and the largest value among the remaining n-2 maximum values ​​is taken as the maximum value of dynamic electrical data.

3. The method according to claim 2, characterized in that, The maximum value of the dynamic electrical data of each channel in the earliest update cycle is used as the initial reference value; If the current update cycle is not the earliest update cycle, and the difference between the maximum value of the dynamic electrical data of each channel in the current update cycle and the corresponding reference value does not exceed the preset threshold, the reference value corresponding to the current update cycle is updated based on the maximum value of the dynamic electrical data of each channel in the current update cycle. If the current update cycle is not the earliest update cycle, and the difference between the maximum value of the dynamic electrical data of any channel in the current update cycle and the corresponding reference value exceeds the preset threshold, the internal overvoltage waveform collected within the first recording time corresponding to the current update cycle is latched.

4. The method according to claim 1, characterized in that, Before calculating the active power and the first power quality index based on the steady-state electrical data, the method further includes: The zero-point suppression threshold is determined based on the noise level and the sampling frequency; The validity of zero-point crossover is determined based on the zero-point suppression threshold and discrimination conditions of the steady-state electrical data. After the discrimination is passed, the first zero-crossing time is determined based on adjacent sampling points using linear difference calculation. The first zero-crossing moments corresponding to multiple power frequency cycles are averaged to obtain the second zero-crossing moment. The second zero-crossing moment is used to determine the phase difference between voltage and current, and the phase difference is used to determine the active power.

5. The method according to claim 4, characterized in that, Based on the zero-point suppression threshold and discrimination conditions, the zero-point crossover validity is determined for the steady-state electrical data, including: If the aforementioned discrimination conditions are met, a valid zero-crossing event is considered to have occurred, and the zero-crossing validity discrimination is passed. The discrimination conditions include: The waveform sample value in the steady-state electrical data changes from a positive value to a negative value, or from a negative value to a positive value, in consecutive sampling points; The values ​​of the waveform sampled values ​​before and after the positive and negative changes are both outside the range determined based on the zero-point suppression threshold; Within the sampling window corresponding to the positive and negative changes of the waveform sample values, the positive and negative directions of the waveform sample values ​​remain consistent.

6. The method according to claim 1, characterized in that, Based on the direction and amplitude of the active power, and in conjunction with preset amplitude and duration thresholds, the reverse power monitoring result is determined, including: When the direction of the active power is negative, the amplitude of the active power is greater than or equal to a first preset amplitude threshold, and the duration is greater than or equal to a first preset time threshold, the low-voltage transformer is determined to be in reverse power operation state. If the low-voltage transformer in the distribution area is in reverse power operation, and the amplitude of the active power is greater than or equal to the second preset amplitude threshold and the duration is greater than or equal to the second preset time threshold, the low-voltage transformer in the distribution area is determined to be in reverse power overload state. The preset amplitude thresholds include the first preset amplitude threshold and the second preset amplitude threshold; the preset duration thresholds include the first preset time threshold and the second preset time threshold; and the reverse power monitoring results include whether the low-voltage transformer is in reverse power operation state or in reverse power overload state.

7. The method according to claim 1, characterized in that, Before acquiring steady-state and dynamic electrical data of the low-voltage side of the low-voltage transformer in the low-voltage distribution area using multi-channel synchronous sampling, the method further includes: The electrical signals transmitted by the voltage transformer and the current transformer are isolated to obtain an isolated signal, wherein the voltage transformer and the current transformer are located on the low-voltage side of the low-voltage transformer in the low-voltage distribution area. The isolated signal is acquired by using a multi-channel synchronous sampling method to obtain the steady-state electrical data and the dynamic electrical data.

8. A monitoring device for reverse power and power quality of a low-voltage distribution transformer, characterized in that, include: The data acquisition module uses a multi-channel synchronous sampling method to collect steady-state electrical data and dynamic electrical data from the low-voltage side of the low-voltage transformer in the low-voltage distribution area. The low-voltage side of the low-voltage transformer in the low-voltage distribution area is connected to distributed photovoltaics. The sampling frequency of the multi-channel synchronous sampling is determined according to Shannon's sampling theorem and the bandwidth of the electromagnetic voltage transformer. The electromagnetic voltage transformer is used at least to collect the dynamic electrical data. The data acquisition module includes the electromagnetic voltage transformer. The main control module calculates active power and a first power quality index based on the steady-state electrical data; determines the reverse power monitoring result based on the direction and amplitude of the active power, combined with a preset amplitude threshold and duration threshold; calculates the maximum value of dynamic electrical data for each channel within the update cycle based on the dynamic electrical data; updates the reference value based on the maximum value of dynamic electrical data for each channel if the difference between the maximum value of dynamic electrical data for each channel and the reference value does not exceed a preset threshold, wherein the update cycle is determined based on the power frequency cycle and a preset number of cycles; latches the internal overvoltage waveform collected within a first recording time if the difference between the maximum value of dynamic electrical data for any channel and the reference value exceeds the preset threshold, wherein the first recording time is the sum of the update cycle and a preset second recording time; and determines the power quality monitoring result based on the first power quality index and the internal overvoltage waveform. The storage module is used to store the raw sampling data collected by the data acquisition module, as well as the active power data, power quality data and event log information determined by the main control module. The communication module, connected to the main control module, is used for periodic data reporting, event-triggered active data reporting, and remote command issuance and response. The power module, connected to the main control module, is equipped with an internal battery and an external power interface for power supply.

9. The apparatus according to claim 8, characterized in that, The power module has an isolation transformer with a turns ratio of 1:1 connected in series on its power input side.

10. The apparatus according to claim 8, characterized in that, The data acquisition module is equipped with 6+m synchronous sampling channels, and each synchronous sampling channel is connected to the low-voltage side of the low-voltage distribution transformer through an isolation transformer. Among them, 6 synchronous sampling channels are used to collect three-phase voltage signals and three-phase current signals. The three-phase voltage signals and the three-phase current signals are used to determine the steady-state electrical data and the dynamic electrical data. The m synchronous sampling channels are set as redundant channels and extended channels.

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