Distribution network electric energy quality monitoring system for distributed power supply grid connection

Abstract

The invention relates to the technical field of power grid monitoring, in particular to a distribution network electric energy quality monitoring system for distributed power supply grid connection. According to the technical scheme, a data acquisition layer is arranged at key nodes and distributed power supply grid-connected points of a power distribution network and used for acquiring electric energy quality data in real time, a communication transmission layer is used for uploading the data to a monitoring master station layer, and the monitoring master station layer comprises a data management module, a resonance analysis module, a monitoring and early warning module and a man-machine interaction module. Wherein the data management module is used for receiving, storing and managing electric energy quality data, the resonance analysis module is used for establishing a distributed power supply grid-connected model based on the electric energy quality data to analyze system resonance characteristics caused by distributed power supply access, the monitoring and early warning module is used for generating early warning information, and the man-machine interaction module is used for visually displaying information. According to the invention, through electric energy quality monitoring and multi-inverter resonance analysis, the electric energy quality and the operation stability of the high-proportion distributed power supply access power distribution network are effectively improved.

Description

Technical Field

[0001] This invention relates to the field of power grid monitoring technology, and in particular to a power quality monitoring system for distribution networks with distributed power generation. Background Technology

[0002] With the large-scale integration of distributed generation (DG), especially photovoltaic (PV) power generation systems, power quality issues in medium- and low-voltage distribution networks have become increasingly prominent. After the integration of DG, the power grid exhibits highly random and nonlinear characteristics, posing a series of power quality challenges to the previously stable distribution system, including:

[0003] Inverter switching introduces high-frequency harmonics, which can easily cause voltage and current distortion and may affect the lifespan of grid equipment and power safety. Photovoltaic power generation is affected by weather conditions, resulting in frequent voltage fluctuations at local nodes, which may exceed the grid's allowable range in severe cases. Multi-point distributed access may cause three-phase load imbalance. At the same time, power exchange between the inverter and the grid causes reactive power fluctuations. When multiple inverters are connected in parallel, grid impedance coupling can easily form a resonant circuit, generating circulating current, which can lead to excessive current distortion and equipment damage risks.

[0004] Existing power quality monitoring methods mainly rely on local sampling and single-point analysis, which makes it difficult to achieve real-time monitoring of the entire network and accurate location of resonant sources under large-scale distributed power generation grid connection. In addition, traditional monitoring systems lack the ability to perform multi-inverter coupling analysis and are also unable to provide the dispatch center with actionable resonant suppression strategy data.

[0005] To address this issue, we propose a power quality monitoring system for distributed power generation grid connection to solve existing problems. Summary of the Invention

[0006] The purpose of this invention is to address the problems existing in the background technology by proposing a power quality monitoring system for distributed power generation grid connection.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a power quality monitoring system for distributed power generation grid connection, comprising:

[0008] The data acquisition layer is deployed at key nodes of the power distribution network and grid connection points of distributed power sources to collect power quality data in real time.

[0009] The communication transmission layer is used to preprocess, package, and encrypt the raw power quality data acquired by the data acquisition layer, and then upload it to the monitoring master station layer through wired and wireless communication to ensure the real-time performance, integrity, and security of data transmission.

[0010] The monitoring master station layer includes a data management module, a resonance analysis module, a monitoring and early warning module, and a human-computer interaction module;

[0011] The data management module is used to receive, store, classify and manage the massive amounts of power quality data uploaded by the communication transmission layer, and supports data retrieval and historical data tracing.

[0012] The resonance analysis module is used to establish an equivalent model of distributed power grid connection based on the power quality data, and to analyze the system resonance characteristics caused by the connection of distributed power sources. The resonance characteristics include resonance frequency, resonance amplitude and resonance distribution range.

[0013] The monitoring and early warning module is used to compare the resonance analysis results with a preset threshold, generate early warning information based on the comparison results, and output it to the power grid dispatch center and the terminal of operation and maintenance personnel.

[0014] The human-computer interaction module is used to visualize the power quality operation status, resonance analysis results and early warning information, and supports operation and maintenance personnel to perform strategy configuration and intervention operations.

[0015] Preferably, the analysis performed by the resonance analysis module includes:

[0016] The equivalent model for distributed power grid connection is an equivalent model for a multi-inverter parallel system. This equivalent model integrates multiple photovoltaic inverters, their LCL filters, and grid impedance into a unified model.

[0017] Based on the equivalent model, sensitivity analysis is performed on changes in grid impedance parameters, filter capacitor parameters, number of parallel inverters, and distribution network structure.

[0018] Based on the analysis results, the resonance characteristic parameters under different operating conditions are extracted, including the resonant frequency offset range, the trend of resonant amplitude variation, and the expansion of the resonant distribution range.

[0019] Preferably, the resonance analysis module is further used to detect and locate resonance sources in the distribution network, and its detection and location include:

[0020] Identify anomalous resonance components in power quality data through spectrum analysis;

[0021] The node or region where the resonance point is located is determined based on impedance measurement methods;

[0022] The resonant source is simulated and compared using an equivalent model of a parallel inverter system to achieve precise location of the resonant source.

[0023] Preferably, the data acquisition layer includes:

[0024] Power quality monitoring devices deployed at key nodes of the distribution network are used to collect power quality data: voltage, current, harmonics, three-phase imbalance and power data parameters;

[0025] The intelligent measurement and control unit built into the distributed power inverter is used to collect the inverter's output current, voltage waveforms, and inverter operating status information in real time.

[0026] Preferably, the distributed power source includes a photovoltaic power generation system and its inverter. The inverter adopts a voltage source converter (VSC) structure and is equipped with an LCL filter to suppress switching harmonics injected into the power grid.

[0027] Preferably, the resonance analysis module further includes a harmonic suppression and impedance control unit, which is used for:

[0028] Active damping control is adopted for the inverter, and the energy conversion efficiency of the system is improved by introducing a virtual damping factor in the control loop.

[0029] By combining special control impedance design, the output characteristics of the inverter are adjusted to reduce the characteristic harmonic components in the grid-connected current.

[0030] To suppress the resonance of the LCL filter and ensure that the grid-connected current meets international power quality standards.

[0031] Preferably, the resonance analysis module is used to analyze the coupling relationship between parallel inverters caused by grid impedance, and the analysis includes:

[0032] A multi-inverter circulating current model is established to describe the circulating current path formed by the inverter output current through grid impedance coupling;

[0033] Evaluate the impact of the magnitude and phase of the circulating current on the output current quality of each inverter.

[0034] Determine whether there is resonant frequency amplification and excessive current distortion due to circulating current coupling.

[0035] Preferably, the monitoring master station layer is communicatively connected to the power grid dispatch center, and the communication connection is used for:

[0036] Real-time power quality data, resonance analysis results, and early warning information are uploaded to the power grid dispatch center.

[0037] Receive control instructions from the dispatch center, including instructions for operating mode adjustment, load switching, and inverter parameter setting;

[0038] To achieve centralized monitoring, remote management, and collaborative dispatch of the power distribution network operation status.

[0039] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0040] By deploying high-precision power quality monitoring devices and inverter-built-in measurement and control units at key nodes of the distribution network and distributed power access points, full coverage acquisition of parameters such as voltage, current, harmonics, three-phase imbalance and power can be achieved, and transient disturbances and high-frequency resonance phenomena can be captured.

[0041] By using the equivalent model of a multi-inverter parallel system, we can analyze the impact of grid impedance changes, filter parameters, the number of parallel inverters and grid structure on resonance characteristics, and achieve accurate prediction of resonance frequency, amplitude and distribution range.

[0042] Through spectrum analysis, impedance measurement, and simulation comparison, the system can accurately locate the resonant source; a circulating current model is established to analyze the coupling effect between inverters and identify the risks of resonant frequency amplification and current distortion caused by circulating current.

[0043] The system compares the resonance analysis results with the threshold, generates graded early warning information, and displays it intuitively through the human-machine interface, providing operation and maintenance personnel with operable intervention solutions, such as inverter parameter adjustment, load switching, or grid optimization.

[0044] By coordinating closed-loop control with the dispatch center, the system can achieve coordinated management of distributed power sources and the power grid, reduce resonance and circulating current risks, improve power quality, and ensure the long-term stable operation of the power grid.

[0045] This system supports wired and wireless communication and a multi-node distributed database architecture. It can adapt to various application scenarios such as high-proportion distributed power access, urban power distribution networks, and industrial parks, and has good scalability and promotion value. Attached Figure Description

[0046] Figure 1 This is a schematic diagram of the system flow of the present invention;

[0047] Figure 2 This is a schematic diagram of the distributed power grid connection model of the present invention. Detailed Implementation

[0048] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0049] Example 1

[0050] like Figures 1-2As shown, the present invention proposes a power quality monitoring system for distributed power generation grid connection, which includes three parts: a data acquisition layer, a communication transmission layer, and a monitoring master station layer. Each part is interconnected through standardized interfaces and communication protocols.

[0051] Data Acquisition Layer

[0052] The data acquisition layer is the front-end of the system, directly deployed at key operating nodes of the distribution network and grid connection points of distributed power sources. Its main function is to acquire power quality operating parameters of the distribution network in real time and comprehensively. In this embodiment, the data acquisition layer includes:

[0053] Power quality monitoring device: Installed at the busbars, feeder ends, and important branch nodes of the distribution network. This device features a high-precision sampling module with a sampling frequency exceeding 10kHz, enabling real-time recording of voltage and current waveforms and calculation of key parameters such as harmonic content, three-phase imbalance, power factor, active power, and reactive power. The device incorporates electromagnetic interference resistance design, adapting to complex power system environments. Its sampling waveform can be described by the following formula:

[0054]

[0055] in,

[0056] The instantaneous voltage waveform acquired;

[0057] : Fundamental voltage amplitude;

[0058] : Fundamental angular frequency;

[0059] Fundamental phase;

[0060] : No. Second harmonic amplitude;

[0061] : No. Subharmonic phase;

[0062] : Upper limit of harmonic order.

[0063] This formula is used to calculate real-time harmonic content and total harmonic distortion (THD):

[0064]

[0065] The distributed power inverter has a built-in measurement and control unit: This unit relies on the inverter's own sensors to collect output current and voltage waveforms, while simultaneously monitoring the inverter's operating status (such as temperature, DC bus voltage, and switching status). The data acquisition cycle can be shortened to the millisecond level, ensuring the capture of transient disturbances and resonance phenomena. This unit collects the inverter's output current. and voltage waveform And calculate the instantaneous power of the system in real time:

[0066]

[0067] in,

[0068] Instantaneous active power;

[0069] Instantaneous reactive power.

[0070] The data collected by this layer is recorded with a millisecond sampling period, which can cover low-frequency disturbances and high-frequency resonance phenomena. Through the coordinated deployment of the above devices, the data acquisition layer can achieve full coverage of the power quality operation status, ensuring both overall monitoring of the distribution network level and local monitoring of distributed power access points.

[0071] Communication transport layer

[0072] The communication transmission layer, acting as a data channel, is responsible for uploading the raw power quality data from the acquisition layer to the monitoring master station. To ensure high reliability and real-time performance, the communication transmission layer in this embodiment has the following characteristics:

[0073] For core nodes, wired methods such as fiber optic Ethernet and industrial Ethernet are used to ensure transmission speed and anti-interference performance; for remote areas, 4G / 5G wireless communication and dedicated power wireless links are used to improve flexibility and coverage.

[0074] Before uploading data, the acquisition device performs filtering, compression, feature extraction, and timestamp marking to avoid redundant data causing transmission congestion.

[0075] Data encryption algorithms (such as AES or RSA) are used, along with CRC checksum and breakpoint resume mechanism, to ensure the integrity and security of data transmission.

[0076] The transmission latency of the core link is controlled within 50ms, which can meet the real-time requirements of power quality monitoring.

[0077] The communication transmission layer ensures real-time and secure data transmission from the acquisition end to the monitoring master station. Data transmission can be described as follows:

[0078]

[0079] in,

[0080] : Transmitting data;

[0081] Raw collected data;

[0082] Compression factor;

[0083] Encoding and encryption correction factors.

[0084] Monitoring main station layer

[0085] The monitoring master station layer, deployed in the power grid dispatch center or regional control center, is the core part of the system and mainly includes the following modules:

[0086] Data Management Module: It centrally receives and stores massive amounts of power quality data uploaded from the communication transmission layer, classifies and archives the data according to parameters such as voltage, current, frequency, and harmonics, and supports historical data backtracking and retrieval across time periods. It also supports a distributed database architecture and can handle the high data traffic generated after large-scale access of distributed power sources.

[0087] Resonance Analysis Module: Based on power quality data, an equivalent model of a multi-inverter parallel system is established. The model includes inverters, grid impedance, and LCL filters. Based on this model, the impact of changes in grid impedance parameters, filter capacitance, the number of parallel inverters, and adjustments to the distribution network topology on resonance characteristics is analyzed. Key characteristic parameters such as resonant frequency, resonant amplitude, and resonant distribution range are output. Abnormal resonance components are identified through spectrum analysis combined with impedance measurement. The simulation comparison method is used to accurately locate the resonance source, indicating the node or region where resonance occurs.

[0088] The single-inverter LCL filter model can be expressed as a frequency domain transfer function:

[0089]

[0090] in,

[0091] Inverter-to-grid current transfer function;

[0092] Laplace transform of the current injected into the power grid;

[0093] : Inverter output voltage Laplace transform;

[0094] Inverter-side inductance;

[0095] : Grid-side inductance;

[0096] : Filter capacitor.

[0097] Resonant frequency:

[0098]

[0099] Equivalent model of multi-inverter parallel system, for The total current injected into the grid by the parallel inverters is as follows:

[0100]

[0101] in,

[0102] : No. The inverter's output voltage;

[0103] Equivalent impedance of inverter and filter;

[0104] : Power grid impedance.

[0105] In the formula for detecting a resonant source, the spectrum analysis method is used to determine the resonant amplitude. calculate:

[0106]

[0107] in,

[0108] : Amplitude of the Fourier transform of voltage or current;

[0109] Predict the resonant frequency;

[0110] Frequency scanning window;

[0111] like If the entropy value exceeds the set value, the system will trigger an early warning.

[0112] Monitoring and early warning module: It compares the resonance analysis results with preset thresholds. When the resonance frequency shift, harmonic distortion rate or current distortion exceeds the limit range, it immediately generates early warning information. The early warning information is sent synchronously to the dispatch center and operation and maintenance terminal through a dedicated network to realize the rapid transmission of alarms. It has an early warning classification mechanism that can distinguish between general early warning, severe early warning and emergency early warning, which facilitates the classified response of operation and maintenance personnel.

[0113] Early warning index It can be defined as:

[0114]

[0115] in,

[0116] Total harmonic distortion (THD);

[0117] Allowable THD threshold;

[0118] : Actual resonant frequency;

[0119] Fundamental frequency;

[0120] , Weighting coefficients;

[0121] when When the value is greater than 1, the system issues an alarm.

[0122] Human-computer interaction module: It adopts a graphical interface to dynamically display the power quality operation status, resonance analysis results and early warning information, and provides various visualization forms such as trend curves, spectrum diagrams and topology diagrams to intuitively reflect the evolution of power quality; it supports operation and maintenance personnel to issue scheduling instructions or policy configurations through the interface to achieve remote intervention.

[0123] Distributed power source characteristics and control

[0124] In this embodiment, the distributed power source is a photovoltaic power generation system, the inverter adopts a voltage source converter (VSC) structure, and is equipped with an LCL type filter.

[0125] Active damping control is introduced into the inverter control strategy to improve system stability through a virtual damping factor. Harmonic suppression and impedance control unit is configured in the resonance analysis module. Through special control impedance design, the inverter output characteristics are adjusted to suppress the harmonic content in the grid-connected current. This ensures that the grid-connected current distortion rate meets international power quality standards such as IEEE 519 and IEC 61000.

[0126] The monitoring master station layer maintains real-time interaction with the power grid dispatch center through a communication interface:

[0127] It uploads real-time power quality data, resonance analysis results, and early warning information to the dispatch center; receives control commands from the dispatch center for operating mode adjustment, load switching, and inverter parameter setting; and achieves coordinated operation of distributed power sources and the power grid through closed-loop control, thereby improving the overall safety and economy of the power grid.

[0128] In another application scenario, the system is used in urban power distribution networks with high penetration rates of distributed photovoltaic (PV) grid integration.

[0129] When a large number of parallel inverters are connected in a certain area, the resonance analysis module can identify the circulating current phenomenon between inverters caused by grid impedance coupling by establishing a circulating current model.

[0130] The system evaluates the impact of the circulating current amplitude and phase on the inverter output current quality. When the resonant frequency amplification or current distortion rate exceeds the limit, the monitoring and early warning module is immediately triggered.

[0131] Based on the early warning prompts, maintenance personnel can issue adjustment commands through the human-machine interaction module, such as modifying inverter control parameters, switching some loads, or optimizing the grid structure, in order to suppress circulating current and resonance problems.

[0132] Circulation analysis formula:

[0133]

[0134] in,

[0135] : No. The circulating current of the inverter.

[0136] This embodiment demonstrates that the present invention can achieve rapid identification, precise location and effective suppression of resonance problems under complex operating conditions, thereby significantly improving the power quality and operational stability of the distribution network under distributed power generation grid connection conditions.

[0137] The above specific embodiments are merely several preferred embodiments of the present invention. Based on the technical solutions of the present invention and the relevant teachings of the above embodiments, those skilled in the art can make various alternative improvements and combinations to the above specific embodiments.

[0138] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A power quality monitoring system for distribution networks with distributed power generation, characterized in that, include: The data acquisition layer is deployed at key nodes of the power distribution network and grid connection points of distributed power sources to collect power quality data in real time. The communication transmission layer is used to preprocess, package, and encrypt the raw power quality data acquired by the data acquisition layer, and then upload it to the monitoring master station layer through wired and wireless communication to ensure the real-time performance, integrity, and security of data transmission. The monitoring master station layer includes a data management module, a resonance analysis module, a monitoring and early warning module, and a human-computer interaction module; The data management module is used to receive, store, classify and manage the massive amounts of power quality data uploaded by the communication transmission layer, and supports data retrieval and historical data tracing. The resonance analysis module is used to establish an equivalent model of distributed power grid connection based on the power quality data, and to analyze the system resonance characteristics caused by the connection of distributed power sources. The resonance characteristics include resonance frequency, resonance amplitude and resonance distribution range. The monitoring and early warning module is used to compare the resonance analysis results with a preset threshold, generate early warning information based on the comparison results, and output it to the power grid dispatch center and the terminal of operation and maintenance personnel. The human-computer interaction module is used to visualize the power quality operation status, resonance analysis results and early warning information, and supports operation and maintenance personnel to perform strategy configuration and intervention operations.

2. The power quality monitoring system for distributed power generation grid connection according to claim 1, characterized in that: The analysis performed by the resonance analysis module includes: The equivalent model for distributed power grid connection is an equivalent model for a multi-inverter parallel system. This equivalent model integrates multiple photovoltaic inverters, their LCL filters, and grid impedance into a unified model. Based on the equivalent model, sensitivity analysis is performed on changes in grid impedance parameters, filter capacitor parameters, number of parallel inverters, and distribution network structure. Based on the analysis results, the resonance characteristic parameters under different operating conditions are extracted, including the resonant frequency offset range, the trend of resonant amplitude variation, and the expansion of the resonant distribution range.

3. A power quality monitoring system for distributed power generation grid connection according to claim 2, characterized in that: The resonance analysis module is further used to detect and locate resonance sources in the distribution network, and its detection and location include: Identify anomalous resonance components in power quality data through spectrum analysis; The node or region where the resonance point is located is determined based on impedance measurement methods; The resonant source is simulated and compared using an equivalent model of a parallel inverter system to achieve precise location of the resonant source.

4. A power quality monitoring system for distributed power generation grid connection according to claim 1, characterized in that: The data acquisition layer includes: Power quality monitoring devices deployed at key nodes of the distribution network are used to collect power quality data: voltage, current, harmonics, three-phase imbalance and power data parameters; The intelligent measurement and control unit built into the distributed power inverter is used to collect the inverter's output current, voltage waveforms, and inverter operating status information in real time.

5. A power quality monitoring system for distributed power generation grid connection according to claim 1, characterized in that: The distributed power source includes a photovoltaic power generation system and its inverter. The inverter adopts a voltage source converter (VSC) structure and is equipped with an LCL filter to suppress switching harmonics injected into the power grid.

6. A power quality monitoring system for distributed power generation grid connection according to claim 5, characterized in that: The resonance analysis module further includes a harmonic suppression and impedance control unit, which is used for: Active damping control is adopted for the inverter, and the energy conversion efficiency of the system is improved by introducing a virtual damping factor in the control loop. By combining special control impedance design, the output characteristics of the inverter are adjusted to reduce the characteristic harmonic components in the grid-connected current. To suppress the resonance of the LCL filter and ensure that the grid-connected current meets international power quality standards.

7. A power quality monitoring system for distributed power generation grid connection according to claim 1, characterized in that: The resonance analysis module is used to analyze the coupling relationship between parallel inverters caused by grid impedance. The analysis includes: A multi-inverter circulating current model is established to describe the circulating current path formed by the inverter output current through grid impedance coupling; Evaluate the impact of the magnitude and phase of the circulating current on the output current quality of each inverter. Determine whether there is resonant frequency amplification and excessive current distortion due to circulating current coupling.

8. A power quality monitoring system for distributed power generation grid connection according to claim 1, characterized in that: The monitoring master station layer is communicatively connected to the power grid dispatch center, and the communication connection is used for: Real-time power quality data, resonance analysis results, and early warning information are uploaded to the power grid dispatch center. Receive control instructions from the dispatch center, including instructions for operating mode adjustment, load switching, and inverter parameter setting; To achieve centralized monitoring, remote management, and collaborative dispatch of the power distribution network operation status.

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