Generalized lateral differential protection method for 400v photovoltaic substation generating unit

Abstract

The application discloses a generalized transverse difference protection for 400V photovoltaic substation power generation units, which comprises the following steps: collecting information data of detected electrical quantities; judging the state of the collected data; and performing corresponding operations according to different state conditions. The generalized transverse difference protection for 400V photovoltaic substation power generation units can distinguish potential faults or electrical short-circuit faults and take different protection measures respectively. The method has low dependence on communication and high self-adaptability, and is suitable for the low-cost scheme requirement of 400V substations. In the method, the communication online self-checking mode is adopted, for the power generation units with abnormal communication, the adaptive method is adopted to eliminate the corresponding data and lock the protection.

Description

Technical Field

[0001] This invention relates to the technical field of relay protection, specifically a generalized differential protection method for 400V photovoltaic power generation units. Background Technology

[0002] With the increasing prominence of energy and environmental issues, the construction of new power grids is gradually being put on the agenda, and a large number of photovoltaic power sources are being connected to the grid. Conventional distribution networks have trunk, radial, and ring network structures. The relatively simple grid connection structure is the radial structure, which performs well in terms of wiring, protection capacity setting, and capacity expansion. In this type of distribution network, photovoltaic power stations are added, and overcurrent limiting protection circuit breakers and automatic reclosing circuit breakers can be installed throughout the structure.

[0003] Information exchange and reliable transmission between photovoltaic (PV) power plants and the control station rely on communication systems. Agreements, rules, and protocols for data transmission formats necessary for initiating and maintaining communication must be established in advance. PV power plants are equipped with numerous measurement, control, protection, and other automated devices to collect operational and status information from PV arrays and booster equipment, transmitting this information to the back-end monitoring computer and control agency. The control station sends control commands to the measurement and control equipment via data transmission channels and automated devices such as remote communication workstations, thereby controlling the PV power plant. Currently, the vast majority of PV power plants use wired communication systems, with fiber optic communication being the most prevalent.

[0004] Traditional distribution network protection employs current protection and overload protection, but with the integration of numerous photovoltaic power sources, the structure of the distribution network has undergone significant changes, rendering traditional relay protection measures inapplicable and placing higher demands on relay protection. New protection measures can be proposed under conditions of good communication. Summary of the Invention

[0005] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0006] In view of the above-mentioned problems, the present invention is proposed.

[0007] Therefore, the technical problem solved by this invention is: if a photovoltaic unit has the potential to fail, this power generation unit can be disconnected after a long delay to prevent the internal fault from affecting other power generation units, serving as backup protection; after an electrical short circuit fault occurs on the 400V line, the fewest photovoltaic units can be selectively disconnected, serving as the main protection. This method has low dependence on communication and high adaptability, making it suitable for the low-cost solution requirements of 400V distribution areas.

[0008] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a generalized transverse differential protection method for photovoltaic power generation units, comprising:

[0009] Collect and detect electrical quantity information data;

[0010] Perform status assessment on the collected data;

[0011] Perform the corresponding operation based on the different status conditions.

[0012] As a preferred embodiment of the generalized transverse differential protection method for photovoltaic power generation units described in this invention, it is characterized by comprising:

[0013] When a photovoltaic unit has relatively centralized or decentralized photovoltaic power generation units, and a potential fault or anomaly is detected, such power generation units are disconnected after a long delay.

[0014] For relatively dispersed single-phase photovoltaic power generation units, the harmonic spectrum characteristics of these power generation units are the same;

[0015] For a relatively concentrated three-phase photovoltaic power generation unit, the three-phase power is symmetrical and the three-phase harmonic spectrum characteristics are the same;

[0016] If the above conditions are not met, it is considered an abnormal state;

[0017] When an electrical short circuit fault occurs on a 400V line, the fewest photovoltaic units can be selectively disconnected, avoiding the high cost and low efficiency of longitudinal differential protection.

[0018] As a preferred embodiment of the generalized transverse differential protection method for 400V photovoltaic power generation units described in this invention, the information data of the collected and detected electrical quantities are obtained by detecting electrical quantities such as current, voltage, power, and harmonics at the output of each power generation unit.

[0019] As a preferred embodiment of the generalized transverse differential protection method for 400V photovoltaic power generation units described in this invention, the abnormal state judgment is based on the photovoltaic power generation unit or three phases, under the condition of meeting communication requirements, to propose a generalized transverse differential protection, to compare information data, and according to the statistical law of faults, the abnormal state of the power generation unit can be determined.

[0020] As a preferred embodiment of the generalized differential protection method for 400V photovoltaic power generation units described in this invention, the corresponding operation involves sending the detection data to the manager, which determines that the data of a certain power generation unit is abnormal. Based on the statistical pattern of the fault, the manager can determine that the state of the power generation unit is abnormal and sends an alarm to the control center. After a long delay, the manager sends a trip command to the output switch of the power generation unit.

[0021] As a preferred embodiment of the generalized transverse differential protection method for 400V photovoltaic power generation units described in this invention, the photovoltaic power generation unit, from the 400V distribution transformer outlet to the photovoltaic power generation unit or load equipment, is a radial network structure.

[0022] As a preferred embodiment of the generalized transverse differential protection method for 400V photovoltaic power generation units described in this invention, the method is characterized in that: when an electrical short circuit fault occurs upstream of the branch box, the output current and direction of each photovoltaic inverter of the same model downstream of the branch box are the same. After receiving the signal, the manager determines that the fault occurs upstream of the branch box, so the branch box switch and all equipment switches trip.

[0023] When an electrical short circuit occurs on one of the outgoing lines downstream of the branch box, the output current and direction of the photovoltaic inverters of the same model downstream of the branch box will vary significantly. After receiving the signal, the manager determines that the fault is downstream of the branch box, so the corresponding equipment switch trips, which can narrow the scope of the fault and improve the selectivity of fault clearing. In order to prevent misjudgment, the distribution current protection trips after a short delay.

[0024] As a preferred embodiment of the generalized differential protection method for 400V photovoltaic power generation units described in this invention, the differential protection is characterized in that: the differential protection is applied in parallel circuits, and its operation depends on the unbalanced distribution of current between circuits. The voltage and current data from the secondary side of voltage and current transformers are digitized and shared through a communication unit to provide short-circuit voltage and current data for the protection device.

[0025] As a preferred embodiment of the generalized transverse differential protection method for 400V photovoltaic power generation units described in this invention, the communication conditions are characterized by: adopting an online self-testing method for communication; for power generation units with abnormal communication, an adaptive method is adopted to remove the corresponding data and lock out the protection.

[0026] As a preferred embodiment of the generalized transverse differential protection method for 400V photovoltaic power generation units described in this invention, the method is characterized by: generalized meaning: having low correlation with specific topology and distribution location, being unrelated to quantity, and using dynamic data.

[0027] The beneficial effects of this invention are as follows: The generalized differential protection method for 400V photovoltaic power generation units can distinguish between potential faults and electrical short-circuit faults, and take different protection measures accordingly. If a photovoltaic unit has the potential for a fault, it can be disconnected after a long delay. If an electrical short-circuit fault occurs on the 400V line, the fewest photovoltaic units can be selectively disconnected as the main protection. This method has low dependence on communication and high adaptability, making it suitable for the low-cost solution requirements of 400V power generation areas. It employs an online self-test method for communication; for power generation units with abnormal communication, an adaptive method is used to remove the corresponding data and lock out the protection. Attached Figure Description

[0028] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein:

[0029] Figure 1 The first embodiment of the present invention provides an overall flowchart of a generalized transverse differential protection method for photovoltaic power generation units;

[0030] Figure 2 This is a structural diagram of a generalized transverse differential protection method for photovoltaic power generation units provided in the first embodiment of the present invention;

[0031] Figure 3 The schematic diagram of normal operation and external short circuit demonstration of a generalized transverse differential protection method for photovoltaic power generation units provided in the second embodiment of the present invention;

[0032] Figure 4 This is a schematic diagram illustrating the short circuit at point D1 within a photovoltaic power generation unit, as provided in the second embodiment of the present invention. Detailed Implementation

[0033] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the protection scope of the present invention.

[0034] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0035] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0036] This invention is described in detail with reference to the schematic diagrams. When detailing the embodiments of this invention, for ease of explanation, the cross-sectional views illustrating the device structure may be partially enlarged, not adhering to the usual scale. Furthermore, the schematic diagrams are merely examples and should not be construed as limiting the scope of protection of this invention. In actual fabrication, the three-dimensional spatial dimensions of length, width, and depth should be included.

[0037] Furthermore, in the description of this invention, it should be noted that the terms "upper," "lower," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are used solely for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. In addition, the terms "first," "second," or "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0038] Unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" in this invention should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; similarly, they can refer to mechanical connections, electrical connections, or direct connections, or indirect connections through an intermediate medium, or internal connections between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0039] Example 1

[0040] As one embodiment of the present invention, a load balancing method for a computing platform based on a particle swarm genetic algorithm is provided, comprising:

[0041] S1: Collect and detect electrical quantity information data;

[0042] For potential faults or anomalies, and for relatively concentrated photovoltaic power generation units (usually three-phase), the feature is that, under the condition of meeting communication requirements, a generalized differential protection is proposed to detect electrical quantities such as current, voltage, power, and harmonics at the output of each power generation unit.

[0043] Furthermore, for potential faults or anomalies, and for relatively dispersed photovoltaic power generation units (usually single-phase), the feature is that, under the condition of meeting communication requirements, a generalized differential protection is proposed to detect electrical quantities such as current, voltage, power, and harmonics at the output of each power generation unit.

[0044] S2: Perform status checks on the collected data;

[0045] For relatively dispersed, typically single-phase, photovoltaic power generation units, the harmonic spectrum characteristics of these units are similar;

[0046] For relatively concentrated photovoltaic power generation units, which are usually three-phase, the three-phase power should be basically symmetrical, and the three-phase harmonic spectrum characteristics should also be similar.

[0047] Under the same lighting and weather conditions, if the above conditions are met,

[0048] Furthermore, for relatively dispersed photovoltaic power generation units of the same or similar models, under the same light and weather conditions, if the above conditions are not met, the detection data will be sent to the manager, and the manager will determine that the data of a certain power generation unit is abnormal.

[0049] S3: Execute the corresponding operation based on different state conditions;

[0050] Based on the statistical patterns of the faults, if the state of the power generation unit is determined to be abnormal, an alarm can be sent to the control center, and after a long delay, a trip command can be sent to the output switch of the power generation unit, which is equivalent to backup protection.

[0051] Furthermore, when an electrical short-circuit fault occurs upstream of the branch box, the output current and direction of all identical photovoltaic inverters downstream of the branch box are the same. Upon receiving the signal, the manager determines that the fault is upstream of the branch box, therefore the branch box switch and all equipment switches trip to prevent islanding. Conversely, when an electrical short circuit occurs on a line downstream of the branch box, the output current and direction of the identical photovoltaic inverters downstream of this branch box vary significantly. Upon receiving the signal, the manager determines that the fault is downstream of the branch box, therefore the corresponding equipment switch trips. This narrows the fault isolation range and improves the selectivity of fault isolation. To prevent misjudgment, the distribution current protection trips after a short delay.

[0052] Furthermore, the differential protection device is installed at the photovoltaic unit equipment end, load port and branch box. It digitizes and shares the voltage and current data from the secondary side of the voltage and current transformers through the communication unit, providing short-circuit voltage and current data for multiple protection devices.

[0053] It should be noted that the online communication self-test method is adopted. For power generation units with abnormal communication, an adaptive method is used to remove the corresponding data and lock out the protection.

[0054] It should also be explained the principle of transverse differential protection for photovoltaic power generation units:

[0055] Horizontal differential protection is a relay protection device that responds to the magnitude and direction of the phase-to-phase differential current in parallel operating lines, thereby selectively disconnecting the faulty line. Horizontal differential directional protection responds to internal faults in parallel lines, but not to external faults. Its operating current should be greater than the maximum unbalanced current caused in the differential current loop during a through-fault.

[0056] It should also be noted that the "generalized" in "generalized transverse difference protection" means that it has a low correlation with specific topological structures and distribution locations, and is unrelated to quantity. The data used is dynamic.

[0057] Example 2

[0058] Reference Figure 3 , 4 As an embodiment of the present invention, this paper provides a single-phase differential protection principle, taking the single-side power supply load side differential protection as an example. In order to verify the beneficial effects of the present invention, scientific demonstration is carried out through economic benefit calculation and simulation experiment.

[0059] During normal operation or when there is an external short circuit at point D, the fault currents flowing through the parallel lines are equal in magnitude and in the same direction. Assume the current transformer ratio is n. ct The differential current flowing into the differential protection starting element LJ is:

[0060]

[0061] The differential protection does not activate.

[0062] When a short circuit occurs at point D1 on line A, the fault currents flowing through the parallel lines are equal in magnitude but opposite in direction. The differential current flowing into starting element LJ is:

[0063]

[0064] When the differential current reaches or exceeds the setting value of the differential protection, the differential protection will trip the circuit breaker on line A. Similarly, when a short circuit occurs within the zone on line B, the protection will trip line B.

[0065] To prevent the cross-connected differential protection from malfunctioning during external faults when operating on a single line, the DC power supply of the protection is series-locked through the normally open auxiliary contacts of two switches on the parallel line. The protection only activates when both switches are connected simultaneously.

Claims

1. A generalized transverse differential protection method for a 400V photovoltaic power generation unit, characterized in that, include: Collect and detect electrical quantity information data; Perform anomaly detection on the collected data; Perform the corresponding operation based on the different status conditions; The corresponding operation is to send the detection data to the manager, the manager determines that the data of a certain power generation unit is abnormal, and based on the statistical pattern of the fault, it can determine that the state of the power generation unit is abnormal, and send an alarm to the control center, and after a long delay, send a trip command to the output switch of the power generation unit. When a photovoltaic unit has relatively centralized or decentralized photovoltaic power generation units, and a potential fault or anomaly is detected, such power generation units are disconnected after a long delay. For relatively dispersed single-phase photovoltaic power generation units, the harmonic spectrum characteristics of these power generation units are the same; For a relatively concentrated three-phase photovoltaic power generation unit, the three-phase power is symmetrical and the three-phase harmonic spectrum characteristics are the same; If the above conditions are not met, it is considered an abnormal state; When an electrical short circuit fault occurs on a 400V line, the fewest photovoltaic units can be selectively disconnected, avoiding the high cost and low efficiency of longitudinal differential protection. When an electrical short circuit fault occurs upstream of the branch box, the output current and direction of each photovoltaic inverter of the same model downstream of the branch box are the same. After receiving the signal, the manager determines that the fault occurs upstream of the branch box, so the branch box switch and all equipment switches trip. When an electrical short circuit occurs on one of the outgoing lines downstream of the branch box, the output current and direction of the photovoltaic inverters of the same model downstream of the branch box will vary significantly. After receiving the signal, the manager determines that the fault is downstream of the branch box, so the corresponding equipment switch trips, which can narrow the scope of the fault and improve the selectivity of the fault clearing. In order to prevent misjudgment, the current distribution protection trips after a short delay. The "generalized" in the generalized transverse differential protection method for 400V photovoltaic power generation units refers to the method being less correlated with specific topology and distribution location, unrelated to quantity, and using dynamic data.

2. The generalized transverse differential protection method for a 400V photovoltaic power generation unit as described in claim 1, characterized in that: The information data collected and detected in the electrical quantities are obtained by detecting current, voltage, power, and harmonic electrical quantities at the output of each power generation unit.

3. The generalized transverse differential protection method for a 400V photovoltaic power generation unit as described in claim 2, characterized in that: The abnormal state judgment is based on a generalized differential protection method proposed by the photovoltaic power generation unit under the condition of meeting communication requirements. By comparing information data and based on the statistical law of faults, the abnormal state of the power generation unit can be determined.

4. The generalized transverse differential protection method for a 400V photovoltaic power generation unit as described in claim 3, characterized in that: The photovoltaic power generation unit is a radial network structure from the 400V distribution transformer outlet to the photovoltaic power generation unit or load equipment.

5. The generalized transverse differential protection method for a 400V photovoltaic power generation unit as described in claim 4, characterized in that: The differential protection is applied in parallel circuits. Its operation depends on the imbalance of current distribution between circuits. It digitizes and shares voltage and current data from the secondary side of voltage and current transformers through a communication unit, providing short-circuit voltage and current data for the protection device.

6. The generalized transverse differential protection method for a 400V photovoltaic power generation unit as described in claim 5, characterized in that: The communication conditions include using an online self-test method, and for power generation units with abnormal communication, adopting an adaptive method to remove the corresponding data and lock out the protection.

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