Photovoltaic power generation intelligent insulation detection system

Abstract

The invention is mainly used in the technical field of photovoltaic power generation. The invention discloses a photovoltaic power generation intelligent insulation detection system which comprises a host and a plurality of subsystems. Each subsystem comprises an extension set, a photovoltaic direct current assembly composed of a plurality of photovoltaic strings, and a detection device; the extension set is respectively connected with each photovoltaic string in the photovoltaic direct current assembly and is used for controlling each photovoltaic string to be in an on state or an off state and sending a detection instruction aiming at a target photovoltaic string to the detection device; the detection device is used for performing insulation resistance detection on the target photovoltaic string when receiving the detection instruction and feeding back a detection result to the corresponding extension set; and the host is in communication connection with each extension set and is used for acquiring the insulation detection results and the operation data of all the photovoltaic group strings in each subsystem and carrying out data analysis. According to the invention, the safety and reliability, the operation and maintenance efficiency and the digital management level of a large-scale photovoltaic system can be improved.

Description

A photovoltaic power generation intelligent insulation detection system Technical Field

[0001] This invention relates to the field of photovoltaic power generation technology, specifically to a photovoltaic power generation intelligent insulation detection system. Background Technology

[0002] As a crucial component of clean energy, photovoltaic (PV) power generation has experienced rapid and large-scale development globally in recent years. With the continuous expansion of PV power plant capacity, the insulation safety of the DC-side high-voltage system has become increasingly prominent. DC arcing and insulation faults have become major causes of fires in PV power plants, seriously threatening the safety of power plant assets and the lives of personnel.

[0003] Currently, insulation testing in photovoltaic power plants mainly relies on traditional insulation monitoring devices, which typically employ passive or centralized testing strategies, exhibiting significant limitations. Existing systems have limited data management capabilities and have failed to establish a comprehensive system for recording, tracing, and analyzing insulation testing data, thus failing to provide data support for long-term operation and maintenance optimization and energy management research. As photovoltaic power plants develop towards larger scale and greater intelligence, the number of strings is surging, and the DC-side topology is becoming increasingly complex. Traditional insulation testing methods are no longer sufficient to meet the demands of refined management and predictive maintenance. Without independent intelligent testing and full lifecycle data management of massive numbers of strings, not only will fault response be delayed and maintenance resources wasted, but the digital upgrade and sustainable development of the photovoltaic industry in the context of the energy internet will also be hindered. Summary of the Invention

[0004] This invention provides an intelligent insulation detection system for photovoltaic power generation, which can improve the safety, reliability, operation and maintenance efficiency, and digital management level of large-scale photovoltaic systems.

[0005] This invention provides a photovoltaic power generation intelligent insulation detection system, comprising a main unit and multiple subsystems. Each subsystem includes a secondary unit, a photovoltaic DC module composed of multiple photovoltaic strings, and a detection device. The secondary unit is connected to each photovoltaic string in the photovoltaic DC module and is used to control each photovoltaic string to be in a conducting or de-conducting state, and to send a detection command for a target photovoltaic string to the detection device. The detection device, upon receiving the detection command, performs insulation impedance detection on the target photovoltaic string and feeds back the detection result to the corresponding secondary unit. The main unit is communicatively connected to each secondary unit and is used to acquire the insulation detection results and operating data of all photovoltaic strings in each subsystem and perform data analysis.

[0006] Optionally, the host is further configured to: receive insulation test results sent by all the sub-units; if the insulation test results fed back by each sub-unit are normal, record the corresponding equipment status as normal grid connection; if the insulation test results fed back by one or more sub-units indicate that there are photovoltaic strings with insulation abnormalities, record the data of the abnormal photovoltaic strings and generate a maintenance instruction for the abnormal photovoltaic strings; if the insulation test results fed back by one or more sub-units multiple times indicate that there are multiple photovoltaic strings with insulation abnormalities, send an inspection and maintenance notification to the maintenance personnel terminal.

[0007] Optionally, the extension unit is further configured to: control the current photovoltaic string to connect to the detection device; send a detection command to the detection device for the current photovoltaic string; receive the insulation impedance detection result fed back by the detection device, wherein if the detection result is normal, the current photovoltaic string is controlled to be in a conducting state, and if the detection result is abnormal, the current photovoltaic string is controlled to be in a turning-off state, and the abnormal information of the current photovoltaic string is recorded; according to a preset order, the next photovoltaic string is selected as the current photovoltaic string, and the step of controlling the current photovoltaic string to connect to the detection device is returned to be executed until the detection of all photovoltaic strings in the subsystem where the extension unit is located is completed.

[0008] Optionally, the sub-unit is further configured to: send a data security transmission matching command to the detection device before performing conduction control and insulation detection of the photovoltaic string, to detect the first data transmission channel, the second data transmission channel, and the communication link with the host, wherein the first data transmission channel is used to control the photovoltaic string and read data from the photovoltaic string, and the second data transmission channel is used to send insulation impedance detection commands, receive the detection results from the detection device, and acquire data from the photovoltaic inverter; if the first data transmission channel, the second data transmission channel, and the communication link are all detected to be in a normal state, then control the target photovoltaic string to perform energy transmission with the detection device; if any of the first data transmission channel, the second data transmission channel, and the communication link are detected to be in an abnormal state, then generate and output an error message.

[0009] Optionally, each photovoltaic string in the photovoltaic DC module is equipped with a switching device; the sub-unit is used to control the photovoltaic string to input DC power to the detection device through the energy transmission channel; the detection device is used to detect the photovoltaic string, and when the detection result is an abnormal insulation impedance, it sends an abnormal command to the sub-unit; the sub-unit is also used to control the corresponding switching device to turn off the abnormal photovoltaic string according to the abnormal command, and control the normal photovoltaic string to connect to the detection device for grid-connected power generation.

[0010] Optionally, the detection device includes a photovoltaic power input module, an insulation detection and protection module, and a control module; the photovoltaic power input module is used to acquire the direct current; the insulation detection and protection module includes an insulation impedance equivalent unit, a sampling unit, and a mode switching unit; the sampling unit is connected to the insulation impedance equivalent unit and is used to sample the voltage of the insulation impedance equivalent unit when the direct current is input to it; the mode switching unit is connected to the sampling unit and the control module respectively, and is used to adjust the voltage sampling mode of the sampling unit in response to the control command sent by the control module, so that the sampling unit outputs the sampling voltage corresponding to each voltage sampling mode; the control module is used to determine the equivalent resistance value of the photovoltaic string based on all the sampled voltages, and when the equivalent resistance value is outside a preset threshold range, it determines that the insulation impedance of the photovoltaic string is abnormal.

[0011] Optionally, the insulation impedance equivalent unit includes a first equivalent resistance for inputting positive current and a second equivalent resistance for inputting negative current; the sampling unit includes a first sampling subunit and a second sampling subunit; the first sampling subunit is connected to the first equivalent resistance and is used to sample the positive voltage of the first equivalent resistance; the second sampling subunit is connected to the second equivalent resistance and is used to sample the negative voltage of the second equivalent resistance.

[0012] Optionally, the first sampling subunit includes a first sampling resistor and a second sampling resistor; one end of the first sampling resistor is connected to one end of the first equivalent resistor, and the other end of the first sampling resistor is connected to one end of the second sampling resistor; the other end of the second sampling resistor is connected to the other end of the first equivalent resistor and grounded; the second sampling subunit includes a third sampling resistor and a fourth sampling resistor; one end of the third sampling resistor is connected to one end of the second equivalent resistor, and the other end of the third sampling resistor is connected to one end of the fourth sampling resistor; the other end of the fourth sampling resistor is connected to the other end of the second equivalent resistor and grounded.

[0013] Optionally, the mode switching unit includes a first switch; one end of the first switch is connected to one end of the second sampling resistor, and the other end of the first switch is connected to the other end of the second sampling resistor and grounded; the mode switching unit includes a second switch; one end of the second switch is connected to one end of the fourth sampling resistor, and the other end of the second switch is connected to the other end of the fourth sampling resistor and grounded.

[0014] Optionally, the control module controls the first switch and the second switch; when the first switch is open and the second switch is open, the control module obtains a first sampled voltage value; when the first switch is on and the second switch is on, the control module obtains a second sampled voltage value; when the first switch is open and the second switch is on, the control module obtains a third sampled voltage value; when the first switch is on and the second switch is open, the control module obtains a fourth sampled voltage value; based on the first sampled voltage value, the second sampled voltage value, the third sampled voltage value, and the fourth sampled voltage value, the resistance value of the first equivalent resistor and the resistance value of the second equivalent resistor are determined; when the resistance values ​​of the first equivalent resistor and the second equivalent resistor are both within the standard resistance value range, the insulation impedance of the photovoltaic string is determined to be normal.

[0015] This invention offers at least the following advantages: In this technical solution, each subsystem is equipped with an independent transmitter and detection device, enabling control of the conduction or shutdown of individual photovoltaic strings and insulation impedance detection. This overcomes the granularity limitations of traditional centralized detection, achieving precise fault location and improving safety and reliability. The transmitter dynamically switches string states based on host commands or preset logic. Combined with real-time feedback from the detection device, it supports on-demand detection and fault isolation, reducing manual intervention and improving operation and maintenance efficiency. The host aggregates detection and operational data from multiple subsystems for centralized data analysis, providing data support for predicting insulation performance degradation trends and preventative maintenance, thus achieving digital management. In the three-tiered communication architecture of host, transmitter, and detection device, dispersed string-level detection is integrated into a unified system, balancing detection flexibility and centralized management, making it particularly suitable for large-scale applications in large-scale photovoltaic power plants. Attached Figure Description

[0016] The accompanying drawings are provided to further understand the technical solutions of the present invention and constitute a part of the specification. They are used together with the embodiments of the present invention to explain the technical solutions of the present invention, and do not constitute a limitation on the technical solutions of the present invention.

[0017] Figure 1 is a structural schematic diagram of a photovoltaic power generation intelligent insulation detection system; Figure 2 is a circuit diagram of a detection device in a photovoltaic power generation intelligent insulation detection system; Figure 3 is a flowchart of a photovoltaic power generation intelligent insulation detection system where the detection device performs insulation impedance detection. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0019] It should be noted that although functional modules are divided in the system diagram and the logical order is shown in the flowchart, in some cases, the steps shown or described may be performed in a different order than the module division in the system or the order in the flowchart. The terms "first," "second," etc., in the specification, claims, and the aforementioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0020] In photovoltaic (PV) power generation systems, PV inverters play a crucial role in the conversion of electrical energy from the DC side of the PV system to the AC side of the grid. Currently, PV inverters offer insulation detection and protection for the DC side of PV power plants through methods such as active identification and automatic shutdown. These detection methods include the balanced bridge method and the low-frequency signal injection method.

[0021] This research found that while this type of photovoltaic inverter can actively identify and shut down individual photovoltaic strings, it cannot independently determine and issue on / off commands to all photovoltaic strings in a photovoltaic power station. It also cannot comprehensively record and analyze anomalies in all DC strings, making it unsuitable for future large-scale photovoltaic power generation system safety and energy research. This implies a significant waste of equipment and resources.

[0022] To address the aforementioned technical issues, this technical solution provides a photovoltaic power generation intelligent insulation detection system. This system can independently assess all photovoltaic strings in a photovoltaic power station and issue on / off commands. It can comprehensively record and analyze all abnormal points in all photovoltaic strings, making it applicable to future large-scale photovoltaic power generation system safety and energy field research, comprehensively ensuring the safety of photovoltaic power generation systems and supporting big data research in the energy field. The following are various embodiments of this technical solution.

[0023] Please refer to Figure 1, which is a schematic diagram of a photovoltaic power generation intelligent insulation detection system.

[0024] This embodiment provides a photovoltaic power generation intelligent insulation detection system, including a main unit and multiple subsystems; each subsystem includes a sub-unit, a photovoltaic DC module composed of multiple photovoltaic strings, and a detection device.

[0025] Each unit is connected to each photovoltaic string in the photovoltaic DC module and is used to control each photovoltaic string to be in a conducting or off state, and to send detection commands to the detection device for the target photovoltaic string.

[0026] The detection device is used to perform insulation resistance detection on the target photovoltaic string when a detection command is received, and to feed back the detection results to the corresponding sub-unit.

[0027] The main unit communicates with each sub-unit to obtain insulation test results and operating data of all photovoltaic strings in each subsystem and perform data analysis.

[0028] Understandably, in this embodiment, each subsystem is configured with an independent transmitter and detection device, capable of controlling the conduction or shutdown of individual photovoltaic strings and detecting insulation impedance. This breaks through the granularity limitations of traditional centralized detection, enabling precise fault location and improving safety and reliability. The transmitter dynamically switches string states based on host commands or preset logic, and combined with real-time feedback from the detection device, supports on-demand detection and fault isolation, reducing manual intervention and improving operation and maintenance efficiency. The host aggregates detection and operational data from multiple subsystems for centralized data analysis, providing data support for predicting insulation performance degradation trends and preventative maintenance, thus achieving digital management. In this three-tiered communication architecture of host, transmitter, and detection device, dispersed string-level detection is integrated into a unified system, balancing detection flexibility and centralized management, making it particularly suitable for large-scale applications in large-scale photovoltaic power plants.

[0029] Optionally, both the host and the extensions are PCs. The host is the main PC, and the extensions are PC1, PC2, ..., PCn.

[0030] In some embodiments, the main PC collects data from each PC for data analysis in the energy and economic fields. Here, PC refers to equipment or other media authorized by the relevant authorities to collect and analyze data from photovoltaic power generation systems. The main PC can collect, store, and analyze data from PC1, PC2, PCn, etc. The content is not limited to anomaly point records and analysis for each brand string, but may also include data such as photovoltaic temperature and humidity, photovoltaic input voltage, current, and power.

[0031] In some embodiments, the host is further configured to: receive insulation test results sent by all extensions; if the insulation test results reported by each extension are all normal, record the corresponding device status as normal grid connection; if the insulation test results reported by one or more extensions indicate that there are photovoltaic strings with insulation abnormalities, record the data of the abnormal photovoltaic strings and generate maintenance instructions for the abnormal photovoltaic strings; if the insulation test results reported by one or more extensions multiple times indicate that there are multiple photovoltaic strings with insulation abnormalities, send an inspection and maintenance notification to the maintenance personnel terminal.

[0032] In one specific embodiment, firstly, the sub-PC independently turns the photovoltaic strings on and off and issues an instruction for insulation impedance detection. Photovoltaic string 1 is connected first, and then the internal system of the photovoltaic inverter judges whether the insulation impedance is normal. If it is normal, it feeds back to the sub-PC and continues to connect photovoltaic string 2 for detection, and so on until photovoltaic string n is detected. If it is abnormal, the photovoltaic string is disconnected. The system will eventually connect all photovoltaic strings that meet the requirements, complete the insulation impedance detection, and remove the abnormal photovoltaic string.

[0033] Second, the PC1, PC2, and PCn in the multiple subsystems consisting of the intelligent insulation detection and protection circuits and control systems of each photovoltaic power generation system feed back data to the main PC for storage and analysis.

[0034] When all the insulation tests received by the sub-PCs are normal, the main PC will also record it as normal, determine that the equipment is normal, and record that the strings in each region can be connected to the grid normally.

[0035] When one or more sub-PCs receive an anomaly, they will shut down the corresponding string, issue a string maintenance instruction, and transmit the abnormal data to the main PC for recording. During this process, if the sub-PCs monitor a large-scale string insulation anomaly for an extended period, the main PC will output instructions to the relevant authorities to conduct operating environment inspections, personnel assessments, and equipment maintenance in the region.

[0036] Understandably, the host system enhances its intelligence through a three-tiered decision-making mechanism: automatic grid connection under normal conditions, generation of targeted maintenance instructions for single-point anomalies, and proactive push of maintenance notifications for frequent multi-point anomalies. This design enables graded fault response and closed-loop operation and maintenance management, transforming passive detection into proactive early warning, shortening fault response time, reducing manual inspection costs, and further improving the automation level and timeliness of fault handling in large-scale photovoltaic systems.

[0037] In some embodiments, the extension unit is further configured to: control the current photovoltaic string to connect to the detection device; send a detection command to the detection device for the current photovoltaic string; receive the insulation impedance detection result fed back by the detection device, wherein if the detection result is normal, the current photovoltaic string is controlled to be in a conducting state; if the detection result is abnormal, the current photovoltaic string is controlled to be in a turning-off state, and the abnormal information of the current photovoltaic string is recorded; according to a preset sequence, the next photovoltaic string is selected as the current photovoltaic string, and the step of controlling the current photovoltaic string to connect to the detection device is returned, until the detection of all photovoltaic strings in the subsystem where the extension unit is located is completed.

[0038] Understandably, the sub-units implement string-level autonomous inspection and intelligent protection: they automatically poll and detect each string in a preset order, control the on / off state in real time based on the detection results, and automatically isolate and record any abnormalities. This design enables rapid on-site fault handling, prevents faulty strings from operating with defects, and reduces the risk of insulation faults escalating; at the same time, it reduces the communication burden on the host unit and improves system response speed and reliability.

[0039] In some embodiments, the extension unit is further configured to: send a data security transmission matching command to the detection device before performing conduction control and insulation detection of the photovoltaic string, to detect the first data transmission channel, the second data transmission channel, and the communication link with the host, wherein the first data transmission channel is used to control the photovoltaic string and read data from the photovoltaic string, and the second data transmission channel is used to send insulation impedance detection commands, receive detection results from the detection device, and acquire data from the photovoltaic inverter; if the first data transmission channel, the second data transmission channel, and the communication link are all detected to be in normal condition, then control the target photovoltaic string to perform energy transmission with the detection device; if any of the first data transmission channel, the second data transmission channel, and the communication link are detected to be in an abnormal condition, then generate and output an error message.

[0040] Specifically, the sub-PC issues a data security transmission matching command to check whether data transmission 1, data transmission 2, and communication are normal. Only when everything is normal will the photovoltaic string and photovoltaic inverter be allowed to perform energy transmission 1. If anything is abnormal, an error message should be displayed. Data transmission 1 can control the on / off state of the photovoltaic string and read the photovoltaic string data. Data transmission 2 can issue detection commands, receive detection judgments from the photovoltaic inverter, and read the photovoltaic inverter data.

[0041] Understandably, the multi-channel security verification mechanism at the front end of the substation verifies the integrity of the control channel, detection channel, and host communication link, ensuring the reliability of the transmission link before energy transmission and detection operations can be performed. This design achieves inherent safety in the detection process, preventing misjudgments or control failures due to communication faults, blocking the risk of energy interaction under abnormal conditions, improving the system's anti-interference capability and fault tolerance, and ensuring the safety and stability of large-scale photovoltaic system operation.

[0042] In some embodiments, each photovoltaic string in a photovoltaic DC module is provided with a switching device.

[0043] The sub-unit is used to control the photovoltaic string to input DC power to the detection device through the energy transmission channel.

[0044] The detection device is used to detect photovoltaic strings. When the detection result shows abnormal insulation resistance, it sends an abnormal command to the sub-unit.

[0045] The sub-unit is also used to control the corresponding switching equipment according to abnormal instructions to shut down the abnormal photovoltaic string, and to control the normal photovoltaic string to connect to the detection device for grid-connected power generation.

[0046] Specifically, the photovoltaic (PV) strings input DC power to the PV inverter via energy transmission 1. The PV inverter performs an insulation check internally. If an insulation abnormality is detected, it instructs the sub-PC to shut down the corresponding PV string via data transmission 2. The remaining normal strings can be connected to the PV inverter for grid-connected power generation. The PV strings are equipped with intelligent switching devices such as circuit breakers capable of single-circuit intelligent on / off operations.

[0047] Understandably, the unit achieves string-level physical isolation through hardware switching devices. In case of an anomaly, the photovoltaic strings quickly disconnect from the energy transmission channel, while normal strings seamlessly switch back to grid-connected power generation. This design ensures a balance between precise fault isolation and continuous system operation, avoiding system-wide shutdowns caused by single-point failures and maximizing power generation benefits. At the same time, physical shutdown provides fail-safe protection, eliminating the risk of DC arcing under abnormal insulation conditions and improving system availability and intrinsic safety.

[0048] In some embodiments, the detection device includes a photovoltaic power input module, an insulation detection and protection module, and a control module.

[0049] The photovoltaic power input module is used to acquire the direct current input from the photovoltaic string to the detection device through the energy transmission channel.

[0050] The insulation detection and protection module includes an insulation impedance equivalent unit, a sampling unit, and a mode switching unit.

[0051] The sampling unit, connected to the insulation impedance equivalent unit, is used to sample the voltage of the insulation impedance equivalent unit when DC power is input to it.

[0052] The mode switching unit is connected to the sampling unit and the control module respectively. It is used to adjust the voltage sampling mode of the sampling unit in response to the control command sent by the control module, so that the sampling unit outputs the sampling voltage corresponding to each voltage sampling mode.

[0053] The control module is used to determine the equivalent resistance value of the photovoltaic string based on all sampled voltages. When the equivalent resistance value is outside the preset threshold range, the insulation impedance of the photovoltaic string is determined to be abnormal.

[0054] Understandably, the detection device dynamically adjusts the voltage sampling method through a mode switching unit to achieve multi-dimensional and accurate measurement of insulation impedance. This design overcomes the limitations of a single sampling mode, improving the adaptability and accuracy of detection under complex operating conditions. The control module determines anomalies based on multiple sampling voltage thresholds, reducing the false positive rate and achieving highly reliable insulation fault identification, providing hardware-level technical support for string-level precise protection.

[0055] In some embodiments, the insulation impedance equivalent unit includes a first equivalent resistance for inputting positive current and a second equivalent resistance for inputting negative current.

[0056] The sampling unit includes a first sampling subunit and a second sampling subunit.

[0057] The first sampling subunit is connected to the first equivalent resistor and is used to sample the positive voltage of the first equivalent resistor; the second sampling subunit is connected to the second equivalent resistor and is used to sample the negative voltage of the second equivalent resistor.

[0058] In some embodiments, the first sampling subunit includes a first sampling resistor and a second sampling resistor; one end of the first sampling resistor is connected to one end of a first equivalent resistor, and the other end of the first sampling resistor is connected to one end of the second sampling resistor; the other end of the second sampling resistor is connected to the other end of the first equivalent resistor and grounded; the second sampling subunit includes a third sampling resistor and a fourth sampling resistor; one end of the third sampling resistor is connected to one end of the second equivalent resistor, and the other end of the third sampling resistor is connected to one end of the fourth sampling resistor; the other end of the fourth sampling resistor is connected to the other end of the second equivalent resistor and grounded.

[0059] In some embodiments, the mode switching unit includes a first switch; one end of the first switch is connected to one end of the second sampling resistor, and the other end of the first switch is connected to the other end of the second sampling resistor and grounded; the mode switching unit includes a second switch; one end of the second switch is connected to one end of the fourth sampling resistor, and the other end of the second switch is connected to the other end of the fourth sampling resistor and grounded.

[0060] In some embodiments, the control module controls the first switch and the second switch; when the first switch is open and the second switch is open, the control module obtains a first sampled voltage value; when the first switch is on and the second switch is on, the control module obtains a second sampled voltage value; when the first switch is open and the second switch is on, the control module obtains a third sampled voltage value; when the first switch is on and the second switch is open, the control module obtains a fourth sampled voltage value; based on the first sampled voltage value, the second sampled voltage value, the third sampled voltage value, and the fourth sampled voltage value, the resistance values ​​of the first equivalent resistor and the second equivalent resistor are determined; when the resistance values ​​of both the first equivalent resistor and the second equivalent resistor are within the standard resistance value range, the insulation impedance of the photovoltaic string is determined to be normal.

[0061] Please refer to Figure 2, which is a circuit diagram of a detection device in a photovoltaic power generation intelligent insulation detection system.

[0062] This embodiment provides a photovoltaic DC module including 3+3 photovoltaic strings, and a detection device for a photovoltaic inverter using 2 MPPTs. The detection device can be used for multiple PV input photovoltaic strings and multiple MPPT circuits.

[0063] As shown in Figure 2, PV1+, PV1-, PV2+, PV2-, PV3+, and PV3- are three photovoltaic modules connected in series to form one MPPT1 circuit. PV4+, PV4-, PV5+, PV5-, PV6+, and PV6- are three photovoltaic modules connected in series to form one MPPT2 circuit. The MPPT1 and MPPT2 circuits are connected to the BUS bus. In this embodiment, the MPPT1 and MPPT2 circuits serve as photovoltaic power input modules.

[0064] RX is the first equivalent resistance used to determine whether the insulation resistance between BUS+ and PE is normal, and RY is the second equivalent resistance used to determine whether the insulation resistance between BUS- and PE is normal. RX and RY are values ​​set according to standards. According to the current domestic certification standard NB / T 32004, the protection threshold is UmaxPV / 30mA. If the input voltage is 1000V, the insulation resistance threshold can be calculated to be 33KΩ. Furthermore, if the insulation resistance is normal, the resistance value should be in the MΩ range. The values ​​of RX and RY are determined by the actual operating environment, and a wide range of RX and RY resistance values ​​must be possible to determine.

[0065] R1, R2, R3, and R4 are the first, second, third, and fourth sampling resistors, respectively, all with known resistance values. R1 equals R4, R2 equals R3, and R1 does not equal R2. K1 and K2 correspond to the first and second switches. The drive circuit can drive the switches to turn on and off. The detection circuit samples the voltage from PE to BUS-. The controller is the central unit that issues drive commands to the drive circuit, analyzes and judges the data provided by the detection circuit, and transmits and displays the results of the analysis and judgment. Based on Kirchhoff's current law, the circuit equation is as follows: When K1 is open and K2 is open, Equation 1 is:

[0066] Wherein, Ubus represents the voltage from BUS+ to BUS-, and UPB1 represents the voltage from PE to BUS- when K1 and K2 are in the switching state.

[0067] When K1 is on and K2 is on, equation 2 is:

[0068] Wherein, Ubus represents the voltage from BUS+ to BUS-, and UPB2 represents the voltage from PE to BUS- when K1 and K2 are in the switching state.

[0069] When K1 is off and K2 is on, equation 3 is:

[0070] Wherein, Ubus represents the voltage from BUS+ to BUS-, and UPB3 represents the voltage from PE to BUS- when K1 and K2 are in the switching state.

[0071] When K1 is on and K2 is off, equation 4 is:

[0072] Wherein, Ubus represents the voltage from BUS+ to BUS-, and UPB4 represents the voltage from PE to BUS- when K1 and K2 are in the switching state.

[0073] The detection device is connected to the photovoltaic string, and the photovoltaic inverter begins insulation resistance detection. The control module controls the on / off state of the first switch K1 and the second switch K2 through the drive circuit, and obtains the voltage from PE to BUS- through the detection circuit to determine whether BUS+ and BUS- meet the insulation requirements. When the first switch K1 is open and the second switch K2 is open, the first sampling voltage value UPB1 is obtained; when the first switch K1 is on and the second switch K2 is on, the second sampling voltage value UPB2 is obtained; when the first switch K1 is open and the second switch K2 is on, the third sampling voltage value UPB3 is obtained; when the first switch K1 is on and the second switch K2 is open, the fourth sampling voltage value UPB4 is obtained. UPB1, UPB2, UPB3, and UPB4, derived from these four equations, are used to determine whether the insulation resistance meets the requirements.

[0074] According to Equation 1, UPB1 can be obtained as:

[0075] According to Equation 2, UPB2 can be obtained as:

[0076] According to Equation 3, UPB3 can be obtained as follows:

[0077] According to Equation 4, UPB4 can be obtained as follows:

[0078] Please refer to Figure 3, which is a flowchart of a detection device performing insulation impedance detection in a photovoltaic power generation intelligent insulation detection system.

[0079] To facilitate the explanation of insulation detection and protection control, the following process will be explained: "K1 open, K2 open" is state one, "K1 on, K2 on" is state two, "K1 open, K2 on" is state three, and "K1 on, K2 open" is state four. Ubus represents the voltage from BUS+ to BUS-. The switch is initially defined as a normally open relay. UPB represents the voltage from PE to BUS- in step (1).

[0080] (1) The detection circuit detects UPB and Ubus in the circuit. Under normal circumstances, Ubus should be greater than UPB; otherwise, it is judged as abnormal.

[0081] (2) The controller controls the drive circuit to switch the relay to state one, two, three and four, and obtains the values ​​of UPB1, UPB2, UPB3 and UPB4.

[0082] (3) UPB1, UPB2, UPB3, UPB4 and UBUS will be fed into the controller after passing through the sampling circuit. The controller will process them and input them into equations 1, 2, 3 and 4.

[0083] (4) In order to improve the accuracy and error tolerance of the detection, equations 1, 2, 3 and 4 will be used as four equations to solve the values ​​of RX and RY in pairs, resulting in a total of six equations. The arithmetic mean of RX and RY will be calculated.

[0084] (5) Compare the obtained RX and RY with the standard resistance values ​​to determine whether the insulation resistance of BUS+ to PE is normal. RY is used to determine whether the insulation resistance of BUS- to PE is normal. Only when the insulation resistance is normal can the insulation resistance be judged to be normal. Otherwise, they are all abnormal or the insulation resistance of BUS+ to PE is abnormal or the insulation resistance of BUS- to PE is abnormal.

[0085] (6) To increase reliability, if step (1) detects and determines an abnormality, it will continue to detect twice before reporting an error; if steps (2)-(5) detect and determine an abnormality, it will continue to detect twice before reporting an error.

[0086] It should be noted that when the photovoltaic inverter is working and insulation testing is not performed, R1, R2, R3, and R4 are connected in the circuit. The function of R1, R2, R3, and R4 is to act as balancing resistors when the power is purchased from the grid or when the load is on, so that the voltage of BUS+ and BUS- to BUSN (in some cases, PE is used directly, i.e., PE=BUSN) is equal. On the other hand, it can also be used as a residual voltage discharge resistor on the bus capacitor after the grid-connected power generation ends, that is, during the period from the start to the stop of the machine, so as to make the photovoltaic inverter safer and reduce the number of discharge resistors.

[0087] The terms “first,” “second,” “third,” “fourth,” etc. (if present) in the specification and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented, for example, in orders other than those illustrated or described herein. Furthermore, the terms “comprising” and “having,” and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatuses.

[0088] It should be understood that in this application, "at least one (item)" means one or more, and "more than" means two or more. "And / or" is used to describe the relationship between related objects, indicating that three relationships can exist. For example, "A and / or B" can represent three cases: only A exists, only B exists, and both A and B exist simultaneously, where A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. "At least one (item) of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, at least one (item) of a, b, or c can represent: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, and c can be single or multiple.

[0089] In the several embodiments provided in this application, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be indirect coupling or communication connection through some interfaces, apparatuses, or units, and may be electrical, mechanical, or other forms.

[0090] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0091] Furthermore, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0092] Although the description of this application has been quite detailed and particularly focused on several of the described embodiments, it is not intended to limit itself to any of these details or embodiments or any particular embodiment. Rather, it should be considered as effectively covering the intended scope of this application by referring to the appended claims and taking into account the prior art, which provides for a broad possible interpretation of these claims. Furthermore, the foregoing description of this application with respect to embodiments foreseeable by the inventors is intended to provide a useful description, and non-substantial modifications to this application that have not yet been foreseen may still represent equivalent modifications.

Claims

1. A photovoltaic power generation intelligent insulation detection system, characterized in that, The system includes a main unit and multiple subsystems; each subsystem includes a sub-unit, a photovoltaic DC module composed of multiple photovoltaic strings, and a detection device; the sub-unit is connected to each photovoltaic string in the photovoltaic DC module, and is used to control each photovoltaic string to be in a conducting or turning-off state, and to send a detection command for the target photovoltaic string to the detection device; the detection device is used to perform insulation impedance detection on the target photovoltaic string when it receives the detection command, and to feed back the detection result to the corresponding sub-unit; The host is communicatively connected to each of the sub-units and is used to acquire the insulation test results and operating data of all the photovoltaic strings in each subsystem and perform data analysis.

2. The intelligent insulation detection system for photovoltaic power generation according to claim 1, characterized in that, The host is also configured to: receive insulation test results sent by all the sub-units; if the insulation test results reported by each sub-unit are normal, record the corresponding equipment status as normal grid connection; if the insulation test results reported by one or more sub-units indicate that there are photovoltaic strings with insulation abnormalities, record the data of the abnormal photovoltaic strings and generate a maintenance instruction for the abnormal photovoltaic strings; if the insulation test results reported by one or more sub-units multiple times indicate that there are multiple photovoltaic strings with insulation abnormalities, send an inspection and maintenance notification to the maintenance personnel terminal.

3. The intelligent insulation detection system for photovoltaic power generation according to claim 1, characterized in that, The extension unit is also used for: controlling the current photovoltaic string to connect to the detection device; sending a detection command to the detection device for the current photovoltaic string; receiving the insulation impedance detection result fed back by the detection device, wherein if the detection result is normal, the current photovoltaic string is controlled to be in a conducting state, and if the detection result is abnormal, the current photovoltaic string is controlled to be in a turning-off state, and the abnormal information of the current photovoltaic string is recorded; according to a preset order, the next photovoltaic string is selected as the current photovoltaic string, and the step of controlling the current photovoltaic string to connect to the detection device is returned to be executed until the detection of all photovoltaic strings in the subsystem where the extension unit is located is completed.

4. The intelligent insulation detection system for photovoltaic power generation according to claim 1, characterized in that, The sub-unit is also used to: send a data security transmission matching command to the detection device before performing conduction control and insulation detection of the photovoltaic string, so as to detect the first data transmission channel, the second data transmission channel, and the communication link with the host. The first data transmission channel is used to control the photovoltaic string and read its data, while the second data transmission channel is used to send insulation impedance detection commands, receive the detection results from the detection device, and acquire data from the photovoltaic inverter. If the first data transmission channel, the second data transmission channel, and the communication link are all detected to be in normal condition, the sub-unit controls the target photovoltaic string to transmit energy to the detection device. If any of the first data transmission channel, the second data transmission channel, or the communication link is detected to be in an abnormal state, an error message is generated and output.

5. The intelligent insulation detection system for photovoltaic power generation according to claim 1, characterized in that, Each photovoltaic string in the photovoltaic DC module is equipped with a switching device; the sub-unit is used to control the photovoltaic string to input DC power to the detection device through the energy transmission channel; the detection device is used to detect the photovoltaic string, and when the detection result is an abnormal insulation impedance, it sends an abnormal command to the sub-unit; the sub-unit is also used to control the corresponding switching device to turn off the abnormal photovoltaic string according to the abnormal command, and control the normal photovoltaic string to connect to the detection device for grid-connected power generation.

6. The intelligent insulation detection system for photovoltaic power generation according to claim 5, characterized in that, The detection device includes a photovoltaic power input module, an insulation detection and protection module, and a control module. The photovoltaic power input module is used to acquire the direct current. The insulation detection and protection module includes an insulation impedance equivalent unit, a sampling unit, and a mode switching unit. The sampling unit is connected to the insulation impedance equivalent unit and is used to sample the voltage of the insulation impedance equivalent unit when the direct current is input to it. The mode switching unit is connected to both the sampling unit and the control module and is used to adjust the voltage sampling mode of the sampling unit in response to control commands sent by the control module, so that the sampling unit outputs a sampling voltage corresponding to each voltage sampling mode. The control module is used to determine the equivalent resistance value of the photovoltaic string based on all the sampled voltages, and to determine that the insulation impedance of the photovoltaic string is abnormal when the equivalent resistance value is outside a preset threshold range.

7. The intelligent insulation detection system for photovoltaic power generation according to claim 6, characterized in that, The insulation impedance equivalent unit includes a first equivalent resistance for inputting positive current and a second equivalent resistance for inputting negative current; the sampling unit includes a first sampling subunit and a second sampling subunit; the first sampling subunit is connected to the first equivalent resistance and is used to sample the positive voltage of the first equivalent resistance; the second sampling subunit is connected to the second equivalent resistance and is used to sample the negative voltage of the second equivalent resistance.

8. The intelligent insulation detection system for photovoltaic power generation according to claim 7, characterized in that, The first sampling subunit includes a first sampling resistor and a second sampling resistor; one end of the first sampling resistor is connected to one end of the first equivalent resistor, and the other end of the first sampling resistor is connected to one end of the second sampling resistor; the other end of the second sampling resistor is connected to the other end of the first equivalent resistor and grounded; the second sampling subunit includes a third sampling resistor and a fourth sampling resistor; one end of the third sampling resistor is connected to one end of the second equivalent resistor, and the other end of the third sampling resistor is connected to one end of the fourth sampling resistor; the other end of the fourth sampling resistor is connected to the other end of the second equivalent resistor and grounded.

9. The intelligent insulation detection system for photovoltaic power generation according to claim 8, characterized in that, The mode switching unit includes a first switch; one end of the first switch is connected to one end of the second sampling resistor, and the other end of the first switch is connected to the other end of the second sampling resistor and grounded; the mode switching unit includes a second switch; one end of the second switch is connected to one end of the fourth sampling resistor, and the other end of the second switch is connected to the other end of the fourth sampling resistor and grounded.

10. The intelligent insulation detection system for photovoltaic power generation according to claim 9, characterized in that, The control module controls the first switch and the second switch; when the first switch is open and the second switch is open, the control module obtains a first sampled voltage value. When the first switch is turned on and the second switch is turned on, the control module obtains the second sampled voltage value; When the first switch is open and the second switch is closed, the control module obtains a third sampled voltage value; when the first switch is closed and the second switch is open, the control module obtains a fourth sampled voltage value. Based on the first sampling voltage value, the second sampling voltage value, the third sampling voltage value, and the fourth sampling voltage value, the resistance values ​​of the first equivalent resistor and the second equivalent resistor are determined; when the resistance values ​​of the first equivalent resistor and the second equivalent resistor are both within the standard resistance value range, the insulation impedance of the photovoltaic string is determined to be normal.

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