Photovoltaic string power transmission line protection device for photovoltaic power station
By designing protection devices with current and voltage sampling modules on the transmission lines of photovoltaic strings in photovoltaic power plants, faults can be identified and disconnected, thus solving the shortcomings of photovoltaic string line protection and improving the safety and stability of photovoltaic power plants.
Patent Information
- Application Number
- CN202520359698.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-03
- Publication Date
- 2026-01-23
- Estimated Expiration
- 2035-03-03
AI Technical Summary
Photovoltaic power plants are prone to short circuits or open circuits in their photovoltaic string transmission lines. The lack of effective, low-cost protection measures leads to fire hazards and damage to components. Furthermore, the penetration rate of existing photovoltaic optimizers is low, making it impossible to provide comprehensive protection.
Design a photovoltaic string transmission line protection device, comprising a current sampling module, a voltage sampling module, a microprocessor, a power supply module, and a protection module. The device identifies faults by sampling current and voltage and controls a contactor to disconnect the line to prevent damage.
It effectively prevents damage to photovoltaic strings and combiner boxes during short circuits or open circuits, reduces the risk of fire, and improves the stability and safety of photovoltaic power plants.
Smart Images
Figure CN223829026U_ABST
Abstract
Description
Technical Field
[0001] This utility model relates to the field of power transmission line protection technology, specifically a power transmission line protection device for photovoltaic strings in photovoltaic power plants. Background Technology
[0002] In a photovoltaic (PV) power station, PV modules are connected in series to form strings, which output power to a combiner box. Multiple strings are then connected in parallel at the combiner box and output to an inverter, which then outputs AC power to the transformer substation. The insulation of the transmission lines from the strings to the combiner box may age or be damaged by rodents, potentially leading to short circuits or open circuits. Currently, there is a lack of effective and low-cost automated protection methods. Short circuits and open circuits are particularly dangerous, as the voltage can reach around 800V, potentially causing arcing and posing a significant fire hazard, while also damaging the PV modules. PV power stations typically have a large number of strings (over 20,000 in a typical large-scale station), and the PV area is often far from the control area. Even if faults are detected by the control system, timely handling is difficult, posing a threat to the stable operation and safe production of the PV power station.
[0003] Currently, there are no devices on the market specifically designed to protect the output circuits of photovoltaic (PV) strings. However, PV optimizers can provide protection for PV modules. Because PV optimizers need to be deployed at the module level and are relatively expensive, their penetration rate is currently low, projected to reach only 30% by 2030. Therefore, the current situation is that most PV strings and combiner boxes lack effective protection against short circuits or open circuits in transmission lines. Utility Model Content
[0004] The purpose of this utility model is to provide a photovoltaic string transmission line protection device for photovoltaic power plants in order to solve at least one of the above-mentioned technical problems.
[0005] In a first aspect, this utility model provides a photovoltaic string transmission line protection device for a photovoltaic power station, applied to a photovoltaic string in a photovoltaic power station; the output end of the photovoltaic string is connected to the combiner box of the photovoltaic power station via a transmission line; it includes: a current sampling module, a voltage sampling module, a microprocessor, a power supply module, a capacitor, and a protection module; wherein, the sampling end of the current sampling module is connected in series on the transmission line, the sampling end of the voltage sampling module is connected in parallel with the output end of the photovoltaic string, and the output ends of both the current sampling module and the voltage sampling module are connected to the microprocessor; the protection module includes a contactor and a drive circuit, the contactor is connected in series on the transmission line, the control end of the contactor is connected to the output end of the drive circuit, and the input end of the drive circuit is connected to the microprocessor; the input end of the power supply module is connected to the output end of the photovoltaic string, and the output end of the power supply module is connected to the microprocessor; the capacitor is connected in parallel with the output end of the power supply module.
[0006] Furthermore, the contactor includes a high-voltage DC contactor; wherein the parameters of the high-voltage DC contactor include: contact resistance of normally open contacts less than 10mΩ, coil voltage of 12V, holding current of 0.25A, rated power ≤3W, pull-in voltage ≤9V, release voltage ≥1V, and coil resistance of 48Ω.
[0007] Furthermore, the current sampling module includes a current sampling resistor and a first analog-to-digital converter; the current sampling resistor is connected in series on the transmission line, the input terminal of the first analog-to-digital converter is connected in parallel with the two ends of the current sampling resistor, and the output terminal of the first analog-to-digital converter is connected to the microprocessor.
[0008] Furthermore, the voltage sampling module includes a first voltage divider resistor, a second voltage divider resistor, and a second analog-to-digital converter; the first voltage divider resistor and the second voltage divider resistor are connected in series and then connected in parallel with the output terminal of the photovoltaic string; the input terminal of the second analog-to-digital converter is connected in parallel with the two ends of the second voltage divider resistor; and the output terminal of the second analog-to-digital converter is connected to the microprocessor.
[0009] Furthermore, the power module includes a DC high-voltage input isolated power supply and a low-voltage power supply; the input terminal of the DC high-voltage input isolated power supply is connected to the output terminal of the photovoltaic string, the output terminal of the DC high-voltage input isolated power supply is connected to the input terminal of the low-voltage power supply, and the output terminal of the low-voltage power supply is connected to the microprocessor; the DC high-voltage input isolated power supply is used to convert the high-voltage DC power output from the photovoltaic string into a low-voltage DC power supply; the low-voltage power supply is used to power the microprocessor.
[0010] Furthermore, the maximum input voltage of the DC high-voltage input isolation power supply is 1000VDC, the output power is 12V, and the output power is 5W; the output voltage of the low-voltage power supply is 3.3V.
[0011] Furthermore, the capacitor includes a farad capacitor.
[0012] Furthermore, the microprocessor includes a microcontroller and a memory; the memory is used to store abnormal information of the photovoltaic string.
[0013] Furthermore, it also includes a reset button, connected to the microprocessor, used to clear abnormal information stored in the memory.
[0014] This invention provides a photovoltaic string transmission line protection device for photovoltaic power plants. By sampling the current and voltage of the transmission line between the photovoltaic string and the combiner box, it can identify short-circuit and open-circuit faults, and further control the on / off state of the transmission line by controlling the contactor. This can effectively prevent damage to the photovoltaic string and combiner box when a short-circuit or open-circuit fault occurs in the photovoltaic string transmission line, and alleviate the technical problem that most existing photovoltaic strings and combiner boxes lack effective protection measures for short-circuit or open-circuit conditions of the output line. Attached Figure Description
[0015] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.
[0016] Figure 1 This is a schematic diagram of the structure of a photovoltaic string transmission line protection device for a photovoltaic power station, provided as an embodiment of the present invention.
[0017] In the diagram: 1. Photovoltaic string, 2. Transmission line, 3. Current sampling module, 31. Current sampling resistor, 32. First analog-to-digital converter, 4. Voltage sampling module, 41. First voltage divider resistor, 42. Second voltage divider resistor, 43. Second analog-to-digital converter, 5. Microprocessor, 6. Power supply module, 61. DC high-voltage input isolation power supply, 62. Low-voltage power supply, 7. Capacitor, 8. Contactor, 9. Drive circuit, 10. Reset button. Detailed Implementation
[0018] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.
[0019] Figure 1 This is a schematic diagram of a photovoltaic string transmission line protection device for a photovoltaic power station according to an embodiment of the present invention. The device is applied to photovoltaic string 1 in the photovoltaic power station; wherein the output terminal of photovoltaic string 1 is connected to the combiner box of the photovoltaic power station via transmission line 2. Specifically, as shown... Figure 1 As shown, it includes: current sampling module 3, voltage sampling module 4, microprocessor 5, power supply module 6, capacitor 7, and protection module.
[0020] Specifically, such as Figure 1 As shown, the sampling terminal of the current sampling module 3 is connected in series on the transmission line 2, the sampling terminal of the voltage sampling module 4 is connected in parallel with the output terminal of the photovoltaic string 1, and the output terminals of both the current sampling module 3 and the voltage sampling module 4 are connected to the microprocessor 5.
[0021] The protection module includes a contactor 8 and a drive circuit 9. The contactor 8 is connected in series on the transmission line 2. The control terminal of the contactor 8 is connected to the output terminal of the drive circuit 9, and the input terminal of the drive circuit 9 is connected to the microprocessor 5.
[0022] The input terminal of power module 6 is connected to the output terminal of photovoltaic string 1, and the output terminal of power module 6 is connected to microprocessor 5; capacitor 7 is connected in parallel with the output terminal of power module 6.
[0023] Specifically, contactor 8 is used to disconnect and connect transmission line 2. In this embodiment of the invention, the basic operating conditions of photovoltaic string 1 are voltage <1000V and current 0-10A.
[0024] In one optional embodiment of this utility model, the contactor 8 includes a high-voltage DC contactor; wherein the parameters of the high-voltage DC contactor include: the contact resistance of the normally open contact is less than 10mΩ, the coil voltage is 12V, the holding current is 0.25A, the rated power is ≤3W, the pull-in voltage is ≤9V, the release voltage is ≥1V, and the coil resistance is 48Ω.
[0025] Specifically, such as Figure 1As shown, the current sampling module 3 includes a current sampling resistor 31 and a first analog-to-digital converter 32; the current sampling resistor 31 is connected in series on the transmission line 2, the input terminal of the first analog-to-digital converter 32 is connected in parallel with the two ends of the current sampling resistor 31, and the output terminal of the first analog-to-digital converter 32 is connected to the microprocessor 5.
[0026] Specifically, the current sampling module 3 is used to convert the current on the transmission line 2 into a voltage value, and then convert it into a digital signal through the first analog-to-digital converter 32 and transmit it to the microprocessor 5.
[0027] In one optional embodiment of this utility model, the current sampling resistor 31 is connected in series with the positive terminal of the photovoltaic string 1, and the sampling current value is calculated by the voltage value across the current sampling resistor 31.
[0028] Specifically, such as Figure 1 As shown, the voltage sampling module 4 includes a first voltage divider resistor 41, a second voltage divider resistor 42, and a second analog-to-digital converter 43; the first voltage divider resistor 41 and the second voltage divider resistor 42 are connected in series and then connected in parallel with the output terminal of the photovoltaic string 1; the input terminal of the second analog-to-digital converter 43 is connected in parallel with the two ends of the second voltage divider resistor 42; and the output terminal of the second analog-to-digital converter 43 is connected to the microprocessor 5.
[0029] Specifically, the first voltage divider resistor 41 and the second voltage divider resistor 42 divide the output voltage of the photovoltaic string 1, and then convert it into a digital signal through the second analog-to-digital converter 43, which is then transmitted to the microprocessor 5. Both the first voltage divider resistor 41 and the second voltage divider resistor 42 are high-voltage resistors, and the ratio of the first voltage divider resistor 41 to the second voltage divider resistor 42 is determined based on the selection of the second analog-to-digital converter 43.
[0030] Specifically, such as Figure 1 As shown, the power module 6 includes a DC high-voltage input isolation power supply 61 and a low-voltage power supply 62; the input terminal of the DC high-voltage input isolation power supply 61 is connected to the output terminal of the photovoltaic string 1, the output terminal of the DC high-voltage input isolation power supply 61 is connected to the input terminal of the low-voltage power supply 62, and the output terminal of the low-voltage power supply 62 is connected to the microprocessor 5.
[0031] DC high voltage input isolation power supply 61 is used to convert the high voltage DC power output from photovoltaic string 1 into low voltage DC power.
[0032] Low-voltage power supply 62 is used to power microprocessor 5.
[0033] This utility model uses a DC high-voltage input isolation power supply 61 to draw power from the photovoltaic array string 1 to power the protection device.
[0034] In one optional embodiment of this utility model, the maximum input voltage of the DC high-voltage input isolation power supply 61 is 1000VDC, and the output power supply meets the working requirements of this protection device. For example, the output power supply is 12V and the output power is 5W; the output voltage of the low-voltage power supply 62 is 3.3V.
[0035] Specifically, such as Figure 1 As shown, the low-voltage power supply 62 supplies power to the microprocessor 5 while also charging the capacitor 7.
[0036] Preferably, capacitor 7 includes a farad capacitor.
[0037] Preferably, the microprocessor 5 includes a microcontroller and a memory; wherein the memory is used to store abnormal information of the photovoltaic string.
[0038] Because the string voltage drops to 0 during a short circuit, the power supply cannot provide power. Therefore, a supercapacitor (or a supercapacitor) is needed to maintain power for a short time during the short circuit, allowing the protection device to perform logic calculations and output control signals to drive the contactor to cut off power. Simultaneously, the microprocessor 5 needs to write the status values into memory.
[0039] Specifically, the microprocessor 5 performs logical judgments on the sampled string current and voltage: if the voltage suddenly drops to a very low level (e.g., below 50V) and the current is not interrupted, it is judged as a short circuit; if the voltage remains unchanged or increases, but the current suddenly drops to close to 0, it is judged as an open circuit.
[0040] In the case of a short circuit, the DC high voltage input isolation power supply 61 cannot draw power because the voltage drops to a very low level. At this time, capacitor 7 discharges to maintain the operation of the circuit.
[0041] When the microprocessor 5 detects a short circuit or open circuit, it controls the contactor 8 to trip, thus protecting the string output circuit.
[0042] Specifically, contactor 8 is a normally open contact. When the control coil is not powered, it is in the open state. When it is closed, the working power is 3W (voltage 12V). In the circuit design, the control coil of contactor 8 should be powered by DC high voltage input isolation power supply 61, and the on and off of the power supply line should be controlled by a microcontroller.
[0043] While performing protection actions, the microprocessor 5 writes the abnormal status to the memory. If the device is powered on again after a power outage at night, it will first read the status in the memory. If it is an abnormal status, the contactor 8 will not be closed.
[0044] Specifically, after contactor 8 is disconnected, the input voltage of DC high voltage input isolation power supply 61 will be restored immediately. This DC high voltage input isolation power supply 61 restores power to microprocessor 5. After microprocessor 5 is powered on and restarted, it reads the status value in the memory as a short circuit state, thus preventing contactor 8 from closing.
[0045] Specifically, such as Figure 1 As shown, it also includes a reset button 10, which is connected to the microprocessor 5 and is used to clear the abnormal information stored in the memory.
[0046] After the operator has dealt with the fault, they manually press the reset button 10. The microprocessor 5 detects that the reset button 10 has been pressed, performs a closing operation on the contactor 8, and clears the abnormal state in the memory at the same time.
[0047] The device provided by this utility model includes a reset button 10, which allows maintenance personnel to reset the equipment after troubleshooting line faults, clear the abnormal state in the memory, close the contactor 8, and restore the power supply to the string.
[0048] The protective device described in this invention should fully consider the requirements for waterproofing, moisture-proofing, and dustproofing in the field during structural design, and the protection level should not be lower than IP65.
[0049] In this embodiment of the invention, at the moment the combiner box resumes power transmission to the inverter, due to the presence of internal capacitors in the inverter, the voltage may be significantly pulled down as the combiner box charges the inverter capacitors. This could cause the microprocessor to misjudge a short circuit, thus incorrectly controlling the high-voltage DC contactor to trip. The solution is to set a voltage threshold. Since the short-circuit voltage is even lower, when the microprocessor detects that the voltage is below a certain threshold and the current is not interrupted, it can determine that there is a short circuit; otherwise, it will not perform short-circuit protection.
[0050] As described above, this utility model provides a photovoltaic string transmission line protection device for photovoltaic power plants, which can solve the following technical problems:
[0051] (1) The output cables of photovoltaic strings are easily chewed by rodents, which can damage the cable insulation layer, expose the metal, and cause short circuits. Although the combiner box has fuses and anti-reverse diodes to protect the string transmission line from short circuits, it can only protect the combiner box side and is powerless to protect the string side.
[0052] (2) The output cables of the photovoltaic string may be bitten and broken by rodents, forming an open circuit. At this time, since the positive and negative cables are exposed and close together, arcing may occur, which may ignite the surrounding dry grass and cause a fire; at the same time, the exposed cables also pose a threat to the operation and maintenance personnel of the photovoltaic power station or nearby residents.
[0053] To address problem (1), this invention utilizes the characteristic that the output voltage of a photovoltaic string drops instantaneously during a short circuit. By collecting the output voltage of the string, it judges the voltage change within a certain time range. If the voltage drops to a set threshold within a certain time width and the current is not interrupted, it can be judged as a short circuit. The voltage of a photovoltaic string is generally between 600 and 800V, and considering a certain redundancy, it is designed for 1000V. Using a voltage transformer to collect the voltage would be costly. Since the number of strings in a photovoltaic power station is very large (more than 20,000), the protection device on the string side is very sensitive to cost. Therefore, this invention uses two high-voltage resistors to divide the string voltage and then collects the voltage through A / D conversion. For current acquisition, a current sampling resistor is connected in series at the positive terminal of the string, and the current is calculated by the voltage across the sampling resistor. Since the voltage acquisition is only for judging voltage drops and accuracy is not required, the cost can be greatly reduced.
[0054] When the voltage drops below the threshold in a short period of time, it can be determined that a short circuit has occurred. The microprocessor outputs a signal to control the coil of the high-voltage DC contactor to perform a circuit breaking action, cutting off the output circuit of the string.
[0055] Regarding problem (2), since the current drops to zero in a short time when a power transmission line experiences a circuit breaker fault, this invention samples the current and determines whether a circuit breaker fault has occurred based on the change in current. Figure 1 As shown, the current sampling resistor does not require high precision and is only used for circuit breaking detection. A voltage signal is connected across the current sampling resistor, converted into a digital signal by an A / D converter chip, and then input to the microprocessor. The microprocessor calculates the current value based on the input signal. If the current drops to zero within a short time, while the voltage does not drop significantly, a circuit breaking condition can be determined. The microprocessor then controls the coil of the high-voltage DC contactor to perform a circuit breaking action, disconnecting the string's output circuit.
[0056] This utility model provides a photovoltaic string transmission line protection device for photovoltaic power plants. By sampling the current and voltage of the transmission line between the photovoltaic string and the combiner box, it can determine short-circuit and open-circuit faults, and further control the on / off state of the transmission line by controlling the contactor. This can effectively prevent damage to the photovoltaic string and combiner box when a short-circuit or open-circuit fault occurs in the photovoltaic string transmission line, and alleviate the technical problem that most existing photovoltaic strings and combiner boxes lack effective protection measures for short-circuit or open-circuit conditions of the output line.
[0057] It will be apparent to those skilled in the art that this invention is not limited to the details of the exemplary embodiments described above, and that it can be implemented in other specific forms without departing from the spirit or essential characteristics of this invention. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of this 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 this invention. No reference numerals in the claims should be construed as limiting the scope of the claims.
[0058] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.
Claims
1. A photovoltaic string transmission line protection device for photovoltaic power plants, characterized in that, A photovoltaic string used in a photovoltaic power station; the output terminal of the photovoltaic string is connected to the combiner box of the photovoltaic power station via a transmission line; it includes: a current sampling module, a voltage sampling module, a microprocessor, a power supply module, capacitors, and a protection module; wherein, The sampling terminal of the current sampling module is connected in series on the transmission line, the sampling terminal of the voltage sampling module is connected in parallel with the output terminal of the photovoltaic string, and the output terminals of both the current sampling module and the voltage sampling module are connected to the microprocessor. The protection module includes a contactor and a drive circuit. The contactor is connected in series on the transmission line. The control terminal of the contactor is connected to the output terminal of the drive circuit, and the input terminal of the drive circuit is connected to the microprocessor. The input terminal of the power module is connected to the output terminal of the photovoltaic string, and the output terminal of the power module is connected to the microprocessor; the capacitor is connected in parallel with the output terminal of the power module.
2. The photovoltaic string transmission line protection device for photovoltaic power plants according to claim 1, characterized in that: The contactor includes a high-voltage DC contactor.
3. The photovoltaic string transmission line protection device for photovoltaic power plants according to claim 1, characterized in that: The current sampling module includes a current sampling resistor and a first analog-to-digital converter; the current sampling resistor is connected in series on the transmission line, the input terminal of the first analog-to-digital converter is connected in parallel with the two ends of the current sampling resistor, and the output terminal of the first analog-to-digital converter is connected to the microprocessor.
4. The photovoltaic string transmission line protection device for photovoltaic power plants according to claim 1, characterized in that: The voltage sampling module includes a first voltage divider resistor, a second voltage divider resistor, and a second analog-to-digital converter; the first voltage divider resistor and the second voltage divider resistor are connected in series and then connected in parallel with the output terminal of the photovoltaic string; the input terminal of the second analog-to-digital converter is connected in parallel with the two ends of the second voltage divider resistor; and the output terminal of the second analog-to-digital converter is connected to the microprocessor.
5. The photovoltaic string transmission line protection device for photovoltaic power plants according to claim 1, characterized in that: The power module includes a DC high-voltage input isolated power supply and a low-voltage power supply; the input terminal of the DC high-voltage input isolated power supply is connected to the output terminal of the photovoltaic string, the output terminal of the DC high-voltage input isolated power supply is connected to the input terminal of the low-voltage power supply, and the output terminal of the low-voltage power supply is connected to the microprocessor. The DC high-voltage input isolation power supply is used to convert the high-voltage DC power output from the photovoltaic string into a low-voltage DC power supply. The low-voltage power supply is used to power the microprocessor.
6. The photovoltaic string transmission line protection device for photovoltaic power plants according to claim 5, characterized in that: The maximum input voltage of the DC high-voltage input isolation power supply is 1000VDC.
7. The photovoltaic string transmission line protection device for photovoltaic power plants according to claim 1, characterized in that: The capacitor includes a farad capacitor.
8. The photovoltaic string transmission line protection device for photovoltaic power plants according to claim 1, characterized in that: The microprocessor includes a single-chip microcomputer and a memory; the memory is used to store abnormal information of the photovoltaic string.
9. The photovoltaic string transmission line protection device for photovoltaic power plants according to claim 8, characterized in that: It also includes a reset button, connected to the microprocessor, used to clear abnormal information stored in the memory.