Photovoltaic string connection terminal protection method of photovoltaic inverter
By detecting the temperature and current of the photovoltaic string connection terminals and comparing the current, the accurate diagnosis and protection of the photovoltaic string connection terminals is achieved, which solves the problem of insufficient precision in the existing technology, and improves the fault diagnosis rate and protection effect.
Patent Information
- Application Number
- CN202510405221.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-01
- Publication Date
- 2025-06-27
AI Technical Summary
In existing photovoltaic inverters, the temperature detection and protection strategy of the photovoltaic string connection terminals is not perfect and accurate enough, and there are problems of misjudgment of terminal status and inability to ensure accurate protection under special operating conditions.
By detecting the temperature and current of the photovoltaic string connection terminal, comparing the current, taking the average value and the maximum value for the difference judgment, the accurate diagnosis and protection of the photovoltaic string connection terminal is achieved.
It realizes accurate and efficient diagnosis of photovoltaic string connection terminals, accurately locates faults, reduces the fault false alarm rate, and provides a relatively complete temperature protection strategy.
Smart Images
Figure CN120222275A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a protection method for a photovoltaic string connection terminal of a photovoltaic inverter. Background Art
[0002] Photovoltaic inverters usually have photovoltaic string connection terminals. The photovoltaic string connection terminals are connected to photovoltaic panels to achieve DC input, and the current generated by the photovoltaic panels is transmitted to the inside of the inverter. After inversion processing, electrical energy is finally output to the power grid or users. In this process, the photovoltaic string connection terminals are key devices, and it is necessary to ensure their stable operation and prevent them from being damaged or even burned at high temperatures, resulting in damage to the photovoltaic inverter. To avoid this problem, the new generation of inverters monitors the photovoltaic string connection terminals by sampling the temperature of the photovoltaic string connection terminals, thereby realizing the protection of the photovoltaic string connection terminals. However, the current temperature detection protection strategy is not perfect and accurate enough, and there are various problems such as misjudgment of the terminal state and inability to accurately protect under special working conditions.
[0003] The above information disclosed in the background art section is only used to enhance the understanding of the background of the present application, and therefore it may include information that does not constitute the prior art known to those of ordinary skill in the art. Summary of the Invention
[0004] The present invention provides a protection method for a photovoltaic string connection terminal of a photovoltaic inverter. By detecting the temperature and current of the photovoltaic string connection terminal and combining them for diagnosis, the photovoltaic string connection terminal with a fault is accurately located, and the false alarm rate of the fault is reduced.
[0005] To achieve the above object, the present invention adopts the following technical solutions:
[0006] A protection method for a photovoltaic string connection terminal of a photovoltaic inverter includes the following steps:
[0007] S1. Obtain the temperature and current of the n photovoltaic string connection terminals of the photovoltaic inverter;
[0008] S2. Take the maximum value Tmax of the temperatures of the n photovoltaic string connection terminals, and the current of the photovoltaic string connection terminal with the highest temperature is I0;
[0009] S3. Compare the currents of the remaining n - 1 photovoltaic string connection terminals with a set current comparison threshold;
[0010] S4. Take the average value of the temperatures of the photovoltaic string connection terminals with currents greater than the current comparison threshold as Tmean1;
[0011] S5. Determine whether the difference between Tmax and Tmean1 is greater than the first temperature threshold;
[0012] If the determination result is yes, it is determined that overheating occurs, and overheat protection for the connection terminals of the photovoltaic string is triggered; if the result is no, it is determined that the temperature is normal, and the photovoltaic inverter operates normally.
[0013] In a preferred embodiment, in step S3, if there is no connection terminal of the photovoltaic string with a current greater than the current comparison threshold, it jumps to the following steps S6 and S7;
[0014] Step S6: The average value of the currents of the n - 1 connection terminals of the photovoltaic strings is taken as Tmean2;
[0015] Step S7: Determine whether the difference between Tmax and Tmean2 is greater than the second temperature threshold;
[0016] If the result is yes, it is determined that overheating occurs, and overheat protection for the connection terminals of the photovoltaic string is triggered; if the result is no, it is determined that the temperature is normal, and the photovoltaic inverter operates normally.
[0017] In a more preferred embodiment, the second temperature threshold is greater than the first temperature threshold.
[0018] In a preferred embodiment, the current comparison threshold is m * I0, where m is a coefficient greater than 0 and less than or equal to 1.
[0019] In a preferred embodiment, in step S2, first sort the temperatures of the n connection terminals of the photovoltaic strings, and then take the maximum value Tmax of the temperatures.
[0020] In a preferred embodiment, the method for protecting the connection terminals of the photovoltaic string further includes step S20 before step S2: Set a current screening threshold. When the current of a certain connection terminal of the photovoltaic string is less than the current screening threshold, this connection terminal of the photovoltaic string does not participate in the temperature comparison in step S2.
[0021] In a preferred embodiment, the method for protecting the connection terminals of the photovoltaic string further includes step S21 before step S2: Set a temperature screening threshold. When the temperature of a certain connection terminal of the photovoltaic string is less than the temperature screening threshold, this connection terminal of the photovoltaic string does not participate in the temperature comparison in step S2.
[0022] In a preferred embodiment, the temperature of each connection terminal of the photovoltaic string is collected by a thermistor.
[0023] In a preferred embodiment, each connection terminal of the photovoltaic strings is respectively connected to a current sampling circuit to collect the current of each connection terminal of the photovoltaic string.
[0024] In a preferred embodiment, if overheating is determined, the photovoltaic inverter shuts down.
[0025] The above solution adopted by the present invention has the following advantages:
[0026] By detecting and comparing the temperature and current of the connection terminals of the photovoltaic string, the present invention realizes accurate and efficient diagnosis, accurately locates the faults of the connection terminals of the photovoltaic string, and provides a relatively perfect temperature protection strategy compared with the existing solutions, comprehensively considering factors such as the increase in the internal environment temperature of the photovoltaic inverter box and the temperature difference impact brought by the external environment, and has the advantages of higher fault diagnosis rate and lower false alarm rate. Description of the Drawings
[0027] In order to more clearly illustrate the technical solutions of the present invention, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention, and those of ordinary skill in the art can also obtain other drawings based on these drawings without creative efforts.
[0028] Figure 1 Shows a circuit diagram of a photovoltaic inverter according to an embodiment of the present invention.
[0029] Figure 2 Shows a temperature protection flowchart of a connection terminal of a photovoltaic string according to an embodiment of the present invention.
[0030] Figure 3 Shows another temperature protection flowchart of a connection terminal of a photovoltaic string according to an embodiment of the present invention. Detailed Embodiments
[0031] The following elaborates on the preferred embodiments of the present invention in conjunction with the drawings, so that the advantages and features of the present invention can be more easily understood by those skilled in the art. It should be noted here that the description of these embodiments is for helping to understand the present invention, but does not constitute a limitation to the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.
[0032] The following embodiments propose a fault protection logic for the DC terminal fault in the DC side fault of the photovoltaic inverter. A solution for realizing protection is to diagnose by detecting the temperature of the connection terminal of the photovoltaic string connecting the DC string. For the current temperature detection protection strategy, it is not perfect and accurate enough, and there are various problems such as misjudgment of the terminal state and inability to accurately protect under special working conditions. Based on this situation, the present embodiment proposes a more perfect temperature protection strategy, comprehensively considering factors such as the increase in the internal environment temperature of the cavity of the photovoltaic inverter and the temperature difference impact brought by the external environment, and realizes accurate and efficient fault diagnosis by detecting the temperature of the DC terminal and calculating according to different situations.
[0033] Refer to Figure 1 As shown, the PV inverter includes an inverter module (MPPT Converter) for converting DC power from a PV panel into AC power. The DC side of the inverter module is provided with n PV terminal circuits, including PV string connection terminals for connecting PV strings, so as to feed the electric energy from the PV strings into the inverter module. Each PV terminal circuit also includes a temperature detection device for detecting the temperature of each PV string connection terminal. The temperature detection device can specifically be a thermistor circuit connected in series with the PV string connection terminal. Each PV string connection terminal is also connected to a current sampling circuit to collect the current flowing through each PV string connection terminal. Through this structure, the temperature and current of each PV can be collected, and whether there is a fault can be confirmed by comparing their relative relationships.
[0034] Figure 2 Figure 7 shows a temperature protection method for a PV string connection terminal of this embodiment. As Figure 2 shown, this temperature protection method includes the following steps:
[0035] S1. Obtain the temperature and current of the n PV string connection terminals of the PV inverter;
[0036] S2. Take the maximum value Tmax of the temperatures of the n PV string connection terminals, and the current of the PV string connection terminal with the highest temperature is I0;
[0037] S3. Compare the currents of the remaining n - 1 PV string connection terminals with a set current comparison threshold, and the current comparison threshold is m * I0, where m is a coefficient greater than 0 and less than or equal to 1;
[0038] S4. Take the average value of the temperatures of the PV string connection terminals with currents greater than the current comparison threshold as Tmean1;
[0039] S5. Determine whether the difference between Tmax and Tmean1 is greater than the first temperature threshold Ta;
[0040] If the determination result is yes, it is determined that overheating occurs, and overheating protection for the PV string connection terminal is triggered; if the result is no, it is determined that the temperature is normal, and the PV inverter operates normally.
[0041] Figure 3 Figure 8 shows another temperature protection method for a PV string connection terminal of this embodiment. As Figure 3 shown, this temperature protection method includes the following steps:
[0042] S1. Obtain the temperature and current of the n PV string connection terminals of the PV inverter;
[0043] S2. Take the maximum value Tmax of the temperatures of the connection terminals of n photovoltaic string arrays. The current of the connection terminal of the photovoltaic string array with the highest temperature is I0.
[0044] S3. Compare the currents of the connection terminals of the remaining n - 1 photovoltaic string arrays with a set current comparison threshold, where the current comparison threshold is m*I0, and m is a coefficient greater than 0 and less than or equal to 1.
[0045] In step S3, if there is a connection terminal of a photovoltaic string array whose current is greater than the current comparison threshold, then jump to the following step S4; if there is no connection terminal of a photovoltaic string array whose current is greater than the current comparison threshold, then jump to the following steps S6 and S7.
[0046] S4. Take the average value of the temperatures of the connection terminals of the photovoltaic string arrays whose currents are greater than the current comparison threshold as Tmean1.
[0047] S5. Determine whether the difference between Tmax and Tmean1 is greater than the first temperature threshold Ta.
[0048] If the determination result is yes, then it is determined that there is overheating, and trigger overheating protection for the connection terminals of the photovoltaic string arrays; if the result is no, then it is determined that the temperature is normal, and the photovoltaic inverter operates normally.
[0049] Step S6. Take the average value of the currents of the connection terminals of the n - 1 photovoltaic string arrays as Tmean2.
[0050] Step S7. Determine whether the difference between Tmax and Tmean2 is greater than the second temperature threshold Tb.
[0051] If the result is yes, then it is determined that there is overheating, and trigger overheating protection for the connection terminals of the photovoltaic string arrays; if the result is no, then it is determined that the temperature is normal, and the photovoltaic inverter operates normally.
[0052] The second temperature threshold is greater than the first temperature threshold.
[0053] In the above two temperature protection methods, in step S2, first sort the temperatures of the connection terminals of the n photovoltaic string arrays, and then take the maximum value Tmax of the temperatures. In another optional embodiment, the temperatures of the connection terminals of multiple photovoltaic string arrays are not sorted, and the average value and the maximum value are directly compared to set the threshold.
[0054] Specifically, in step S5 or step S7, if it is determined that there is overheating, then the photovoltaic inverter shuts down.
[0055] In step S3, it is judged whether there is I > m*I0 for the remaining n-1 PV currents I. Among them, the coefficient m is determined by the temperature condition actually measured by the photovoltaic inverter under normal working conditions, which is affected by the position of the thermistor NTC on the PCB, the distance between the photovoltaic string connection terminal, and the copper plating at the position where the thermistor NTC is located. It should be noted that in actual tests, it must be carried out in accordance with the standards, requiring good terminal crimping and correct plugging and unplugging to prevent the temperature rise under abnormal working conditions from affecting the threshold setting.
[0056] In step S5, it is judged whether Tmax - Tmean1 > Ta? In step S7, it is judged whether Tmax - Tmean2 > Tb? Tb > Ta. Among them, the two temperature thresholds Ta and Tb are set according to the temperature condition actually measured by the photovoltaic inverter under normal working conditions, which is affected by the position of the thermistor NTC on the PCB, the distance between the photovoltaic string connection terminal, and the copper plating at the position where the thermistor NTC is located. It should be noted that in actual tests, it must be carried out in accordance with the standards, requiring good terminal crimping and correct plugging and unplugging to prevent the temperature rise under abnormal working conditions from affecting the threshold setting.
[0057] Furthermore, the method for protecting the photovoltaic string connection terminal may further include step S20 before step S2: setting a current screening threshold. When the current of a certain photovoltaic string connection terminal is less than the current screening threshold, this photovoltaic string connection terminal does not participate in the temperature comparison in step S2, nor in the calculation of the current average value, and the comparison is carried out by other paths.
[0058] Or the method for protecting the photovoltaic string connection terminal further includes step S21 before step S2: setting a temperature screening threshold. When the temperature of a certain photovoltaic string connection terminal is less than the temperature screening threshold, this photovoltaic string connection terminal does not participate in the temperature comparison in step S2, nor in the calculation of the current average value, and the comparison is carried out by other paths.
[0059] The temperature protection method of this embodiment diagnoses by detecting the temperature of the DC terminal and combines the current for temperature protection, accurately locates the faulty DC terminal, reduces the false alarm rate of faults; realizes more accurate protection for the DC terminal, and has a higher fault diagnosis rate. It realizes accurate and efficient diagnosis, accurately locates the DC terminal fault, and has the advantages of higher fault diagnosis rate and lower false alarm rate compared with the existing scheme.
[0060] As shown in this specification and the claims, the terms "comprising" and "including" only indicate the inclusion of the clearly identified steps and elements, and these steps and elements do not constitute an exclusive list. The method or device may also include other steps or elements. The term "and / or" used herein includes any combination of one or more of the related listed items.
[0061] It should be noted that, unless otherwise specified, when a certain feature is referred to as "fixed" or "connected" to another feature, it can be directly fixed or connected to the other feature, or indirectly fixed or connected to the other feature. In addition, the descriptions such as upper, lower, left, and right used in the present invention are only relative to the mutual positional relationship of the components of the present invention in the drawings.
[0062] The above embodiments are only for illustrating the technical concept and features of the present invention, and are a preferred embodiment. The purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly, and it is not intended to limit the protection scope of the present invention. All equivalent transformations or modifications made according to the principle of the present invention should be covered within the protection scope of the present invention.
Claims
1. A method for protecting photovoltaic string connection terminals of a photovoltaic inverter, characterized in that: The steps include: S1, obtaining the temperature and current of the connection terminals of n photovoltaic strings of the photovoltaic inverter; S2, taking the maximum value Tmax of the temperature of the n photovoltaic string connection terminals, the current of the photovoltaic string connection terminal with the maximum temperature is I0; S3, comparing the currents of the remaining n-1 photovoltaic string connection terminals with the set current comparison threshold; S4, taking the average value of the temperature of the connection terminals of each photovoltaic string whose current is greater than the current comparison threshold as Tmean1; S5, determining whether the difference between Tmax and Tmean1 is greater than a first temperature threshold; If the result of the determination is yes, it is determined to be over-temperature, triggering over-temperature protection for the photovoltaic string connection terminals; If the answer is no, it is determined that the temperature is normal and the photovoltaic inverter operates normally.
2. The method for protecting photovoltaic string connection terminals of a photovoltaic inverter according to claim 1, characterized in that: In step S3, if there is no photovoltaic string connection terminal with a current greater than the current comparison threshold, jump to the following steps S6 and S7; Step S6: taking the average current of the n-1 photovoltaic string connection terminals as Tmean2; Step S7: Determine whether the difference between Tmax and Tmean2 is greater than a second temperature threshold; If the result is yes, it is determined to be over-temperature, triggering over-temperature protection for the photovoltaic string connection terminals; If the answer is no, it is determined that the temperature is normal and the photovoltaic inverter operates normally.
3. The photovoltaic string connection terminal protection method of the photovoltaic inverter according to claim 2, characterized in that: The second temperature threshold is greater than the first temperature threshold.
4. The photovoltaic string connection terminal protection method of the photovoltaic inverter according to claim 1, characterized in that: The current comparison threshold is m*I0, where m is a coefficient greater than 0 and less than or equal to 1.
5. The method for protecting photovoltaic string connection terminals of a photovoltaic inverter according to claim 1, characterized in that: In step S2, the temperatures of the connection terminals of the n photovoltaic strings are first sorted, and then the maximum temperature Tmax is taken.
6. The method for protecting photovoltaic string connection terminals of a photovoltaic inverter according to any one of claims 1 to 5, characterized in that: The photovoltaic string connection terminal protection method also includes step S20 located before step S2: setting a current screening threshold value. When the current of a photovoltaic string connection terminal is less than the current screening threshold value, the photovoltaic string connection terminal does not participate in the temperature comparison in step S2.
7. The method for protecting photovoltaic string connection terminals of a photovoltaic inverter according to any one of claims 1 to 5, characterized in that: The photovoltaic string connection terminal protection method also includes a step S21 located before step S2: setting a temperature screening threshold. When the temperature of a photovoltaic string connection terminal is lower than the temperature screening threshold, the photovoltaic string connection terminal does not participate in the temperature comparison in step S2.
8. The method for protecting photovoltaic string connection terminals of a photovoltaic inverter according to claim 1, characterized in that: The temperature of each photovoltaic string connection terminal is collected through thermistors.
9. The method for protecting photovoltaic string connection terminals of a photovoltaic inverter according to claim 1, characterized in that: Each photovoltaic string connection terminal is connected to a current sampling circuit to collect the current of each photovoltaic string connection terminal.
10. The method for protecting photovoltaic string connection terminals of a photovoltaic inverter according to claim 1, characterized in that: If it is determined to be over-temperature, the photovoltaic inverter is shut down.