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Introduction
As the “branch traffic hub” of the photovoltaic system, the combiner box undertakes the core functions of collecting, monitoring, and isolating the current of the photovoltaic module branch, and the current sensor is the “core sensing unit” that realizes the judgment of the branch status. Actual operation and maintenance data shows that about 27% of the faults in the combiner box are caused by “branch misjudgment” of the current sensor – in complex working conditions such as component partial obstruction, branch aging, and severe weather, the sensor falsely reports “branch open circuit” and “overcurrent fault”, resulting in the combiner box mistakenly cutting off normal branches or ignoring real faults, directly affecting the power generation efficiency and operation and maintenance decisions of the power station. With the decentralized deployment of distributed photovoltaics and the large-scale development of large power plants, the number of branch circuits in the combiner box has increased from 8 to 32 or even more. The scene adaptation capability of sensors has become a key bottleneck restricting the reliable operation of the combiner box.
1、 Complexity of current operating conditions in the combiner box scenario
The working environment and current characteristics of photovoltaic combiner boxes pose extremely challenging adaptation requirements for current sensors:
Firstly, the extreme imbalance of branch currents. Partial occlusion (such as tree shadows, dust accumulation, bird droppings) is a high-frequency scenario in photovoltaic power plants. Single component occlusion can cause the corresponding branch current to drop sharply from 100% of the rated value to 10% -30%, while adjacent branches still maintain full load current. The current difference between branches can reach several times or even tens of times, forming a complex situation of “coexistence of strong current and weak current”.
Secondly, dynamic fluctuations and instantaneous shocks. When the rapid movement of clouds causes a sudden change in light intensity, the branch current will fluctuate by ± 20% within milliseconds; Component hot spot effect, inverter start stop and other working conditions can also cause short-term peak current surges, with peak currents reaching more than 1.5 times the rated current.
Thirdly, the cumulative impact of harsh environments. Confluence boxes are often deployed on rooftops and outdoor supports, facing environmental challenges such as temperature changes ranging from -40 ℃ to 85 ℃, high humidity, and ultraviolet radiation. At the same time, the dense internal branch wiring can cause complex electromagnetic interference, further exacerbating the difficulty of sensor signal acquisition.
2、 Shortcomings in scene adaptation of traditional current sensors
The root cause of the misjudgment problem of traditional current sensors widely used in current combiner boxes under complex branch conditions lies in three major adaptation shortcomings:
One issue is the insufficient accuracy of small current detection. Traditional sensors generally have a linear error of over 2% in the weak current range of 10% -30% of the rated current. Some products are even unable to stably capture branch signals below 5% of the rated current. When a branch experiences weak current due to obstruction, the sensor is prone to misjudging it as a “branch open circuit”, causing the combiner box to cut off the branch and resulting in unnecessary power generation losses. Data from a 10MW distributed power station shows that traditional sensors mistakenly cut off normal branches 3-5 times a month, resulting in a loss of approximately 200 kWh of power generation due to a single mistake.
The second is weak dynamic response and anti-interference ability. The response time of traditional sensors is often over 5 μ s, which makes it difficult to synchronously capture millisecond level fluctuations in branch currents, and can easily mistake normal instantaneous current changes for “overcurrent faults”; At the same time, its electromagnetic shielding design is insufficient, and in the electromagnetic environment inside the combiner box, the misjudgment rate caused by signal clutter interference is as high as 15% or more.
Thirdly, there is a significant deviation in branch consistency. If the initial accuracy consistency deviation of multiple sensors in the same combiner box exceeds ± 1%, it will cause the combiner box to misjudge the “branch current imbalance fault” – a power station once caused 32 combiner boxes to frequently report “imbalance faults” due to sensor consistency issues, but the operation and maintenance personnel did not find any component or wiring problems after repeated troubleshooting, wasting a lot of manpower costs.
3、 Optimization Path for Sensor Scene Adaptation Technology
For the complex working conditions of the combiner box branch, the current sensor needs to achieve scenario based optimization from the three core dimensions of “accuracy, response, and consistency”:
One is to improve the measurement accuracy of wide dynamic range. By using new sensitive materials such as giant magnetoresistance (GMR) and tunneling magnetoresistance (TMR), the effective measurement range of the sensor is extended to 1% -120% of the rated current, and the linear error in the weak current range is controlled within 0.5%, ensuring accurate capture of branch currents under shielding conditions and avoiding “open circuit misjudgment”.
The second is to strengthen dynamic response and anti-interference design. By optimizing the sensor signal processing circuit, the response time is compressed to within 1 μ s, achieving synchronous capture of instantaneous current fluctuations; At the same time, the anti-interference structure of “shielding cover+differential output” is adopted to enhance the suppression ability of electromagnetic interference inside the combiner box, reducing the misjudgment rate caused by clutter to below 3%.
The third is to strictly control the consistency calibration of branches. In the sensor production process, add a multi temperature point and full range consistency calibration process to ensure that the accuracy deviation of sensors in the same combiner box is ≤ ± 0.3%; Simultaneously supporting batch calibration at the level of combiner boxes, reducing false alarms caused by consistency issues.
Conclusion
The “branch misjudgment” of the combiner box may seem like a local fault, but it is actually a concentrated manifestation of the insufficient adaptability of the current sensor scene. The complex working conditions of photovoltaic systems determine that sensors cannot only meet the requirements of “qualified parameters in standard environments”, but also need to achieve “reliable adaptation in complex scenarios”. Starting from solving specific pain points such as weak current detection, dynamic response, and consistency deviation, the scenario based technology optimization of current sensors can not only reduce the misjudgment rate of combiner boxes and minimize power generation losses, but also provide accurate data support for photovoltaic operation and maintenance, promoting the transformation of power plants from “passive maintenance” to “precise operation and maintenance” – this is the core value of technology landing in the industry, which is to find optimization paths in the pain points of actual scenarios and lay a solid foundation for the reliable operation of photovoltaic systems.
