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In the construction of photovoltaic power plants, high-power centralized inverters and string inverters coexist for a long time. The differences in system size, power level, and operation mode between the two architectures determine that their current measurement requirements are not the same. If we ignore the differences at the system level and simply use the same current sensing scheme, it is often difficult to achieve a balance between performance, reliability, and cost.
1、Differences in system architecture determine different measurement priorities
Centralized inverters are usually connected to a large number of photovoltaic arrays, with high DC side current levels and large convergence scales. Their core goal is high efficiency, high-power stable operation. Under this architecture, current measurement serves more for overall power control and system level protection, emphasizing stability and reliability under high current conditions.
The string inverter is characterized by multiple independent MPPTs, with each string having a relatively small current but a large quantity and wide distribution. Its current measurement is not only used for power control, but also directly participates in the judgment of single string operation status and fault location. This difference places higher demands on the resolution and consistency of current measurement in string systems.
2、 Different challenges in measuring DC side current
In centralized inverters, there is usually a single or a few high current inputs on the DC side, with a large busbar size and high magnetic field strength. At this point, the current sensor needs to have good resistance to external magnetic interference and high current linearity to avoid saturation or measurement compression under high loads.
In contrast, the DC side current amplitude of string inverters is lower, but the operating current span is larger, with significant changes from low light to full load. The difficulty of current measurement lies not in the rated current, but in the stability and zero point consistency in the low current region. If the measurement noise or drift is too large, it is easy to cause MPPT judgment deviation, which affects the power generation.
3、 The emphasis of communication side measurement is different
The AC side of centralized inverters usually has high grid connected current and system inertia, and strict requirements for grid connected stability. Current measurement requires good dynamic response capability and phase accuracy to support power grid scheduling and protection strategies. At the same time, electromagnetic interference is more significant in high-power environments, which puts higher demands on the anti-interference ability of sensors.
Due to the small single machine power, the AC side current of the string inverter is relatively controllable, but the number of parallel machines is large. At this point, measurement consistency and inter channel differences are more critical. If the measurement deviation between different inverter units is too large, it may affect system level power coordination and operational evaluation.
4、 The difference between reliability and maintenance strategies affects the selection approach
Centralized inverters are usually deployed in centralized power stations, with long maintenance cycles and high downtime costs. This makes the current measurement scheme more focused on long-term stability and reliable operation under extreme working conditions, sacrificing some costs to reduce long-term risks.
String inverters are characterized by their large quantity and wide distribution, emphasizing modular design and cost control. On the premise of ensuring basic performance, current sensors need to have good batch consistency and replaceability to adapt to large-scale applications.
5、 Enlightenment on the division of labor in current sensing technology
From a system perspective, the difference in current measurement requirements between high-power centralized and string inverters is not reflected in a single parameter, but in a comprehensive consideration of measurement objectives, operating conditions, and maintenance strategies. Centralized systems tend to focus more on high current stable measurement and system level reliability, while string systems rely more on low current performance and multi-channel consistency.
Conclusion
The difference between high-power centralized and string inverters determines that their current measurement schemes cannot be completely identical. Only by starting from the system architecture and operational goals, and understanding the real requirements of different inverters for current signals, can a reliable and efficient current measurement system be constructed in engineering practice. This selection approach based on system differences is an important guarantee for the long-term stable operation of photovoltaic equipment.
