Abstract
Grid-tied photovoltaic inverters must fulfill several requirements, including high efficiency and reduced cost and complexity of the overall system. Hence, transformerless operation is advantageous in order to achieve the prior requirements. Meanwhile, such operation results in several demerits, such as the dc current component injection into the grid. This component should be effectively mitigated in order to avoid some impacts, such as the saturation of the transformers in the distribution network. On the other hand, limiting this component up to few milliamperes is a challenging issue due to the various measurement errors. Accordingly, different blocking and measurement techniques have been proposed and studied to overcome this issue, where some demerits are seen behind each technique such as the implementation complexity, the common-mode voltage problems, and the high filter requirements. Moreover, none of them measures the dc component directly, but predicts its value using different approaches. Hence, this letter proposes a new technique to measure this dc current component with high accuracy using a coupled inductor combined with a small-range Hall effect current sensor in order to achieve the lowest possible cost with the highest possible accuracy. The proposed technique is introduced, analyzed, and tested experimentally to verify its principle of operation. Also experimental measurement of the dc current component using a 5-kVA transformerless grid-tied voltage-source inverter is introduced with and without the proposed technique in order to validate its operation.
Highlights
The use of grid-tied photovoltaic (PV) inverters is continuously increasing and several requirements have to be fulfilled in order to achieve the highest possible performance of the employed power conditioning stage (PCS)
Even though the gained merits from the transformerless operation, it results in several problems, where the dc current component injection into the grid is a major one
It is worth to note that there are some current sensors with very high accuracy that can be used to detect the dc current component with higher accuracy, but these sensors are usually more suitable for measurement equipment
Summary
The use of grid-tied photovoltaic (PV) inverters is continuously increasing and several requirements have to be fulfilled in order to achieve the highest possible performance of the employed power conditioning stage (PCS). Transformerless operation, i.e. eliminating the low frequency power transformer from the grid-tied PV inverter, is followed in order to improve the PCS efficiency and reduce its cost and volume [1]–[5]. Even though the gained merits from the transformerless operation, it results in several problems, where the dc current component injection into the grid is a major one. This dc current component might exist due to one or more of the following reasons [5]: an asymmetry in the switching scheme;.
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