Design methodology of a passive damped modified LCL filter for leakage current reduction in grid-connected transformerless three-phase PV inverters

Design methodology of a passive damped modified LCL filter for leakage current reduction in grid-connected transformerless three-phase PV inverters

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Although grid-connected transformerless photovoltaic (PV) inverters present higher efficiency and power density compared with inverters with a transformer, the leakage current caused by the inverter common-mode voltage introduces several problems. Among the techniques to reduce the leakage current, the modified LCL (MLCL) filter with passive damping is an effective and simple solution. However, the classical design of the filter damping resistance is not adequate for ensuring both proper leakage current attenuation and control system stability. Therefore, this study proposes a methodology to design the resistance in a low-loss passive damping structure applied to the MLCL filter. In addition to the conventional specifications for LCL-type filters, this study includes the leakage current limit in the design procedure. Simulation and experimental results for a 10 kW PV inverter show the damping resistance impact on the leakage current. The results related to the efficiency and grid inductance variation are also presented. Therefore, it is possible to conclude that the proposed design methodology is very useful for obtaining a damping resistance that ensures control system stability and a leakage current in conformity with PV standards.


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