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Design of Parallel Converters with L-Filter and Reduced Filter Size

Parallel converters have been widely applied in distributed generations. The use of LCL filter in parallel converters may induce several stability challenges due to the filter resonance. To eliminate the filter resonance related issues, this paper presents a system level design that allows the use of small L filter without sacrificing system current quality. The key of the design is to identify the required number of converters in parallel. The L-filter based design is applicable in systems with either common or separate DC links. In this paper, parallel two-level converters with separate DC links are considered in the design, showing that the required number of converters is irrelevant to system parameters like DC voltage or power rating. Multilevel converters are also included in the study. Furthermore, the behaviour of dominant harmonics in different load condition is also investigated, using common DC link type parallel converters as an example. Simulation results and preliminary experimental results are obtained and presented.