LCL-filter Optimization Design Considering Stability of Grid-Connected Inverters in Microgrid

Abstract

As the existing optimized filter of grid-connected inverter design schemes give no consideration to the effect of grid impedances and current controllers, it will eventually cause the grid-connected LCL-filtered inverters lose stability when operating under the microgrid with small short-circuit ratio. This article thus presents a LCL-filter optimization design taking into account stability of grid-connected inverters. In the proposed approach, a multiple-objective optimal model is established, the objective functions of which are minimal damping power loss, minimal cost and optimum current tracking performance, and the constraint about stability is obtained by the impedance analysis method. PSO algorithm with compression factor is used to solve the optimization problem for its unique advantage on the convergence. Compared with conventional design methods, such as optimized design of LCL filter for minimal damping power loss, the optimization in this article has a higher standardized satisfaction value, which means it can balance well cost and filtering performance and stability margin, especially suited for LCL filter parameters design under microgrid with small short-circuit ratio. For improving practical value of the proposed method, it is further demonstrated that the damp resistance has the most remarkable affect to the optimization results, so the precise selection of damp resistance is indispensable for achieving the desired performances. Moreover, the proposed method has a strong robustness for variation of the main circuit parameters, which makes the optimization design has a better practical value. Finally, the comparative simulaton results verify the effectiveness of the proposed method.