The Interaction Mechanism and Parameters Optimization of Multiple DC Filters for Second-order Harmonics in DC Microgrids

DC microgrid is one of the development direction of power distribution system. Affected by factors such as non-linear equipment and unbalanced load, the system is prone to second harmonic generation, which seriously threatens the stability of system operation and the safety of electrical equipment. The coordination of multiple active filters has become one of the methods for controlling second harmonics in DC microgrids. However, due to the coupling interference between the filters, the filtering performance and effect are quite different. This paper establishes the Norton equivalent grid-connected model of multiple filters. Based on the relative gain matrix theory, an analysis method of the interaction mechanism of multiple filters is proposed. The matrix relationship between the change of the filter output current and the change of the harmonic source current is constructed and the influence of DC microgrids line parameters and filter control parameters on the filtering effect is analyzed. An optimization model based on the influence factors of coupling interference is established, and NSGA-II is used to optimize the configuration of electrical and control parameters. Finally, a DC microgrid model with multiple DC filters is established in PSCAD/EMTDC to verify the rationality of the parameter analysis that affects the filtering effect in the scenario of multiple harmonic sources. The results show that the interaction between filters can be effectively suppressed and the effect of multi-filter cooperative filtering can be improved by optimizing the electrical distance and the parameters of filter controllers.