Research On VSG-based Grid-connected Inverter With LCL Filter

Facing the dual threat of natural resource depletion and ecological environment deterioration, the use of renewable energy power attracts unprecedented attention. Renewable power is connected to power system in the form of distributed generators (DGs) by grid-connected inverters. As the percentage of inverter type DGs becomes larger and larger, the spinning reserve capacity will relatively reduce, and the Power systems may become unstable. To solve this problem, the inverters can be controlled to behave like synchronous generators using concept of "Virtual Synchronous Generator (VSG)". So, it is a significant subject to research on VSG-based grid-connected inverter with LCL filter.To solve the stability problems for power system, which caused by the wider application of power electronic converters, the VSG-based control system for grid-connected inverter with LCL filter is established. The VSG-based control is proved to perfectly mimic the power output characteristics and dynamic performances of synchronous generators, through the analysis of VSG’s key parameters and grid-connected operation simulation on PSCAD.The output filters of grid-connected inverter limit the harmonic current, also influence the output impedance and dynamic performance of inverter. An active damping method based on introducing capacitor current feedback is designed to solve the stability problem around the resonance frequency of LCL filters. In order to design the LCL filter parameters without multiple attempts and repeated calculations, the multi-objective optimization model of active damping LCL filter and optimization algorithm based on NSGA-II are presented. Example analysis proved that the LCL filter parameters figured out by the method have greater filter performance when costs are the same.The small-signal model of VSG is developed to identify the stability of the VSG-based grid-connected inverter control system by the method of eigenvalue analysis. The investigation of the eigenvalue’s sensitivity with respect to the system parameters provides reference for inverter’s parameters selection.