Admittance Modeling, Analysis, and Reshaping of Harmonic Control Loop for Multiparalleled SAPFs System

Large-scale harmonic current pollution exists widely in power grid due to the massive applications of power electronic equipment, which affects the efficiency and reliable operation of the whole system. Owing to its excellent controllability, dynamic response performance, and compensation precision, the multiparalleled shunt active power filters (SAPFs) is widely used in the past few decades. However, under the weak grid condition, a coupling relationship between multiple grid-connected inverters is formed through PCC because of the non-negligible grid impedance, which will cause the harmonic instability problem. Compared with the application fields of renewable energy generation and energy storage, the stability analysis for multiparalleled SAPFs system not only needs to consider the current loop, but also the harmonic control loop and harmonic load comprehensively, which increases the complexity of stability analysis and control. In this article, taking harmonic suppression as the application background, the global-admittance-based stability analysis method for multiparalleled grid-connected inverters system under the non-negligible grid impedance condition is proposed. Through admittance reshaping, the active damping method for suppressing system instability is given. Besides, the description and cause analysis for common instability cases are also presented. The simulation and experimental results verify the effectiveness of the proposed method.