Modeling of Interconnected Voltage and Current Controlled Converters With Coupled LC-LCL Filters

Nowadays, more and more converters under voltage control mode with LC filter and current control mode with L/LCL filter are interconnected, forming a more complicated impedance network and resulting in coupled control behaviors. This type of interconnected converter system can be commonly seen in a stand-Alone microgrid and some advanced testing benches for power electronics converters. In this article, a system consisting of a voltage-controlled converter with LC filter and a current-controlled converter with LCL filter have been studied. A detailed mathematical model is proposed to describe the stability and coupling characteristics of such system. It is found that the stability problem in this type of configuration may arise in an uncommon way, which is different from the typical resonance in a grid-connected converter system and can be triggered in higher frequency band. Meanwhile, the voltage and current behaviors of interconnected converters are strongly coupled through the complicated filter impedances and control loops in low-frequency band and mid-frequency band.