Current control based on zero-placement strategy for grid-connected LCL-filtered inverters

The under-damped resonance phenomenon in grid-tied LCL-filtered inverters yields much difficulty in designing the controller. By adding one or more state feedback, the multi-variable feedback control methods are commonly used. However, the revealed studies are quite limited and cannot explain the essential mechanism of the multi-variable feedback control. In this paper, a systematic analysis method based on zero-placement is provided to detail the control mechanism of one family of multivariable feedback strategy. Through a combination of the easily-measured current and voltage states in LCL filters, a novel state variable of which the zeros can be assigned is produced. By assigning the zeros to cancel the resonance poles, the close-loop control based on the feedback of this novel state variable is easily designed and is capable of satisfactory dynamic. In summary, with the systematic analysis, a family of multi-variable feedback methods is deduced.