Strong Adaptability Control Based on Dual-Division-Summation Current Control for an LCL-Type Grid-Connected Inverter

The nonignorable grid impedance is one of the characteristics of a weak grid. Meanwhile, the filter inductance also fluctuates with temperature or aging factors. The resonant frequency offset of an LCL filter will be caused by the change in power grid impedance and filter inductance. To this end, a strong adaptability control based on dual-division-summation (D-D-S) control is proposed in this article, which considers both the accuracy of grid-connected current tracking and resonance suppression under the variation of grid impedance and filter inductance. A full inductance parameter identification method based on an extended Kalman filter for simultaneously estimating filter inductance and grid impedance is proposed without remote voltage sampling. An enumeration method of the Routh array with less calculation is proposed. The algebraic relationship between control parameters and total inductance parameters is obtained by the Routh criterion. A gain correction method to realize strong adaptive control is proposed to deal with the variation of grid impedance and filter inductance. The experimental results prove the feasibility of D-D-Sigma control in a three-phase LCL-type grid-connected inverter under the variation of grid impedance and filter inductance.