Use of boundary control with second-order switching surface to reduce the system order for deadbeat controller in grid-connected inverter

This paper introduces a new perspective of using boundary control with second-order switching surface to decouple the LCL filter into an “LC” + L structure to control the output current of a grid-connected inverter. The boundary control (inner loop) converts the switching network together with the “LC” filter into a first-order delay term. Then, the deadbeat control (outer loop) deals with the low-order system, including the first-order delay term and the “L” filter to regulate the output current. Mathematical modeling will be studied. A simple online grid inductance estimation algorithm will be proposed to assure sufficient phase margin under an extremely weak-grid condition. A 2 kW, 220V, 50Hz prototype with the switching frequency of 8 kHz has been built and evaluated.