A Digital Delay Compensation Method to Improve the Stability of LCL Grid-Connected Inverters

Abstract

Grid-connected inverters are an important part of the connection between distributed power generation units and the large grid, and their stability is the basis for ensuring the safe operation of distributed power generation units. This study found that there is an inherent digital control delay in the three-phase LCL grid-connected inverter system. This characteristic causes the effective range of capacitive current feedback active damping to be reduced, the selection range of the active damping coefficient to be limited, and the phase at the open-loop cutoff frequency to be reduced. In order to reduce the impact of digital delay, this article conducts a detailed analysis of the characteristics of the first-order lead link that can be used as delay compensation, pointing out that its infinite gain when it obtains the optimal compensation effect will bring noise to the inverter system. This paper proposes a method of cascading digital filters for the first-order leading link to suppress its infinite gain. An improved delay compensation link that is more suitable for numerically controlled inverter systems is constructed. Finally, the effectiveness and necessity of the proposed improved delay compensation link are verified by a simulation platform and an experimental platform.