Influence of Delay on System Stability and Delay Optimization of Grid-Connected Inverters With LCL Filter

Delay is inevitable in digital-controlled system and the delay will change system phase-frequency characteristic, thus affecting system stability. The system stability of inductor-capacitor-inductor (LCL)-type grid-connected inverter with single-loop control based on inverter-side current and single-loop control based on grid-side current is analyzed both in continuous and discrete domains. The influence of delay time on system stability is systematically studied. A delay time control method that is capable of adjusting delay time is further proposed to improve system stability. The proposed delay time control method is applied in the experiment, making an unstable system to be stable, and verifies the analysis result and proposed method.