Analysis of delay effects in single-loop controlled grid-connected inverter with LCL filter

Delay in a grid current single-loop controlled inverter with LCL filter has a great influence on the system stability. The unstable problem of grid-connected inverters with LCL filter is clearly explained from positive feedback concept, and the positive role of delay in system stable control is explored in this paper. Then the range of delay time is calculated to guarantee the system stable. The effects of delay on dynamic and steady state performance of system are also revealed. An optimized delay time is designed to realize stable operation, fast dynamic response and low harmonics of resonance frequency based on the theoretical analysis. Experimental results validate the theoretical analysis about the effects of delay.