A multiple loop control method for grid-connected inverter integrating renewable sources with LCL filter

Grid-connected inverters are the interfaces for renewable energy sources into the active distribution networks. Usually typical grid-connected inverters use pulse width modulation control, resulting in the grid currents contain a lot of high-order harmonics. Traditionally, grid-connected inverters use L filter to eliminate the harmonics. And in grid-connected inverters´ AC side, it uses LCL filter to get better effect. But this increases the complexity of the system and reduces the system stability. Therefore, under non-ideal network conditions the system usually requires controlling grid current to ensure the grid power quality and power factor. In this paper, a multiple loop control method for grid-connected inverter with LCL, based on grid current and capacitive current is presented. It introduces an active damping control method for LCL filter under damped oscillation characteristics in order to improve system stability. The multiple loop controller adopts the parameters designed by the proposed method, and ensures the stability and dynamic performance of the single phase current-control grid-connected system, which is verified by the experimental results.