The Design of a New Double Loop Controller For Simultaneous Adjustment of Input and Output Voltages of Single-Phase Grid-Connected Inverter

Although LCL filters are used widely in the grid connected inverters to reduce high-order harmonics, such a system increases system order and therefore sustainable design of closed-loop controller system will be complicated. Recently, the single-loop control strategy has been suggested for L or LC filter based grid-connected inverters. However, the use of single-loop control directly in LCL filter-based inverters may cause instability. In this paper, a new doubleloop control strategy is presented which includes a voltage external loop and an internal loop of filter capacitor current. The external loop controls the input voltage of the grid-connected inverter. The internal loop improves system stability margin and removes the resonance of LCL filter. To obtain the transfer function of system, single-phase instantaneous power theory is used. The computer simulation has proved the feasibility of the proposed control.