A decentralized quasi-hierarchical control scheme for droop-controlled AC island microgrids

To avoid the communication constraints and improve system performance, a decentralized quasi-hierarchical control scheme is proposed for droop-controlled microgrids with both voltage-controlled voltage source converter (VCVSC) and current-controlled voltage source converter (CCVSC) interfaced distributed generators (DGs). Compared with conventional approach, the functions of three-level centralized hierarchical control (TLHC, i.e., the primary, secondary and tertiary control) are implemented locally in DGs without any communication, only by utilizing the local frequency measurement and a nonlinear droop curve. Consequently, the frequency restoration and economic dispatch can be realized locally. Two low-pass filters are designed to tackle the possible problems caused by the locally implemented secondary and tertiary control. To analyze the dynamics of the microgrid, the small signal analysis is performed. Numerical simulation verifies the effectiveness of the control scheme.