Power Flow Control of Interconnected AC–DC Microgrids in Grid-Connected Hybrid Microgrids Using Modified UIPC

This paper introduces a new approach for power flow control of interconnected ac–dc microgrids in grid-connected hybrid microgrids based on implementing a modified unified interphase power controller (UIPC). A typical grid-connected hybrid microgrid including one ac microgrid and one dc microgrid is considered as studied system. Instead of using the parallel-connected power converters, these microgrids are interconnected using a modified UIPC. As the first contribution of this paper, the conventional structure of UIPC, which uses three power converters in each phase, is modified so that a reduced number of power converters is implemented for power exchange control between ac and dc microgrids. The modified structure includes one power converter in each phase (line power converter (LPC)), and a power converter which regulates the dc bus voltage (bus power converter (BPC)) here. The ac microgrid is connected to the main grid through the LPCs which their dc buses are linked and can operate in capacitance mode or inductance mode. A fuzzy logic controller is used in the control structure of the LPCs. The fuzzy inference system is optimized based on
${H}_{{\infty }}$
filtering method to reduce the errors in membership functions design. Through the BPC, the dc voltage of LPCs is supplied by the dc microgrid. However, since the dc microgrid voltage is provided here by a photovoltaic system, the dc link voltage of the LPCs is fluctuating. Thus, as the second contribution to stabilize the dc link fluctuations, a new nonlinear disturbance observer-based robust multiple-surface sliding mode control strategy is presented for dc side control of the BPC. The simulation results confirm the effectiveness of the proposed power flow control strategy of the improved UIPC for hybrid microgrids.