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

ABSTRACT:

  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-DC microgrids. The modified structure includes one power converter in each phase, named as line power converter (LPC), and a power converter which regulates the DC bus voltage, named as 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 (CM) or inductance mode (IM). A fuzzy logic controller is used in the control structure of the LPCs. The fuzzy inference system is optimized based on H∞ 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 PV 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 (NDO-MS-SMC) 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.

KEYWORDS:

 

1.      Hybrid microgrid

2.      UIPC

3.      Power control

4.      Disturbance observer

5.      Multi-surface SMC

SOFTWARE: MATLAB/SIMULINK

CONCLUSION:

The hybrid microgrid structure is the most probable option in the future smart grids to gather together the renewable resources as well as AC/DC loads. This is due to the fact that this structure has the merits of both AC and DC microgrids simultaneously. One conventional problem with this structure is the power exchange control between interconnected AC and DC microgrids. In this study, a UIPC based solution has been proposed as a superior alternative to the parallel-connected power converters which have brought many problems. A modified structure of the UIPC has firstly been proposed and then effective control strategies have been introduced for the modified UIPC. The simulation results validated the modified model as well as the power exchange control performance between AC and DC microgrids.

REFERENCES:

[1] Runfan Zhang, Branislav Hredzak, "Distributed Finite-Time Multi-Agent Control for DC Microgrids with Time Delays”, IEEE Transactions on Smart Grid, Early Access, 2018.

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[3] Haifeng Qiu, et al, " Bi-level Two-stage Robust Optimal Scheduling for AC/DC Hybrid Multi-microgrids", IEEE Transactions on Smart Grid, Early Access, 2018.

[4] Pengfeng Lin, et al, "A Distributed Control Architecture for Global System Economic Operation in Autonomous Hybrid AC/DC Microgrids", IEEE Transactions on Smart Grid, Early Access, 2018.

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