Abstract
The grid-connected control technology of ac/dc hybrid microgrids affects power quality, stability, robustness, and other indicators. In order to achieve high-quality and reliability of ac/dc hybrid microgrids connected to a distributed network, this paper proposes a robust control method for grid-connected ac/dc hybrid microgrids based on mixed sensitivity. First, the grid-connected model of ac/dc hybrid microgrids is equivalent to the superposition theorem; then, the problem of how to control grid-connection can be transformed to the problem of how to deal with mixed sensitivity by considering the influence of the distributed network on ac/dc hybrid microgrids as a disturbance. Second, the grid-connected robust controller can be obtained by using the Riccati method repeatedly, which can ensure good nominal performance of the system and enhance the robustness of the system. Finally, the validity and feasibility of the proposed control method can be verified with three simulation conditions.
Highlights
In order to make full use of the flexibility, controllability, stability, and comprehensive economic benefits brought by distributed resources (DRs) operating on grid-connected modes, the concept of microgrids is becoming well-established.1,2 An ac/dc hybrid microgrid needs to fully utilize of the advantages of ac microgrids and dc microgrids to improve the permeability and efficiency of DRs
In view of the above discussion, this paper analyzes the control mechanism of ac/dc hybrid microgrids and proposes a robust control method on grid-connected ac/dc hybrid microgrids based on mixed sensitivity
In this proposed robust control method, the effect of Us on the system is considered as the disturbance in the mixed sensitivity problem model, and the effect can be eliminated by a feedforward system shown in (11) and (12); the effect of Us on the system is not considered when designing a robust controller
Summary
In order to make full use of the flexibility, controllability, stability, and comprehensive economic benefits brought by distributed resources (DRs) operating on grid-connected modes, the concept of microgrids is becoming well-established. An ac/dc hybrid microgrid needs to fully utilize of the advantages of ac microgrids and dc microgrids to improve the permeability and efficiency of DRs. A deadbeat power control scheme under unbalanced grid voltages is proposed to improve the steady-state and transient performances of PWM rectifiers, as given in Ref. 12. The control of the ac/dc hybrid microgrid can be “selfcontrol in each part and coordinated control between every parts” to ensure efficient and stable operation of the ac/dc hybrid microgrid It means that the ac grid and dc grid should be controlled by itself to meet the demands of power in each grid and ac grids and dc grids can transmit power to each other by BPCs when supply and demand of power between DGs, loads, and energy storages are unbalanced in pure ac or dc grids, which can ensure power balance of supply and demand in the whole ac/dc hybrid microgrid. This paper focuses on how to ensure high-quality and reliability of ac/dc hybrid microgrids connected to the distributed network when system parameters are perturbed
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