Abstract
Multi-terminal AC/DC interconnection will be an important form of future distribution networks. In a multi-terminal AC/DC system, if scheduled power for the AC/DC converter exceeds limits this may result in instability of the DC network. In order to overcome these limitations and avoid an unstable situation during coordinated control, this paper proposes a general active stabilization method for a low-voltage multi-terminal AC/DC hybrid system. First, the typical coordinated control modes for a hybrid system are analyzed. Second, a multi-level active stabilization controller, using the Lyapunov method, is introduced, and a feedback law allowing large signal stability is proposed. Finally, a system simulation model is further established, and the proposed active stabilization method is tested and verified. Study results show that only low stabilizing power with a slight influence on the DC network dynamic can improve the system’s stability and ensure stable system voltage.
Highlights
It can be seen from this proof that u0 is the state feedback law which can prove the global stability of a LV multi-terminal AC/DC hybrid system
In order to stabilize the LV multi-terminal AC/DC hybrid system, the active stabilization-control method is proposed based on Equations (2)–(6), and its main purpose is to implement additional damping control on the existing coordinated control system
The simulation results show that active stabilization control of the multi-terminal Voltage-Source Converter (VSC) and DC/DC converter can overstep the power limitation in order to prove the stability of a LV multi-terminal AC/DC hybrid system with a stable DC voltage, even under an unstable operation point defined before the implementation of the active stabilization control
Summary
In [17], typical operation modes for low-voltage (LV) AC/DC micro-grids are proposed, and a coordination-control method of utility-interfacing VSC, storage energy, PV, and direct-driven. This research mainly takes the DC bus voltage signal (DBS) as the judgment criterion in order to propose a hierarchical or coordinated control strategy based on different operating system modes, and adjusts each converter to ensure power balance under various conditions. This method can only make DC voltage maintain the ideal reference value when the utility grid is normal; in other cases, DC voltage will deviate from the ideal reference point, which obeys a differential regulation.
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