There are difficulties in analyzing the stability of microgrids since they are located on various network structures. However, considering that the network often consists of passive elements, the passivity theory is applied in this paper to solve the above-mentioned problem. It has been formerly shown that when the network is weakly strictly positive real (WSPR), the DC microgrid is stable if all interfaces between the microgrid and converters are made to be passive, which is called interface passivity. Then, the feedback passivation method is proposed for the controller design of various DC-DC converters to achieve the interface passivity. The interface passivity is different from the passivity of closed-loop systems on which the passivity based control (PBC) concentrates. The feedback passivation design is detailed for typical buck converters and boost converters in terms of conditions that the controller parameters should satisfy. The theoretical results are verified by a hardware-in-loop real-time labotray (RTLab) simulation of a DC microgrid with four generators.
Islanding detection is a crucial technique for distributed generation (DG) system. An islanding detection method based on system identification is proposed in this study. Regarding the grid as an RLC load, a recursive least square method is used to estimate the equivalent RLC parameters. Then a logistic regression classifier is applied to determine whether DG is disconnected from the grid or not by the data sets of the estimated parameters of the system. An experiment demonstrates that the algorithm is effective and fast for detecting an islanding event.
This study presents a strategy using the synchronized output regulation method (SOR) for controlling inverters operating in stand-alone and grid-connected modes. From the view point of networked dynamic systems, SOR involves nodes with outputs that are synchronized but also display a desirable wave shape. Under the SOR strategy, the inverter and grid are treated as two nodes that comprise a simple network. These two nodes work independently under the stand-alone mode. An intermediate mode, here is named the synchronization mode, is emphasized because the transition from the stand-alone mode to the grid-connected mode can be dealt as a standard SOR problem. In the grid-connected mode, the inverter operates in an independent way, in which the voltage reference changes for generalized synchronization where its output current satisfies the required power injection. Such a relatively independent design leads to a seamless transfer between operation modes. The closed-loop system is analyzed in the state space on the basis of the output regulation theory, which improves the robustness of the design. Simulations and experiments are performed to verify the proposed control strategy.
This paper studies the H∞ output regulation problem for linear systems with disturbance unable to be modeled. The goal is to suppress the impact of disturbance on the regulation error to the given H∞ norm. The feed-forward controller, as well as the internal model controller for the uncertain system, are presented by means of the linear matrix inequalities (LMIs). Simulation results are given to illustrate the analytic results.
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