Abstract
To avoid transient jumps at the switching time between two operating modes in microgrids, this paper proposes a linear quadratic-based optimal bumpless controller with two degrees of freedom (DOF) to suppress the transient disturbance and realize seamless switching between mode-dependent controllers. By minimizing the transient performance criteria, which contains both the reference tracking error and the controller tracking error, this bumpless algorithm not only effectively forces the latent controller to track the active controller, but also guarantees the plant output track the reference as close as possible. For the different control objectives of the two modes, a current-based networked PI controller is proposed in islanded mode to achieve power sharing, as well as suppressing circulating current, and a power-based PI controller is designed in grid connected mode to supply required P and Q, as well as effectively synchronize f and v safely with the main grid. A microgrid test system with two operation modes was built in Matlab/Simulink. Several operating cases were executed to verity the feasibility and effectiveness of this optimal bumpless control strategy.
Highlights
Microgrids are one of the most important ways to solve energy and environmental problems, which are small-scale autonomous independent power systems with the integration of various distributed renewable energy sources
Motivated by the analysis above, this paper presents a novel optimal bumpless controller with two degrees of freedom to compensate the reference tracking error more flexibly, and several operating cases have been simulated in Matlab/Simulink to verify the feasibility and effectiveness of the proposed cascaded bumpless transfer control strategy
It is easy to see that the results of no compensator, it can be observed that the voltage peak is over 0.9 pu and the frequency proposed bumpless transfer control strategy can effectively restrict the transient behavior within a peak is over 47 Hz for a prolonged duration without any bumpless comparison
Summary
Microgrids are one of the most important ways to solve energy and environmental problems, which are small-scale autonomous independent power systems with the integration of various distributed renewable energy sources. This LQ-based bumpless transfer method is adopted in microgrids in [23], it does not consider the impact of the different control objectives on system input references It just focuses on the transient behavior of the tracking error of the reference and the system output when the mode changes. The tracking references of the two modes will be quite different and cause terrible bumps in the process of mode switching, which would cause extreme disturbance of voltage and power angles, so we need to fully consider this reference step factor on the transient performance when designing a bumpless controller to compensate the reference step flexibly by adding another degree of control freedom. PI controller of islanded mode, and the power-based PI controller of grid connected mode can smoothly switch between each other by minimizing the difference of the proposed performance index function
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