Feedback Linearized Controller Design and Switching Frequency Sensitivity Analysis of Distributed Generators

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Copyright: Mahmud, Md Rasel
The conventional power system undergoes a massive change owing to the penetration of distributed generators into distribution networks and the standalone operation of microgrids. The characteristics of distributed generators largely depend on power electronic interfaces that are not matched with conventional synchronous machine-based generation systems. The changing behaviours of the distribution side of the electrical network continue to provide new challenges to power system design and operation engineers. To overcome such issues, the design of high-performance controllers plays a crucial role. In addition, investigation of the dynamic behaviours of the power electronic interfaces, including switching frequency is essential, which is the critical characteristic of the distributed generators. The first contribution of this dissertation is the design of a robust nonlinear controller to enhance the transient stability of distributed generators. In this work, the feedback linearization technique is used to linearize the standalone solar photovoltaic including battery energy storage, grid-connected fuel cell, and grid-connected solar photovoltaic including battery energy storage systems. Robust H_\infty mixed-sensitivity loop-shaping controllers are designed to stabilize the linearized part of the nonlinear feedback linearized control laws. The proposed robust H_\infty controller for the feedback linearized control scheme provides several benefits over the existing feedback linearization that is stabilized by the conventional PI controller. The second and unique contribution of this thesis is the developed single-input two-output feedback linearized control scheme based on the conventional single- input single-output feedback linearization approach. The third contribution of this dissertation is single-input two-output controller design for the islanded DC, AC, and hybrid DC/AC microgrids to enhance the voltage stability and minimize the circulating current among parallel-connected distributed generators. The fourth and final contribution of this work is the developed multi-frequency averaging based dynamic phasor model of a standalone, grid-connected, and two-stage distributed photovoltaic generators. The developed dynamic phasor models are provided with switching frequency-dependent characteristics, showing the switching frequency effect on the distributed generators. This contribution provides the idea of a suitable switching frequency range for power electronic interfaces.
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