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Grid integration of renewable energy sources via virtual synchronous generator

University of British Columbia

Ongoing efforts toward environmentally sustainable electricity generation give rise to gradual displacement of synchronous generators by renewable energy resources (RESs). This paradigm shift reshapes power system dynamics and presents numerous challenges to reliable and efficient grid operations. For example, our power system will have reduced inertia and be at higher risk of instability, since the RESs generally interconnect to the grid via power-electronic converters with less or no inertia. Motivated by these challenges arising from RES integration, the concept of virtual synchronous generator (VSG) has been proposed to provide virtual inertia by emulating the SG dynamics in the RES controller. Among all VSG designs, synchronverter is a representative one with concise structure. However, this dissertation finds that conventional synchronverter designs lack in control degrees of freedom, require trial-and-error tuning process, synchronize with the grid slowly, and suffer from output-power coupling. Also, their active-power transfer capacity has not been studied, especially under weak-grid conditions. In order to address these problems and integrate more RESs into our system, my dissertation has five major contributions ranging from control design to tuning method to operation characteristics. First, in order to improve the synchronverter control degrees of freedom, I augment the synchronverter with a damping correction loop, which freely adjusts its response speed without affecting the steady-state performance. In order to simplify the tuning process, I propose a tuning method that evaluates the feasible pole-placement region and directly computes synchronverter parameters to achieve desired dynamics. My proposed tuning method completely avoids the trial-and-error tuning process and thus has overwhelming advantages over conventional tuning methods. Next, in order to synchronize the synchronverter quickly to the grid and enable the flexible ``plug-and-play" operation of RESs, this dissertation proposes a self-synchronizing synchronverter design with both fast self-synchronization speed and easily tuneable parameters. Then, to further improve the tracking performance, I propose a design with reduced output-power coupling. Finally, in order to integrate synchronverter-based RESs in weak grid, this dissertation analytically studies its active power transfer capacity and proposes two countermeasures to improve it. All my proposed designs and analyses are verified through extensive numerical or experimental studies.

Text

2019-11-27

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/72442

Electrical and Computer Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/