Novel Virtual Synchronous Generator Design With Dynamic Virtual Inertia and Bounded Frequency, Current and Voltage Characteristics

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Abstract
In this paper, a novel Virtual Synchronous Generator (VSG) architecture is proposed in order to improve the dynamic response of the conventional VSG using dynamic virtual inertia, and additionally ensure that the frequency, the output current and the output voltage always remain within predefined limits. In particular, the proposed control law dynamically alters the virtual inertia of the VSG proportionally to the frequency gradient and frequency deviation, ensuring small values for the Rate of Change of Frequency (RoCoF) and for the maximum frequency deviation after disturbances. Meanwhile, it is always guaranteed that the virtual inertia will remain within a predefined range at all times, without introducing non-continuous dynamics. The boundedness of the frequency, current and voltage, as well as the virtual inertia, is analytically proven using vector field theory and the ultimate boundedness theorem. A detailed stability analysis is provided for the cases where the proposed VSG is connected to an infinite bus and when a complete power system consisting of multiple VSGs and synchronous generators is considered. The effectiveness of the proposed solution compared to conventional VSG structures with constant and varying virtual inertia is tested after load demand variations and short-circuit faults, on a 14-bus power system created in the Typhoon HIL real-time digital simulator and on an experimental setup consisting of an inverter connected to either a variable load or to the grid.

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