Inertia Emulation Through Supercapacitor for a Weak Grid

Abstract

Renewable energy sources (RES) have been widely incorporated into the power generation to offset fossil fuels in order to minimize carbon emissions. Typically, RES based power generation integrated into the power grid through the power electronic converters. These power electronic converters decouple the source from the load without providing inertia. As a result, inertia of the power grid decreases, resulting in undesirable load shedding and cascading failures under power imbalances. In order to preserve stability during contingency events, it is important to add inertia support to the grid. This article demonstrates inertia emulation from the supercapacitor (SC) to resolve the low-inertia issue. Inertia emulator based on supercapacitor (IESC) is formulated to generate inertial power by proportionally linking the grid frequency to the active power reference of SC. This article proposes an enhanced emulated inertia control (EIC) technique based on the frequency deviation and frequency derivative to address low inertia. EIC technique controls the inverter associated with IESC to exhibit the equivalent inertia characteristics as the synchronous generator. Further, the selection of the capacitance value of SC is derived to achieve the required inertia constant. The small-signal stability of IESC is demonstrated using the power angle curve. Further, the stability of the EIC is verified through bode plot. Simulation and hardware-in-loop (HIL) results are provided to verify the effectiveness of EIC employed IESC in a weak grid.

Keywords

• Frequency
• low-inertia power system
• renewable energy sources
• supercapacitor