Grid tied converter with virtual kinetic storage

The increase of relatively small scale dispersed power generation (DG) is likely to impact the structure and operation of power generation and distribution systems. The current power system comprises multiple generators. Their intrinsic kinetic energy buffer (rotor inertia) plays an important role in short term system stability. Generators that are connected via power electronic power converters lack these kinetic buffers. Optimal power transfer from source to grid is often used as a control objective to optimize the energy yield. At power system level this approach may compromise stability. In this paper it is demonstrated that by emulation of rotor inertia, stability problems on a system level can be mitigated. For that purpose a short-term energy buffer is added to the system that can be controlled at a fast rate, thereby forming a so-called Virtual Synchronous Generator (VSG). Power system stability support then becomes an additional control objective of the DG. Maximum rotor angular speed deviation and maximum critical clearing time are used as performance indicators for the evaluation. Sizing of the short term buffer constitutes a second topic of this paper.