Verification of the uninterrupted transition from grid parallel to island grid operation of the Virtual Synchronous Machine in a microgrid

Abstract

The classic energy supply system is mainly based on the stabilising properties of electromechanical synchronous generators. The structural change of the electrical energy supply system towards a decentralised grid structure means that ancillary services must now also be provided at the distribution grid level. The Virtual Synchronous Machine (VISMA) was developed at the Institute of Electrical Power Engineering at the Clausthal University of Technology with the aim of making a decentralised generation unit in the grid behave like a real synchronous machine and thus actively provide relevant ancillary services. The VISMA is based on a three-phase inverter that can comply with grid requirements by adding an energy storage device in the DC link and using a special control algorithm. The focus of the investigations shown here is on the uninterrupted transition from grid-parallel operation of the VISMA to island grid operation and the subsequent stable continued operation of this island grid. A controller changeover, as most feed-in inverters would require in order to change the operating mode, is not necessary here. It is shown that the transients have subsided after 5 ms, which means that the VISMA has completely taken over the supply of the load, and the new steady state is reached after 40 ms.