Ralf Hesse

Virtual synchronous machine

Demands in the area of electrical energy generation and distribution, as a result of energy policies, are leading to far reaching changes in the structure of the energy supply, which is characterised, on the one hand, by the substitution of conventional power stations by renewable energy generation, a decision which has already been made, and, on the other hand, by the changeover from centralised to decentralised energy generation. From an electrical engineering point of view, a new situation will arise for consumers concerning security of supply and power quality, which calls for further technical measures by the grid operators to ensure that the increasingly stringent supply criteria can be met. This article describes a new power electronics based approach which allows a grid compatible integration of predominantly renewable electricity generators even in weak grids making them appear to be electromechanical synchronous machines. As a consequence, all the proven properties of this type of machine which have so far defined the grid continue to do so, even when integrating photovoltaic or wind energy. These properties include, for instance, interaction between grid and generator as in a remote power dispatch, reaction to transients as well as the full electrical effects of a rotating mass. In addition, this new development can be operated in such a way that it provides primary reserve allowing, from a grid point of view, electricity generators such as wind and PV to be regarded as conventional power stations.

Investigation of the Virtual Synchronous Machine in the island mode

In this paper the investigation results of the Virtual Synchronous Machine (VISMA) in the island mode are presented. The increasing integration of the distributed generation units leads to continual growing of the amount of the inverter interface in the electrical grid. Therefore, the characteristics of inverters will more and more significantly influence the grid operation. The VISMA is a novel control method for the inverter to make it possible that an inverter-interfaced decentralized generation unit can be operated as a real electromechanical synchronous machine, which up to now as the main generation unit in the electrical grid has many advantages in consideration of the grid stability. These advantages can be implemented in the VISMA and are proved experimentally in the grid-connected operation mode. The island-mode is another important operation mode that will be necessary for a stand-alone grid without connecting of the main grid or when the main grid fails due to a disturbance. Therefore this operation mode of the VISMA is focused in this paper.

Phasen- und amplitudenfehlerfreie Filterung von störbelasteten Messsignalen mit quasistationärer Basiskomponente (Phase- and Amplitude Errorless Filtering of Measurement Signals with Quasi Stationary Fundamental Frequency Component)

Zur Vermeidung von Abtastproblemen und zur Vorbehandlung von störbelasteten Messsignalen werden bei einer vorgesehenen Verarbeitung auf Mikrorechnern oft Vorfilter eingesetzt. Die Vorfilterbehandlung führt zu Phasen- und Amplitudenfehlern am Basisfrequenzanteil des Messsignals, welche mit dem vorgestellten Verfahren kompensiert werden können. To avoid sampling problems and suppress signal disturbances, an analog prefilter is often inserted in front of the ADC input port of the process-control computer. Particularly in the case of noice-disturbed field process signals, prefiltering is obligatory. The disadvantage of phase shift and amplitude attenuation of the fundamental frequency component, e. g. the power grid frequency in such measurement signals, can be prevented with the approach described in this paper.