Power quality of distributed generation systems as affected by electromechanical oscillations - definitions and possible solutions

Electromechanical oscillations (EMO) are natural responses of synchronous generators to a mismatch in their net torques and therefore are present in every distribution system equipped with such generators. Underdamped oscillations are of major concern for power system stability, and indeed shall be treated as such. However, in this study these oscillations are discussed from the power quality (PQ) point of view. In this work, it is claimed that such oscillations can lead to PQ phenomena. The EMO are characterised in this study using both theoretical and numerical analyses, which lead to the definition of several PQ phenomena that can be induced by such oscillations. The obtained results show that EMO in distribution systems can indeed be a significant source of PQ problems, as opposed to the widespread empirical belief that these two problems (power system stability and PQ) are not linked to each other. As a possible solution to mitigate the defined PQ problems, the usage of classical power system stabilisers is proposed in this study, since these controllers are usually available in the excitation systems of the generators but are not commonly used in distributed generation systems.