Overexcitation and Volts/Hertz Limiter Structures for Operation Under Unbalanced Load Conditions

This paper presents an analysis of the main effects caused by unbalanced operating conditions on the overexcitation and Volts/Hertz limiters of distributed synchronous generators (DSG). These generators, especially under islanded conditions, may operate close to their limits and, as consequence, the actions of the limiters are fundamental to avoid machine overheating. This paper shows that standard structures of these limiters may fail to identify steady-state violations under unbalanced operating conditions. Since this problem can persist for a long time without being noticed, it may reduce the life cycle of the generator. Simple modifications in both structures are then proposed to enable proper functioning of the limiters even under unbalanced conditions.