Modification in Model of Load-Frequency Control Loop of Power Plants Considering Damping Coefficient of Turbine

Maintaining desired megawatt output of a generator unit is an essential role of Automatic Load-Frequency Control (ALFC) loop for secure operation of power system. In modeling this control loop, a major part concerns with the modeling of the mechanical behavior of turbine-generator. While, the efficiency of turbines normally depends on the speed they are operated, in most studies it is not included in the accurately modeling. In cases that this dependency is considered, its effect, together with load frequency dependency is included in load frequency factor (D). On other hand, it should be mentioned that the frequency dependency of a turbine indicated by its damping coefficient relates to its own physical properties, while the load frequency dependency concerns to the rest of the system. Therefore, considering these two properties in the modeling with one parameter may not accurately express the characteristics of the whole system. In this paper, a developed model for automatic load frequency control loop is proposed in which the turbine dependency coefficient is accurately considered. It is shown that while the traditionally used approximate models for ALFC may lead to not acceptable conclusions, accurate modeling of ALFC will result in more accurate and reliable results.