This invention relates to a method and a system for operating a wind power plant (1) connected to a power grid (2), the wind power plant comprising a number of wind turbine generators. The method comprises the steps of: setting up (101) a number of different models, each model emulating an electrical behavior of an electrical system, such as a load or a power generating unit, connected to the power grid; detecting (102) value(s) of a number of power grid parameters; selecting (103) one of the number of models, based on a number of values out of a set comprising the detected power grid parameter value(s) and ambient parameter value(s), or based on an external command signal; in the selected model, calculating (104) electrical output values of the model, based on the detected grid parameter values; calculating (105) electrical reference values for the wind power plant, based on the calculated electrical output values of the model; and calculating (106) electrical reference values for each wind turbine generator based on the calculated electrical reference values for the wind power plant. The method may further comprise controlling (107) the wind turbine generators according to the calculated electrical reference values for each wind turbine generator.