Proposed in this paper is an improved analytical method of generator aggregation parameters． This method
first adds a phase shift transformer to a common bus to eliminate the voltage deviation caused by moving coherent generators，and then directly obtains the parameters of the equivalent generating units based on the coefficient matrices structure preservation characteristic of the generator structure and the fact that the sum of the current phasor on every axis of the synchronous planes is equal． This method overcomes the deficiencies of the traditional methods，which depend on the transfer function fitting in the frequency domain or the time domain simulation and thus rely on the setting of working points and the selection of optimization directions． Therefore，the proposed method is more adaptive for generating unitsand can be applied to the on-line calculation．