DQ impedance of a regulated synchronous machine

Impedance based stability techniques have been developed since the 80s for stable filter and converter designs. More recently, similar impedance techniques have been used to impose stability requirements on power systems including distributed converters. Significant effort has been spent on the development of models and impedance characterizations for regulated DC-DC converters and AC-DC converters. For rotating machinery however, and in particular synchronous machines, very little has been published on impedance characterizations. In this paper, the DQ impedance of a regulated synchronous machine is developed and compared to a hardware-validated Saber model of the synchronous machine. The DQ impedance expressions are derived based on the fixed-field impedances, the droop parameter, and simplified transfer functions for the exciter and the regulator. The analytical results are compared to the numerical results obtained from the Saber model.