Identification of generalized models of synchronous machines from time-domain tests

Recent developments have shown that numerical models of synchronous machines are, in many cases, improved by introducing an increased number of dampers or dynamic constants. The major issues affecting the model identification by such an extension, which in fact becomes necessary when the machine possesses a solid rotor are discussed from a time-domain point of view. The first result is that all methods which determine the equivalent circuit from test data in an indirect manner give rise to systematic errors in the subtransient and sub-subtransient time constants of the estimated circuits. It is demonstrated by simulation that if the direct approach is applied to such a test, with pulse wave modulated (PWM) voltages as the excitation signals a numerically cheap and accurate one-step procedure for time-domain identification of circuit models is obtained