Asymmetrical transient modeling and analytical research of SCR-motor systems

Three-phase symmetrical and two-phase asymmetrical transient operations of induction motor frequently appear alternately for SCR-motor systems, such as rapid soft switch and soft transfer. For the transition from symmetrical to asymmetrical condition, a method for modeling the two-phase asymmetrical operation of induction motor based on space vector is presented. Firstly, three stator complex reference frames are declared and three new definitions of space vector are proposed by extending the original definition of the space vector. Second, the three kinds of vectors are used respectively to build three asymmetrical transient models of motor. Third, based on the coordinates transformation among vectors and the special constraints existed in the asymmetrical operation, three asymmetrical models of motor described by the original definition of space vector are obtained which are helpful to link the transient process between the symmetrical operation and asymmetrical operation. Finally, a transition of no-load motor from symmetrical to an asymmetrical operation is researched analytically using the proposed models. And the analytical expression of stator current vector is given in detail using the initial values of currents and power source voltage. Additionally, analytical calculation is implemented in the transient process and the results are consistent with the results of numerical simulation and experiment. And the fact verifies the correctness of both the two-phase asymmetrical transient models and analytical research on motor based on vector.