Analytical research on asymmetrical transient model of induction motor during a thyristor-based bus transfer

In some important industrial applications, motor bus transfer often takes place in order to guarantee the reliability and stability of the power supply. However, in the adverse condition, the stator transient currents of motor are very considerable during bus transfer. A thyristor-based control method, which can suppress the stator inrush currents, is presented for the motor soft transfer between sources. Under the implementation of the method, the phase-sequence of the stator windings connected to power source would be BC-ABC-AB-ABC-CA-ABC-. In order to study the complicated transition process between two-phase and three-phase connection, an analytical method is employed in this paper since it is more rapid and efficient than the numerical simulation when the rotor speed is nearly invariant. Then, a group of consistent mathematic models based on space vector is proposed for the alternative transient, especially for three different asymmetrical transient of motor with two-phase connection. Thereafter, the analytical method is detailed for the asymmetrical transient. The results of analytical calculation for two cases are shown and compared with field test and numerical simulation respectively. And the accordance of results verifies the validity and effectiveness of the proposed analytical method and transient models.