ANALYSIS OF VOLTAGE-CONTROLLED INDUCTION-MOTORS USING QUASI-ROTATING REFERENCE FRAME

Speed control of induction machines using back-to-back thyristors in each phase of the machine is a simple scheme. Yet, even the steady state analysis of this system becomes complex since voltage adjustment is obtained by sequentially open-circuiting the stator phases. In this paper, a new analytical approach for predicting the steady state performance of this system is presented. By using a dq model and properly choosing the dq frame, the steady state solution can be obtained with minimal complexity. In particular, by utilizing a special ''quasi-synchronously'' rotating reference frame, only three modes of the system need be defined rather than seven, and the steady state solution is simply a combination of these modes. Simulation results are included to show the validity of this scheme. It is shown that the method can be extended to model transient behavior with the proper precautions.