The Analysis of Induction Machines Controlled by Series Connected Semiconductor Switches

The widespread interest in applying semiconductor switching elements to induction motor speed control has created. a need for a fast and accurate means of predicting motor performance under the unconventional excitation inherent in these systems. In many cases this excitation takes the form of alternate periods of normal sine-wave excitation and periods of open-circuit operation. This paper presents an analytic means of determining steady-state performance under these conditions. Use of the techniques presented permits direct computer solution without iteration. Solution time is thus much shorter than can be achieved by iterative solution of the system differential equations and the necessarily long computation times required to allow the solution to reach steady state from arbitrary initial conditions. Computer results for a single-phase motor and for a capacitor run motor are presented. Results include average torque, motor losses, and efficiencies, and instantaneous torque, current, and voltage as a function of speed. Run time on an IBM 1620 Model II is approximately 100 seconds for each of the desired speeds. The method is thus well suited to evaluation of proposed motor designs and subsequent design optimization.