A COMBINED FINITE ELEMENT-STATE SPACE MODELING ENVIRONMENT FOR INDUCTION-MOTORS IN THE ABC FRAME OF REFERENCE - THE NO-LOAD CONDITION

This paper centers on the development of a modeling environment to predict performance and operating characteristics of squirrel cage induction motors. The model basically consists of two sections, a Finite Element computation algorithm coupled to a State-Space algorithm, hence the term Combined Finite Element-State Space (CFE-SS) modeling environment. The output of the FE section is the entire set of winding inductances which represents the key input data to the SS portion. Conversely the output of the SS portion is the entire set of winding (circuit) currents which are the key input data to the FE portion. The model is iterative in nature, in that the user continues cycling through the two sections (FE and SS) until the desired degree of convergence is achieved. The CFE-SS environment uses only design data such as, physical dimensions, magnetic circuit geometry, winding particulars and cage layouts and hence does not depend on the existence of actual hardware. This can be very useful since many design issues can be resolved without ever building a prototype. The modeling environment is totally within the ABC frame of reference, therefore no approximating assumptions such as sinusoidally distributed mmf's or current sheets have been made. The resulting torque and current profiles include the full effects of magnetic circuit saturation, winding layout, and magnetic circuit geometry. The model was verified by comparing its results with experimental test data for a 1.2-hp, 200 Volt 3-phase squirrel cage induction motor, and very favorable agreement was realized. This paper concentrates on the model derivation and the no-load simulation, while a companion paper completes the analysis and simulation of the blocked-rotor and load operating conditions.