Dynamic Modeling and Simulation of the Efficiency-Optimized Operation of Squirrel-Cage Induction Machines Based on Electrical Quantities and Rated Data

Abstract:
In this paper, a dynamic model for induction machines with squirrel cage rotors is developed. The modeling is based on a space vector equivalent circuit diagram, which is based on the Γ equivalent circuit diagram with concentrated leakage in the rotor circuit for the steady state. In addition to the stator and rotor winding losses, this model also takes into account the core losses in the stator, which are often neglected in dynamic considerations, as well as load-dependent additional losses and current displacement effects in the rotor bars. However, any temperature dependencies of the ohmic resistances are neglected in this paper. Saturation phenomena are also not taken into account, so that constant inductances are assumed. In [1] and [2] it is shown that for stationary operating points there is a pair of values for the stator voltage and stator frequency at which operation with maximum efficiency is achieved. The special feature here is the approximate calculation of the efficiency-optimized stator voltage and stator frequency based on electrical quantities and rated data. For this purpose, the stator current is also calculated approximately as a function of the torque. This paper examines whether efficiency-optimized operation can also be achieved within the dynamic model using the values for stator voltage and stator frequency that were determined as optimal in terms of efficiency using the stationary model. The results of the stationary and dynamic models are compared with each other and compared with measurement results at steady-state operating points. In addition, the temporal behavior during the transition to efficiency-optimized operation is examined. The influence of unexpected torque jumps during efficiency-optimized operation is also analyzed.