Compensation of Stray Load and Iron Losses in Small Vector-Controlled Induction Generators

Standard vector controllers for induction machines (IMs) are based on the conventional IM model. Consequently, they are unaware of the existence of stray load and iron losses. However, these losses may induce a considerable mismatch between the actual and reference flux vectors in vector controllers. This mismatch is greatly affected by the operating flux and load. In this paper, two different approaches are considered for compensation of this mismatch-the first involves investment in IMs with low stray load and iron losses, whereas the other involves development of a control algorithm in which both these losses are compensated. The performance of the developed vector controller is compared to the standard controller and tested on three small IMs of different efficiency class and rotor cage material (aluminum versus copper). Simulation and experimental testing is carried over wide ranges of loads, speeds, and magnetization levels. The estimated rotor speed is used as a measure of the controller detuning. A standard estimator that utilizes rotor flux-linkage estimates within the model reference adaptive system is here for the first time modified to include stray load and iron losses. Finally, problems regarding numerical integration, sampling frequency, and temperature-induced variations of IM parameters are addressed.