Limitations of sensor-less flux determination in induction motors based on saturation effect using low magnitude high frequency magnetizing current

Observer-based flux estimation without shaft encoder, by injecting high frequency test current is the newly emerging control scheme for all kind of flux operated system, especially for standard induction motors. This scheme is free of integration and in relation to the demand of a high performance at very low frequencies. The determination is based on saturation effect using high frequency magnetizing curt-rent. We discuss the effect that appears in the region of magnetic saturation. The paper focuses on the method of evaluating the rotor flux estimation from stator voltage and currents, and highlights the limitations of the proposed scheme.