The stator flux and electromagnetic torque are directly controlled in a DTC system using space vector modulation technique. In DTC, torque and flux ripples increases at low speeds. A DTC-SVM induction motor drive at very low speeds is investigated here and High Frequency Signal Injection (HFSI) method is adopted to mitigate the low speed issues. In this method a sinusoidal wave of small amplitude and high frequency is injected.
Mini Sujith, Anu, K. M., and Dinesh, M. N., “HFSI—A Promising Solution to Very Low Speed Issues in DTC-SVM Induction Motor Drive”, in Emerging Research Areas: Magnetics, Machines and Drives (AICERA/iCMMD), 2014 Annual International Conference on, 2014.