Double-Inverter Fed Independent Direct Torque Control of Slip-Ring Induction Machine

In this article, both the stator and rotor sides of the slip-ring induction motor (SRIM) are controlled using two distinct direct torque control (DTC) strategies, resulting in a dual DTC (DDTC) architecture. The SRIM is treated as a combination of two independent virtual induction machines (IMs), where each IM is operated individually through the stator and rotor terminals, respectively. In this work, a current model-based approach is employed to estimate the stator and rotor fluxes, which eliminates the need for conventional integration-based flux estimation and enabling more efficient digital implementation. Moreover, a flux sharing strategy based on the minimization of total copper losses is proposed to enhance the flux control performance. Further, field-weakening (FW)-based control is investigated under the DDTC scheme, wherein the motor is operated up to 2.2 per unit (pu) speed, with a base speed of 2 pu, in a doubly fed configuration. A flux-sharing mechanism based on airgap and leakage fluxes is considered to determine the appropriate magnitudes of the stator and rotor fluxes. The proposed DDTC approach is experimentally validated using a 2.2 kW SRIM test setup.