Mitigating Flux Droop in Low-Speed Steady-State DTC for Three-Phase Induction Motors

Direct torque control (DTC) three-phase induction motors experience stator flux droop at low speeds, especially under heavy loads, primarily due to the significant influence of stator resistance. This resistance distorts the flux trajectory, making it difficult to reach its reference value and reducing the effectiveness of the voltage vector in regulating flux within the hysteresis band. To address this challenge, this paper proposes a modification to conventional DTC switching sector based on speed and torque variations to enhance flux performance while preserving DTC's simplicity. A sector rotation strategy (SRS) optimizes voltage vector selection to enhance flux magnitude for mitigate flux droop. The study investigates the impact of stator resistance on stator flux and voltage control, particularly at low speeds where maintaining reference flux becomes challenging. The proposed approach is validated through MATLAB/Simulink simulations and experimental verification using a DSP-based induction motor drive system. Testing at 400 rpm and 100 rpm with a load torque of 1 Nm demonstrates a significant difference in flux droop, with the proposed SRS achieving flux droop reduction of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{8 1. 8 2 \%}$</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{9 5. 5 6 \%}$</tex> respectively. The results demonstrate significant improvements in flux regulation and current performance without deteriorating torque response, establishing the proposed method as a viable solution for industrial and electric vehicle applications.