New approach of sector rotation strategies for improving the dynamic and capability of induction motor

• Main Author: Muhamad Sabri, Nurul Syahada
• Format: Thesis
• Language: English; English
• Published: 2025
• Subjects: T Technology; TK Electrical engineering. Electronics Nuclear engineering
• Online Access: http://eprints.utem.edu.my/id/eprint/29432/

Direct Torque Control (DTC) is a well-established control technique for three-phase induction motors due to its simple structure, fast torque response, and independence from coordinate transformation. However, DTC faces notable performance degradation at low speeds, primarily caused by the influence of stator resistance. At low speed, the reduced back-electromotive force (back-EMF) makes it difficult to sustain the desired flux level, and the voltage drop across the stator resistance significantly impacts flux estimation. This condition results in flux droop, particularly evident during the application of zero-voltage vectors and across the boundaries of conventional fixed sectors. The conventional DTC’s sector-based switching strategy becomes less effective as the contribution of active voltage vectors becomes uneven due to stator resistance, which disrupts flux symmetry and reduces the control accuracy of flux under dynamic and low-speed operations. To address these limitations, this thesis introduces a new approach of sector rotation strategy that dynamically adjusts the voltage vector selection based on real-time torque and speed variations. This is achieved through the development of an analytical model that calculates the appropriate shifted angle to rotate the sector position. By adjusting the sector boundaries, the proposed strategy enables the optimal alignment of voltage vectors with the stator flux trajectory, effectively minimizing the adverse effects of stator resistance and improving flux magnitude consistency during transitions. This adaptive approach retains the inherent simplicity of DTC while significantly enhancing its performance under low-speed and dynamic conditions. The effectiveness of the proposed method was validated through extensive simulations using MATLAB/Simulink and real-time experimental verification using a DS1104 dSPACE digital signal processor. The experimental testbed includes a 1.1 kW three-phase induction motor coupled with a 2 kW DC generator load and a two-level inverter for control implementation. Comparative studies were performed against the conventional DTC method under identical conditions. The results show that the proposed strategy achieves a significant improvement, including: 1) a reduction in stator flux droop up to 65.4%, 2) stabilizes flux error status, and 3) smoother current waveforms with reduced distortion, approaching a sinusoidal form. Overall, the proposed sector rotation strategy demonstrates a practical and effective enhancement to the conventional DTC method, providing improved control precision, smoother motor operation, and robustness in low-speed regions while maintaining the low computational burden and simplicity that make DTC attractive for industrial applications. This advancement holds relevance for applications requiring precise control in dynamic or low-speed environments, such as electric vehicles and robotics.