Adaptive Harmonic Elimination for Model Predictive Direct Torque Control of Asynchronous Motor

With the rapid development of the economy and society, three-phase induction motors are widely used in aerospace, steel, electric power, and various industrial sectors due to their simple design, reliable performance, and cost-effectiveness. However, the operation of the asynchronous motor frequency drive system can generate harmonics, causing issues such as torque pulsation in generators, increased losses, and other challenges. These factors directly impact the efficiency and performance of the motor, sometimes resulting in failures in production processes or electromechanical systems. This paper proposes a model predictive direct torque control (AHE-MPDTC) method with an adaptive harmonic elimination strategy to ensure the system response speed based on the effective elimination of the 5th to 25th harmonics. Firstly, a least mean square (LMS) adaptive algorithm is used to estimate the harmonic interference components while updating the weighting coefficients of cosine and sinusoidal signals online. Secondly, the adaptive algorithm is applied to the model predictive direct torque control (MPDTC) method to obtain the magnetic chain harmonic components and torque harmonic components to be filtered. Thirdly, multiple harmonics are eliminated by adding a single module, and the control system output is added to the output of the harmonic elimination module. All the harmonic voltage values that need to be eliminated are obtained and added to the system transfer function. Finally, the multiple AHE algorithm is embedded into the MPC, and the output current of the AC motor is transformed to obtain the MT axis. The sinusoidal and co-sinusoidal components of the frequencies that need to be eliminated are introduced into the MF_AHE and the 5th to 25th harmonic voltages are obtained. In addition, the optimal MT axis voltages in the model-predicted direct torque control generate the space vector pulse width modulation (SVPWM) reference voltage vector. The experimental results verify the AHE-MPDTC method and the following conclusions can be drawn. (1) The dead time compensation strategy of the asynchronous motor drive system, the current harmonic suppression method of the harmonic extractor, and the electromagnetic torque pulsation suppression method of the motor with resonance digital filter are studied. The output stator current of the motor has a much lower THD under the AHE-MPDTC method. (2) Comparison between the AHE-MPDTC and MPDTC methods demonstrates that adding the AHE method does not affect the response speed of the motor's electromagnetic torque and stator magnetic chain. Additionally, the AHE-MPDTC strategy achieves a remarkable reduction of approximately 85.2% in motor torque pulsation and 60.0% in stator magnetic chain pulsation compared to the MPDTC strategy. (3) The AHE method does not compromise the system's response speed, and the AHE-MPDTC strategy improves system stability while maintaining excellent dynamic performance. © 2025 China Machine Press. All rights reserved.