Bulletin of the Polish Academy of Sciences: Technical Sciences

Abstract

The continuing efforts to reduce the torque and flux ripples using Finite Set Model Predictive Direct Torque Control methods (FS-MPDTC) have been currently drawing great attention from the academic communities and industrial applications in the field of electrical drives. The major problem of high torque and flux ripples refers to the consideration of just one active voltage vector at the whole control period. Implementation of two or more voltage vectors at each sampling time has recently been adopted as one of the practical techniques to reduce both the torque and flux ripples. Apart from the calculating challenge of the effort control, the parameter dependency and complexity of the duty ratio relationships lead to reduced system robustness. Those are two notable drawbacks of these methods. In this paper, a finite set of the voltage vectors with a finite set of duty cycles are employed to implement the FS-MPDTC of the induction motor. Based on the so-called Discrete Duty Cycle-based FS-MPDTC (DDC-FS-MPDTC), a base duty ratio is first determined based on the equivalent reference voltage. This duty ratio is certainly calculated using the command values of the control system, while the motor parameters are not used in this algorithm. Then, two sets of duty ratios with limit members are constructed for two adjacent active voltage vectors to apply at each control period. Finally, the prediction and the cost function evaluation are performed for all the preselected voltage vectors and duty ratios. However, the prediction and the optimization operations are performed for only 12 states of the inverter. Meanwhile, time-consuming calculations related to SVM has been eliminated. So, the robustness and complexity of the control system have been respectively decreased and increased, and both the flux and torque ripples are reduced in all speed ranges. The simulation results have verified the damping performance of the proposed method to reduce the ripples of both the torque and flux and accordingly, the experimental results have strongly validated the aforementioned statement.