On the Benefits of Model Predictive Control for Cascaded-H-Bridge-Fed IPMSM Drives Operating at Very-Low Switching Frequency

This work investigates the technical and economic benefits of finite control set model predictive control for cascaded-H-bridge-fed permanent magnet synchronous motor drives operating at very-low switching frequencies. The key novelty of this work deals with quantifying the electric drive efficiency improvement and the annual expenditure reduction achieved with model predictive control through an extended experimental comparative analysis. Indeed, such an analysis is missing in the literature and allows for motivating its entrance in the medium voltage drives industry. To this end, the voltage-vector-based model predictive control is selected from the scientific literature due to its multiobjective capability and compared with the field-oriented control strategy, as it represents the current standard in industrial applications. The experimental comparative analysis is conducted over a wide working area of 20 working points, defined as a function of the motor speed and torque, and for switching frequency values in the range 250-500 Hz. As performance metrics, the current total demand distortion, the motor harmonic losses, motor efficiency, inverter efficiency, and overall electric drive efficiency are adopted. These metrics are organized into distortion, losses, and efficiency maps and employed to estimate the annual operative expenditure reduction for a 3.4 MW medium voltage drive case study. Results show that the adopted model predictive control outperforms the standard field-oriented control, guaranteeing a reduction of the current total demand distortion up to 12%, a reduction in the motor harmonic losses up to 15%, an increase in the electric drive efficiency up to 4%, and an annual expenditure reduction in the range 10-24 k€, depending on the considered load and duty profiles. Thus, model predictive control represents an excellent candidate to replace standard control strategies in the medium voltage drives industry.