Expanded Limit Boundary Explicit Model Predictive Direct Speed Control for PMSMs

The utilization of the explicit model predictive (EMP) control method for direct speed control (DSC) of permanent magnet synchronous motors (PMSMs) achieves high-bandwidth speed control and excellent dynamic performance. However, the commonly used regular hexagonal current and voltage constraints restrict the motor's operational region, resulting in a narrow speed range and low load capacity. In addition, the conventional formula-based field-weakening method leads to undesirable allocation of $d$- and $q$-axis currents, reducing the degree of freedom in adjusting the motor's operating point. These drawbacks restrict the EMP-DSC method's application in the motor's extreme operation. Therefore, this article proposes an expanded limit boundary EMP-DSC method to realize cascade-free speed control with a wider speed range and higher load capacity. First, the proposed method constructs irregular hexagonal constraints, expanding the limit boundary of the motor's operational region in the $i_{\mathrm{d}}$–$i_{\mathrm{q}}$ plane to broaden the speed and load ranges simultaneously. Then, based on these new constraints, an easily implementable optimal-trajectory field-weakening method is skillfully designed to optimize the current distribution, maintain the operating point near the optimal position, and improve field weakening performance. The proposed method enhances the competitiveness of EMP control in motor servo drive fields, and its feasibility is verified by experiments.