Model Predictive Control for Wound Rotor Synchronous Machines Based on Closed-Form Solution and Fixed Switching Frequency

Wound rotor synchronous machine (WRSM), also known as electrically excited synchronous machine (EESM) and hybrid excited synchronous machine (HESM), can represent solutions to address the problem associated with the usage of rare earth materials for the construction of permanent magnets. When compared to other synchronous machines (e.g., permanent magnet or synchronous reluctance), they offer several benefits. However, the coupling between stator and rotor, although necessary for torque production, introduces a new degree of freedom, namely the rotor current, and complicates the current dynamics. Accurate and coordinated current control must be, therefore, designed. A novel fixed-switching frequency model predictive control (MPC) technique based on closed-form solution is proposed in this paper, aiming at improving the accuracy of current regulation, especially during rotor current transients (which are fundamental to be considered to minimize the overall machine Joule losses), while providing a simpler way to handle the available rotor and stator voltage, and keeping limited implementation requirements. Two versions, namely hybrid MPC and full MPC, have been investigated. The former allows for reducing the computational burden without almost no performance penalty. The description of the proposed strategies and complete analytical developments are reported. Relevant simulation results are included, proving the effectiveness of the proposal and better performance with respect to a standard PI-based FOC de-coupling controller. Implementation hints and preliminary results are also reported.