Design of excitation current estimation algorithm for wireless excitation system of electrically excited motors based on S-N resonant topology

Although wireless excitation improves the reliability of electrically excited synchronous motors (EESMs), the rotor field current cannot be directly measured due to the rotation of the rotor. Using the widely adopted S-N topology as a representative framework, this paper reveals the prediction principle of excitation current and proposes five distinct excitation current estimation methods. By comprehensive comparison, the method of estimating the excitation current using the input voltage and the RMS value of the primary current exhibits excellent characteristics across all aspects. It eliminates the need for high-frequency phase detection, is robust to load variation, and provides a reliable technical solution for the closed-loop control of wireless excitation systems. Sensitivity analysis shows that, within a normalized sweep of 0.90–1.10, the estimation error remains within an engineering-acceptable range, providing tolerance-setting and sensor-selection guidance. Experimental validation on an 80 kHz prototype achieves primary-side ZVS, and a maximum steady-state error of 2.4% over 1–4 A setpoints, demonstrating effectiveness and practical feasibility.