Estimation Algorithm for Current and Temperature of Field Winding in Electrically Excited Synchronous Machines With High-Frequency Brushless Exciters

Electrically excited synchronous machines have become one of the potential alternatives to permanent magnet synchronous machines in electric vehicles to avoid rare-earth materials. Utilizing high-frequency brushless exciters for rotor excitation is a promising choice to reduce friction losses and maintenance effort and cost. However, with the usage of brushless exciters, the field current and temperature cannot be measured directly. In this article, an algorithm is proposed to dynamically estimate the field current as well as the field winding temperature. The dc-link current is utilized as a feedback to correct the estimation. The performance of the estimation algorithm is initially evaluated in simulations and then verified by experimental measurements in a prototype. Based on the estimation algorithm, closed-loop control of the field current is developed and verified experimentally.