A Novel Brushless Excitation System Capable of Bipolar Field Current Control from the Stator of Electrically/Hybrid-Excited Synchronous Motor

Electrically/hybrid-excited synchronous motors (EESMs/HESMs) are increasingly being preferred for high-performance applications over permanent magnet synchronous (PMAC) motor for improved and reliable field weakening, reduction in PM use and better over-loading capability. However, both EESM and HESM require controlled electrical excitation to their rotary field winding. This paper proposes a novel brushless bipolar field excitation system for EESMs/HESMs. This is achieved using a series resonant converter in conjunction with a rotary transformer (RT), having one primary (in the stator) and two secondary windings (in the rotor). Selective multiple excitation frequency control is adopted to energize one secondary winding at a time. This helps in realizing the bipolar field current control entirely from the stator, thus eliminating the need for the controller and wireless communication in the rotor and improving robustness. Additionally, the bipolar field current control helps improving the torque density of HESMs.