Derivation of equivalent circuit rotor current from rotor bar current measurements in brushless doubly-fed machine

This paper presents a method to estimate the BDFM equivalent circuit rotor current from rotor bar current measurements. Rotor currents are measured using a specially designed hardware that incorporates Rogowski coils and Bluetooth wireless transmission. The measurement of rotor currents enables the parameters in the BDFM's full equivalent circuit to be extracted unambiguously. In particular, stator and rotor leakage inductances can be estimated from experimental tests, which was not possible before from terminal measurement. The method is presented for a nested-loop rotor design and experimental measurements are shown for a prototype D180 frame BDFM.