Comparison of carrier signal based approaches for sensorless wound rotor synchronous machines

Wound rotor synchronous machines enable a large variety of approaches for carrier signal based sensorless control since the rotor voltage serves as an additional input to the system and the rotor current as an additional, easy to measure, state variable. Consequently it is possible to use the rotor winding either as the transmitter or as the receiver of a carrier signal. In these cases the mutual inductance between the d-axis and the rotor winding is of major importance. Moreover a rotor saliency can be evaluated if the stator is used as the transmitter and as the receiver of the carrier signal. If voltage injection is used, the rotor winding acts like a damper winding for the carrier signal and consequently the evaluated saliency differs from the saliency which is utilized for sensorless control of permanent magnet synchronous machines. Carrier current control on the other hand offers the possibility to evaluate a magnetic saliency regarding the inductances in the d- and q-axis. This work provides a detailed review of the aforementioned approaches and analyses the prerequisites. In addition to this the different approaches are made comparable in terms of signal-to-noise ratio and cross saturation. This is done by introducing suitable intensity terms. With the help of identified parameters the most promising approach for the investigated machine is found. Experimental results confirm the validity of the comparison.