Sensorless control of wound rotor synchronous machines using the switching of the rotor chopper as a carrier signal

Wound rotor synchronous machines open up new possibilities in carrier signal based sensorless control since the rotor voltage serves as an additional input to the system and the field current as an additional, easy to measure, state variable. Approaches for sensorless control of PMSMs use the stator as the transmitter and as the receiver of the carrier signal. A new alternative for wound rotor synchronous machines is to use the field winding as the transmitter and the stator as receiver. Since the field inductance is usually very large, a signal injection into the rotor is not reasonable because large rotor voltages are obligatory to create detectable stator currents. Therefore the presented approaches make use of the switching of the dc-field chopper as a carrier signal. Two methods are compared: The first method evaluates the stator currents in rotor fixed coordinates using a tracking observer. The second one uses the stator currents in stator fixed coordinates to directly compute the rotor position. Both methods consider cross saturation effects. In contrast to approaches for carrier signal based sensorless control of PMSMs no differential magnetic saliency is mandatory. Moreover no additional signal injection is necessary. Experimental results prove the performance of the proposed methods.