Carrier signal based sensorless control of electrically excited synchronous machines at standstill and low speed using the rotor winding as a receiver

This paper presents a new carrier signal based approach for motion sensorless control of electrically excited synchronous machines. In the case of permanent magnet synchronous machines sensorless control at standstill and low speed is mostly done by injecting a high-frequency voltage and evaluating the resulting current response. Hence, the stator is used as the transmitter and as the receiver of the carrier signal. The major drawback is that a magnetic saliency is mandatory. In the case of electrically excited synchronous machines the rotor voltage serves as an additional input to the system and the resulting field current as an additional, easy to measure, state variable. The presented approach makes use of this fact and uses the field winding as the receiver of a carrier signal, which is injected into the stator winding. Like this no magnetic saliency is mandatory in order to track the position. The new approach is compared to a well-known carrier signal based method, in which the stator works as the transmitter and as the receiver of the carrier signal. In this case a magnetic saliency is mandatory which differs from the saliency necessary for permanent magnet synchronous machines. The applicability of both approaches is proven in experiments.