Sensorless control of a super synchronous slip ring induction machine

This thesis presents the development and verification of a novel sensorless control scheme for a super synchronous slip ring induction machine (SRIM). The novel scheme overcomes the limitations of the encoder-based system, with a reduced cost.;This research re-utilised a LUED slip power facility, previously funded by SERC in the 80s.;The SRIM uses a conventional current source inverter (CSI) connected between the supply and the rotor windings. Two techniques of slip power recovery, the Kramer and the Scherbius system, are discussed. The Kramer system recovers slip power to the supply. The Scherbius system is capable of four-quadrant operation, with the main advantage of twice the rated shaft output power when operating at twice the rated speed.;The CSI is investigated and its commutation problems studied. For stable operation the commutation sequence in the CSI is synchronised electrically with the varying rotor e.m.f.'s. When motoring sub-synchronously, or generating super-synchronously, the rotor e.m.f.'s are in the direction to aid the commutation process. However, when motoring super-synchronously or generating sub-synchronously, the rotor e.m.f.'s oppose commutation. These limit the performance of the CSI.;Provided the rotor terminal voltages are isolated from the mains, the rotor speed and phase information can be derived from the measured and filtered rotor terminal voltages. The derived signals can synchronise the CSI to the secondary e.m.f., thereby eliminating the need of an encoder. This novel scheme is different to the techniques known for cage type machines, and is not affected by the inherent machine parameter variations.;The SRIM harmonics are analysed. From which, a novel adaptive filter was developed to remove the rotor speed dependent harmonics and to track the varying e.m.f. with negligible phase delay. The filter and the scheme were verified using an analogue method, although a DSP system may provide better flexibility