Sensorless control of a super synchronous slip ring induction machine for wind turbine operation

Modern drive designs aim to remove conventional sensors such as tachos and incremental shaft encoders on grounds of cost, reliability, and adverse environmental factors in which the machine may operate. This paper describes a novel technique for the sensorless control of a slip ring induction machine for sub or supersynchronous operations. Slip ring machines have a distinct advantage over conventional cage motors, where the rating of the power converter may be less than that for a cage drive when in supersynchronous operation. Full four quadrant sensorless control of a conventional Scherbius current source inverter is possible with the use of a novel adaptive filter using only analogue implementation. The four-quadrant operation allows the wind turbine to overcome the difficulties in starting at low wind speeds. The sensorless system reduces the complexity of the tacho system with an improved reliability.