Torque and Reactive Power Control of a Doubly-Fed Induction Machine by Position Sensorless Scheme

Doubly fed wound rotor induction machine with vector control is very attractive to the high performance, variable speed drive and generating applications[ 1-31. In variable speed drive application, the so-called slip power recovering scheme is a common practice where the power due to the rotor slip belowlabove synchronous speed is recovered to/supplied from the power source, resulting a high efficiency variable speed system. In variable speed generating application, the doubly fed induction machine is most suited for variable-speed constant-frequency generating systems in which the speed of the prime mover is allowed to vary within a certain range (suband super synchronous speed), but the output electrical power is always maintained at a constant frequency. In such a case, the doubly fed induction machine is actually in the dual mode of variable speed drive system. scheme is proposed. Compared to the other position sensorless schemes for doubly fed machine, &e proposed control method uses only the rotor voltages and currents as the feed back signals, which substantially reduces the costs and enhances relibility of the position sensorless control scheme of the doubly fed AC machine[8,9]. Independent control of torque and reactive power is also possible, and the doubly fed system can achieve unity or leading power factor, in addition to variable speed operation.