| This research introduces a new method to solve the sensorless control problem for a grid-connected Doubly-Fed Induction Machine (DFIM). The proposed method is based on high-frequency signal injection and the fact that the rotor of a DFIM can be seen as a rotating secondary of an induction transformer.;The currently used sensorless techniques, besides being parameter sensitive, fail during fault ride-through conditions. This fact makes these techniques almost irrelevant for wind turbines applications since, due to new grid codes and regulations, wind turbines are required to stay connected during a fault. Hence, even if the machine in the wind turbine is equipped with a sensorless control algorithm, an encoder (or resolver) is still needed in order to be able to control the machine during fault ride-through conditions.;The proposed sensorless algorithm works by applying a high-frequency voltage to the rotor and measuring the produced high-frequency voltage on the stator. The high-frequency voltage applied to the rotor is independent of, and superimposed on, the control voltage applied to the rotor. It will be shown that the rotor position information is encoded in the phase of the space vector of the high-frequency voltage measured at the stator; hence, the proposed sensorless method is implemented by filtering out the high-frequency voltage at the stator, and determining the phase of its space vector. This results in a relatively easy implementation.;The proposed sensorless method, besides being parameter independent, remains fully functional during grid faults. Moreover, as opposed to other high frequency injection methods, the proposed method does not require rotor saliency; hence, it is not necessary to induce saturation in the machine.;The mathematical principle of the proposed technique and its implementation are presented. Computer simulations and experimental results are also included for verification. |
