Positive and Negative Sequence based Sensorless Control for Stand-Alone Slip-Ring Generator

A stand alone power generation system with doubly fed induction generator and its control method is presented in the paper. A slip-ring induction generator is equipped with the stator connected capacitances for filtering the switching frequency harmonics produced by the rotor connected power electronics converter. The proposed direct voltage control method, based on the stator voltage vector reference, provides fixed frequency and amplitude of the generated stator voltage operation. Different types of load (linear nonlinear) can be supplied keeping high quality voltage. A star connected stator provides the four wires system, supplying a single phase or unbalanced load. However the high load asymmetry produces the unbalanced stator voltage and in this case the additional part of the voltage control method is necessary for voltage asymmetry correction. As the main part of the control method bases of the positive sequence component of the stator voltage vector, the asymmetry correction algorithm bases on the negative sequence components. To extract both positive and negative sequence components of the stator voltage vector, two independent rotating frames are used. The coordinates systems rotates in opposite directions with synchronous and counter to synchronous angular speed. A PSIM software is used for control method design and prototyping. A proposed stand alone power generation system was build and tested. The developed stator voltage control with voltage asymmetry algorithm is proved by simulations and by oscillograms from laboratory tests