Combined direct-indirect adaptive speed control strategy for wind induction generator

Considerations Regarding the Design of a Minimum Variance Control System for an Induction Generator

“…Similarly, and are voltage projections of stator load winding on d-q axis (and also projections of generator terminals voltage on d-q axis). Because the terminal voltage ( ) is the controlled output, solving the equations system (12) and (13) to compute the voltage projections, results the following relations: The considered situation is often found in reality, when the generator (connected to a power grid through a long transmission line) has also equipment and devices (that provide certain related functions absolutely necessary for the normal functioning of the power plant) or even some industrial consumers (close to the plant), which are directly supplied from the generator terminals. The connection between the induction generator and the power system, including local electrical consumers connected at generator terminals, can be described by a quadripole (as shown in Figure 1).…”

“…Therefore, two current supply sources, injecting current into quadripole, can be noticed. The terminals of the stator load winding being the generator terminals, the relationship between the stator load currents i d2 and i q2 (see Equations (1)-(7)) and the projections i d and i q of I terminals current on d-q axis (see Equations (12) and (13) describing the current at corresponding quadripole end) is given by the equalities:…”

“…Similarly, V d and V q are voltage projections of stator load winding on d-q axis (and also projections of V t generator terminals voltage on d-q axis). Because the terminal voltage (V t ) is the controlled output, solving the equations system (12) and (13) to compute the voltage projections, results the following relations:…”

“…), being an attractive alternative for the renewable energy sector. Moreover, a dual fed induction generator allows advanced control techniques [10][11][12][13]. Therefore, the wind turbines equipped with double-fed induction generators (DFIGs) are widely used in the wind power industry, with issues regarding their modeling and control being a topic of great interest in technical literature [14][15][16][17].…”

“…Obviously, it is possible to approximate the generator behavior by a 7th order linear model, obtained through linearization in the vicinity of a functioning point. The specialized literature [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] shows that the order of the nonlinear model (and also the order of the simplified linear model) can be reduced to five, four or even three, this still being able to approximate with sufficient accuracy the functioning regimes of the considered process. This order reduction can be achieved considering various simplifying assumptions, for example, neglecting the effect of magnetic saturation, the influence of temperature over the resistance of windings, etc.…”