A novel PI gain scheduler for a vector controlled doubly-fed wind driven induction generator

Wound-rotor induction generator has numerous advantages in wind power generation over other generators. One scheme for wound-rotor induction generator is realized when a converter cascade is used between the slip-ring terminals and the utility grid to control the rotor power. This configuration is called the doubly-fed induction generator (DFIG). A vector control scheme is developed to control the rotor side voltage-source converter. This scheme allows the independent control of the generated active and reactive power as well as the rotor speed to track the maximum wind power point. Conventionally, the controller type used in vector controllers is of the PI type with a fixed proportional and integral gain. In this paper, a simple yet efficient way by which the controller can change its behavior is proposed. In the proposed controller, different characteristics representing the variation in the proportional and the integral gains as a function of the absolute value of the discrepancy between the set speed (for max. power generation) and the actual rotor speed, i.e. the error, is used. These characteristics are expressed by linear, exponential, piece wise linear, second- and fourth-order functions. The transient speed responses using the aforementioned characteristics are compared with the ones determined by using the conventional PI controller with fixed gains. By using the proposed controller, it can be seen that more accurate control and quicker transient response is achieved for different operating conditions