Generator Voltage Control

Generator voltage control is crucial for maintaining the stable operation of synchronous generators and wind turbines. In older models, a DC generator driven by the rotor delivers DC power to the rotor's field winding, and the power is transferred through slip rings and brushes. In the latest models, static or brushless exciters are used. Static exciters rectify AC power from the generator terminals and then transfer the DC power directly to the rotor. Brushless exciters, on the other hand, use an inverted synchronous generator in which AC power is obtained from armature windings and rectified via diodes mounted on the rotor, eliminating the need for slip rings and brushes.

The block diagram provides a standardized method for visualizing generator voltage control systems. The IEEE Type 1 exciter uses a shaft-driven DC generator to create the field current, with a voltage regulator that adjusts the field current based on terminal voltage measurements.

In the block diagram, terminal voltage, V_t is measured and compared with a reference voltage V_ref. The difference between these two is used to adjust the field voltage. The voltage regulator processes the voltage error with a gain (K_a) and time constant (T_a). The output of the voltage regulator is the field voltage applied to the generator's field winding, which adjusts the terminal voltage. These models represent the exciter and generator dynamics, providing a clear method for analyzing and improving stability.

Type 1 wind turbines employ squirrel cage induction machines without direct voltage regulation. Type 2 systems utilize wound rotor induction machines with adjustable external resistance, modeled as an exciter, to maintain consistent power output despite wind speed variations. Type 3 and Type 4 configurations manage both real and reactive power. Generator voltage control involves methodologies to ensure the stable and reliable operation of synchronous generators and modern wind turbines.