Robust AVR design for the synchronous generator

Conventional automatic voltage regulator (AVR) schemes use thyristor-based rectifiers in which the generator field voltage is varied by changing the thyristor's firing angle. The conventional AVR has been known to cause voltage sags and extended under-voltages, especially under fault conditions. Several control schemes such as digital proportional–integral–derivative (PID) controllers, adaptive control schemes, and intelligent control schemes have been proposed in the literature. However, these schemes increase the complexity of the system. This work proposes a DC−DC converter-based AVR as an alternative to the rectifier-controlled AVR. The DC−DC converter is arranged in step-down (buck-type) configuration. The DC−DC converter uses metal-oxide-semiconductor field-effect transistor/insulated-gate bipolar transistors and has a faster response than the thyristors, thereby resulting in faster and precise control of the generator field voltage. The DC−DC converter is connected to the field circuit of the generator, and the terminal voltage of the generator is regulated by a PI controller by varying the converter duty cycle to control the generator field voltage. Simulation and experimental investigation has shown that the proposed scheme exhibits a better transient response and is robust under DC input voltage variation and generator load changes.