PWM converter for excitation of induction generators

Due to its low cost and low maintenance characteristics, the induction generator is an important option for low power generation and nonconventional energy sources exploitation, such as, for example, wind engines. Nevertheless, the main drawback of these machines is that its excitation must be provided by external means. A reactive controllable power source which enables efficient induction generator excitation over large speed and load ranges is presented. The device consists of a three phase PWM inverter driven by a capacitor in the DC bus. The inverter output currents are controlled to provide the necessary excitation for the generator and the active power required to keep the DC capacitor voltage constant or to supply a DC load. The work is illustrated by dynamic simulation, where the start-up of the DC bus voltage and the self-excitation process and the dynamic behavior of the system are investigated and control policies are presented