Self-excited induction generator/force-commutated rectifier system operating as a DC power supply

The paper presents a new DC energy generation system based on a 3-phase self-excited induction generator coupled to a force-commutated rectifier. This rectifier is switched in such a way that its input current fundamental component is advanced with respect to the corresponding voltage, producing a capacitive characteristic on its terminals. This characteristic helps the self-excitation and improves the direct output voltage regulation, with respect to load variation, to the range of 1 to 2%, for some firing angle. Also, this capacitive effect greatly increases the output power limit, and allows the system to supply a constant direct output voltage over a reasonably wide range of rotor speed variation. The steady-state performance of the system is analysed based on a simplified mathematical model, which is validated experimentally. A study on the influence of the smoothing reactor size is presented and it is shown that the system can operate properly even without this reactor, if there is no limit for current ripple in the load.