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A three-phase cage rotor induction machine works as an induction generator if it is driven by a prime mover and self-excited by a capacitor connected to its terminal and residual magnetism of the machine. The machine of this type is called a self-excited induction generator and is used mainly as an independent power source isolated from a commercial power network. The reactive output power of the induction generator is limited because the capacitance used for self-excitation is fixed. The article analyzes the experimental facts from theoretical viewpoints taking into account the core saturation characteristics of the machine. The relation between the machine and circuit constants and the control range is clarified.

An induction generator has been proposed that works stably over a wide-speed range. The only disadvantage of this generator is that a reactive power has to be supplied from a power source on the inverter side. This article proposes a means to solve the difficulty by connecting a dc chopper to the dc side of the inverter. The chopper works not only as a bypass circuit of dc current but also as a forced commutation circuit of inverter. A scheme is proposed to control the primary flux to keep the total efficiency maximum over wide ranges of generator speed and output power. In this case, the power factor of induction machine at low and output power level is also improved. A disadvantage of the proposed scheme is that the main circuit and the control circuit are a little complicated.

In this paper, a novel version of the dual voltage converter is presented with improved voltage regulation and enabling a wide range of voltage control by using self-turn-off devices (power transistors) instead of diodes. Further, this system operates with unity displacement factor. We have obtained the analytical expressions of this circuit. The results are, however, quite complex. We could calculate values of the voltage and current waveforms by using a computer. The calculated values are essentially in agreement with the experimental values. Experimentally, an ideal load characteristics with null voltage regulation was obtained by the conduction angle control for power transistors. Further, a wide range of voltage from 220 V to 39 V was obtained. A disadvantage for this system is the requirement for snubber circuits with a larger value of capacitor in order to suppress the surge voltages a turn-off periods. [ABSTRACT FROM AUTHOR]