Variable speed, constant frequency induction generator system

Abstract

The disclosed voltage generating system includes certain known components, such as an induction machine driven as a generator, the output connections of which are coupled to the normal load connections of a switching system, which can be a bridge-type inverter. The system switching frequency f.sub.1 is regulated by firing pulses from a logic circuit in turn controlled by an oscillator. By controlling operation of the inverter switches with respect to the synchronous frequency (mechanical rotational speed) of the machine, a d-c voltage is provided on the normal inverter bus conductors. In the disclosed system the conventional inverter switches (such as SCR's) are replaced by true two-way power switches, capable of passing current in either direction. In addition the firing signals provided by the usual logic circuit and applied to these power switches are modified so that the switching occurs as a function not only of the first oscillator frequency f.sub.1 but also of signals received from a second oscillator at a frequency f.sub.2. In brief, the switching is accomplished with a gate circuit including an exclusive OR arrangement, fed by both the first and second oscillators, to produce an a-c output voltage on the inverter bus conductors. The frequency of this a-c output voltage is controllable independently of the generator speed, and the output voltage amplitude is controllable independently both of generator speed and load variations. By using an induction machine with multiple windings, and plural switching systems, multi-phase voltages can be supplied over multiple conductors to energize an a-c load.