An induction machine driven as a generator has its output connections coupled to the output connections of a static inverter circuit, connected to operate not as an inverter but as a switching system. A capacitor is coupled to the bus conductors of the switching system. D-c excitation is furnished to the induction generator system only for starting, and is then disconnected. At rated speed the static inverter circuit operates as a switching system to regulate connection of the capacitor to the induction generator on a time-sharing basis, replacing the directly connected capacitor bank in known systems. In multi-phase systems the capacitor is not required, as the switching system periodically directs the flow of reactive energy from one phase to another of the inductive machine. By regulating the frequency of the switching operation the overall system can be made to generate effectively over a wide range of input speeds. An a-c output voltage is available from the common terminals between the induction generator and the switching system, and a d-c output voltage is also available from separate conductors of the switching system.
An induction machine is driven to operate as a generator, and has its electrical output conductors coupled to a switching system, which can be an inverter circuit. An oscillator and logic circuit are connected to regulate the switching of the power switches, such as thyristors, in the inverter circuit which operates as a switching system. The thyristors in the switching system are regulated to switch at a frequency sufficiently below the synchronous frequency of the induction machine to enable the machine to build up and operate as a generator. A modulator is connected to the oscillator to vary the oscillator frequency, and thus change the switching frequency of the switching system, above and below a reference level to provide a corresponding a-c output voltage, with a d-c average level, on the d-c bus conductors of the inverter circuit which operates as the switching system. The amplitude and frequency of the a-c output voltage are controllable over a wide range of variations in both the shaft speed of the induction machine and/or the electrical load. The system is also capable of producing an a-c voltage and a separate d-c voltage, and both the a-c and d-c voltages can be separately controlled.
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.
A background discussion of induction machine equivalent circuits, including operation as an induction generator, is provided. Selective shorting of the machine terminals is described, to convert at least some of the mechanical input energy into electrical field energy for the machine. Systems are described for accomplishing the selective shorting with a single-phase machine, including sensing of the zero-crossing of the output voltage to insure that the shorting is effected at the appropriate time to replenish the field. The shorting time duration can be varied as a function of load. A three-phase shorting circuit is then described.
A background discussion of induction machine equivalent circuits, including operation as an induction generator, is provided. Selective shorting of the machine terminals is described, to convert at least some of the mechanical input energy into electrical field energy for the machine. Systems are described for accomplishing the selective shorting with a single-phase machine, including sensing of the zero-crossing of the output voltage to insure that the shorting is effected at the appropriate time to replenish the field. The shorting time duration can be varied as a function of load. A three-phase shorting circuit is also described.
An electric power generating device including an induction type electric rotating machine rotating in interlock with an engine comprises an inverter connected at the AC side to and end of an armature winding and at the DC side to an electric power storing device, a detecting means for detecting the quantity of state related to the electric power generating voltage of the induction type electric rotating machine excluding the measured RPM of the induction type electric rotating machine but including the electric power storing voltage of the electric power storing device, and an electric power generation controlling means for maintaining the electric power storing voltage within the preset range by controlling the frequency of the controlling voltage of the inverter based on the quantity of state related to the electric power generating voltage. This electric power generating device can control the electric power generation without using any RPM detecting device for the induction electric machine, and as a result, the composition of the device can be simplified. The frequency can be controlled so that the frequency can be changed in the direction in which the difference between the electric power storing voltage and the preset reference voltage is reduced.
