Patent GB-975102-A (GB)
Title: Improvements relating to electric generating apparatus
Inventor: FORD ARTHUR WILLIAM
IPC: H02P9/42
Filed: 1960-01-27
Abstract: 975,102. Induction generators. ENGLISH ELECTRIC CO. Ltd. Jan. 27, 1961 [Jan. 27, 1960; Feb. 12, 1960], Nos. 2906/60 and 5103/60. Heading H2A. [Also in Division G3] Relates to an induction generator apparatus having a variable speed drive e.g. an aircraft generator, and control means to provide preferably a constant voltage constant frequency output or more broadly to maintain the output frequency in accordance with a predetermined law. As shown, Fig. 1, the generator comprises two polyphase stator windings 11a, 12a and respectively associated rotors on a common shaft having windings 13a, 14a connected together in a closed circuit there being no mutual inductance between each stator and between each rotor. In Fig. 4 the stator winding 11a of the generator CG is connected at terminal T1 to a converter means S via a frequency changer FC and acts as a control winding. The converter S may be the bus-bars of another power system or a capacitor of another dynamo-electric machine such that can supply power to or receive power from the winding 11a. The winding 12a with terminal T2 acts as the output winding. The frequency changer FC may be any known type of directcurrent link changer incorporating transistor controlled rectifiers or the like. The output frequency f1 and voltage output V1 of the frequency changer FC to winding 11a are varied automatically by a frequency regulator FR and voltage regulator VR. The frequency regulator embodies means for comparing the frequency f 2  at the terminals T2 with a reference frequency (e.g. quartz crystal) deriving a signal proportional to the difference between f 1  and f 2  and thereby regulates the output frequency of FC and hence the output frequency at T2. The reference frequency may be constant or varying, and in the latter case the output frequency f 2  will vary proportionally to the reference frequency. At speeds above cross-over speed i.e. the speed at which the cascade frequency f c  equals the output frequency f 2  (where fc = f 1  + f 2 ). The converter means S receives power from winding 11a. The transfer of power and the frequency of the power transferred into or out of winding 11a is a function of the control means (S, FC, FR) which in turn is controlled by variations in f 2 . In an alternative embodiment (Fig. 6, not shown) the winding 11a may be energized from the winding 12a or from a capacitor C or synchronous machine SM. In a further embodiment, Fig. 8 (not shown), the generator unit CG may have pole changing means. In another embodiment, Fig. 9 (not shown), the prime mover is coupled to a differential gear-box with output shafts driving respectively a synchronous generator, the stator of which acts as the converter means, and the generator CG so that the generator CG will rotate at a speed representing the difference between the speed of the prime mover and the synchronous generator speed which latter speed is substantially constant. The generator unit CG may have common stator and common rotor cores provided the windings have different numbers of poles.