GB894161A - Improvements in and relating to alternating current generators - Google Patents

Abstract

894,161. Control of permanent magnet machines; battery-charging systems with variable speed A.C. generators. CIBIE, P. June 10, 1960 [June 16, 1959; Jan. 18, 1960], No. 20579/60. Classes 35 and 38 (4). An A.C. generator having a permanent magnet rotor is regulated by D.C. saturation of part of its stator core. In the form shown in Fig. 1, the stator core between adjacent polepieces is divided into two parallel elements 4a, 4b wound with control windings 6a, 6b. The control windings are series connected in such a sense as to produce flux in a closed circuit 7 which saturates the element 4a and thus prevents flux passing, through the output coils 2. Equal and opposite e.m.f.s. are induced in the control windings by the rotor flux 5 thus having no resultant effect. In one embodiment (Fig. 3, not shown), only one control winding is wound between successive stator poles about element 4a which includes an air gap, but the successive windings are connected in series or series-parallel to produce no resultant induced e.m.f. A three-phase machine (Fig. 5, not shown), in which the stator windings each embrace three adjacent poles and are displaced by one polepiece relative to the preceding winding, has one control winding wound on the yoke between each pair of poles. An electromagnetic control system as in Fig. 4 has two main windings 2a, 2b, connected in parallel through rectifiers 8a, 8b to a battery 9. A shunt winding 11 connected to 2b through rectifier 12 normally maintains contact 14a of the relay blade 13 in contact with contact 15a so that winding 2b is connected through rectifier 8b and series winding 16 to the battery. Should the output voltage of 2b exceed an optimum value blade 13 is attracted to the magnet armature contacting 14b and 15b and causing a saturating current to flow in control winding 6. Winding 2a may be controlled by a known device 17 operating in accordance with the gas evolution of a battery. In Fig. 8 is shown a current limiter incorporating a Zener diode Z. Current is fed from generator winding E through rectifier R to the primary B1 of a transformer. The current induced in the secondary B2 is then fed through rectifier D1 to Zener diode Z and control winding 6 only if it exceeds the breakdown value of the Zener diode, which value is chosen to limit the generator current to a safe value. A voltage limiter using the same Zener diode may also be connected as shown by the dotted lines.