Patent GB-778852-A (GB)
Title: Improved method of and device for controlling synchronous motors
IPC: H02P25/02
Filed: 1954-06-10
Abstract: 778,852. Control of A.C. motors. ETABLISSEMENTS E. JAEGER. June 10, 1954 [June 11, 1953], No. 17142/54. Class 38(3) [Also in Group XL(b)]  An arrangement for controlling a threephase synchronous motor from single-phase synchronizing signals comprises an inter-. mediate circuit having a single input for the synchronizing signals and three output lines to which are applied in succession signals corresponding to the first, second and third signals of each successive group of the single-phase signals to derive a three-phase current, having a frequency one third that of the single-phase signals, which is amplified by electronic means to effect the direct energization of the threephase synchronous motor. The synchronizing pulses at frequency f are applied at 1 to a triode 3 with its cathode connected to the cathodes of valves 4, 5, 6 connected in a "ring-of-three" circuit so that impulses are fed in succession from resistors 8 to intermediate valves 14, 15, 16 controlling pentodes 17, 18, 19 whose anode circuits include tuned primary windings of transformers 20, 21, 22 whose secondary windings are connected at 26, 27, 28 to the windings of a three-phase motor. The grid circuits of the valves 4, 5, 6 incorporate a network of resistors 9, 10, 11, 12 with a capacitor 13 in parallel with the resistors 9 and 11. and the anode of each valve is connected to the grid circuits of the remaining two valves. The arrangement operates in such a way that at any time only one of the triodes 4, 5, 6 is conducting and a positive synchronizing pulse at the input 1 causes this valve to become now conducting and renders conducting one of the two valves which was previously blocked. The valve which conducts cuts off its associated valve 14, 15, 16 which consequently applies a positive pulse to the connected valve 17. 18 or 19 which becomes conducting and generates a pulse in the primary winding of its tuned transformer 20. 21 or 22. The arrangement may be employed to calibrate a tachometer by the direct or indirect method, i.e. by employing a frequency to produce a number of revolutions per second corresponding to a predeter, mined speed and observing the indication on the dial of the instrument, or by modifying the frequency and consequently the. rotational speed, to obtain a desired indicated value. In the former case, the frequency from a quartz-controlled oscillator 30 operating, for example, at 270 Kc. is divided by fifteen by circuits 35, 36 to provide a frequency of 18,000 c.p.s. which can be further divided by one or more of the circuits 45...52 to obtain the single-phase. synchronizing or driving pulses which are fed to a circuit 7 similar to that shown in Fig. 1 to provide the frequency to drive the motor 33 of the tachometer 34 at predetermined selected rotational speeds. In this case the indicated speed value is compared with the theoretical or expected value. In the alternative method of calibration, the quartz-controlled oscillator 31 is adjustable by capacitors 40, 41 and is initially checked against the standardoscillator 30 by a beat indicator comprising a neon tube 42 connected vit division cir-. cuits 43, 44 halving the frequency of the outputs of the circuitis 36, 38 so that the frequency tested is 9 Kc. The frequencysupplied to drive the tachometer is then varied so that the desired speed is indicated. The switch member 53, operable to select a predetermined driving frequency from the circuit 32. is connected to a further switch 54 to vary the tuning capacitors 23, 24. 25 of the transformers 20. 21, 22 to accord with the driving frequencyapplied to the motor 33. The frequencydividing circuits may be as described in Specification 754,971 [Group XL(c)].