Patent GB-1463770-A (GB)
Title: System for operating motors
IPC: H02P5/46
Filed: 1974-04-16
Abstract: 1463770 Automatic speed control of a number of AC motors TOKYO SHIBAURA ELECTRIC CO Ltd 16 April 1974 [12 April 1973] 16429/74 Headings G3N and G3R [Also in Division H2] Groups 3, 4, 5 of motors, each comprising at least one motor connected to a load having a very small mechanical loss and a large inertia, are energized from a source 1 through switches SWA, SWB, SWC intermittently opened and closed in sequence by a control circuit 6. The closed periods of the switches may be successive, Fig. 2 (not shown) or overlapping, Fig. 7 (not shown) and the control may be applied to accelerate or decelerate the motors or operate them at a substantially constant speed. Whilst the control is of general application to motors, mention is made of controlling induction motors and the control is compared with a conventional one, in which the source 1 is permanently connected to the motors, for the parameters of normal speed and power loss, it being shown that the control of the invention enables the use of a source 1 for three motor groups of capacity only slightly greater than that necessary to operate a single motor group, due to the reduced power loss of the control caused by the use of induction motors operated at a high frequency and at a normal speed lower than that produced by the conventional control. The closed periods of the switches SWA, SWB, SWC may be the same or different according to the load demands on the respective groups. For varying loads the speeds of the motors may be sensed, each switch being closed when the speed falls below a minimum value and opened when it exceeds a maximum value. Such control, Figs. 8 and 9 (not shown) may be used to accelerate the motors which, if they are of induction type, may each have a capacitor connected thereacross to produce an induced voltage for speed sensing. For equal loads speed sensing may be replaced by closure of each switch for a predetermined time corresponding to the loads and the desired acceleration. Deceleration may involve regenerative braking and also variation of the voltage or frequency of the source 1, the latter controls also being applicable to  acceleration. Fig. 10 shows a circuit employing voltage increase of the source 1 for acceleration, members 15-20 operating to open and close switches SWA, SWB, SWC until all the motors have reached a minimum speed set by member 17, whereupon the member 19 raises the setting of members 17, 20 by one step, member 20 causes increase of the voltage of source 1 by one step and further cycle of switching brings the motors up to the new minimum speed. Circuits for members 17, 16 and 18, 19 are described, Figs. 11, 12 and 13 (not shown). A reserve power source 14 may be used if desired during acceleration or deceleration (when Fig. 10 is used for this purpose). An openloop system may be used to accelerate the motors, Fig. 14 (not shown), the various load operating parameters such as friction torque and windage loss being computed and used to determine predetermined times during which the respective switches SWA, SWB, SWC are closed, followed by stepwise increase of the voltage of source 1 after each cycle of closure. The circuit of Fig. 1 may be triplicated with parallel connection of the sources 1 and the motor groups, Fig. 15 (not shown).