Patent GB-628828-A (GB)
Title: Improvements in control systems for electric motors
IPC: H02P5/68
Filed: 1946-09-20
Abstract: 628,828. Exciting dynamo-electric machines. HOLLYER, E. B., and METROPOLITANVICKERS ELECTRICAL CO., Ltd. Sept. 20, 1946, No. 28267. [Class 35] [Also in Group XXXVII] In the type of control system wherein the motors are supplied with constant or controlled currents by varying the field excitation of dynamo-electric machines through which the motors are energized from the line, means are provided for limiting the line current to a pre-determined value. Such means comprise means for producing a voltage or current dependent on, or representative of, the line current acting in opposition to a standard or reference voltage or current in a circuit including a rectifier and a controlling element governing the operation of the motor by control of the dynamo-electric machine through which the motor is adapted to be supplied from the line, said rectifier operating for line currents below a given value to prevent said voltage or current dependent on, or representative of, the line current from acting on the system through said controlling element, but when said line current rises above said given value to allow an energization of said element producing a correcting effect on the line current tending to maintain the latter at said given value. A metadyne transformer MT supplies traction motors M1 and M2 and is provided with a regulator machine RD which is mechanically coupled to the metadyne and which is connected to a field winding RW thereof con. trolling the primary current of the machine MT. The winding RW is connected in series with the machine RD and a battery B, the voltages .of the machine and battery being balanced when the speed of the machine MT is at a desired value. Any deviation of the speed of the main machine from the desired value will so vary the output of the machine RD, and the excitation of the winding RW, that the metadyne primary current, is altered to remove such deviation. The metadyne is provided with a main control winding C and an opposing field winding C1 controlling the secondary current of the machine. The field winding C1 is adapted to be energized to reduce the metadyne secondary current, by the applica. tion of the difference of the voltage of the machine RD and of that across a portion of the tapped resistor P shunting the battery B, when the voltage of the regulating machine falls due to a decrease of metadyne speed in the event of excessive primary current being taken from the line, so restoring the primary current to a desired lower value. A rectifier R prevents energization of the winding C1 during normal operation. Fig. 2 (not shown), illustrates the application to a metadyne transformer as described in Specification 628,827. When the system is adapted to control the maximum current returned to the line during regenerative operation, the resistor P is connected across the regulator machine RD, and the rectifier R is arranged to allow passage of current from the negative terminal of the battery B through the winding C1 to the resistor P, Fig. 3 (not shown). A system effective for both motoring and regenerative operation is afforded, Fig. 4 (not shown). Switches may be employed to interchange the motoring and regenerative connections. The system may be applied to an arrangement such as that according to Specification 628,831, Fig. 5 (not shown), an additional rectifier being connected between windings RW and C1 so that these windings are connected in parallel when the voltage of the machine RD exceeds that of the source B.