Patent GB-1475990-A (GB)
Title: Dc motor systems
IPC: H02P7/298
Filed: 1973-06-09
Abstract: 1475990 Control of D.C. motors CAV Ltd 5 June 1974 [9 June 1973] 27574/73 Heading H2J A D.C. motor comprising two armature windings 20, 22 and a shunt field winding 26 is controlled by variation of the field current through a chopper controller 54, operation of a changeover contactor 17 to connect the windings 20, 22 in series or parallel and operation of a contactor 24 to connect a resistor 15 in or out of circuit, the controller 54 and power amplifiers 28, 29, 30 being controlled by an arrangement of flipfiops, AND and OR gates, inverters and field and armature current sensors (all control circuit connections being shown by dotted lines) to provide the following sequence of motor operations:- (1) Switches 12, 14 are closed and current flows through members 15, 20, 22, in series, feedback loop 21, 32, 55 setting the field current at a maximum value. (2) When the armature current has fallen to a predetermined value, sensor 59 operates members 30, 24, 25 to short circuit the resistor 15. (3) The motor is accelerated by manual adjustment of an acutator 56 to reduce the field current, the module 55 being responsive to armature current to limit the decrease of field current and so limit the armature current. (4) When the field and armature currents have been reduced to predetermined values, AND gate 48 causes a module 57 to switch the field current to its maximum value, thus putting the motor into the generator mode and changing its armature current direction. As the current reaches zero in this direction change, sensors 50, 52 and gates 43, 47 (already primed by members 31, 34, 35, 37, 42) cause operation of members 44, 29 to change over contactor 17 at zero current and connect the windings 20, 22 in parallel. (5) Changeover of flip-flop 44 restores field current control to members 39, 52, 55, which adjust the current to the desired value for the armature current exisitng after changeover of windings 20, 22. (6) Further acceleration by field weakening is produced by adjustment of member 56, with module 55 again limiting the amount of field current decrease. (7) Adjustemt of member 56 to increase the field current produces motor deceleration by regenerative braking. If the motor is slowed to below the speed at which changeover from series to parallel connection occurs and then the field current is decreased to produce acceleration, there is an immediate change from parallel to series connection at zero current in a manner similar to that described in (4) above. Thereafter if the field current is decreased sufficiently, another charge from series to parallel connection occurs as in (4) above. If a sudden load is applied to the motor during the parallel connection, members 38, 39, 41 effect a changeover to the series connection. The windings 20, 22 may be wound on separate mechanically-coupled rotors and may have separate field windings connected in series or parallel by a control circuit associated with the amplifier 28. Members 34, 39, 40, 54, 55, 57, 58 are described. Figs. 2 to 6 (not shown) and the contacts 16, 19, 23 of the contactor 17 may be replaced by three semiconductor switches, each comprising an anti-parallel connected diode and thyristor, Fig. 8 (not shown).