Patent GB-724412-A (GB)
Title: Improvements in and relating to control apparatus for electrically driven vehicles
IPC: B60L9/12
Filed: 1953-02-11
Abstract: 724,412. Control of several D.C motors. BRITISH THOMSON-HOUSTON CO., Ltd. Feb. 11, 1953 [Feb. 11, 1952], No. 3844/53. Class 38 (3). Traction motors 1, 2, are supplied through a mercury arc rectifier 18 and, in the event of wheel-slip, the phase of the grid voltage applied to the rectifier is retarded so as to reduce the' supply voltage to the slipping motor and to enable the wheel driven thereby to regain it grip 'upon the rail. The condition of wheel-slip is detected by the unbalance of voltages across the armatures 3, 4, of the traction motors, such unbalance being sufficient for the potential at point 71 to be greater than that at tapping 72 or lower than that at tapping 73 of the potentiometer 70. The out-of-balance current is passed through rectifiers to energize the control winding 66 of a magnetic amplifier 60 which is connected in series with a bridge rectifier 58 shunted by resistor 59. The voltage output of the rectifier 58 opposes that of a rectifier 57 in the circuit of a number of saturable reactor windings 39, 40, 48, 49, forming part of a phase-displacement device 28 for controlling the rectifier 18. Energization of the winding 66 thus reduces the regulating current in windings 39, 40, 48, 49, and retards the phase of the grid voltages. This results in a lowering of the driving torque and enables the slipping wheels to regain a grip with the rail. When equality between the armature voltages of the traction motors has been restored, the voltage-output of the rectifier 18 is not immediately re-established at its full value due to the time constant of the phase displacement circuit and that of the winding 66. This prevents hunting. A similar control arrangement may be used for four series traction motors having their armatures connected in series, Fig. 2 (not shown). When the motors are connected in parallel, as in Fig. 3, the field windings 205a, 205b, 205c, are shunted by stabilizing resistors 227a, 227b, 227c. If the axle corresponding to the motor 201a, for example, slips, the potential at point 271a falls below that at connections 272b and 272c and a winding 266 is energized. This winding has the same function as the winding 66 of Fig. 1. A number of rectifiers connected in the circuit of the winding 266 prevents the energization of the winding under normal operating conditions of the traction motors. A rectifier 276 delays the collapse of current in the winding 266 after the wheel-slip condition has been removed, and so prevents hunting. Fig. 4 (not shown) illustrates a system comprising two series-connected motors wherein wheel-slip is detected by the difference in potential between a common armature terminal and the mid-point of a potentiometer shunted across the two armatures. An amplifier, such as the magnetic amplifier, 60 is used in this embodiment. The means for preventing the appreciable energization of the winding 66 in the event of only small differences between the armature voltages of the traction motors, shown in Fig. 1, may be modified by connecting rectifiers 74, 76, to the mid-point 79, and by arranging that resistor 78 has a non-linear characteristic.