Patent GB-859370-A (GB)
Title: Improvements relating to electrically propelled vehicles
Inventor: ABBINK-SPAINK JOHANN HERMANN
IPC: B60L15/04
Filed: 1957-02-28
Abstract: 859,370. Control of several D.C. motors. ENGLISH ELECTRIC CO. Ltd. Feb. 26, 1958 [Feb. 28, 1957], No. 6725/57. Class 38 (3). Electric traction motors M1-M3 having armatures A1-A3, interpole field windings TF1-IF3, main separately-excited field windings MF1-MF3, and balancing field windings BF1-BF3, are supplied from a tapped transformer 10 through rectifiers 12-14. The field windings MF1 - MF3 are excited by the rectified output of a magnetic amplifier 18 which is provided with two cores and five control windings, each with a section on one core. Control winding 18a is energized in accordance with the total armature current of the motors, whilst bias winding 18b is supplied from transformer winding 10d through a rectifier and variable resistor. Under no-load conditions the magnetic amplifier has a low output, but subsequent flow of armature current causes the winding 18a to oppose the winding 18b and so increases the motor excitation. In this manner, the motors are made to operate with a series characteristic when the armature current is changing, but with a shunt characteristic under steady conditions. Field weakening is obtained by adjustment of potentiometer 21. The balancing field windings are controlled so that each motor takes substantially the same armature current, these field windings being supplied from magnetic amplifiers 24-26 having bias windings 24d-26d adapted to reduce the output of the amplifiers. Considering the amplifier 24, the control windings 24a-24c are energized in accordance with the currents passing through the interpole field windings of the motors M1- M3, respectively, the windings 24b and 24c being in opposition to the winding 24a. Since the winding 24a has twice the number of turns of the other windings, the balancing field winding BF1 will not be excited when all the armature currents are equal. Similar conditions apply to the magnetic amplifiers 25, 26. Thus, each magnetic amplifier balances the armature current of one motor against the average current of the other two, so that, if the current taken by one motor exceeds the average, the corresponding field winding acts to restore the current-balance. The motors are braked by connecting resistors 28-30 across armatures A1-A3, the winding 18a not being used during this operation. The degree of brake application is controlled by variable resistor 23 in circuit with bias winding 18b, whilst control windings 18c-18e are connected across resistors 28-30 to provide negative feed-bad. In another arrangement, a separate magnetic amplifier is provided for the field winding of each motor, each amplifier having a control winding responsive to the armature current and a separate biasing winding. The balancing field windings are omitted from this embodiment, but the magnetic amplifiers have windings which function in the same way as the windings 24a-26c. Dynamic braking is controlled by connecting control windings of the amplifiers across the braking resistors, Fig. 2 (not shown). In a further embodiment, the armatures of the motors are supplied through a magnetic amplifier having control windings energized respectively in accordance with a reference current and with the total load current which is thereby limited to a desired value, Fig. 3 (not shown). Other forms of amplifier may be used.