Patent GB-1475542-A (GB)
Title: Operating apparatus for electrically driven vehicles
IPC: B60L3/00
Filed: 1974-05-11
Abstract: 1475542 Control of D.C. motors MEIDENSHA KK 11 May 1974 [15 Oct 1973 (3) 29 Nov 1973 (2)] 06140/74 Heading H2J An electric vehicle is driven by a D.C. series motor 3a, 3b supplied from a battery 1 through a chopper 2 having main and auxiliary thyristors 2a, 2c controlled by an ON-pulse oscillator 71 and an auxiliary thyristor 2b controlled by an OFF-pulse oscillator 82, the mark-space ratio of the chopper being determined by the setting of the tap 60a of a potentiometer 60, which controls the oscillators 71, 82 and is coupled to the vehicle accelerator, or by the signal from an overcurrent limiting circuit 90 connected to a reactor 2e of the chopper to be responsive to the motor current, the energization of the motor and its direction of rotation being controlled by changeover contacts 4, 5 connected to the series field winding 3b. The oscillators 71, 82 are controlled by the interaction of a delay circuit 50, the accelerator circuit 58 and a soft start circuit 63, the arrangement being such that for normal loads on the motor the mark-space ratio is determined by the setting of tap 60a of circuit 58, which controls the conductivity of a transistor 64 to determine via a transistor 75 the charging time of a capacitor 76 and hence the firing frequency of a PUT 72 in the oscillator 71, whose pulses from a transformer 77 are applied to a gating circuit 2g for thyristors 2a, 2c. Discharge of capacitor 76 (to cause firing of thyristors 2a, 2c) turns off a transistor 53 to allow charging of a capacitor 86a in the oscillator 82, whose PUT 83 fires after a time determined by members 85a, 95b, 85d, 95e, 86a to fire thyristor 2b via members 87, 2h and so turn off the main thyristor 2a. With normal loads the progressive movement of the acclerator produces an increase in mark-space ratio as shown by line l 1  in Fig. 3A. With heavy loads the signal from the circuit 90 exceeds that from the tap 60a and progressively reduces the mark-space ratio until a predetermined constant value is reached, for example 65% as shown by line l 4  in Fig. 3A. When the accelerator is sufficiently depressed, for example to correspond to a mark-space ratio of 80% in Fig. 3A, a contact 30 closes to by-pass the chopper and an auxiliary contact 30b closes in circuit 50. The voltage at junctions F and G in the latter circuit respectively increase and decrease to turn off transistor 64 and the oscilltor 71, the voltage at junction F and the value of resistor 65 determining a nominal value of mark space ratio whilst contact 30 is closed, for example as shown by the line f 1  or f 2  in Figure 3A with a value of 30% being preferred. Thus when the accelerator is released sufficiently to open contacts 30, 30b, the mark-space ratio increases gradually from 30% (or f 1 ,f 2 ) to 80% if the load is normal or to 65% if the load is heavy, the gradual increase to the latter value shown by lines b 1 , b 2  in Fig. 3A ensuring that commutation failure does not occur in the chopper during the period td (Fig. 3A) following opening of the contact 30. Characteristics of motor current before, during and after operation of contact 30 are discussed, Fig. 4 (not shown), a comparisson being made with known arrangements for chopper operation after opening of the contact 30, taking into consideration such factors as variation of voltage on the chopper capacitor 2d and the storing of energy in the motor inductance during closure of contact 30. The circuit 90 may be connected to the chopper reactor 2f, Fig. 6 (not shown), typical detected voltages for this connection and that of Fig. 1B being discussed, Figs. 5 and 7 (not shown). Plug braking of the motor.-When the contacts 4, 5 are changed over to produce reverse current braking of the motor, a transistor 124 becomes conductive to transmit a motor current signal (sensed by circuit 123, 124, 125) through a time delay circuit 120 to the junction H. As a result the mark-space ratio of say 10%, determined by the tap 60a during plugging, is not immediately obtained after changeover of contacts 4, 5, but is reached by a gradual increase of mark-space ratio to the value of 10%, Fig. 8B (not shown). This ensures that, following changeover, the peak value of the commutation capacitor voltage is always greater than the peak value of motor current, Fig. 9B (not shown), a comparison being made with known arrangements. Figs. 8A and 9A (not shown) wherein a high value capacitor is used to prevent commutation failure. Circuits 58 and 120 may be modified, Fig. 10 (not shown) to delay the start of operation of the oscillator 71 after changeover of the contacts 4, 5. Starting sequence for the vehicle and closure of contact 30.-Switch 8a or 8b is closed to select a desired motor direction and depression of the accelerator closes a contact 7. The resultant application of voltage to oscillator 82 (via 13a or 13b, 27, 14 and 84h) causes its PUT 83 to turn on to fire a thyristor 11 and so energize coil 4a or 5a to change over contact 4 or 5 and so complete the motor supply circuit. When the accelerator is sufficiently depressed, a contact 29 closes and a thyristor 33 is fired to energize a coil 30a and so close contacts 30, 30b. A circuit 45 is responsive to the voltage at point P in the motor circuit and hence to the chopper markspace ratio, delay elements 35, 36, 37a and 37b, 38 in the circuit 45 ensuring that PUT 34 and hence thyristor 33 are fired a predetermined time after a preselected mark-space ratio (corresponding to closure of contact 29) is reached, whereby the motor speed has time to increase to its corresponding value before the contact closes. Protective and other arrangements.-A circuit 12, comprising a thyristor (16) controlled by an arrangement of diodes and resistors, a capacitor (19) and a transistor (17), Fig. 2 (not shown), is responsive to the conductive state of the thyristor 2a, to cycle transistor (17) on and off. If the thyristor 2a becomes continuously conductive, transistor (17) remains off to cause firing of thyristor (16), turn-off of the thyristor 11 and change over of contact 4 or 5 to de-energize the motor. Closure of the contact 30 causes transistor (17) to be maintained conductive to prevent operation of circuit 12 during the by-pass condition of the chopper. Other circuit components and interconnections ensure that thyristor 33 cannot be fired before thyristor 11, that the latter cannot be fired if a failure occurs in a constant voltage power supply 46, that the oscillator 71 is synchronized with the chopper 2 and oscillator 82, that the oscillator 71 is clamped during starting to be unaffected by variations in the closing action of switches 8a, 8b, and that oscillator 82 functions after switch 7 is opened to interrupt the chopper circuit before the contact 4 or 5 changes over.