Patent GB-1480055-A (GB)
Title: Control circuit for an electrically driven vehicle
IPC: B60L11/18
Filed: 1973-06-30
Abstract: 1480055 Automatic current control LUCAS INDUSTRIES Ltd 11 June 1974 [30 June 1973] 31312/73 Heading G3R [Also in Division H2] The D. C. series motor 12, 13 driving an electric vehicle is controlled by a thyristor chopper circuit 15-19, whose thyristors 15, 18 and 16 are respectively fired by drive circuits 38 and 37 when the output of a two state operational amplifier 33 is respectively negative and positive, the amplifier having a feedback circuit 34, 35 to ensure that the amplifier remains in each state for a predetermined minimum time, thereby ensuring that the thyristor 15 is on and off sufficiently long for the thyristor 18 to reverse the charge on capacitor 17 and then turn off and for the thyristor 16 to charge capacitor 17 (after turning off thyristor 15) and then turn off. In general the provision of a minimum off-time for thyristor 15 is of primary importance. The motor current is maintained at a valve set by a tapped resistor 26 whose output, together with the signal of actual motor current from a sensor 14, is applied to an operational amplifier 28 which produces, in response to its increasing or decreasing analogue signal input, a respective positive or negative output signal when the actual and set current signals are equal. A trigger circuit, including an operational amplifier 31 fed by the output of amplifier 28, produces a corresponding negative or positive output signal when the actual current is above or below the set current by a predetermined amount, the signal from amplifier 31, for example (-)2 or (+)2 volts, being applied to amplifier 33 which produces a corresponding (+)15 or (-)15 volt output signal to respectively operate the circuit 37 or 38. If, for example, the input signal to amplifier 33 has just changed from (+)2 to (-)2 volts, the changes in potential at the output and the non-inverting input of this amplifier cause discharge and then charge of capacitor 34 from an initial voltage of 10 volts to an opposite voltage of 15 volts. Until capacitor 34 has discharged 2 volts, a change of signal from (-)2 to (+)2 volts at the inverting input will not cause the amplifier to change state, thus ensuring that thyristor 15 remains off at least for the predetermined time taken by the capacitor to discharge to 2 volts. A similar delay operation occurs when, after the expiry of the predetermined time, the signal change from (-)2 to (+)2 volts changes the amplifier state, or when the expiry causes the change of state if the signal change has occurred during the predetermined time, Figs. 2b and 2c (not shown). The above operation only obtains for potential variations at the inverting input of amplifier 33 within a predetermined range e.g. (+) and (-)10 volts. A capacitor 44 provides interference rejection and any fluctuations in the  2 volt input signal do not change the amplifier state, changeover occurring at the end of the predetermined time, Fig. 2d (not shown) or thereafter when the signal changes to the correct polarity, Fig. 2e (not shown). Amplifier 31 and its associated components may be omitted, in which case amplifier 33 is arranged to act as its own trigger circuit, capacitor 34 is shunted by a register (40) and capacitor 44 by a resistor (50), Fig. 3 (not shown).