Patent GB-1493302-A (GB)
Title: Arrangement for supplying a load from a dc voltage source
IPC: H02P7/29
Filed: 1975-04-02
Abstract: 1493302 Control of DC motors SEB-RAGONOT 2 April 1975 [5 April 1974] 13470/75 Heading H2J A load 2, for example a D.C. motor driving an electric vehicle, is supplied from a D.C. source 1 through a number of parallel switching assemblies, for example four, each comprising a seriesconnected transistor and inductance 3, 7; 4, 8; 5, 9; 6, 10, diodes 11-14 transferring energy from the inductances 3-6 to the motor during off-periods of the transistors, which are successively made conductive for the same time t during a common period T, the interval between successive conduction of the transistors being equal to T/n, where n is the number of switching assemblies. Transistors 7-10 are switched on and off by the control circuit shown in Fig. 2, the time of conduction t being determined by adjustment of a potentiometer 38 and the method of operation producing a resultant motor current waveform (M), Fig. 7 (not shown) whose peak-to-peak variation is reduced, compared with that of the waveform (D) Fig. 6 (not shown) of a single transistor, inductance and diode supply circuit, by a factor dependent on the number n. By adjusting the potentiometer 38 to make the time t equal to T/4, T/2 or 3T/4, the waveform (M) of the motor current becomes a direct current, Figs. 8 and 9 (not shown). A first signal generator 31 produces, at its output 32, master pulses of period T which are applied to a second signal generator 35 and a flip-flop 15 controlling the transistor 7, the other three transistors 8, 9, 10 being controlled by respective flip-flops 16, 17, 18. The output 33 of generator 31 produces a sawtooth waveform of amplitude V and period T, which is applied through threshold circuits 46, 47, 48 to flipflops 16, 17, 18 to cause successive closure of transistors 8, 9, 10 at equal intervals along the base of each sawtooth. Generator 35 produces pulses, delayed by a time t with respect to the master pulses and supplied to flip-flop 15 and a flip-flop 39, which controls a third signal generator 44 producing a sawtooth waveform of the same slope and period as that of generator 31, but delayed by time t with respect thereto and having an amplitude of 3V/4 and base of 3T/4. Generator 44 applies its waveform to flip-flops 16, 17, 18, through threshold circuits 49, 50, 51, to cause successive opening of the transistors 8, 9, 10 at equal intervals along the base of each sawtooth, the transistor 7 being respectively closed and opened by a master pulse from generator 31 and a delayed pulse from generator 35. Feedback from members 15, 51 resets members 35, 39 whereby, with generator 35 also being reset by master pulses at its input 34, the delayed pulses from generator 35 may be suppressed by adjusting potentiometer 38 to make the time t greater than the period T, all the transistors 7-10 then being permanently conductive. A typical cycle of operations is described with reference to the various waveforms of the sawtooth signals, the pulses, the flip-flop outputs and the currents conducted by the transistors, Figs. 3, 4 and 5 (not shown), and to the difference in threshold values between consecutive pairs of threshold circuits 46, 49; 47, 50 and 48, 51. The current of each transistor 7-10 is sensed by a respective resistor 68-71 controlling flip-flops 15-18 through threshold circuits 52-55, whereby a transistor is switched off when the current therethrough reaches a predetermined overload value, switch-on occurring when the next cycle of operations takes place.