Patent GB-1443915-A (GB)
Title: Electric motor control
IPC: H02P3/14
Filed: 1974-12-11
Abstract: 1443915 Automatic control of speed J C FITTER 11 Dec 1974 [21 Dec 1973] 53637/74 Heading G3R [Also in Division H2] A D.C. shunt field motor has its armature MA connected across a D.C. supply AB through switches R1-R4 and diodes D1-D4, the switches R1-R4 being of the controlled semi-conductor type (e.g. thyristors, transistors or triacs) and being controlled by trigger units T1, T2 to provide reversible motor operation with regenerative braking in each direction and return to the supply of the energy stored in the armature during each pulse of current therefrom. Switches R1-R4 are simultaneously opened and closed in pairs R1, R4 and R2, R3 under the respective control of units T1 and T2 to provide four quadrant control as follows:- First quadrant. Switches R2, R3 are open and switches R1, R4 are intermittently opened and closed to drive the motor in one direction, the diodes D2, D3 returning to the supply, when switches R1, R4 are open, the energy stored in the armature when they are closed. Second quadrant. Switches R1, R4 are open and switches R2, R3 are intermittently opened and closed, with the motor regenerating to the supply through diodes Dl, D4 which also return to the supply, when switches R2, R3 are open, the energy stored in the armature when they are closed. Third quadrant. Switches Rl, R4 are open and switches R2, R3 are intermittently opened and closed to drive the motor in the other direction, the diodes D1, D4 again providing the return path to the supply for the stored energy. Fourth quadrant. Switches R2, R3 are open and switches R1, R4 are intermittently opened and closed with the motor regenerating through the diodes D2, D3 which also provide the return path for the stored energy. Typical waveforms of armature voltage, current and back EMF are discussed for all four quadrants, Fig. 2 (not shown), with particular reference to the variation of the energy stored in the armature during acceleration and deceleration of the motor and the charging of a battery forming the supply AB. Motor speed and current control. Application of the motor to drive a battery electric vehicle or a mine winder is envisaged, the former constituting the embodiment shown in The Figure which could provide merely manual control of the trigger units T1, T2 by a potentiometer P1 adjustable through an accelerator pedal of the vehicle, but which controls the units T1, T2 in accordance with signals representative of the speed and current of the motor to maintain a desired speed set by the pedal and limit the current during acceleration and regenerative braking. The speed is sensed by a signal from the armature representative of back EMF (or from a tacho-generator if the motor has a series field winding), which signal is applied through an attenuator AN, an inverting amplifier I1 and resistor SR1 to one input of a voltage control amplifier VC, whose other input receives the output signal of potentiometer P1 through resistor SR2 and a ramp function generator RF, the potentiometer P1 being fed via switch 51 with a reference voltage B1 or B2 according to the desired direction of vehicle movement. Reference voltage B1 is also applied to variable and pre-set potentiometers P2, P3 whose outputs are respectively applied to the inputs of an inverting summation amplifier S1 feeding the inputs of limiting amplifiers L1, L2 respectively directly and through an inverting amplifier 12. The output of amplifier VC, limited by the amplifiers L1, L2, is fed via resistor SR3 to the input of a current control amplifier CC also fed via resistor SR4 with a current signal from sensing resistor S in the motor circuit. Trigger unit T1 or T2 is actuated by amplifier CC according to the polarity of the error signal from amplifier VC, a further inverting amplifier 13 and diodes (unreferenced) ensuring that the output of amplifier CC cannot operate switches R1-R4 simultaneously. During acceleration potentiometer P2 is set at zero and potentiometer P1 is adjusted, the rate of change of the latter reference signal being limited by generator RF and the output of amplifier VC being limited by amplifier L2 in accordance with the setting of potentiometer P3, which thus determines the limit of current during acceleration and normal running. During deceleration (with potentiometer P1 returned to zero) the current limit may be increased if required, by adjustment of potentiometer P2 which controls the limiting action of amplifier L1 on the output of amplifier VC, further deceleration being produced by mechanical braking, initiated when potentiometer P2 exceeds a predetermined setting.