Patent GB-1256273-A (GB)
Title: A reversible electrical converter
Inventor: HERMANSSON BO
IPC: H02M7/155
Filed: 1969-03-17
Abstract: 1,256,273. Converting; control of D.C. motors. ALLMANNA SVENSKA ELEKTRISKA A.B. 17 March, 1969 [18 March, 1968], No. 13832/69. Headings H2F and H2J. [Also in Division G3]   In a converter for feeding a D.C. load (e.g. motor 9) with reversible polarity from an A.C. network, and being capable of inversion, the dead time between the various switching steps is reduced by means of a current regulator 7 arranged to be responsive to the combination of the desired output control 13, the D.C. current 16 and the D.C. output voltage 17. In the speed control servo shown in Fig. 3, relays 10 and 11 are arranged to reverse the polarity of the D.C. output of the converter 8 supplied from A.C. network 1, in response to the speed and direction demanded by potentiometer 13. The output of potentiometer 13 is compared at 14 with the output of a tachogenerator 12 so as to determine the output JR of the reference current source 15. The signal JR is supplied via one or other of switches 2, 3 (controlled by relays 10 and 11) to a summing junction 18, a polarity-reverser 4 being included so that the sign is independent of the desired direction of rotation of motor 9. The output of the summing junction 18 is fed to a current regulator 7 which provides a control voltage Es arranged to control the timing of the control pulses of converter 8 so that the motor 9 runs at the desired speed. Polarity control of reversible converter.-If it is desired to drive motor 9 in the forward direction, signal JR will be negative and will not pass a sign discriminator 501 (Fig. 4). Bi-stable stages 505 and 509 will thus be in their zero setting so as to energize relay 10 via AND gate 510. The relay 10 provides the correct connections between converter 8 and motor 9 for forward rotation and closes switching device 2 so as to feed reference current JR to the regulator 7. The motor 9 now accelerates until the signals provided by members 12,13 and 16 are balanced. When the motor is to be reversed, potentiometer 13 is set to give negative polarity so that the output from source 15 is now positive. The control signal Es will now tend to retard the converter 8 towards inverting operation so that the motor current decreases and signal JS becomes zero. The gate 503 will thus pass the signal from sign discriminator 501 so that bistable circuit 505 will be set to its 1-state, releasing relay 10 and disconnecting the motor 9 from the converter 8. A voltage dependent on the voltage of motor 9 is developed by a Hallgenerator 17 (or D.C. current transformer) and is slightly reduced by a resistance network in block 6 before being fed via resistor 77 to the converter 8 so as to provide a rectified voltage which is arranged to be less than the armature voltage of motor 9 by a quantity which corresponds to the output ripple of the converter 8. This voltage is stored in a feedback capacitor 72 in regulator 7. After a delay due to member 513, bi-stable stage 509 is set to its 1-state so as to energize relay 11 which reverses the connections between converter 8 and motor 9. The motor is thus braked by converter 8, operating as an inverter with decreasing control angle. When this passes 90 degrees the converter is transferred to rectifying operation, the motor is then driven in reverse until the required reverse speed is achieved. A current limit source 73 is provided. Modifications.-In Fig. 5 (not shown), relays 10 and 11 are replaced by four thyristors controlled by the outputs of gates 510 and 511. In Fig. 6 (not shown), the motor is connected in parallel with a pair of inverse converters having a single control pulse generator coupled to them via a pair of gates.