Patent GB-1444662-A (GB)
Title: Converter circuits
IPC: H02H7/12
Filed: 1974-01-07
Abstract: 1444662 Automatic current and voltage control WESTERN ELECTRIC CO Inc 7 Jan 1974 [10 Jan 1973] 610/74 Heading G3R [Also in Division H2]  A converter includes means for regulating the output current and means for disabling said regulating means in response to the output current increasing above a predetermined level and means for disabling the converter in response to the output current exceeding a current level greater than the regulated current level. The invention is applicable to converters having their D.C. outputs 231, 232 connected in parallel, each converter having a voltage/current characteristic as shown in Fig. 2 with provision for detecting faulty converters or converters not supplying their share of the load. D.C.-D.C. conversion. The D.C. input at 221, 222 is arranged sequentially to charge and discharge capacitors 224, 225 resonantly via the primaries 209, 219 of transformer 210 under control of thyristors 215, 216 triggered simultaneously by a normally free-running blocking oscillator 235. The resulting output from the secondary 208 is rectified at 226 to provide the necessary D.C. output at 231, 232. Power limit control. The current in the secondary 208 is monitored by winding 220 diode 237 providing a signal which turns on transistor 236 which inhibits the blocking oscillator 235 while the main rectifying diode 226 is conductive. This arrangement thus minimizes the short-circuit current. Automatic voltage control. The voltage on the live side of the D.C. output 232 is monitored by an operational amplifier 211 after comparison with a reference 28. The output ripple voltage is monitored by an amplifier 212 which compares it with reference 28 and feeds a resulting voltage to a comparator 213. If the output of amplifier 211 exceeds that of 212, comparator 213 feeds a signal via diode 248 to turn on transistor 236 which inhibits operation of the blocking oscillator 235 until the output voltage is reduced to the regulated value shown by curve a in Fig. 2. The D.C. output current in resistor 229 is monitored by amplifier 201 the output of which is fed to a further amplifier 202 which compares it with a reference 26. In the event of the output current becoming very low, a signal is produced by amplifier 202 which modifies the action of the voltage regulating amplifier 211 so as to provide an uptilt as shown at d. This ensures that each amplifier of a parallel-connected combination contributes to the main output. An alarm may be operated when an individual converter is within this region. Automatic current control. The main D.C. output current in resistor 229 is monitored by amplifier 203 the output of which is compared with a reference 21 and fed to a current regulating amplifier 204 the output of which is added by means of a diode 251 to the output of the voltage regulating amplifier 211. When the output current exceeds a predetermined limit, the signal from the current regulating amplifier 204 takes control giving the curve shown at b in Fig. 2. If the output current should rise above predetermined limits breakdown diode 299 becomes conductive and the automatic current control is inhibited giving curve g in Fig. 2. Any further increase in output current as detected by amplifier 201 is compared with a reference 24 and operates amplifier 206 which breaks down diode 255, turns on SCR 257 which inhibits the blocking oscillator 235 and opens a circuit breaker 273. Capacitor 264 ensures that the overcurrent shut down arrangements do not respond to transients. High voltage shut down circuit. The output voltage is compared with a reference 22 and monitored by amplifier 214 which responds to excessive output voltage by breaking down diode 255, which triggers SCR 257 which inhibits blocking oscillator 235 and opens circuit breaker 273. The overvoltage threshold is made to have a function of current curve c of Fig. 2 by feeding a current signal to the lower input of amplifier 214. Reverse current protection. The output current in resistor 229 is monitored by amplifier 203 which feeds a signal to a diode bridge 267. Resistor 233 provides a signal which is a function of reverse current in the filter capacitor 230. If either current is in the reverse direction, e.g. due to a breakdown in capacitor 230, amplifier 205 provides a signal which breaks down diode 255, turns on SCR 257 which inhibits blocking oscillator 235 and opens circuit breaker 232.