Patent GB-1447912-A (GB)
Title: Dc voltage regulation
IPC: H02M7/12
Filed: 1974-05-16
Abstract: 1447912 Automatic voltage control MOSKOV ENERGETICHE INST 16 May 1974 21715/74 Heading G3R [Also in Division H2] A method of regulating D.C. voltage across a load 22 comprises providing a main inverter 4 and additional inverters 5 ... 7, superimposing the outputs of inverters 4 ... 7 and rectifying the resultant at 21 to provide the required D.C. voltage across load 22, comparing outputs of the inverters 4 ... 7 with a reference voltage 8 and controlling the sign of the output of appropriate ones of the additional inverters 5 ... 7 so as to minimise the effect of variation in supply voltage 1 to the inverters on the output voltage across the load 22. As described, a master oscillator 2 has an output transformer 3 which supplies squarewaves to the bases of the transistors in the main inverter 4 and the additional inverters 5 ... 7 via secondary windings 3 2  ... 39. The control circuits to the additional inverters 5 ... 7 are completed when control transistors 12 ... 14 are made conductive by a logic circuit comprising auxiliary measuring windings 4 4  ... 65 coupled to the primary windings 4 1  ... 62 on the output transformer of the main inverter 4 and to some of the additional inverters 5, 6. The squarewaves across these windings are rectified by diodes 9 ... 11 and compared with a reference voltage 8 derived from an auxiliary full-wave rectifier (not shown) from a transformer coupled to the master oscillator 2 or to the main inverter 4 and stabilized by a Zener diode (not shown). The reference voltage may be adjustable so as to vary the output voltage. The magnitude of the squarewaves from each inverter 4 ... 7 is dependent on that of the supply 1, so that, for different levels of voltage from supply 1, the logic circuit diodes 9 ... 11 produce cut-off voltages for the control transistors 12 ... 14 associated with certain additional inverters 5 ... 7 so that the inverse diodes 19, 20 of those inverters rectify part of the main output and return the surplus energy to the source 1. This has the effect of reversing the sign of the rectifying inverter and thus tends to minimise the effects of change in the supply voltage. The negative half cycles of the squarewaves from the master oscillator 2 are fed via diodes 46, 47 to the additional inverters 5 ... 7 so as to ensure that the control transistors 12 ... 14 are always conductive, except when turned off by the voltage regulating logic circuit and the other transistors of the additional inverters 5 ... 7 are always non-conductive except when their appropriate control transistor is conductive. The Specification suggests that the turns ratio of the transformers 1 ... 4 may be in the ratio 1:0À143:0À071:0À036 and states that for a 20% variation in supply voltage, the output voltage variation is not more than 3-6%. Modifications. A self-oscillating main inverter 4 may be utilized. The control transistors 12...14 may be replaced by composite transistors or Schmitt triggers. An additional inverter may be connected in series with the load so as to provide improved regulation. The D.C. supply 1 may be derived by means of a three-phase bridge rectifier without additional filtering.