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SVEIN MICHELSENFOLKE EKELUNDKJELLRUNDKVISTPower Supply DepartmentTelefonaktiebolaget LM EricssonFunctionThe function of the booster convertersystem has been described in a previousissue of Ericsson Review 1 , and thus onlya brief description will be given here.Fig. 2 shows a simplified block diagram.The whole sequence during a mainsfailure and the subsequent rechargingof the battery or batteries is illustrated infig. 3.During normal operation the output voltageof the system is kept at the prescribedlevel by the rectifiers, which arefed from the public AC mains network.The value of the regulated voltage,which is the same as the battery voltage(51 V±0.5%), was chosen in order toprovide suitable floating for the battery.In this operational mode the boosterconverters are in what is known as passiveoperation, which means that theygive no output voltage but are alwaysready to be activated if additional voltageshould be required. In passive operationthe booster converters cause avoltage drop of approximately 1 V, andhence the system output voltage U D isapproximately 50 V.If a mains failure occurs, the batterytakes over the power feeding and as aresult its voltage falls. The booster converters,which are fed from the battery,are then activated, and their rising outputvoltage is added to the successivelydecreasing battery voltage, so that theoutput voltage of the system remainsconstant.When the mains voltage is restored therectifiers automatically resume thepower feeding and also recharge thebattery. The output voltage from thebooster converters decreases graduallyand when the normal voltage level hasagain been reached the converters returnto passive operation. So-calledoperating charge is then started in orderto charge the battery quickly and completely.This is done by sending a signalfrom the charging control system to therectifiers, which causes them to increasetheir output voltage to the charginglevel (normally 2.35 V/cell) of 54 V.When the battery is fully charged thecharging signal ceases and the rectifiersreturn to the normal level.Fig. 2Power supply system BZD 112 with highfrequencybooster convertersFig. 3Booster converter system 48 V with 23 batterycells. Working cycle during a mains failure andthe subsequent recharging