Design considerations of microprocessor-controlled multiphase battery charger with fast-charging strategy

A microprocessor-controlled multiphase battery charger, to enhance current utilisation of the power supply unit (PSU) and also avoid overvoltage problems during regenerative periods, is presented. The charger consists of a PSU and three sets of independent current-controlled buck-derived converters that adopt time-shifted pulse-charging current commands. Owing to the multiphase pulse-charging current control scheme, the output-current utilisation of the PSU can be improved remarkably. Moreover, the negative pulse-discharging current is recycled back to the next phase positive pulse-charging current, and thus compensates for the overvoltage of the PSU during this period. According to output voltage specification of the PSU, maximum output-power limitation, duty ratio and current ripples of the output inductor, the desired output voltage and maximum amplitude of the pulse-charging current command can be determined for the small capacity sealed lead-acid battery. The design procedures of the multiphase battery charger are given. Finally, some simulation and experimental results to show the overvoltage problem of the PSU, during negative discharging period, can be improved significantly by the proposed multiphase battery charging scheme.