Abstract
Switched-capacitor converters can deliver better performance, power density, and switch utilization compared to inductor-based power converters, but they suffer from current spikes during switching due to capacitor charge redistribution. This can be solved by methods such as split-phase control, which was developed to address charge redistribution in Dickson SC converters by controlling the charging and discharging of the circuit's flying capacitors, such that the equivalent branch voltages line up when the circuit switches states. However, split-phase control is most effective at compensating for charge redistribution when all the circuit's flying capacitors are matched in capacitance value. Differences between the capacitance values of the circuit flying capacitors may result in split-phase control not being able to fully compensate for charge redistribution, due to the different charge/discharge rates of the flying capacitors. The work presented in this paper provides an in-depth analysis of the sensitivity of the split-phase Dickson converter to mismatches in flying capacitor values, as well as discussions regarding the design considerations and prototype test results of a split-phase Dickson converter for high-current loads.
Highlights
The emerging 48-volt power architecture for data centers has the potential to offer up to 30% reduction in conversion losses, as well as up to 16 times reduction in distribution losses throughout the server rack [1]
This clearly indicates that the split-phase Dickson converter exhibits a significant sensitivity pertaining to variances in the sizes of the flying capacitors relative to each other; the unequal capacitor charging and discharging rates caused by capacitor mismatch results in split-phase control not fully eliminating the problem of charge redistribution
As a conclusion to this analysis, for best performance, the flying capacitors of the split-phase Dickson converter should be matched in capacitance as closely as possible, to reduce the effects of charge redistribution arising from unequal capacitor charging/discharging caused by mismatch of capacitors
Summary
The split-phase control theory [18] was developed to overcome the charge redistribution problem in the Dickson switched capacitor converter (Fig. 1) without needing to implement. Split-phase control eliminates the branch voltage differences by setting slightly lower duty cycles on some of the circuit‟s switches This allows the charging and discharging of the flying capacitors to be controlled, such that the branch voltages are equalized before switching takes place. Both the conventional two-phase [19,20] and the split-phase [14,15,18] have seen implementations, these have generally been either for low-current applications of no more than 10 A [14,15,18,20] or utilize large flying capacitors to mitigate the effects of charge redistribution [19].
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