Abstract
In the past literature on virtual impedance to series systems, most of the discussion focused on stability without in-depth research on the system design of the series converter and the overall output impedance. Accordingly, this study takes an open-loop resonant LLC converter series-connected closed-loop Buck converter as an example. First, the conditions required for the direct connection of the small-signal model in the series, the effect of feedback compensation on the input impedance of the load stage, the operating frequency, and passive components of the two-stage converter are discussed in detail―the relationship between the matching and the output impedance. Afterwards, a mathematical model is used to discuss the effect of adding parallel virtual impedance on the output impedance of the overall series converter and then derive an optimized virtual impedance design. Finally, an experimental platform of 48 V to 12 V and maximum wattage of 96 W are implemented. The output impedance of the series converter is measured with an impedance analyzer to verify the theoretical analysis proposed in this paper.
Highlights
The series converter architecture is used extensively in various applications to compensate for the shortcomings of single-stage converters incapable of having both high efficiency and wide voltage conversion ratio
In the past literature discussing virtual impedance to series systems, most of the discussion focused on stability without in-depth research on the system design of the series converter and the overall output impedance
The conditions required for the direct connection of the small-signal model in series, the effect of feedback compensation on the input impedance of the load stage, the operating frequency, and passive components of the two-stage converter are discussed in detail—the relationship between the matching and the output impedance
Summary
The series converter architecture is used extensively in various applications to compensate for the shortcomings of single-stage converters incapable of having both high efficiency and wide voltage conversion ratio. In server power applications, the post-stage usually uses an open-loop LLC architecture to reduce the complexity and cost of control and increase the overall converter’s robustness. The conditions required for the direct connection of the small-signal model in series, the effect of feedback compensation on the input impedance of the load stage, the operating frequency, and passive components of the two-stage converter are discussed in detail—the relationship between the matching and the output impedance. Individual Review of the Small-Signal Model of LLC and Buck Converters and Discussion on
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