Analysis and Comparison of Series Resonant Converter With Embedded Filters for High Power Density DCX of Solid-State Transformer

Abstract

A series resonant converter (SRC) operating as a DC transformer (DCX) is a candidate for the isolated bidirectional DC/DC converters of solid-state transformers (SSTs). However, the input/output current ripple of the SRC is relatively high, which requires bulky parallel capacitors and low-pass filters such as C/LC filters. These additional components reduce the power density. In addition, to operate an SRC as a DCX, a small resonant inductance is desired to reduce the voltage gain variation and achieve a faster transient response. To resolve these problems, a SRC with embedded filters is studied. Adding a clamping capacitor between split transformers not only significantly reduces current ripples and the harmonic components of the input/output currents but also connects resonant inductors in parallel to reduce the equivalent resonant inductance. In addition, dividing the resonant current into two split windings reduces the RMS current of the transformer. This paper presents a detailed analysis, a design methodology, and a comprehensive comparison with the conventional half-bridge CLLC converter with C/LC filters. 1-kW prototypes with a 600-V input voltage and 200-V output voltage demonstrate the superiority of the proposed converter; the second harmonic of the output current was significantly suppressed by 19.3 dB compared with that of the conventional converter with the same power density. The loss breakdown showed the proposed converter mitigated copper loss by 9.47% and eliminated the losses of the filter and DC-link capacitors. The prototype of the proposed converter had the highest efficiency of 95.4% at full-load among prototypes.

Bidirectional Isolated Hybrid Ripple-Cancel Dual Active Bridge Converter with Automatic Voltage Sharing for High Voltage Application

“…A detailed quantitative analysis of the ripplecancelling characteristics have been presented in Ref. (29), along with the circuit parameter tolerance regarding these characteristics. Therefore, the ripple-cancelling characteristics are briefly explained in this paper.…”

“…The equivalent average switching model of the ripple cancel circuit based on the average DC current paths was presented in Ref. (29). In a similar manner to that analysis, the equivalent average current sources are paralleled to the clamping capacitors in the proposed converter, whose amplitudes are the same as the input/output currents on the primary and the secondary sides, respectively.…”

Multilevel Switched Capacitor LLC-DCX Converter With Embedded Filter

“…In addition, since this circuit can be applied only to a current-fed converter, it cannot be used with an LLC converter and thus is also unsuitable for a PM. We previously proposed a ripple-cancel technique [32] and applied it to a dual active bridge converter and CLLC converter [33], [34]. As these converters require only an additional clamping capacitor on each port and no extra magnetic components for canceling current ripples, they can improve the power density compared to a CLLC converter with LC filters while maintaining the same current ripple mitigation [34].…”

“…6 shows the decomposition of the proposed converter, which consists of an embedded filter block of a ripple-cancel LLC and three RSCC blocks. The DC equivalent model of the ripple-cancel circuit has already been reported [34], so its derivation is not described in this paper.…”

“…By recombining the model of the ripple-cancel circuit in [34] and the model of RSCC in Fig. 7(c), the DC-equivalent circuit model of the proposed converter can be derived.…”