A Resonant 1:5 Cockcroft-Walton Converter Utilizing GaN FET Switches with N-Phase and Split-Phase Clocking

Abstract

Recent demonstrations of merged inductorcapacitor (LC) switching converters have resulted in record power densities being achieved at high voltage conversion ratios. To do so, sophisticated switch control schemes may be required. This work demonstrates N-phase and Split-phase switching techniques applied to a resonant Cockcroft-Walton converter. For the same hardware, the lower resonant switching frequency of the N-phase scheme significantly improves light-load efficiency relative to the Split-phase scheme. However, the N-phase approach suffers reverse body diode turn-on at large voltage ripple contributing to the Split-phase scheme obtaining the highest power density. Converter performance combining both switching techniques is analyzed using a discrete 1:5 Cockcroft-Walton converter implemented using gallium nitride FETs, multi-layer ceramic chip (MLCC) capacitors, and a 68 nH inductor. The resulting converter achieves a peak efficiency of 94.9% and 94% for the Nphase and Split-phase schemes respectively with the N-phase scheme seeing a 30% reduction in losses at light-load. The converter achieves a maximum output power of 190W, resulting in a record power density of 483.3 kW/liter (7,920 W/inch 3 ) and specific power of 243 kW/kg.

Large Signal Analysis on Variations of the Hybridized Dickson Switched-Capacitor Converter

“…1 (a), could only approach full SSL mitigation under a two-phase switching regime as specific capacitor values impractically tended towards infinity, leading to poor utilization in practice. Subsequent work resolved this by proposing a split-phase switching scheme [6] which enables the S-1Ldirect variant of both Dickson and Cockcroft-Walton (CW) topologies [5] to achieve complete SSL mitigation by introducing tertiary switching phases that emulate the natural zerovoltage switching (ZVS) behaviour of diodes. Expanding upon this concept, split-phase switching was first demonstrated for a step-down converter in [10].…”

“…However, the reduced switching activity of these multi-phase techniques yields improved lightload performance where switching losses dominate. As a result, a converter's efficiency range may be maximized by employing either split-phase or multi-phase switching depending on the converter's operating point [5]. Moreover, classical pulse frequency modulation techniques (PFM), or dynamic off-time modulation (DOTM) in [39], [40], may also be used independently or in conjunction with multi-phase approaches to extend light load efficiency further.…”

“…This technique, termed here as "hybridization", avoids the slow-switching limit (SSL) [1] and allows inductively-assisted capacitor networks to act as highly effective soft-charged energy transfer elements, leading to state-of-the-art power densities being reported in recent years (e.g. [2]- [5]). As hybridized switched-capacitor (HSC) power converters gain popularity, a significant body of work has emerged which describes SSL mitigation in a variety of topologies, with additional work applying zero-voltage/current switching (ZVS/ZCS) [4], [5], [8], [12]- [14] and advanced gate-drive structures [15]- [19] for further improved switching performance.…”

“…[2]- [5]). As hybridized switched-capacitor (HSC) power converters gain popularity, a significant body of work has emerged which describes SSL mitigation in a variety of topologies, with additional work applying zero-voltage/current switching (ZVS/ZCS) [4], [5], [8], [12]- [14] and advanced gate-drive structures [15]- [19] for further improved switching performance. Previous work has proposed general analytical methods by which switched-capacitor topologies can be assessed as to their eligibility for hybridization, with com- Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org.…”

Loss Characterization and Modeling of Ferroelectric Class II Multi-Layer Ceramic Capacitors in Resonant Converters

“…Popular applications of Class II MLCCs include filter capacitors in an AC-tied system, where the MLCCs are exposed to excitation with high amplitude but a relatively low-frequency [2], and energy transfer elements in a resonant switchedcapacitor converter (RSC) [3]. For high-compact RSC applications, which is the focus of this work, Class II MLCC can become the most primary energy transfer device over inductors in a series resonant tank operating at more than 100 kHz [3]- [5], as increasing the capacitance can eliminate physical inductors, resulting in a 'magnetic-free' design [5] [6]. In a typical cascaded RSC, c.f.…”