No abstract

The flying capacitor multilevel (FCML) converter has shown promise for high step-up/down conversion ratio applications due to its relatively low switch stress and small inductor volume. For higher level-count (N ≥ 3) variations of this topology, there is limited research on resonant mode operation, despite its potential to yield considerable performance benefits for fixed conversion ratio applications. When operating resonantly, the decreased inductance requirement compared to regulated operation can further reduce the magnetic volume and improve transient response, while also allowing for zero-voltage/zerocurrent switching (ZCS/ZVS). This work presents and analyzes a clocking scheme required to operate an N :1 FCML converter both at-resonance and above-resonance, while maintaining minimum current ripple for reduced losses. A complete derivation is presented, enabling the calculation of precise phase durations as a function of switching frequency. Moreover, a 5:1 FCML hardware prototype is demonstrated, verifying intended operation both atand above-resonance, in addition to highlighting the achievable loss reduction with the proposed switching scheme.

This paper presents a control technique for flying capacitor multi-level (FCML) converters to achieve zero-voltage switching (ZVS) across the full range of duty cycles, with application in high power density and high efficiency power converters. Previous works have used variable frequency control to enable ZVS at specific duty cycles in FCML converters, but have not been able to use these methods to allow ZVS across the full range. This work uses dynamic level selection and variable frequency control to increase inductor current ripple at duty cycle ranges for which ZVS was previously unattainable. An experimental 5-level FCML prototype has been built using GaN devices on a single-sided PCB to demonstrate this control technique. We demonstrate 4-level and 5-level operation with ZVS at duty cycles that are not possible with 5-level operation alone, as well as a dynamic level transition with active capacitor voltage balancing.

A resolving power, E/ΔE, of ≥13 000 has been achieved with the modified 6 m/160° toroidal grating monochromator (TGM) installed on Beam Line 8-1 at the Stanford Synchrotron Radiation Laboratory. The resolving power of the TGM was increased by replacing the entrance and exit slits with high-precision slits, masking the horizontal part (short radius) of the grating, and improving the TGM scanning mechanisms. To determine the performance of the monochromator, we measured the dependences of resolution and photon flux on the entrance- and exit-slit widths, the exit-slit position, and the masking of the grating. The monochromator resolution in the energy range of 25–65 eV was derived from photoionization measurements of extremely narrow core-excitation resonances in He and Ne. With 10-μm vertical entrance- and exit-slit widths and 32% mask opening of the grating, the monochromator has a resolution (full-width at half maximum) of 5.0±0.7 meV at a photon energy of 64.5 eV and a flux of 2×107 photons/s/100 mA. The results suggest a simple procedure for converting a TGM with moderate resolution into a high-resolution monochromator with a moderate reduction in photon flux due to masking the grating, beyond the reduction attributable to the slit widths.