title: Design of SCALDO based high-current DC power supply

authors: Ariyarathna, Thilanga

subjects: Supercapacitor

abstract: Supercapacitor assisted (SCA) techniques are primarily based on supercapacitors having in the order of one million times more capacitance, together with one to two orders of magnitude smaller equivalent series resistance (ESR), compared with conventional capacitors. In the first successful SCA technique, the supercapacitor-assisted low dropout regulator (SCALDO) combined a linear regulator in series with a supercapacitor to act as a lossless voltage dropper. SCALDO created the opportunity to develop an entirely new family of highly efficient, interference-free, very-low-frequency DC-DC converters, which have evolved further into several branches over the last 6 years.

Leading data centre operators such as Google have announced their intention to move toward 48 V server rack architecture to minimise power losses in distribution lines and to improve overall operating efficiency. This thesis investigated the potential of the SCALDO technique to develop a high-current DC power supply suitable for Google server racks, meeting requirements such as electrical isolation, fast transient response, high efficiency and DC-UPS capability within the converter.

Work related to this thesis proved that by creatively extending the SCALDO technique to achieve higher current at high voltage and further developing a bulk DC-rail from AC input by extending the previously proven fast supercapacitor charger technique, a SCALDO-assisted high-current DC power supply can be achieved. As a proof-of-concept project with a DC output of 12 V (one fourth scale) at 10 A load current capability, several key circuit blocks were developed including: (i) high current discrete LDO of 10 A; (ii) four switch implementation of a SCALDO stage; and (iii) a transformer-isolated input DC stage to feed the output SCALDO stage based on a hybrid-type medium frequency switch mode. This overall implementation is expected to overcome the limitations of a direct-SCALDO stage, maintaining high end-to-end efficiency. Matlab and LTspice simulation models were developed to observe the behaviour of these new power converter techniques.

The thesis discusses the significance of this work, related techniques, the loss-circumventing principle in the RC charging loop, which is the theoretical basis of SCALDO, and the design and simulation details of a novel power conversion technology. It also presents the implementation details of the prototypes built to verify this approach.

text: Design of SCALDO based high-current DC power supply Supercapacitor assisted (SCA) techniques are primarily based on supercapacitors having in the order of one million times more capacitance, together with one to two orders of magnitude smaller equivalent series resistance (ESR), compared with conventional capacitors. In the first successful SCA technique, the supercapacitor-assisted low dropout regulator (SCALDO) combined a linear regulator in series with a supercapacitor to act as a lossless voltage dropper. SCALDO created the opportunity to develop an entirely new family of highly efficient, interference-free, very-low-frequency DC-DC converters, which have evolved further into several branches over the last 6 years.

Leading data centre operators such as Google have announced their intention to move toward 48 V server rack architecture to minimise power losses in distribution lines and to improve overall operating efficiency. This thesis investigated the potential of the SCALDO technique to develop a high-current DC power supply suitable for Google server racks, meeting requirements such as electrical isolation, fast transient response, high efficiency and DC-UPS capability within the converter.

Work related to this thesis proved that by creatively extending the SCALDO technique to achieve higher current at high voltage and further developing a bulk DC-rail from AC input by extending the previously proven fast supercapacitor charger technique, a SCALDO-assisted high-current DC power supply can be achieved. As a proof-of-concept project with a DC output of 12 V (one fourth scale) at 10 A load current capability, several key circuit blocks were developed including: (i) high current discrete LDO of 10 A; (ii) four switch implementation of a SCALDO stage; and (iii) a transformer-isolated input DC stage to feed the output SCALDO stage based on a hybrid-type medium frequency switch mode. This overall implementation is expected to overcome the limitations of a direct-SCALDO stage, maintaining high end-to-end efficiency. Matlab and LTspice simulation models were developed to observe the behaviour of these new power converter techniques.

The thesis discusses the significance of this work, related techniques, the loss-circumventing principle in the RC charging loop, which is the theoretical basis of SCALDO, and the design and simulation details of a novel power conversion technology. It also presents the implementation details of the prototypes built to verify this approach.

year: 2021

title: Structural and functional characterization of a promiscuous feruloyl esterase (Est1E) from the rumen bacterium Butyrivibrio proteoclasticus

authors: Goldston, David C.

subjects: rumen

abstract: The release of polysaccharide from the plant cell wall is a key process to release the stored energy from plant biomass. Within the ruminant digestive system, a host of commensal microorganisms speed the breakdown of plant cell matter releasing fermentable sugars. The presence of phenolic compounds, most notably ferulic acid (FA), esterified within the cell wall is thought to pose a significant impediment to the degradation of the plant cell wall. The structure of a FA esterase from the ruminant bacterium Butyrivibrio proteoclasticus has been determined in two different space groups, in both the apo-form, and the ligand bound form with FA located in the active site. The structure reveals a new lid domain that has no structural homologues in the PDB. The flexibility of the lid domain is evident by the presence of three different conformations adopted by different molecules in the crystals. In the FA-bound structures, these conformations show sequential binding and closing of the lid domain over the substrate. Enzymatic activity assays demonstrate a broad activity against plant-derived hemicellulose, releasing at least four aromatic compounds including FA, coumaric acid, coumarin-3-carboxylic acid, and cinnamic acid. The rumen is a complex ecosystem that efficiently degrades plant biomass and the genome of B. proteoclasticus contains greater than 130 enzymes, which are potentially involved in this process of which Est1E is the first to be well characterized.

text: Structural and functional characterization of a promiscuous feruloyl esterase (Est1E) from the rumen bacterium Butyrivibrio proteoclasticus The release of polysaccharide from the plant cell wall is a key process to release the stored energy from plant biomass. Within the ruminant digestive system, a host of commensal microorganisms speed the breakdown of plant cell matter releasing fermentable sugars. The presence of phenolic compounds, most notably ferulic acid (FA), esterified within the cell wall is thought to pose a significant impediment to the degradation of the plant cell wall. The structure of a FA esterase from the ruminant bacterium Butyrivibrio proteoclasticus has been determined in two different space groups, in both the apo-form, and the ligand bound form with FA located in the active site. The structure reveals a new lid domain that has no structural homologues in the PDB. The flexibility of the lid domain is evident by the presence of three different conformations adopted by different molecules in the crystals. In the FA-bound structures, these conformations show sequential binding and closing of the lid domain over the substrate. Enzymatic activity assays demonstrate a broad activity against plant-derived hemicellulose, releasing at least four aromatic compounds including FA, coumaric acid, coumarin-3-carboxylic acid, and cinnamic acid. The rumen is a complex ecosystem that efficiently degrades plant biomass and the genome of B. proteoclasticus contains greater than 130 enzymes, which are potentially involved in this process of which Est1E is the first to be well characterized.

year: 2010

title: Call and response: Taika Waititi’s ‘Boy’

authors: Perrott, Lisa

subjects: Waititi's film

abstract: Lisa Perrott examines how the construction of Waititi's latest film might engender complex, nuanced responses from audiences.

text: Call and response: Taika Waititi’s ‘Boy’ Lisa Perrott examines how the construction of Waititi's latest film might engender complex, nuanced responses from audiences.

year: 2010